Succulent Soil Guide

Going.Local
Published on July 30th 2020
9
A bowl of salad
I have often said there are as many soil mixes as there are gardeners on the planet. As a result, the most common question beginners ask is: "What type of soil mix should I be using?" The reason behind the many recipes is due to the ability of plants to adapt. This does not always mean your plant will keep growing, but merely that it will try to survive.
To untangle the web of online recipes, we will touch on what ingredients are on the market, give you a master mix and tell you how to test/alter the master mix to suit your environment.
Soil

Making a Master Mix

The best way to go about making your succulent soil is by starting with a stock standard and testing it in your home or garden. The master mix recipe below will react differently depending on where you are, how warm it is (season), what container you use and how humid your environment is.
STEP 1: Make a Master Mix
3 Part - Potting soil
2 Part - Riversand or washed silica (*Sifted)
1 Part - Organic compost (* Sifted)
4 Part - Sandstone pebbles (5-10 mm) / Crushed granite
*Disclaimer: This mix is a general succulent mix, not to be used for subtropical succulents.
Things to avoid:
Leaving dust - Clay dust and river sand will form a hard cement-like mix when dry that will limit drainage and root growth.
Leaving decomposing bark - Some bark may be beneficial, however decomposing bark in compost will attract or contain fungi (so unless sterilised, should be avoided).
Potting soil (in this context) refers to unamended soil without bark/perlite etc.
*If you substitute potting soil with garden soil, make sure the soil does not contain too much clay.
A close up of a piece of wood
Fungal species contain the enzymes necessary to break down wood. Untreated wood can be a source of fungal spores.
STEP 2: Test Mix
You will have to test the soil in the container you will be using (glazed or unglazed ceramic/ plastic). You can perform two easy tests to make sure you have done this correctly.
Test 1
Drench the soil with water and use your hand to squeeze it into a fist. Upon opening your fist, the soil should crumble apart.
Tip | If the soil does not fall apart you can add amendments (see Soil Amendments).
Test 2
Now place the pot in the area you intend to leave it. Use a chopstick to test the soil each day until the stick appears completely dry.
Tip | The container should never stay wet for more than 4-6 days (remember that a container will dry out slightly faster with a plant included).
Soil amendments
Coco chips, perlite, pumice, akadama and leca are but a few amendments one can add to alter your soil.

Soil Amendments: what is on the market?

The master mix is a low-cost, easily accessible soil to use as a starting point. The next step is to understand what constitutes a soil amendment and when it is necessary to add it.
All of the amendments can be categorised in terms of water retention (how much water they hold) and aeration. Both of these properties are related to the porosity of the substrate.
The two classes, porous and non-porous, have the following components for sale:
Porous amendments:
  • Perlite/volcanic glass (water retention is due to surface tension)
  • Pumice (very light and porous volcanic rock)
  • Scoria/ Lava rock
  • LECA (Lightweight Expanded Clay Aggregate)
  • Vermiculite (hydrous phyllosilicate mineral)
  • Akadama (volcanic clay)
  • Diatomous soil (found in kitten litter and will retain more water than akadama)
Non- or semi-porous amendments:
  • Crushed Granite (Chicken grit)
  • Washed silica or sand
  • Zeolite (microporous, aluminosilicate minerals)
  • Expanded shale (semi-porous)
Porous rock
Some amendments merely retain water on the surface, whilst others will absorp it.

Specialised succulent mixes

Certain succulents will require preferential treatment. If a species commonly grows on dolomite or limestone outcroppings, they might have evolved a sensitivity to pH, water hardness and fertiliser concentrations.
This is important to know as tap water can be different from region to region.
Note | Some areas will have high calcium and magnesium concentrations in tap water (e.g. Karoo), whilst others will be slightly acidic due to high humid acids (e.g. Overberg, Western Cape).
Things that affect pH:
  • Limestone or Dolomite Lime
  • Mushroom compost
  • Horse manure
  • Fertiliser
  • Pine bark
Soft Water: Refers to water with a low pH/General hardness or calcium/magnesium concentration.
Hard Water: Refers to water with a high pH/General hardness.
A close up of euphorbia caput medusae

In-soil fertilizers

You will often see that some soil recipes will contain slow-release fertiliser (e.g. Osmocote), worm castings/compost, bone meal, blood meal, lime or manure. This can seem confusing at first but is a way for you to help add nutrients to the soil.
If you have planted a succulent into soil that contains fertiliser, then adding additional feed may stress the plant, so be careful.
Roles of common additives:
  • Blood meal is normally used for nitrogen depleted soils (May lower pH)
  • Bone meal adds phosphorous and calcium (If your soil pH is higher than 7, bonemeal will not help)
  • Manure is animal waste that can be used for nitrogen depleted soils (May affect pH)
  • Worm castings are rich in nutrients and, when untreated, will contain microbes.
  • Lime is added to acidic soils to adjust pH
  • Slow-release tablets will release a small amount of nutrients into the soil every time it is watered

If you have found this article helpful or would like to share your own tips, then please leave your comments below.

Bibliography:
Charles, G. (2014). Cacti and Succulents: An illustrated guide to the plants and their cultivation. The Crowood Press Ltd.
Hazra, G. (2016). Different Types of Eco-friendly Fertilizers: An Overview. Sustainability in Environment, 1(1), 45-70.
Huntley, E. E., Barker, A.V. & Stratton, M.L. (1997). Composition and Uses of Organic Fertilizers. In J.E. Rechcigl & H.C. Mackinnon (Eds.), Agricultural uses of By-Products and Wastes(pp.120-139). American Chemical Society.
Nobel, P.S. (1990). Soil O2 and CO2 Effects on Apparent Cell Viability for Roots of Desert Succulents. Journal of Experimental Botany, 41(8), 1031–1038.
Nobel, P.S., Miller, P.M. & Graham, E.A. (1992). Influence of rocks on soil temperature, soil water potential, and rooting patterns for desert succulents. Oecologia, 92, 90–96.))
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