Written by Angus Stewart
Making your own soil is a great way to make sure you can control the quality of your potting mix and/or garden beds, and it’s also quite a fun and interesting activity to learn more about different soil and potting mix types and plant needs. If you have a container garden, or if you want to improve your existing garden soil by using a raised bed, there are a variety of ingredients you can use to mix up the perfect recipe for any plant you want to grow.
The first thing to note is that most commercial potting mixes are actually growing media that don’t contain soil. Soil varies greatly in composition and texture, whereas potting mix is designed for use in containers and is a mixture of light weight organic and inorganic (mineral) materials that drains freely. In this article, we’ll look at how to make different potting mixes for container gardening and also look at a few ingredients for improving garden soil or for making a mix that can stand alone in a raised garden bed. You can make potting mixes to suit a variety of purposes, such as raising seedlings, rooting cuttings, potting up indoor plants, and for any container gardening outdoors.
One of the best things about making your own mixes is being able to create the perfect growing conditions for your plants. For raising seedlings and rooting cuttings, a light weight and fine textured mixture with mineral components such as perlite that drains freely will work really well, but for growing vegetables you would make a mixture with more organic matter and compost that will hold extra water and nutrients. The basic materials for making your own potting mix or improving your soil are just a few different organic and inorganic (mineral) products.
Well-aged compost or well-rotted animal manure
If you have a compost heap with some mature compost (i.e. compost that is fully decomposed), that makes an excellent ingredient in potting mixes and is also a great addition to improve any type of garden soil, otherwise you can buy (or collect from places like horse stables) some well-rooted manure or mushroom compost. You can test these raw materials for maturity and suitability by sowing some fast germinating seed such as radish. If it grows normally then the material is good to use. In fact this is a quick and simple way to test the final growing mix you come up with.
Again, if you have a worm farm, worm castings make a fantastic addition to potting mixes or to improve garden soil, as they help to create a great soil structure and improve nutrient-holding capacity. The best way to use them is to dry them out first so that they can be more easily mixed with the other ingredients in your home made 'brew'.
Composted Pine Bark
Composted pine bark helps to aerate the soil and improve water circulation. Its an important part of most commercial potting mixes these days and makes a good addition to mixes for potted trees and shrubs as it does not break down as readily as other ingredients such as compost.
Coir (coconut fibre) sometimes sold as Cocopeat
Coir is a compacted coconut fibre which can be bought in small bricks and then expanded in water to add to potting mixes. It is very light in texture, similar to peat moss, and has a pH close to neutral. 100% coir is perfect for raising seedlings.
Perlite is a volcanic mineral that looks like small styrofoam balls butm is in fact a natural inorganic mineral. It is a basic component in many potting mixes. The puffy little balls allow for a high level of air and water permeability, and perlite is a common ingredient in standard potting mixes and plant propagation mixes.
Sand can be added to potting mixes to improve drainage. Coarse is mainly used for cacti and succulent mixes and can also be used in potting mixes for native plants. Fine sand is better for seed raising mixes as it helps the mix hold a bit of extra moisture. Those are the basic materials you’ll need to make a few simple potting mix recipes. There are many more ingredients you can use when making your own soil or potting mix – it’s a fascinating topic to explore!
Here are a few basic recipes for potting mixes to suit different plants.
Regular Potting Mix
This regular potting mix recipe has a balanced combination of ingredients to retain some water while also providing good drainage. Add some slow-release fertiliser when planting.
- One part composted pine bark
- One part mature compost, worm castings or mushroom compost
- One part perlite
- Add a handful of garden lime or dolomite per ten litre bucket of mix.
Australian Native Potting Mix
Natives will need better drainage than just the regular potting mix, but you can use that as the base and then add sand to improve the drainage, as well as some slow-release fertiliser specifically formulated for natives.
- Two parts coarse sand
- Three parts regular general purpose potting mix.
Seedling Potting Mix
Seedlings need a very light mixture, and this combination has been used successfully by many gardeners to raise seedlings.
- One part coir (coconut fibre)
- One part perlite or fine sand