Episode 205: LECA
LECA comes in a range of sizes. Photograph: Jason White on Flickr.
Transcript
Episode 205
[music]
Jane: Leca, hydroleca, hydroton, expanded clay pebbles, lightweight expanded clay aggregate, whatever you call it, this is what we're talking about in today's On The Ledge podcast! I speak to listener Kimberly Black about her experiences with this substrate and share some fascinating Leca facts, including what happens inside a Leca production kiln, how to keep your Leca clean and what you can use it for in the houseplant world.
[music]
Jane: Thank you for all your feedback on last week's thrips episode. I've heard some horror stories but it's great to know that you are finding Professor Kirk's advice useful in terms of controlling infestations from here on out. Just a reminder that I'm still looking for festive questions for the festive Q&A coming up. You will need to get those to me by - hurriedly scrambles for diary - 6th December, at the latest, so that I can try to answer as many as possible. I will accept Poinsettia questions, but I will have a sour look on my face while I answer them! Also, a reminder that the event on 11^th^ December run by listener Tom Cranham is happening at Thornbridge Hall in the Peak District in England. There's still time to get tickets, they're £15 each. The day includes a talk by James Wong and a chance to buy plants from the most excellent Grow Tropicals. All the details are in the show notes if you want to find out more.
[music]
Jane: I'm going to hit you with some Leca facts. I covered this substrate in a little bit of detail in my A - Z of potting mix ingredients, but it's so important to many houseplant growers now that I thought it was worth devoting a whole episode to the stuff, particularly as a follow-up to the Lechuza Pon episode offering a different perspective, perhaps, from our listener Kimberly, about Pon versus Leca.
I use Leca but not Pon. I mainly grow in a soil-based system and one of the interesting things about Leca is that it has so many applications whatever way you're growing. So there's various ways that I use Leca in my soil-based systems. But first, let's get it out of the way, what is Leca, what is it made of? You'll find this stuff sold under many, many different names. Oftentimes it'll be sold under a brand name, I've seen it sold has Hydroton, Hydroleca, Terralite, I think CANNAdo a brand of Leca and it's all effectively made out of the same stuff. Leca is an acronym for lightweight expanded clay aggregate. I'm going to get nerdy here! An acronym is a set of initials that you can say as a word, so Leca qualifies as an acronym. Conversely, CEC, which we'll get onto in a bit, which stands for Cation Exchange Capacity, that is not an acronym because you don't say "kek" you say "C-E-C". So there you go! A little lesson there on acronyms, but let's continue.
So all Leca is made out of the same stuff; clay. That is usually strip-mined from the ground, close to where it is processed. We'll get into sustainability issues surrounding that shortly. It comes out of the ground, it's broken up into pieces and then it heads up a conveyor belt and into what is known as a rotary kiln. I have been watching rotary kiln Leca production videos today. Very exciting! I will post one of these in the show notes, if you want to be a total geek and watch them! Basically, the raw material of the clay heads up little conveyor belts and into a massive metal tube and these vary in terms of exactly how they work, but basically they send the clay round and round and heat it up at a tremendously high temperature, at least 1,000C, so very, very, very hot. Under those kind of temperatures, something happens to the clay; it expands. It almost pops, like popcorn, and the stuff at the other end that comes out is incredibly lightweight and airy, but it's still made of clay, just clay that's undergone a tremendous transformation via the means of very high temperatures.
Leca, used for different industries, is available in different sizes and densities, so you're talking anything from really, really tiny pieces that are smaller than perlite right up to 25 mm / 1 inch. So the size can really vary. The density can vary as well. It's measured in kilograms per metre cubed and you can get densities from 250 to 510. If you go on the website of any Leca maker, you should be able to find information about the size and density of their Leca. For example, I've got the safety data sheet for Westland's products, Hydroleca, in front of me. The granular size is 10 mm to 20 mm and if you read the small print the bulk density is 280 kg/m3. That's probably fairly standard for horticulture.
The other thing with Leca to remember, is that it's used for a lot of things other than horticulture. I'd say probably horticulture is a relatively small proportion of its overall use because it has a lot of applications in building work, it's also used for thermal insulation, for drainage and filtration. It has many different uses. So those are all the things to check out in the small print of your Leca: what size are you getting and what density are you getting?
Let's talk sustainability next. As I said, the clay for the Leca is strip-mined and it goes into a very, very high temperature kiln which is sometimes coal-powered, so you don't need to be told that means that, in terms of carbon footprint, it's not brilliant. I haven't ever seen a proper breakdown of the sustainability grading of a peat-free soil versus Leca. I would love to see one, but that's not something that I've got available. I guess where Leca does have a tick, is that it can be reused over and over again. So, hopefully, if you buy a bag of Leca it will last you a jolly long time. I have only just bought another bag. The first bag that I had, which was a standard compost bag size, has lasted me about eight years and I reuse it over and over again. When bits accidentally get put into the compost heap I literally pick them out because it's stuff that I want to keep hold of. I have only just bought another bag which I haven't yet opened. So it does last a really long time, so that's worth bearing in mind. If anyone does find a sustainability grading for different houseplant substrates, I would absolutely love to see it.
