Episode 158: an A to Z of potting mix ingredients, part three

Transcript

Episode 158

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Jane: Are you ready to get dirty again? It's time for part three of my potting mix ingredients A - Z. My name's Jane Perrone and I'm the host of this here podcast, On The Ledge; a cornucopia of houseplant info. Today, I bring you the final part of my epic three-part series into the things that make up the stuff that goes around the roots of your houseplants. I can't put it any more plainly than that. Plus, I answer a question about mixing it up, putting more than one plant of different species in the same pot.

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Jane: In fact, because I feel like it, we're going to start with Question of the Week this week, which comes from Jill, who says they're an avid outdoor gardener but new to houseplants. Well, welcome to the world of indoor gardening, Jill! Good to have you on board! Jill has what they describe as "a possibly odd scenario" - I do like an odd scenario! Let's look at the details. Jill, actually, is an ideal candidate to start her own indoor jungle because she has a yarn-dyeing studio. Because she's got big pans of water steaming throughout the day, it's warm and humid. Are you thinking what I'm thinking, listener? Yes, I think Jill's going to end up with a lot of houseplants before long and they're going to absolutely love that warm, humid environment. Jill says that not really knowing much about houseplants, "I potted a Prayer Plant, a Snake Plant and variegated Ficus, all in the same large pot. All seem to be happier and putting up new growth but the Prayer Plant is getting massive. Should I plant them in separate pots, or just let them fill the one they're in? Is now an okay time to repot or should I wait?" Jill is in the North East US.

Well, Jill, what a lovely problem to have. I am all for mixed planting. It's something that comes up now and again in the show. We really should talk more about it because it is a really great way of creating beautiful houseplant displays. The plants that you're talking about in your particular arrangement - you've got a Snake Plant, Sansevieria or Dracaena to use the correct genus name, although I can't quite come to terms with that yet, a Prayer Plant, so presumably something from the Maranta group, we don't know exactly what but whichever one it is, the answer will be the same, and a variegated Ficus. How will they live together? Obviously, for the moment they're living together very well because they're putting on good growth and the Prayer Plant is starting to do its thing and get enormous. So, what should Jill do? I think in the long term, the Snake Plant of that trio is the plant that may be the least happy with that set-up. Snake Plants can cope with a huge spectrum of conditions and that's why they're so popular as houseplants. Ideally, they will like a slightly more free-draining potting mix than the other two and they'll also love a good exposure to full sun. I know lots of people suggest Snake Plants for the deepest shade, but really if you can give them sun and a good blast of heat in the summer, you do get much better growth and results and it opens up the possibility that the plants will flower which is especially nice because Sansevieria flowers are lovely.

I think, going into the autumn, fall for you Americans out there, that it's probably fine to leave the plants as they are for the winter. The only worry, really, is that you'll need to water the Maranta more than the Sansevieria would like. It's a tricky one. I would say, probably, if the Maranta is getting really, really big it is worth taking the time now to separate out the plants and redo the companion planting thing but with a slightly different combination. I would take that set up apart, the Sansevieria, that would look great with other Sansevieria, so you could have a mixed planting of various Sansevieria in the same big pot, I always think that looks amazing. So, you could have one of the tall Sansevieriacylindrica, Trifasciata, and then around it, you could have some of the birds nest types like Hahnii, so think about that as one option. I know it probably involves buying more plants, or you could just pot the Sansevieria up separately and when you do that you can give it a bit of a grittier mix than the other two. Then your Maranta and your Ficus, you could keep those in a mixed planting and replace the Sansevieria with something like a low-growing Fittonia or a low-growing Pilea, the Heart Leaf Fern, Hemionitis arifolia, or you could have something like Pilea libanensis, a trailingPilea trailing over the side of the pot.

You may be wondering why I'm recommending doing this repotting now, at the end of the growing season. Oftentimes people panic about potting at this time of year. With cacti and succulents I'd be cautious about doing it, if you do have to repot cacti and succulents now then make sure the potting mix is pretty much just slightly damp as opposed to soaking wet because the plants are going into their dormant period on the whole. I think with most of these plants which are tropical, sub-tropical plants, they're used to growing all year round and, right now, they'll be fine. The one caveat is don't put them into an enormously bigger pot, try to keep the pot size roughly the same so those root balls aren't surrounded by a massive swathe of unrooted compost. I think it should be fine and offsets the risk of the Sansevieria rotting over the winter because you're having to water the Maranta more than the Sansevieria needs.

