Tom's Potting Soil Recipe

Discussion in 'Indoor and Greenhouse Plants' started by Tom Hulse, Aug 1, 2020.

  1. Tom Hulse

    Tom Hulse Active Member 10 Years

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    I've been getting questions about my recipe, so I'll include it here in a new thread. It's made to only be the base for a range of mixes depending on an individual plant's needs. This would be the most water-retentive, high-organic version I use; then for some plants, like for instance palms, it would get get extra drainage material added. For some caudex-forming plants or hearty (not hardy) succulents it gets lots of extra drainage. For delicate succulents I start completely from scratch with a different mix.
    My goal with this mix is maximum growth for indoor tropical houseplants in an organic mix without having any odor problems for the sensitive non-plant-lovers in my family. I want it to hold water but also lots of air at the same time. I also want the mix to be able to to very well transfer water up and throughout the pot so the top is similar to the bottom and I know better when to water, thereby reducing overwatering problems. The core of mix is one widely used by thousands of container food & medicinal (illicit) growers around the world. It's 1/3 organics (like compost or worm castings), 1/3 drainage (perlite, pumice), 1/3 water retention (peat, coir), plus organic fertilizers, minerals, and pH adjustment. Here is my favorite version that I've slowly developed over about 25 years of using that basic core:

    10 gal long-fibered blonde sphagnum peat moss (like Pro-Moss TBK, not regular peat or plain sphagnum)
    6 gal pumice
    4 gal perlite, washed
    5 gal long-aged compost (must contain no manures for indoor use!)
    5 gal pure worm castings (stay away from brands with lots of filler)
    4 cups ground oyster shell flour
    2 cups kelp meal
    2 cups alfalfa meal
    2 cups azomite
    3 cups greensand
    3 cups gypsum
    4 cups basalt dust
    Makes 4 cu ft, fits perfectly in a Rubbermaid Roughneck 44 gal garbage can on wheels. Premix dry minor ingredients before adding slowly to the majors. With high-organic mixes, let them "cook" for a month, medium-wet, before using; especially if you don't have access to long-aged compost, which is usually not something you can buy off the shelf (I store my compost an extra year after it is finished).
     
    Last edited: Aug 1, 2020
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  2. Tom-Pierre Frappé-S.

    Tom-Pierre Frappé-S. New Member

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    Thanks Tom! Good idea to start a seperate thread.

    I finally found some pumice yesterday so mixed this up - or at least my closest equivalent.

    Can you talk more about the purpose of the oyster shell, azomite, greensand, gypsum, and basalt dust and suggest substitutions for those of us who don't plan to have a fertilizer library ;) ?

    Mainly, I'm assuming some of these are bases to balance the acitdity of the peat. If one were to replace them with one single source of alkalinity, say dolomite lye, how much would you put?

    thanks,
    Tom
     
  3. Tom Hulse

    Tom Hulse Active Member 10 Years

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    Hi Tom. I should point out first that this is my version aimed at reaching for very optimal growth, and you could easily have a more simple mix equivalent to some very expensive potting soils with the just 3 basic ingredients of peat moss, perlite, and compost; plus perhaps a little lime for pH balance.

    I use oyster shell flour to offset some of the acidity in the peat. I prefer it over calcareous or dolomite lime because the one I use has a mix of particle sizes, giving it a slow-release effect for houseplants that may be in a pot for more than one year. The other ingredients, except peat, are near neutral in pH. If you're using dolomite lime, the usual recommendation is 1 cup per cu ft, or 2 TBS/gallon. That is based on the overall volume of total mix, not just the peat.

    The Azomite, greensand, and basalt dust are concentrated mineral dusts for a diverse range of trace elements without spiking the heavy metals. Mineral dusts have been shown to increase growth, increase yields, improve the quality and taste of produce, and improve disease and pest resistance. They to need to be in very fine dust form to be available to the microorganisms which make them usable to the plants. The gypsum is mostly for calcium. None of these are necessary to have a very fine quality potting soil.

    'Fertilizer library', I like that. Yes I'm a little crazy about my dirt. For normal people, it's hard to get maximum results from organic fertilizers without using many ingredients. So if you wanted to really simplify, I would recommend perhaps thinking about a high-quality, liquid, general fertilizer like Dyna-Grow's Foliage Pro. 1/4 tsp/gal at every watering of that added to even very basic soil will guarantee very beautiful, shiny, healthy plants.
     