The great thing about Leca is that it doesn't degrade easily. I have stood on pieces wearing a pair of boots and managed to crush them but unless you do that it doesn't really degrade in the same way that soil does or any soil-based mix that you might be using or, indeed, things like perlite and vermiculite. They can degrade and get dusty over time, whereas Leca pretty much just stays as it is, so that's the plus points of it. I would emphasise that it is worth using and reusing your Leca many, many times.
Coming to the issue of how to reuse, it partly depends on what you've been using it for. I usually keep it very, very simple and just rinse it out. I have been using the inside of an old salad spinner to rinse out my Leca. I did see, the other day, somebody using those mesh laundry bags you can get, which is a great idea because you can put them in the laundry bag, rinse them out, and on a sunny day, just lay them out on a flat surface to dry and you've still got control of them, they're not rolling all over the place. What a good idea that is! I have never done anything more to my Leca than that, but lots of people, particularly those who are more at the hydroponics and semi-hydroponics end of things, like to be absolutely sure there's nothing in those pebbles that can cause problems for their plants. If you're washing them, you are going to get rid of a lot of plant-based organic debris that you might get if you're using them, as I do, for things like a reservoir in a wick-watering system, or as a mulch, and that will also flush out mineral salts that may have accumulated in your pebbles.
Some people want to do more. I have seen people talking about boiling them. Personally, that's not a route I would go down - again, a bit of a waste of energy. There are a few other ways of doing it which don't involve heating. There is, in the UK, a product called Citrox you can buy, which is a totally safe disinfectant that you can use on Leca and other surfaces and gravel and things like that. It's made by Agralan. I don't know if you can buy an equivalent anywhere else in the world? It's made from extract of citrus fruits, not surprisingly, given the name, and you can use it on things like bird feeders, or capillary matting, that kind of thing, so it's a really, really useful product that's widely available at garden centres and also online. That's a great way of treating your Leca with a disinfectant that's natural. You can also use food-grade hydrogen peroxide as a way of disinfecting them. Follow the instructions and make sure that you dilute to the right level. I will include a calculator which allows you to calculate what rate you need to do that at and make sure you rinse them thoroughly afterwards. You can leave them out to dry, if you use that mesh bag technique, or just get a big, clean growbag tray and lay them out on a nice sunny day and they will dry and then you can store them like that. So that enables you to use them over and over again.
So why is Leca good for houseplants, in terms of substrate? Well, they're very lightweight, so you can buy a big bag of them and you can hump them up the stairs of your apartment quite easily. The process of heating them up introduces loads of air into each of those pebbles, they're like popcorn and they just explode and you've got all those air pockets and that allows water and air to be stored in the substrate. Leca has a high Cation Exchange Capacity; CEC. Basically, that's a way of measuring how much a growing medium can hold on to water and nutrients and Leca's CEC is high. It doesn't hold any nutrients in itself, it doesn't contain nutrients, but it can store them until the plant needs them, which is a great quality. That's also a reason why it can accumulate mineral salts if you're watering with tap water, so that's another reason to flush out your Leca every so often. So it's good for holding water and nutrients around roots, but also giving lots of air.
Let me talk first about the ways that I use it. Mulches - fantastic as a mulch on the top of pots so that you're not splashing soil if you're top watering. It keeps things neat and may have a little bit of an impact on fungus gnats. I also use it in reservoirs when I'm wick watering, so it just holds onto the water or if you're doing the classic tray approach for increasing humidity, that's a fantastic thing to use as the pebbles because they're not very heavy and they will just sit there and hold onto the water and slowly release it as it's evaporated into the air.
If you're talking hydro or semi-hydro, you can use it as the complete medium. Some people use a system without any drainage holes, so there's water at the bottom which is topped up and the roots dip into that. Some people use a double-pot system, where you've got the Leca in the main pot and water reservoir below and that can be something that you can make yourself very cheaply or something you can buy. Pretty much any method that you want to use Leca for houseplants in terms of a substrate, you can give it a try. The other thing that is very popular is propagation in Leca and I do have a few prop boxes where the bottom is covered with a deep five to ten centimetre of Leca that's damp and maybe a little bit of moss on the top of that and the plants can root into there. When you get the bag of Leca, see how dusty it is. I would always recommend giving it a rinse through before you use it, just to remove anything that might be sitting in there that could damage your plants. That's enough from me! Now we're going to hear from Kimberly Black, my guest this week, who is talking about her personal experiences with Leca.