When you're setting up a mixed planting, the main thing to think about is what will go well together. They've got to be in the same setting, so choose plants that all like full sun or all like partial shade. Also, think about how much moisture they like around the roots. All these things will make the difference between success and failure when it comes to mixed plantings. Bear in mind that it's not a permanent solution, probably once every one or two years you will have to be breaking them up and moving things on, some plants will grow much faster than others. These arrangements don't last forever but they do look fantastic, so do give it a try. I hope, Jill, that helps you have some ideas for your particular arrangement, I'd love to see a photo of your yarn studio and all the plants in it because it sounds amazing. If you've got a question for On The Ledge, drop me a line to ontheledgepodcast@gmail.com and I will do my best to answer. It really helps if you include your location and pictures and as much information about the plants as you can, because telling me your plant has got yellowing leaves, it could be literally anything, so bung over loads of information and I will do my best to help.

Thanks to all of you who have supported my crowdfunder for my book, Legends of the Leaf. We're at 23% as I speak, which is very exciting, with 156 supporters backing the book. There is still plenty of time to show your support if you would like to claim your copy. The book will not go ahead unless I get 100% funded. Don't worry - if it doesn't get funded, you will get your money back, so there's no risk involved really. It's just a bit of an investment in your future enjoyment of my words which will come as soon as I can get the book written and produced and, I tell you what, I've started doing some research and I've found out some really cool and interesting stuff about one of the plants I plan to feature, so I'm really looking forward, I'm itching to write this book, so please help me out by pledging! The pledges range from £10 for the eBook, to £35 for a collectable signed first edition and your name in the back. Yes, you can get your name in the book! How exciting would that be? So, please do take a look at the different options for pledging. There's lots up there and there will be some new ones being added, so do keep your eyes on my Unbound page. I'll put a link in the show notes and it's also linked in my Instagram profile as well. If you don't have funds to support the project at the minute, I totally understand. Please do send it on to everyone you know who is growing an indoor jungle because I would love to get the word out as far and wide as possible. If you listen to the Skinny Jean Gardener Podcast this week, I'll put a link in the show notes, you can hear me talking a bit more about the book with host Lee Connelly. It's tremendous fun, so do go and have a listen to that.

Thank you to DeeElizabethKay and Kimbral9 in the US, who have left lovely reviews for On The Ledge podcast. I'm glad to hear you've been enjoying the show!

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Jane: It's time to get cracking with our A-Z of potting mix ingredients Part Three and we're on the Ps today. We've got 3 Ps, an R, an S, a V and a W. Are you ready? The first P is peat. I'm not going to talk a huge amount about peat because I've already done an episode on it and I will link that in the show notes. It's episode 103, but I'll summarise here. What is peat? Well, it's basically moss that has broken down over millions of years and turned into peat which is found in acidic wetlands all over the world. The thing about peat is, once you've taken it out of that bog, it's not going to regenerate for millions and millions of years further, so, it's a non-renewable resource. I've been growing without peat for about a year-and-a-half now. I've had no problems. If you remember back to episode 103, I interviewed Sean Higgs of Floralive, which is a carnivorous plant nursery in the UK. Lots of people say you can't grow carnivorous plants without peat, but Sean is proving that you can. So, it's really not a substance that we need in our houseplant world any more. Look out when you're reading potting mix packets because, oftentimes, they won't tell you they contain peat. This is a particular problem with John Innes mixes which I talked about in the last episode. Do look, because it should say somewhere the percentage of peat in the mix and oftentimes you'll find that packets marked "organic" or "natural" will still contain peat because, of course, peat is both organic and natural. These two words are so vague that there isn't any useful meaning to them. I'd urge, if you can, to switch to peat-free suppliers. I use Melcourt SylvaGrow. I've also used Fertile Fibre and Dalefoot here in the UK. I'm not so familiar with the US products but it is worth looking into peat-free options where you can.

P number two is Perlite. If you remember, I've got Mr Houseplant, aka Vladan Nikolic, to help me with these episodes, so I'm going to hand over to Vlad to explain what perlite is and what you can use it for.

