Aroid soil mix

Posted: November 16th, 2020 - In: How do I do it?

One of the first elements of this hobby that I wanted to tackle to improve the condition of my plants was my potting mix.  To begin with like most hobbyists, I started with a bag of potting mix from my local garden centre. These are termed “soilless compost” and will usually have a mixture of components such as: Loam or Peat (yup it’s still I there) sand, grit, pearlite and a mixture of fertilizers.  The first thing I noticed about this stuff was how light and fluffy it was. As soon as I potted up a plant and watered it for the first time, I would find the mixture floating to the surface and then sinking down and forming a heavy, wet soggy mush which in not great for any plants let alone a prized plant from your collection.

I suppose the first steps on this journey of creating my own potting mix other than scouring the internet so see what other people use was to have a think about the type of substrate my plants would be growing in in their natural habitat.  In my case this is generally the rain and cloud forest regions of the Neotropics of south America. Many of the plants I keep begin there life as vines or are completely terrestrial, some of them may end up as Epiphytes as they reach maturity but, in the home, unless you have a huge growing space this is unlikely to ever happen.

So, what is the substrate on the rain forest made up of?  It’s made of 100% degradable components of decaying plant matter, leaves, branches, wood, dead insects and even the carcasses of animals. Teaming with life from microscopic fungi and bacteria to every bug and worm you can possibly imagine (and some you would rather not)!  This will not only be decaying at different rates but will also have a mixture of sizes and shapes running thorough.  Another observation is that it rains ALLOT normally in the afternoon and in an average year will Rainfall will top 110 inches. To put that into context here where I live in the UK we average 23 inches (and people say it always rains in the UK!) What you don’t see in the rainforest is great big puddles of standing water unless the rivers have flooded. So my assumption is this substrate must be very well draining while still being able to retain moisture.

You will find as I did  all sorts of “go to” Aroid potting mixes on the internet and I am pretty sure that they all work very well for there creators and have thriving plants to show for it. What you will notice is that they are all pretty much the same mixture just in differing quantities.  The usual suspects includes a selection of the following, with the aim to create a free draining mixture that will allow air to circulate, retain some moisture but not go soggy.

One thing I have noticed is a tendency for people to go for larger chunks of substrate that are very free draining and that do not hold moisture for very long, for example a mix of Orchid bark, coconut husk and charcoal.  This kind of mix requires you to water your plants more than once a week and the use of a moisture probe in this kind of substrate is very hit and miss as it requires contact with the substrate to work, not easy when it is full of air gaps. This is a mix designed for plants that are Epiphytes rather than substrate growers and that includes any vining plant that has its roots in the ground.  I feel that a missing component from this kind of mix is the finer particulate that holds onto moisture for a little longer and binds the rest together. Now I am not condoning filling your mix completely with a fine particle like Coir and blocking all of the air holes but a small quantity I think helps. It is also worth mentioning that all of the above listed components are pretty much inert with the exception of the worm castings. This means that in order for your plants to thrive you will have to supply additional nutrition through some kind of fertilizing regime.

Ok enough background what do I have in my mix…

Why this combination?

  1. Orchid bark will hold moisture while creating large air gaps in the mix. I suspect a good portion of the soil in your plant’s natural environment will have lumps of bark in it. If your plant is a vine the texture of the bark will be exactly what is it looking for when growing up a tree.
  2. Pearlite is extremely free draining, completely neutral and helps with the exchange if oxygen in your mixture.
  3. Activated charcoal is an amazing addition to your plant mix, it highly porous nature allows for free draining of your soil. There is some debate whether charcoal acts as a filter removing salts and excess nutrients from your soil, it does a very good job in my aquariums so I can’t see why it would not do the same in this environment.  What is does do is absorb excess water that can be the cause of root problems in your plant if you have gone a little crazy and over watered your plant. The microscopic holes in the structure of charcoal also allow it to hold onto nutrients and microbes that are beneficial to your plants.
  4. Coconut Coir is an inert material that is a bi product of the Coconut farming industry. It’s usually supplied in the form of a brick that must ne re-hydrated in a bucket of water before use. I love this material, its great at holding moisture and it will bind the rest of the materials in your mix together. It gives the plants roots something to grow into rather than around which is what I believe you would find in the substrate on the floor of the rainforest.
  5. Worm Castings (Poop)! As I have previously stated all of the other ingredients are essentially neutral, not giving any nutrients to your plants as they breakdown. The addition of worm castings adds a huge boost to your mix for a multitude of reasons, they are rich in nutrients, including substances like zinc, copper, manganese, carbon, cobalt, and iron all of which are absorbed into your potting mix as you water, making nutrients available to The roots right away. In addition there is some evidence that the addition of worm castings will curb certain plant diseases, including root and crown rot, and inhibit some insect pests, including mites, aphids and mealy bugs.  Research at the Cornell Department of Plant Pathology found that worm castings naturally degraded the surface coverings of some insect pests which is a bonus if you fighting them.

So that’s my mix, I don’t add Sphagnum moss unless I have some left over from making moss poles and then I will chuck it in my mix box.  If you weren’t using Coir then I would suggest sphagnum as an alternative but for me it holds to much moisture.  One thing to note is that I am not to religious about this concoction, if I don’t have enough of one or other substance I will chuck in a substitute.

Something to watch out for when creating your own mix is just how quickly it will drain. I kept reading about how your mix should be super free draining allowing almost all of the moisture to run through the pot and I agree with this principle. But it should be noted that the freer draining and the more air pockets your mix has the more you will have to water your plants. Typically, I will water all of my plants every three days. This is not just a little sprinkle of water, I will flush through rain water gently until it is running through the bottom of the pot and leave it to drain for a few minutes.

All of our environments are different and you should experiment with your mix to find something that is suitable for you and your plants. For example perhaps you don’t have time to water your plants twice a week so you will need to add more material that will retain moisture like Coir or Sphagnum moss. Or your environment is very humid and then you may want to add more bark or pearlite.   There is no 100% guaranteed mix that will bring you success but I can guarantee that it will be better than the stuff you get in a bag from the garden centre!

I will often make up a large tub of this mix and just use it as required but be sure to keep a very tight lid on it and don’t let it get wet or you will find you have a large tub of mix full of fungus gnats of some other pest.