[music]
Kimberly: Hello, my name is Kimberly Black. I'm a plant enthusiast for many years. I started as an outdoor gardener in the Rocky Mountains, which was very challenging, and after learning a bit about growing in a challenging environment, shifted that to indoor plant-keeping when we moved to a house without a big garden. So I've been experimenting ever since, for the last year-and-a-half or so, in the new house.
Jane: Fantastic! We're here to talk about your experiences with soilless substrates, which is something we've been talking about on the show recently. I think this is an area where lots of experimentation is necessary to find what works for you, so tell me a bit about where you started with your switching to a mineral base substrate.
Kimberly: My first trauma came with bringing home a plant with fungus gnats, a delightful, magnificent Croton and it subsequently infected every last plant in my house. I didn't know what it was until I looked it up and realised that I had a big problem. I went about all of the recommended by "people without knowledge" information and that didn't work out very well.
Jane: Did they tell you to put cinnamon on the surface of the soil and all that?
Kimberly: In fact, one, yes! Diatomaceous earth, which I knew people use around the house for insects but wasn't sure how that would possibly work on wet soil and my suspicion was that it would fail - that was correct! The frustration with fungus gnats led me to think soil was a bit of a problem for me and I know overwatering is one of the things you worry about when you have fungus gnats in your soil. I really did try everything I could. The one thing I did not do is nematodes and that is very difficult to come by in the United States. When I collected more and more plants, it wasn't just fungus gnats that were a problem, it was also my husband saying to me, "We need to leave the house for two weeks at a time and I need you to figure out how we're going to do that without killing all of these plants that you're purchasing!" so that came into the equation as well, how I was going to manage this number of plants, having now a problem with fungus gnats, getting rid of those and then figuring out how to keep these lovely plants when I'm out of town for two weeks. So, soil-less medium became a potential solution to more than just those two problems. But the chronic over-watering, which was probably additionally contributing to the fungus gnats, was another reason that I felt soil-less growing was maybe a better choice for me.
Jane: Fungus gnats, they are just so evil! It's kind of ironic because they don't do that much damage to plants, but they make up for it by being just so annoying, don't they? People say "Water less!" and all of those solutions. It's a shame you can't get hold of the nematodes because they are very effective and I've also used hypoaspis mites, which are good if you've got drier soil. I agree with you that being able to go away for two weeks and leave your plants happily, that's a big bonus in life. I can really see the benefits of that. Where did you go from there? Was a DIY Pon your first option, or your first experiment?
Kimberly: I tried, at the exact same time, both the Leca and the Pon. I was curious and wanted to run some experiments because the information, unfortunately, coming out, that I saw most of the time on Pon, was very much commercial and likely to be sponsored, so I thought the information was a little bit dubious, especially the stuff coming out of the YouTube space. I find all of that information really questionable. So I wanted to try it without the company influence, but I did read on the website about what the ingredients were, the benefits that they talk about, which are ratios of air to the soil substrate particles. Pon was an interesting idea because it had fertiliser coming with it and so that was something that seemed great. The self-watering system that you can do also seemed great. That way, the Leca seemed like it was more labour-intensive to do, as well as to learn. There was a whole lot to learn about Leca without great information, so I ended up turning to marijuana growers online more than anything. I was familiar with hydroponic growing because I had a friend, once upon a time, who grew marijuana hydroponically and raved about the success, but it also seemed really intensive and with poor information. So mostly the internet: I used some of the Pon information from the company but tried not to be swayed too much by their commercial marketing.
Jane: It's interesting, isn't it? There is a lot of information to be learned from people who are growing cannabis because they really have invested in a lot of this stuff way before houseplant growers were getting interested in this stuff. In fact, I discovered a grow shop in my town the other day, which is selling an enormous range of stuff for hydroponics and products and I was just blown away looking at ranks and ranks of different products and equipment you can buy in grow tents. So that is definitely a good source of information because they've been there, done that, bought the T-shirt on this kind of stuff, haven't they?
Kimberly: Oh yes, they've dedicated so much in research to try and maximise their yields and it covers flowering as well, so when you're using a hydroponic set up, there are recommendations to change the nutrients if you're entering a flowering phase and all of that information is a little bit of information on the little table on the label on the bottle, but doesn't really help you to understand exactly what you're doing to manipulate the solution itself.
Jane: You had some ideas. What were the first plants that you decided to give up on with the soil and switch over?
Kimberly: Sadly, I'm sure there were some of my more established plants but my not-particularly-valuable and easy-to-replace plants. I was aware of issues with rot mainly and it was publicised much more for the Leca, especially trying to transition a plant from soil to Leca led to rot. That was one of the biggest problems. So, preparing the plant to go into Leca was one of the things to research, to get all of the soil off before transitioning. With Pon, it seemed like it was a bit easier, you could rinse off the roots if you had a little soil on them, it wasn't a big deal, and you were able to plant into the medium.