Vlad: Perlite is volcanic rock that is mined and then heated at high temperatures in order to expand and is generally used to improve drainage and provide good aeration. It's light, it's easily available, you can buy it in a lot places and it's very affordable. It's also pH neutral, it has a pH of 7, it comes in different sizes. I like to use coarser perlite and it's generally good practice to get it wet before using it as there can be a lot of dust flying around when you work with perlite. All in all, it's a great amendment. The only disadvantage is it has the tendency to float to the top of the soil after watering.

Jane: Yes, you do have to be careful with perlite because it is incredibly dusty. Wet it first and do wear a mask if you have sensitive lungs because it can be quite evil if you get a lung full of that. Sustainability-wise, perlite is a non-renewable resource. It's lightweight, so it doesn't cost a lot to transport. The argument for perlite is that there's supposed to be a really big amount of it left in the world. We've mined just 1% of the total perlite allowance on the earth, but the stuff still has to be mined and processed, so if we can find an alternative that is renewable, well, all to the good. It's something that I've been looking out for some alternatives to for a while. The difficulty is that perlite, like grit and like vermiculite, because it's not an organic substance, it doesn't break down over time and therefore it's a really good addition to your potting mixes because it holds that soil structure and makes sure those air holes remain, so that's why it's really difficult to find a good alternative to perlite.

So, we'll skip ahead to R, which is for rice husks at this point, and I have been trialling them as an alternative to perlite. What I can tell you is that they're okay, they do break down, within about six months of using them in a potting mix, they were starting to break down, so not really ideal if you're wanting to use them for cacti or succulents because they're not going to help maintain that soil structure in the longer term. They are really high in silica which, as we've heard in previous episodes, can be a good thing, but they're really, really quite expensive compared to perlite. Give them a go but they are an expensive alternative.

One other alternative to perlite that I'm excited about, but haven't yet had a chance to try, are called grow stones and these are made from 100% recycled glass. I'll put a link in the show notes to an interesting article I've found about an experiment that tested perlite and rice husks against grow stones and came out with favourable results. In fact, a product which I have tried - Gnat Nix - seems to be a fine version of the grow stones, which you can use to top pots and discourage fungus gnats, so I'm interested in hearing more about grow stones. If you've tried them, do give me a shout and I'll certainly be looking for a UK supplier to give these a go. If it's using recycled glass, great, big tick, 100% recycled and they're high in silica and they're not causing any damage to the environment, then hey, it sounds like a win-win to me, but I'm still doing my research. So, please do let me know if you've got anything to add on this subject of perlite alternatives.

One perlite alternative we have not mentioned yet is pumice. Over to Vlad to explain.

Vlad: Pumice has advantages over perlite. It's also a volcanic rock, it's mined and crushed and then graded based on its size. It's very porous, it also improves the drainage. I like it better than perlite because it's a little bit heavier so it doesn't float to the top of the pot. For me, it's pretty annoying, after a few waterings and the whole of the top of my soil is covered with perlite but when I used pumice this doesn't happen. The problem with pumice is that it's more expensive and it's not as easily available as perlite, which is probably why not that many people use it.

Jane: I have to admit I do quite like pumice as an ingredient in potting mixes and, as you'll know if you've listened to my Euphorbia episode with Bob Potter, some people use this as 100% of their substrate when they're growing cacti and succulents. Pumice is a volcanic rock and is produced when lava escapes from a volcano, so in some sense it is kind of a renewable resource in that volcanoes are erupting all over the planet all of the time and when it's mined, it's mined from the surface because that's where the lava is flowing. There is an argument to say it's not as invasive a process as mining for other materials. As Vlad points out, it's more expensive than perlite, which is perhaps why people don't use it as much, probably depends on where you are in the world as to how freely available pumice is to you, but it's certainly worth a look as another way of adding aeration to your soil.

