Wednesday, July 29, 2009

Potting soil recipe for tropical plants

One of the many things that I learned on my trip to Steve Lucas's Exotic Rainforest atrium was how to simulate rain forest soil.  Steve showed me the soil that he makes and uses for all of his tropical plants (primarily Aroids) and explained the natural processes that make a very similar soil in the rain forest.

As far as I know, there aren't any potting soils available for purchase that are as good as the one listed below.  If you like growing tropical plants, try making your own soil mixture - it's fun and it's likely to be better than anything you can buy!

Below is the recipe, along with some of my customizations.  You can make this great potting mix pretty cheap, if you're creative.


  • Miracle Grow Moisture Control potting soil

  • Sphagnum Peat Moss - broken up by hand

  • Cedar mulch - only the smallest pieces

  • Charcoal

  • Perlite

  • Orchid Bark Mix

  • Sphagnum Moss - cut into tiny pieces

The goal of this mix is to provide a highly-organic, quick-draining soil.  Many of Steve's Aroids are epiphytic or semi-epiphytic, which means that they grow on trees in nature and require very little soil.  However, in nature their roots are nearly always getting wet.  The idea is that the roots don't need to stay wet long, because another rain will come soon.  The tropics are known for their regular rain fall.  With the chunks of bark and moss in this soil, the roots make contact with moisture in the soil, but will not be sitting in a wet soil for any period of time.

As with all recipes, there is plenty of room for experimentation.

The first ingredient is a suggested base potting soil.  I have purchased a non-name brand potting soil that is a competitor to the Miracle Grow Moisture Control.  It is priced a little cheaper and I can't tell much of a difference, after having bought both of them.  Recently I found a really good potting soil at a local nursery (TLC) that includes some additional organic material, including some small pieces of cedar mulch.  Naturally, this negates the need for adding cedar mulch separately.

Sphagnum peat moss can be purchased in large blocks.  I bought by huge bag about 2 years ago and I'm just now finishing it off.  I have potted some plants exclusively in peat moss, but I usually mix it with equal parts of a potting soil. Make sure to break this apart in to small pieces to that it will mix well with the other ingredients.

Cedar mulch or cypress mulch is one of the ingredients that helps with drainage.  It loosens up the mix and adds more avenues for water to escape from the soil.

You can purchase a couple of different types of charcoal that are safe to add to your potting soil: aquarium filter charcoal and horticultural charcoal are both safe bets, but can be expensive.  The cheaper barbeque charcoal is not safe to add to your potting soil, as there are added ingredients in the processing that can add harmful elements to your soil.  I chose the ultra cheap option, which is to gather some charred wood from fire pits.  There is still a risk of getting charred wood that has lighter fluid on it, but the lighter fluid is likely to have all burned.  I played it safe and used wood from my own fire pit in the backyard, which I knew had never had lighter fluid on it.  The charred wood can either be broken apart by hand or with a hammer.  It's a messy job, but we are talking about dirt, here.

In place of perlite, I substituted vermiculite.  The two ingredients have different properties, but I already had vermiculite on hand, so that's what I used.  I use vermiculite for rooting cuttings and also for my hypertufa pots.  Perlite is much easier to find than vermiculite and can be bought in a number of different sizes.  As with all of these ingredients, if you're planning on messing with plants for the rest of your life, it's probably cheapest to buy the larger size for the long haul.

When it comes to the bark mix, I guess I am luckier than most.  In my backyard there is a huge Sycamore tree and a fairly large Magnolia tree.  Both of these trees shed some bark at certain times throughout the year.  The Sycamore sheds a lot of bark in the middle of the Summer.  Not only do I get free bark for potting soil, but I'm not just raking it up and putting it in cans at the curb.  I crumble the bark in to as small of pieces as I can manage and mix it in with everything else.  Of course, if you don't have a bark factory in your backyard, orchid bark mixes are pretty easy to find these days.  Just look at your local home and garden/hardware store in the potting soil section or houseplants section.

The last ingredient, Sphagnum Moss, can also be found in this section.  It is also used for potting orchids.  If you cut the long, stringy pieces into small pieces no longer than 1 inch, it will work its way into the mixture rather well.

I hope you enjoy making your own potting soil.  Good growing!


  1. Zach, how did you know that I needed this recipe?! Thanks!!!

  2. Have you been able to tell a difference in your plants/survival/growth since you have been making your own potting soil?

  3. In answer to Mary's question:
    Yes, I have noticed a big difference.

    Some of my new Aroids that I got within the last year started to die unexpectedly. I thought I was caring for them as I should. I pulled several out of the soil to see that the rich potting soil was staying wet and the roots were rotting. Most Aroids (Philodendrons, Dieffenbachias, Aglaonemas [Chinese Evergreens]) like to be in "quick-draining" soil, not moisture retentive soils. So I have been adding different things to the soil to make the water drain out of it quicker. It has helped a lot and the plants that I was able to save are doing really well now.

    Of course, many plants want to be in moisture retentive soil, so this would be a bad choice for plants that easily wilt and need to be watered a lot in the heat of the summer. I probably wasn't clear enough about this in my post. For instance, you wouldn't want to plant most annual flowers in this soil mix. They would probably always be thirsty and their roots are too fibrous (tiny) to be in a loose soil mix like the one I described.

    Does that make sense?

  4. Would this be good for banana trees or elephant ears. I plan to move them into the house at the end of summer.

  5. What a great article! I can speak from personal experience--I love tropicals, especially aroids, bananas, and unusual ferns. I have killed off the occasional tropical plant, and from my experience, soil and moisture were the culprits. I have gradually changed my potting mix to where some of my anthuriums and philodendrons are growing in pure orchid bark (likely over-kill in retrospect, but if given regular waterings the plants thrive compared to those grown in potting soil). I will definitely give this mix a try, and recommend it to anyone interested in tropicals.

    A few extra points:
    I don't believe the potting soil is really necessary, and if so, certainly not in any sizeable amount in the mixture.
    Tropical begonias also do well in this mixture.
    Common belief is that bananas, colocasias, and alocasias need wet soil. Colocasias and alocasias do well in a free draining mixture such as this one, provided they receive regular waterings.
    Bananas like to have their rhizomes dry but their roots moist. I plant them in pots in a mix such as this one, then scoop out the soil from around the outer edge of the pot, leaving the rhizome (base) of the bananas on a mound above the surrounding soil in the pot. This way you can water regularly, but still keep the rhizome dry. When I plant bananas outside, I make a mound of peat moss, manure, and humus and plant the banana in this mound so that the rhizome stays comparatively dry. Bananas do very well for me during draughts, but I have killed a few grown in soil that was too wet. The myth about the difficulty of growing the AE AE banana is related to this--folks who kill their AE AE usually don't have it in a soil mixture that drains fast enough and the rhizome then rots.