  4. Tom-Pierre Frappé-S.

    Tom-Pierre Frappé-S. New Member

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    Thanks Tom - appreciated! Looking forward to seeing the results.
     
  5. May Pantaleon

    May Pantaleon New Member

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    Hello again Tom,

    How are you? Hope you are doing well! I've been trying to find some of the ingredients in this soil mix but I can't seem to find azomite, or well aged compost. I found sea compost at one of the big box stores here in Vancouver, BC but I am not sure if that will work as well? Is there anything I can substitute them with? Also, I found this brand called Gaia Rock Dust, can I use this instead of basalt dust? Thanks again in advance!

    Cheers,

    May
     
  6. Tom Hulse

    Tom Hulse Active Member 10 Years

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    Hi May. :) The Gaia Rock Dust looks like a good one. I would be happy to use that myself. Azomite is another kind of rock dust, high in beneficial trace minerals. Down here just across the border we can find it in almost any better quality nursery when they have a section for organic soil amendments. You should also be able to get it on Amazon, or here is a Google search that might help you find it. It's not essential to the mix. You could sub another rock dust like Greensand; or just leave it out.

    Well-aged compost is never sold with title "Well Aged", it's more of a description than a title. You can either keep some cooking longer than it needs in your compost pile, keep some bags stored away in your garage, or verify yourself what the age of your compost is. Mine is local municipal compost (bagged) from yard waste pickup that has been cooked for a minimum of 5 weeks at 150 F/66 C (Cedargrove compost). That is longer and hotter than most local bagged compost. I also buy ahead what I'll need for next year and always have a few bags stashed away from a year ago in my garage. Aged compost is mostly done changing and rotting and is much more stable for a premium houseplant-type mix you would like use for several years in a pot. Conversely, fresh compost is often not done yet. I holds more water when new, changes more over time, and has a higher chance of bringing pests like fungus gnats. However, I think you should just find the best bagged compost you can locally and not worry at all about it (buy some for next year!). It should be just fine as long as you avoid anything that contains manure or sawdust (not really compost). I think sea compost can be great if it is low in sodium salts, but usually it is not appropriate for use in an indoor mix because of the odor (It's everything nasty left over from seafood processing, then composted... an outdoor garden plant's dream).
     
  7. May Pantaleon

    May Pantaleon New Member

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    Thanks again Tom! I found azomite from an online store and bought it! Just need to wait for it to arrive so I can get the soil mix going. I'll be splitting it with friends because it's a lot and I have no room. Haha.

    I'm curious though, there is this soil mix called U-Cann nutrient dense super soil. I found it online from a cannabis hydroponic store. Do you think it's a good mix to use for house plants? Sounds similar to your mix but I am not sure I like the sound of peat moss. I am also assuming this mix is very pungent? Thanks again for your input! You've been a great deal of help!


    Bulk Ingredients: African Night Crawler Worm Castings, Coconut Coir, Compost, Fir Bark, Peat Moss and Perlite

    Nutrient Ingredients: Alfalfa Meal, Azomite, Basalt Rock Dust, Bio Char, Blood Meal, Bone Meal, Feather Meal, Fishbone Meal, Fossilized Carbon Complex, Glacial Rock Dust, Greensand, Gypsum, Insect Frass, Kelp Meal, Limestone Flour, Mined Potassium Sulfate, Mineralized Phosphate,Oyster Shell Flour and Rock Phosphate
     
  8. Tom Hulse

    Tom Hulse Active Member 10 Years

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    That's a great soil for outdoor plants. It's marketed towards cannabis growers who will always have very fast growing, herbaceous plants under very high light. And this type of soil will give very high measured growth rates for those conditions. Two problems for houseplants though: the smell and the higher rate of organics can lead to fungus problems indoors in lower light with slower-growing plants. I would love to use many of those products, but blood meal, bone meal, feather meal, fish meal (also bat guano, seafood meal), and others, will all have odor problems for indoors use. Keep them outside.