Next up, S is for sand. I have to admit I don't really use much sand these days, mainly because it's incredibly heavy. Like the grit, it's something that is going to make your pots weighty to say the least. It's main quality is meant to be improving drainage. Every grower has their own feelings about sand, I find, and some people find that if you use sand that is too fine, less than about one or two millimetres in diameter in terms of particle size, then it just gets really hard like cement in the pot and doesn't actually do the mix any good. If you are going to buy sand, make sure that you buy horticultural sand because regular builder's sand and the like can be way too high in lime. You're looking for more of a neutral pH, to match the pH that your houseplants are going to like. One thing that sand is really useful for is, if you're sowing very fine seeds, mix the seed with a handful of sand and sprinkle that over the surface of your tray and it makes it so much easier to ensure that your seeds aren't clumped in one corner. You'll also find that people have what's called a sand bench, if you're lucky enough to have a glasshouse, which is basically a bench filled with sand and into that you can put cuttings and often there's heating cables underneath to keep it warm and it's a really good way of starting off an awful lot of cuttings if you are lucky enough to have a greenhouse. You could do a much, much smaller version in your house, where you've got a tray of sand with a heat mat underneath and that would work just as well, an alternative to the Leca if you don't have access to that.

Now, the penultimate item in our A - Z is V for vermiculite. Like perlite, this is another mineral that comes from the earth and it's heated and it goes hugely larger, it expands hugely and it produces these long, wormy structures, hence the name, vermiculite, from the Latin vermicularis meaning to breed worms. I'll post a link to a rather interesting website called madehow.com which has an interesting piece on how vermiculite is actually made. Over to Vlad to explain a bit more about its pros and cons.

Vlad: It retains some water, but it also holds air. Its pH value can vary, so it can be from six to nine-and-a-half, depending on where it's been mined and where it's been processed. So, even different batches from the same mine can have different pH values, so you've got to be careful with that. A disadvantage of vermiculite is that it compacts easily. When you touch it almost feels like clay, so with some slight mechanical pressure it can compact and lose its water and air holding properties.

Jane: Is it sustainable? Well, like perlite, it's a non-renewable resource, lots of energy goes into heating it to high temperatures, so it does that wormy thing - I think they call it exfoliation. I would say use vermiculite sensibly and, where you can, find renewable alternatives. That might be things like bark chips, expanded clay pebbles, Leca and coir.

The final ingredient in our potting mix melange is wormcasts. What are wormcasts? It's really just worm poo. I can't put it any more succinctly than that. You can buy these by the bag and they're absolutely jam packed with nutrients, organic matter and beneficial enzymes and bacteria as well. I've got a wormery and I certainly do use those wormcasts in my garden, I don't think I'd be using those on my houseplants though. The stuff that you buy in a bag has been especially screened and they will have removed any worm eggs and other things that you don't want in your houseplant potting mixes. I can't really do that with my garden wormcasts so they tend to go outside. I don't really want a load of worms or indeed slugs hatching into my houseplant potting soil. So this ingredient does have a lot of advantages and if you're growing hungry plants, then it's really worth looking at as a soil addition. I'm thinking here of Aroids, then a good handful of wormcasts when you're repotting would certainly not go amiss. Just remember, if you are adding them to the soil, that you won't need to add any extra fertiliser for a while because they are a really great source of nutrients. It is powerful stuff, so do go easy. You may want to start off - if you're not in the process of repotting - with just sprinkling a small amount of the wormcasts on the top of the soil which will gradually work their way in and see how your plants react. If you want the benefit of the wormcastings without having to add them to the soil then you can buy liquid fertilisers which are made from wormcastings. There's a few different brands out there, so do take a look.

Well, that rounds up my guide to potting mix ingredients. What have I left out? What have I got wrong? What did you like? Please do drop me a line with your thoughts on potting mix ingredients, I'd love to hear from you. Perhaps you can even share with me your top secret potting mix recipe for your particular kind of houseplants. I love those little details of what you include in your potting mix recipes.

Thanks to my guest, Vladan Nikolic, this week. If you want to hear the entire interview I did with Vladan, then you need to be a Patreon subscriber. I'll be putting it up on the Patreon feed over the weekend, so if you're a Patreon subscriber do listen out for that. Michelle, Joshua and Christopher, who have become Patreon subscribers at the Ledge-End level this week, will be able to listen -- enjoy, guys! Find out more about how to become a Patreon on my show notes which are on janeperrone.com and Patreons, how do you feel about another Zoom session? I'm thinking of doing another one of those soon. Let me know if you're up for that and I will organise that hopefully not this weekend but the weekend after. Details to come shortly into your Patreon messages.