Jane: Tell me how it went. What went well? What went hideously wrong?
Kimberly: I think the first thing I noticed... the first bag of Leca that I got was a pretty large size. So, for example, I tried transitioning a Goldfish Plant. That did not go well at all! The individual portions of the plant, I'm not sure if I'm using the right terminology, but each one of the stems of the plant, they would topple over repeatedly within it. So I was, like, obviously the size was a problem. I originally tried with the Pon I was using, Philodendron Prince of Orange was one of my first tries and it did nothing, it didn't rot, but it just sat there miserably. When I would take it out and check the root system, there was no growth in the root system. I tried a Black Velvet Alocasia in the Pon, that one actually was one of the plants that responded well to the Pon. I don't particularly know why I think of Alcosia as probably the most fussy plants I keep, those plus Anthuriums - I've killed a number of Crotons - those were the plants that I thought "If there's going to be a fussy one, an Alocasia is one that I'm not sure would appreciate that kind of substrate!", so I thought that was a reasonable attempt. I also tried a Dragon Scale on the Pon and that poor thing, every last little hair-like root disintegrated and it was a lovely little Dragon Scale and was a spontaneous variegate that I found at the nursery nearby. There was a young man that pointed it out to me, so I was very excited about it. Happily they grow back, so I've had it come back twice, but each time I change its substrate it gets upset with me and drops its leaves. So the Pon did not work whatsoever for the Dragon Scale. It worked okay for the Black Velvet, I had Thaumatophyllum spruceanum, formerly known as Philodendron Go**eldii, I believe, and that one did okay in the Pon. What I found out, and part of what the company recommends, is to start by using the Pon substrate like a standard soil and watering it first so that the plant will establish fresh water roots and it won't rot the soil roots in there. What I found is that I had to have some sort of substrate with the Pon at the bottom because it just stayed too wet. I think that was the reason for the root rot with the Pon. With the Leca, if I kept a really close eye on it, I seemed to do better. There were other plants, I'm trying to think of which other ones failed... I had gotten a really neat Mother and Daughter Croton. Have you ever heard of that?
Jane: No.
Kimberly: They're fascinating, I really fell in love with Crotons and they hate me, or I should say Codiaeum variegatum? I very much appreciated your episode on it! It brought my self esteem up just a hair to know that I wasn't the only person killing Crotonsaround the world!
Jane: Let me tell you, the little one that I bought... because I hadn't had one for a while, that I bought for that episode, got so miserable because it was in my front room, which is south-facing, but it was just too far from the window. I put it in next to the window and it got burned. Anyway, it's now out in my conservatory sunroom-type thing, which is, to be honest, where all my plants should be because they absolutely love it and it's put on a real spurt of growth but it's changed colour completely from what it was originally. They're not the easiest things! I'm glad that I brought you some comfort on that subject.
Kimberly: The Mother and Daughter Croton's really neat because each one of the leaves has a little extension of the mid rib and at the end of it is this little baby leaf. It looks like this funny little Dr Seuss Croton! It's very odd. I was really happy I found it and I was, like, "Well, okay, we're going to try it!" so this transition to Pon and the leaf-drop was spectacular. Within 24 hours it was just a pile on the ground and a stick in a bucket, basically! It was so sad. It was very sad.
Jane: That does sound a bit dramatic! That's the kind of thing you just absolutely dread as a plant-grower, coming down and seeing all the leaves on the ground under the plant.
[music]
Jane: More with Kimberly shortly, but now it's time for Question of the Week which comes from Eliza. We're back to thrips already, just a week after our thrips episode! Eliza has a thrips infestation in her houseplant collection, which is 200 plants in one room. So, yes, I can imagine that you're freaking out, Eliza! Eliza has been using SB Plant Invigorator to spray her plants and treat them for the last few weeks and is wondering whether she can go on doing that over the winter period, whether the fact that the foliar spray contains some nutrients will mean that it'll end up with her plants being over-fertilised. What a good question!
Well, it's interesting. SB Plant Invigorator, this spray that's very popular now in the UK for treating all kinds of pests, it's a foliar spray and I use it myself, it's really great, but there isn't any information out there, that I've found anyway, that explains the nutrient profile of what's in the spray, so how much nitrogen, potassium and phosphorus are in there. What I would say, is if you're spraying it on the leaves, and I suspect with a thrips treatment you may well be spraying it on and then wiping it off to remove the larvae and the adult thrips, you're probably actually not leaving that much on the plants to be absorbed by them. If you're worried, you could certainly swap to using water because, as we heard last week from Professor Kirk, a wash down with water is pretty successful as a way of controlling thrips. But I would think that any plant you've got that isn't something that's really dormant during winter, like a cactus, would be absolutely fine with having a spray of SB Plant Invigorator every couple of days.