    I used to cut my peat moss in half with coconut coir. I like a diversity of ingredients, and coir is almost as good as regular peat moss at holding both air & water at the same time. However the blonde peat is a good jump up better than both at getting more air in the mix while still holding lots of water. Also, coir is pH-neutral, and I need the low-pH property of peat to allow me to get more higher-pH calcium-containing ingredients. In my type of mix where I'm trying to get lots of calcium, I risk the overall pH creeping up too high if I use too much coir. I actually made the switch to all blonde peat when I read some of the formal studies about seedlings growing slower in coir than peat and about the variability of the salt levels. I've also looked deeply at the sustainability issue and I'm now much more comfortable with peat.

    Bark I use in some mixes, but never combined with wetter ingredients like peat & coir. In my opinion they work against each other by having very different drying rates. I also don't like how bark will be like a large dry chunk of perlite at the beginning (water just runs off of it), but a year or two down the road it's a very wet sponge that never dries out in a peat-based mix. So long-term stability is an issue for me there. I prefer to get my drainage component from pumice and perlite.
     
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  9. May Pantaleon

    May Pantaleon New Member

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    Good thing I didn't buy it! I had a hunch it all might be too much for indoor plants. I have bone meal at home and I use it sparingly because of its smell.

    I have noticed my aroid mix always seem to have uneven moisture levels in them. I took note, so, when I repotted a couple of plants earlier today, I ditched the bark in my mix and used spaghnum moss instead.

    What about using soil inoculant like mammoth p? My friend told me about it but we both have no idea how to use it. Is it useful for houseplants as well?
     
  10. Tom Hulse

    Tom Hulse Active Member 10 Years

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    Adding sphagnum moss to aroid mixes has been used by many successful aroid growers, but I've usually seen it without other wet/fine ingredients like peat or coir. Most often it's bark, sphagnum moss, and a couple other various drainage ingredients like perlite or charcoal. So if you include it in a mix, I would want it to be with only medium-sized or larger particles. Even though it is one of the wettest ingredients available, it works when it is 100% by itself because it's structure keeps it open to air and it dries very fast. So you can grow many delicate epiphytes and carnivorous plants in it very well (100% sphagnum) because of the fast dry. However, when you start mixing it with finer ingredients, it still holds that amazingly high amount of water, but now all the spaces around it get filled in with the coir or peat, not air. This risks drying too slowly and causing overwatering problems. You lose the super-aeration quality of this very-wet ingredient. Anecdotally, some have had success using a little sphagnum in a peat-bark-perlite type mix, but I believe it was in spite of the sphagnum, not because of it. Another way to say that is you can afford to include more organic ingredients for faster plant growth, but still get the same air/water balance if you don't use sphagnum together with peat or coir. Hope that makes sense!

    Mammoth P looks like a fine soil microbial inoculant, but the elephant in the room they are not making clear to you is that even though they tested for billions of different types of beneficial bacteria, which could be possible thru artificial selection methods, they only tested it against one plant, cannabis. That bacteria is tuned for hydroponic production of cannabis. Plants in general use a widely varying selection of different bacteria for these beneficial mycorrhizal associations. What works for one plant very likely may not work at all for another plant. There have actually been a lot of formal studies done on which strains are most beneficial to the widest array of different plants, and there are many products available under "mycorrhizal inoculant" that use these more versatile strains. So for houseplants, I would consider something different. :)
     
    Last edited: Oct 5, 2020
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  11. May Pantaleon

    May Pantaleon New Member

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    Wow! That makes sense! Thanks, again! I just received a couple of aroids and I think I will definitely take your advice. I think I will also try using your soil mix for some of my aroids but add extra drainage material. Maybe I'll find a better and a more affordable alternative to Mammoth P. :)

    By the way, does your soil recipe have a best before date? Or would I be able to keep it for 2-3 years and still use it? Or should I just mix what I need and just store the leftover material for future use?
     
  12. Tom Hulse

    Tom Hulse Active Member 10 Years

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    Make sure to use lots of extra drainage for most aroids (except growth monsters like vigorous Alocasia). These ingredients should store just fine for a very long time. I like to store it barely damp in big 44 gallon trash bins. It's designed to last several years in a pot, if you need to.