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Jane: That's all for this week's show. I hope you've enjoyed it. I'll be back next Friday. In the meantime, keep your pecker firmly in the up position. Whether you've got a weekend chockablock with activity, or some seriously-needed downtime with your plants, have fun, stay safe, and everything will be tickety-boo. Bye!

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Jane: The music you heard in this episode was Roll Jordan Roll by The Joy Drops and Overthrown by Josh Woodward. Both tracks are licensed under Creative Commons. See my website janeperrone.com for details.

Subscribe to On The Ledge via Spotify, Apple Podcasts, Player FM, Stitcher, Overcast, RadioPublic and YouTube.

It’s the final part of my run-through of the various things you can use to make up your houseplant potting mixes, including perlite and vermiculite; plus I answer a question about a mixed planter.

Missed the start? Here’s where you can listen to parts one and two of my potting mix A to Z.

Want to help me make my houseplant book Legends of the Leaf a reality? Pledge now! Want to know more about the book? Check out my interview with Lee Connelly, aka the Skinny Jean Gardener, about Legends of the Leaf.

This week’s guest

Thanks so much to Vlad for joining me to talk all things potting this week!

Check the links below as you listen.

P is for PEAT Peat is a non-renewable resource, and takes millions of years to form: National Geographic has called it “the forgotten fossil fuel”. Listen to episode 103, my sustainability special on peat for more information on why we shouldn’t be using peat in our houseplant potting mixes, or anywhere else in the garden.

P is for PERLITE This is another non-renewable source - volcanic glass that’s mined from the ground and heated so it expands: views over its sustainability vary. The perlite industry claims it has good eco-credentials but a lot of energy goes into its production. I’ve been looking for more sustainable alternatives, including rice husks. These work well for some plants but they break down too quickly to be of use for cacti and succulents. I’m also starting to explore Growstone as an alternative: it’s made of 100% recycled glass, and this article suggests it has shown good results.

P is for PUMICE This volcanic rock makes a good alternative to perlite, and may be considered more sustainable as it is available at the surface rather than being mined, plus it does not have to be heated to high temperatures during processing. It is lightweight and does not float to the surface like perlite but it is generally more expensive than perlite.

S is for SAND Sand seems to garner differing opinions among growers: some routinely use it in their mixes as a way of aiding drainage, but others find it to too heavy. Very fine sand (less than 1mm diameter) is best avoided as it can solidify in the pot and do the opposite of improving drainage! Always use horticultural sand as builders’ sand has too much lime in it for houseplants. Sand is useful for heated propagation benches like this, and for mixing with fine seed when sowing.

V is for VERMICULITE Vermiculite is a mineral that makes a useful additive to potting mixes, aiding aeration and holding water. from the Latin ‘vermiculare’ meaning ‘to breed worms’ owing the wormlike shape of the vermiculite as is ‘exfoliates’ under extreme temperatures. Check out my episode with Bob Potter for more on using 100% pumice as a substrate for succulents.

W is for WORMCASTS Worm poo is powerful stuff, containing organic material (humus), nutrients and beneficial bacteria. It’s best to buy screened wormcasts from a reputable supplier to avoid introducing any worm or slug eggs, or any pathogens, to your houseplants. It’s a useful addition to the pots of hungry plants such as aroids, but be sparing as it’s powerful stuff!

Question of the week

Jill wanted to know whether she should separate out her mixed planter of Sansevieria, Ficus and prayer plant: I suggested the Sansevieria would be happier with more succulent planting companions - for instance, other snake plants of different heights such as S. cylindrica and S. hahnii, while the other two could be replanted together with something lower-growing, such as a Pilea, (maybe a trailing one such as Pilea libanensis, Hemionitis airfolia (the heartleaf fern) or Fittonia. Mixed plantings can work really well, but try to make sure the plants all have roughly the same requirements in terms of light, soil mix and watering.

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 and so on.

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CREDITS

This week's show featured the tracks Roll Jordan Roll by the Joy Drops, An Instrument the Boy Called Happy Day, Gokarna by Samuel Corwin and After The Flames by Josh Woodward.

Logo design by Jacqueline Colley.

Houseplant care basicsJane PerroneOctober 2, 2020soil and compostComment