The other thing you can do is just don't fertilise with anything else during this period while you're using the SB Plant Invigorator over winter. If you haven't listened to that episode already, Eliza, 204, do give it a listen. There's loads of biological control measures suggested in that episode and I think with 200 plants in one room that could work really well for you. I don't think the plant invigorator is going to cause any problem. It's used widely in the nursery industry here and I think, as long as the plant is not in a deep dormancy, it's not going to cause any problems. Better to get that thrips problem under control, than leave it over the winter. If you're worried, as I say, just switch to water, or use it a little bit less often. I think with pests, it's always the case that it's better to do something every day than one thing every now and again, when you remember, because that little war of attrition you can get going, breaking the life cycle and removing the pests at different parts of the life cycle, really does help, as dull and boring as it is to just keep on treating your plants. I wish you luck, Eliza! Do let me know how you're getting on. If you've got a question for On The Ledge drop me a line ontheledgepodcast@gmail.com And now it's time to head back to my interview about Pon.
[music]
Jane: So you tried various things with Pon and Leca. It seems like the Pon you've ditched in favour of the Leca, generally, because it seems to have just worked better and suited your purposes more effectively?
Kimberly: Yes, I'll send you the photo that I took of the last time I was trying to clean out the Pon so I could reuse it. That's one of the things I appreciate, also, about On The Ledge: you talk about sustainability and I treat each one of these things as though it's not renewable because it really isn't. A lot of these things are mined, so I want the Pon to be reusable as well. That's one of the things they tell you. I'll send you the picture of my tweezers pulling out these tiny, hair-like, dead bits of root and even the plants that lived when I repotted the Thaumatophyllum spruceanum, which is one of the ones that did not object to the Pon. I still had live roots, but all these really healthy live roots just coming out in the Pon, so then, to reuse it, I sit there and I pull out every last little root and it's just hours of mess! The self-watering idea of it was great, except for that I clearly didn't have whatever routine was right to prevent rot with the Pon, so that was another thing that just... it doesn't take long killing plants before you want to change your mind on what you're doing! I liked the Leca, except for some of the problems that people bring up, like fine root systems seem to do a little bit better in Pon because it supports them and the plants will stay upright better. What you actually will find, if you do a little more research, is Leca comes in different sizes. You can buy the standard IKEA bag and that has sizes between like 4 mm to 10 mm, so it comes in a range of sizes. You also, if you want to, can purchase on eBay micro-Leca, which is actually rather small, and you can mix and match your own Leca. So I use an orchid pot, a large one that has the round holes that are somewhere around 5 mm or 6 mm I think and I use that to sift out the Leca. I have three different boxes: I have my little micro-Leca box and then I have my small, mid-range Leca box and then my larger Leca. Each plant now gets its own combination of sizes in order to make it something where it's an appropriate ratio for the water to the plant, but also with stability for it. So, for example, I have a - depending on who you ask - it's an Alocasia zebrina reticulated version, the one with a very fancy leaf pattern, really fine root system and very top-heavy, as a plant goes. The Leca, if you use all the large balls, will not support it well and the plant's not going to grow. The plant's not stupid, it knows that it's not being supported properly, it's not going to get to be a full and nice, lush plant. Whereas as soon as I put it into a more stable set-up, with more variable size Leca - a lot happier, and the root growth just explodes in front of you as you check the pot each week! I love that I can check the pot each week, for the rot. For Pon, I just watched the plant turning miserable and waited long enough to take it out to see what was going on. Whereas the Leca, it was obvious I could take it out immediately, I could rinse off the roots, treat any rot I wanted to - just clean it up. When it came to cleaning the Leca versus the Pon, I have a spaghetti boiler where you have the colander portion that sits within the larger pot, does that make sense?
Jane: Yes.
Kimberly: I don't cook much, my husband does, so this is how I use our pots! I will boil the Leca in there. Any of the root debris, most of it just comes off and into the water. You can rinse it very simply and reuse it. With the Pon, it has fertiliser in it, so you can't really boil it. I'm sure that will make the small balls of fertiliser melt or disintegrate in some way that I'm sure wouldn't be good for your plants, so not really sterilisable, if that's the word for it? So I'm pulling out little bits of rotten roots and root hairs, very much aware that I can't actually clean this, other than rinsing it. As soon as you make the Pon particles wet, they stick to everything. The Leca doesn't. You can drop the whole box over your kitchen if you want to and you can pick it up, stick it in the boiler, sterilise it and rinse it and you're done. As a surgeon, I'm really pretty focused on hygiene and think it's pretty important to sterilise the medium if you have a plant that's died in it. That whole thing spoke to me and once I was able to get more knowledge, down to how to deal with the hydroponic solution, to me there's nothing that I want to keep in Pon any more. I've left a couple of them in there because they're happy enough, I'm not going to mess with them yet, but there are two left. One is the magnificent Croton, which I put into a very specialised watering system, which is two five gallon buckets, the inner one of which I drilled a bunch of holes in, to make it into a gigantic, dual watering pot, but do not have it in just Pon, I have it with Leca at the bottom with wicks going up through the Leca and into the Pon, so that's the system that I found. If you made your own, DIY self-watering system, it did not seem to rot the roots. I'm sure the company has a pot style that will help with this, but each one of those pots, that's the dedicated purchase, is made of plastic and they're not cheap, so I really didn't like that aspect of using the Pon. I didn't want to have to use a bunch of dedicated pots to make it work.