    If you're going to try mycorrhizae, you might look for a product with several kinds of endomycorrhizal fungi. The other main category, ectomycorrhizae, are only found in about 10% of plant species. Often the better products will also have some bacterial inoculants included too. Here is one product I was considering earlier in the year. I have no association with them and haven't personally tried it.

    When applying these inoculants, mix it with the soil of each individual plant, not to your big batch of soil mix. It looses viability too soon in a stored soil mix (usually too dry) without host plant roots to thrive on. If it is a granular product, try to get the granules in direct contact with the roots, don't rely on watering it in to transfer it to the roots like we do other garden products. When buying try to get it directly from the manufacturer instead of a reseller. These are living products and are susceptible to all sorts of mishandling. It would be best if you ordered during the time of year not the hottest or coldest in your area. Also be aware that even though there is a possibility for increased growth & health, with a soil mix like we discussed above (compost & worm casting are very alive) it is certainly not essential.
     
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  13. bihai

    bihai Well-Known Member 10 Years

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    Hey Tom I ran into Mike at the post office today...he was mailing your plant!
     
  14. Tom Hulse

    Tom Hulse Active Member 10 Years

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    Cool!!!
     
  15. AdrianaCe

    AdrianaCe New Member

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    Hi Tom,
    Would this be a good potting mix for my fiddle fig leaf? Im a newbie plant parent and bought a beautiful specimen but it is so root bound that I’m looking into reporting it - I know now is not the ideal time for that but many of the leaves are dying and turning brown. Debating between Al’s 5:1:1 mix and your recipe. Your guidance us much appreciated. Adriana
     
  16. Tom Hulse

    Tom Hulse Active Member 10 Years

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    Hi Adriana, welcome to the forum. :) Yes this would make an excellent mix for your fig, especially one that has been rootbound. You see circling roots at the top outside of the soil? You can lift the whole root ball intact out of the pot without disturbing the soil? I know the 5:1:1 works fine for these Ficus as well, especially if you tend to be an overwaterer. However, a bark-based mix like that doesn't have any nutrients in the soil (like the compost, worm castings, kelp & alfalfa meals, etc.), so you have to get 100% of your nutrients from added fertilizer. So then you must be much more frequent and diligent with water and fertilizer just to get results that at are the bottom range of the potential of a nutrient-rich soil like I described above. The trade-off for the reduced growth potential is that airy, bark-based mixes are nearly impossible to overwater, if that is your tendency.
    When you repot, water the day before. Tease apart the circling roots and trim any that are dead, dying, or too long to fit in the new pot. Choose a pot usually just one size up from existing, don't go too big. If you are determined to repot now, somehow try to get the plant more light. This is very important! Often low light and low humidity can also be the culprits for the plant's decline you described. So maybe closer to the window, a better window, or by adding supplemental artificial light in addition to what it's getting.
     
  17. emandeli

    emandeli Member

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    Can you tell me why the perlite is washed?
     
  18. Tom Hulse

    Tom Hulse Active Member 10 Years

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    Hi emandeli. It's washed to remove most of the fines, which don't add to the drainage or air holding power, but do add to the amount of water it retains. If you wanted more water-holding ingredients, it would be better to do it with peat instead of perlite fines, because the peat will will hold much more air at the same time it is holding water, which is much better for roots. :)
     
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  19. emandeli

    emandeli Member

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    Sorry this reply is so late. I appreciate the advice thank you.
     
  20. N D

    N D New Member

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    Tom, out of curiosity, where do you get your supplies in the lower mainland? Some of those items are harder to find than others (I seem to have a hard time getting my hands on peat especially!).
     
    Last edited by a moderator: Feb 25, 2021
  21. Tom Hulse

    Tom Hulse Active Member 10 Years

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    ND, around here most home centers & garden centers have 3 cu ft bales of standard peat, which is adequate. Looks like Lowes in Queensborough has lots in stock. I get the long-fibre blonde peat at a nursery supply outlet called Stuber's in Snohomish, Washington. If you wanted that same product, I don't know if you have nursery supply places near you that sell to the public, but you can also try the hydroponics stores, they're all over, and I imagine some would have it under TBK Pro-Moss from Premier Horticulture. The meals & dusts are sold in the organic gardening section of most of the high-quality nurseries around here. Lots of room for substitution though.
     

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