Jane: Yes, I hear you. It is expensive. I've got one that I got from a trade show, or something, quite a few years ago. I don't even use it. It's got a Fishbone Cactus in it and it's in soil and I just put water into the reservoir, but I don't use it with Pon. I totally understand what you're saying. I don't want to spend loads of money on self-watering pots, particularly if you've got a lot of plants - that gets expensive very quickly. I have a mental image of you in the kitchen and your husband coming home saying, "Oh, you're cooking something!" then you go, "No, actually, I'm sterilising my substrate and steaming pots of clay pebbles!". That sounds great, I love it!
Kimberly: The kitchen is for different purposes for different people! I remember the tissue culture episode you're talking about and I was, like, "Alright, well, I think I have enough room in my kitchen, I could..." My husband's like, "You have enough!". I have a whole propagation station in our kitchen. We just happen to have this weird desk area that they had installed fluorescent light strips in, in the kitchen, so I just turned the bulbs into grow light bulbs and so this whole shelf is dedicated to my propagation, so I already have a station! He'd like me to stick to mine, but I need the stove once in a while!
Jane: That's absolutely fair enough, isn't it? So I just need to picture your system for your Leca. So your plants are in regular, plastic nursery pots, or are they filled with Leca and then an outer pot?
Kimberly: Yes, I like to use pots as much as I can. I collect vintage pots, a lot of ones that are from 1940s and 50s because we have a mid-century modern home. I collect these old pots and a lot of them don't have drainage holes - many, many don't have drainage holes - pretty much anything made by Hager or Glidden do not have drainage holes, so they act as my cache pots. Then, for the inner pot, I have reused orchid pots. I find the net pots for orchids really helpful, especially because the clear plastic, you can see through those. Then I actually modify a lot of deli containers. So we have an Indian takeout place, fantastic, and they have all of these clear plastic containers, which it breaks my heart to bring home any kind of plastic container that I'm going to throw immediately into the garbage, so I just started saving all of these. I will heat up a nail from the garage and will use it to turn any one of those deli pots into an inner pot for orchids, so I can reuse all of those. The outer pots are mostly the vintage ones. I had some orchid pots with orchids that sadly had not made it. I've used things that were meant to be containers to hold things like buttons and stuff like that, where it just happens to be a clear plastic container that fits within these orchid pots, so I've got pretty good at spotting those kinds of things! My husband has little paint-mixing buckets that he's had from home depot before, where, if you clean out all the paint and you want to put some holes in it, great - that'll work for you! The pots that I use, I just reuse over and over again. As the plants up-size I just pick a bigger-size orchid pot, or leftover deli or paint container, and it fits inside my delightful vintage pots. It also allows me to redecorate my plant room! I have a dedicated space in my bathroom because I don't use the jacuzzi tub - because why would you? You should just have a plant room! The humidity is high, it's really great. So, in there, as plants are growing and I'm shifting and repotting, I can just choose a different cache pot for it and put it in a different place. So it's not only that the set-up is easy for me, but it also allows me to do a lot of variability and to switch around the pots as things are growing.
Jane: That is very clear, thank you for that. I love the fact your jacuzzi is a plant area! I mean, yes, who needs a jacuzzi!? How does your watering regime work? You said you can go away for two weeks and leave them. How do you make sure that the plants are at the right water levels?
Kimberly: I use a series of larger plastic bins. They're just IKEA shoe bins for storing boots and shoes. I fill the bin a third full with the nutrient solution and then, based on the depth of the particular plants, then cluster them in the boxes appropriately, so that the water level is about a third, which is where it belongs. Putting all the plants together in there, that water does not go away quickly. It takes a really long time and even once the reservoir of water is gone at the bottom, the Leca itself is still holding on to a lot of moisture. So, ten days to two weeks. If you look, I have the same system I use for my propagations, or I have a single box and I have each one of the propagates within our propagules - I learned that from you: propagules! - within that system, and the water will last for a couple of weeks, so I can go away for two weeks. I also have a neighbour who also happens to be a plant enthusiast and there was one trip that was two-and-a-half weeks and I said, "Hey, can you just come into the house once? I'll leave a bottle of distilled water there, just dump it in until it's a third full" and that's all he did! It's the easiest thing in the world: he walked in, he filled up the box of water, he walked back out! So even if you're gone for three or four weeks, you would only need someone to come in and empty a bottle of distilled water into a box for you, not come and try to determine with a moisture probe which of your plants may need watering that day.
Jane: Well, it sounds like a very, very easy and logical system you've got going. Is there anything you miss about soil, or would you say you would never go back now?
Kimberly: The one plant I put back in soil because it was miserable was my Dwarf Meyer Lemon Tree, which broke my heart because that was also one of the two plants where the fungus gnat infestation was just awful. The pot itself is a twelve inch pot, it is a big cylinder pot. The fungus gnats, I think there's just enough soil for them that, regardless of the treatment I was using, I was never able to get rid of them. I was always suppressing them. I used the Bacillus Israelensis, I think is the one that has the natural insecticidal larvae? That one was the one I had used with the most success to suppress in that plant and sure enough, I put that plant back into the soil and started seeing a fungus gnat here or there again. So I'm now looking at suppressing it again with the Bacillus and then I'm looking at ordering the nematodes but they have to be ordered airmail, as far as I can tell, from Germany, I think, was the only source I could find. Maybe someone else has a better idea? I really hope someone knows where you can get it.
Jane: Yes, I'll ask around American listeners because I think I've heard from listeners who have got hold of that within the country. I'll see if I can dig something out for you because I think that would be a good solution. I apply a biological control twice a year and basically all my plants are in soil and that does seem to do the trick. It is still a pain and they do come back, but they do work really, really well. I'm sure, being a surgeon, you would be very scientific about it. You have to just dilute them to a certain level and make sure that every plant gets well soaked, but it does work magic, actually, so that's definitely worth looking into. I'll see if I can find an American source for you. Well, thank you so much for chatting to me about these soil-free options. I'm really fascinated to hear these stories, Kimberly, and find out how things are working for you. Let's hope that some other listeners are inspired. I'm still on my soil journey, apart from anything else, I don't really have time to do too many experiments, but what I am thinking is that maybe I might try, where I'm growing things from cuttings, just starting them off in Leca. Then I don't have to do any adaptation. I can just start them off straight away and see how that goes because that might be my, sort of, baby-steps way of getting into it, but it's really interesting to hear how you've got on and thank you for sharing all your info!
Kimberly: I'll take two more seconds of your time: even with the cuttings, but I think my recommendation would be to grow into, like, a lot of times people say propagate right into Leca. I still had rot propagating right into Leca. What I found was, if I modelled the system after a propagation box and there was this style, I have to thank a guy named TechPlant - who's a really interesting guy who does plant experiments on Youtube - but he set up a propagation box that I think was really helpful just as a system, which is the Leca for several inches at the bottom, but at the top is a couple of inches of fresh sphagnum, with perlite mixed into the two. So the cutting starts its initial roots into the sphagnum and then immediately will start accessing the Leca below. Then when you're ready to actually move the propagule into Leca solo, all you have to do is just clean off the little bit of sphagnum at the top and the plant already has roots that are used to the Leca below.
Jane: That's really good. That's effectively how I propagate a lot of things anyway. I do have prop boxes with Leca and then some sphagnum in there, so that sounds nice and easy. I'll let you know how I get on and thanks very much for sharing.
Kimberly: Thank you, it's been a pleasure! I really appreciate it.
[music]
Jane: Thank you so much to Kimberly for joining me this week and, as ever, do check out the show notes for videos of rotary kilns and other exciting things that you might want to look at. Also, as I said in the intro, all the details for Tom Cranham's event in Derbyshire on 11th December. Thanks for joining me this week, I shall see you next Friday. Bye!
[music]
Jane: The music you heard in this episode was Roll Jordan Roll, by The Joy Drops, The Road We Used To Travel When We Were Kids, by Komiku and Overthrown, by Josh Woodward. All tracks are licensed under Creative Commons. Visit the show notes for details.
Subscribe to On The Ledge via Spotify, Apple Podcasts, Player FM, Stitcher, Overcast, RadioPublic and YouTube.
I find out how LECA is made and talk to LECA convert Kimberly Black, plus I answer a question about using pest sprays during winter.
Check out the notes below as you listen…
Picking roots out of PON, with tweezers. Photograph: Kimberly Black.
My guest this week, Kimberly Black, is a listener to the show: she offered to tell me about her experiences with LECA and her difficulties with PON as a followup to episode 198 on PON.
If you’re wondering, like me, what a ‘mother and daughter’ croton (Codiaeum variegatum) looks like, there are examples here and here.
The YouTuber Kimberly mentions is Techplant, their video on prop boxes is here.
LECA facts
LECA is an acronym (you can say the initials as a word) that stands for Lightweight Expanded Clay Aggregate.
LECA comes in different sizes and densities: with a diameter up to about 2.5cm across, and a density of up to 500kg/m³.
Aside from horticulture, it has many other applications, including as building material, water filtration and thermal insulation.
It is made from clay that is heated to immense temperatures, around 1000C which is 1800F, using rotary kilns, which move the clay particles as they are heated. I’ve watched various videos and they vary in size and complexity, but the kilns look like big metal tubes with conveyor belts running up to them at one end filled with the raw material. There’s a video here if you want to watch a rotary kiln in action. Thanks to listener Bas for pointing out this other, more professional LECA production video!
The raw material - clay - is usually strip mined close to the kiln, because clay is heavy to transport!
LECA and sustainability
The bad news: clay is a finite resource and strip mining is clearly not a carbon neutral activity, nor is firing up a kiln to extremely high temperatures.
On the plus side: LECA is lighter than traditional potting mixes to transport. It can be reused countless times. My original bag has lasted about eight years and I have only just bought another!
Using LECA for houseplants
Always give LECA a rinse when you are using a new supply, so that you remove any debris or dust that could damage your plants. (See below for rinsing equipment and techniques).
LECA has several applications for soil-based growers: I use it to mulch the top of pots, put a layer in the bottom of cachepots to soak up excess water, and use it as the ‘pebbles’ in a pebble tray under plants to boost humidity.
I also use LECA in propagation boxes: a plastic lidded box with a layer 5-10cm deep of LECA at the bottom, kept damp. Cuttings can root easily into this as they have easy access to both air and water. I sometimes add some moss to the top.
LECA can be used in semihydro and full hydroponic growing systems: this could start with something super-simple such as a glass jar filled with LECA.
Rinsing LECA
It’s worth rinsing LECA before first use, and every time you wish to reuse it. This will remove organic matter, buildups of mineral salts and
Some people boil it, but this seems OTT (and not very sustainable) to me. Instead, use a horticultural disinfectant such as Citrox by Agralan, or diluted food grade hydrogen peroxide: there’s a useful dilution calculator here.
I rinse LECA using an old salad spinner but you can also use a garden sieve or a mesh laundry bag. Once rinsed, if you are not using them immediately, spread them out on a plastic tray or tarp to dry, then store in a bin or similar.
QUESTION OF THE WEEK
Eliza is dealing with a pest infestation on her 200 plants and wants to know if using the pest treatment SB Plant Invigorator is a good idea over winter.
This is a spray that treats pests and is also meant to contain nutrients so it has an additional benefit as a foliar feed. Unfortunately there doesn’t seem to be info about the nutrient profile of the product - ie how much nitrogen potassium and phosphorous it contains. I’d suggest that it’s fine to keep using it on plants that are actively growing, but it may be wise not to add any additional feed to the soil, and maybe switch it out for plain water every so often if you are spraying daily.
For more information and advice on thrips control, have a listen to On The Ledge episode 205.
Want to ask me a question? Email ontheledgepodcast@gmail.com. The more information you can include, the better - pictures of your plant, details of your location and how long you have had the plant are always useful to help solve your issue!
HOW TO SUPPORT ON THE LEDGE
Contributions from On The Ledge listeners help to pay for all the things that have made the show possible over the last few years: equipment, travel expenses, editing, admin support and transcription.
Want to make a one-off donation? You can do that through my ko-fi.com page, or via Paypal.
Want to make a regular donation? Join the On The Ledge community on Patreon! Whether you can only spare a dollar or a pound, or want to make a bigger commitment, there’s something for you: see all the tiers and sign up for Patreon here.
The Crazy Plant Person tier just gives you a warm fuzzy feeling of supporting the show you love.
The Ledge End tier gives you access to two extra episodes a month, known as An Extra Leaf, as well as ad-free versions of the main podcast on weeks where there’s a paid advertising spot, and access to occasional patron-only Zoom sessions.
My Superfan tier earns you a personal greeting from me in the mail including a limited edition postcard, as well as ad-free episodes.
If you like the idea of supporting On The Ledge on a regular basis but don't know what Patreon's all about, check out the FAQ here: if you still have questions, leave a comment or email me - ontheledgepodcast@gmail.com. If you're already supporting others via Patreon, just click here to set up your rewards!
If you prefer to support the show in other ways, please do go and rate and review On The Ledge on Apple Podcasts, Stitcher or wherever you listen. It's lovely to read your kind comments, and it really helps new listeners to find the show. You can also tweet or post about the show on social media - use #OnTheLedgePodcast so I’ll pick up on it!
CREDITS
This week's show featured the tracks Roll Jordan Roll by the Joy Drops, The Road We Use To Travel When We Were Kids by Komiku and Overthrown by Josh Woodward.