A quality potting soil is essential for successful container gardening, but if you’ve ever tried to find a commercial mix that doesn’t contain animal products such as manure, blood, and bone, you know it can be a real challenge. The solution is to make your own so you control what goes into the mix, and if you need a lot of it, you might just save some money too.
What is Potting Soil?
Whether you grow indoor or outdoor plants in pots or containers, you’ll need to use a potting soil for the best results. So what’s the difference between garden soil and potting soil? When growing in containers it’s especially important for the soil to be well-drained and aerated to prevent roots from rotting. At the same time you want the soil to hold moisture and nutrients so it doesn’t dry out quickly, which it tends to because the volume of soil is smaller, requiring you to water often. A quality potting soil is light and airy, while garden soil is often too heavy and poorly drained and aerated.
Potting Soil Components
The components of a quality general use potting soil should have the following characteristics:
Drainage & Aeration – prevents roots from rotting and soil becoming anaerobic (lacking oxygen) by creating an open soil with good structure, allowing water to pass through with spaces for air
Moisture Retention – plants need water, but too much of a good thing will starve the roots of oxygen and drown your plants
Beneficial Fungi – improves the health and resilience of your plants by increasing their drought tolerance, disease resistance, and boosting their efficient use of nutrients and water
Nutrients & Organic Matter – provides your plants and the life in the soil with the food they need to thrive
Potting Soil Recipes
There are two types of potting soil: soil-based mixes and soilless mixes.
Soil-Based Mix (replace soil with Leaf MOULD for a soilless mix)
- 1 part disease-free garden loam or topsoil (can be pasteurised to eliminate weed seeds and diseases, but both good and bad biology will be killed, so I prefer to take my chances).
- 1 part aged compost (compost may contain animal products, including mushroom compost, so use your own, or confirm contents with manufacturer). Coconut coir can also be used if compost is unavailable, but it's a less sustainable option and is low in nutrients, so you'll have to add fertiliser.
- 1 part perlite, vermiculite, or coarse/builders sand for drainage.
- Beneficial fungi (mycorrhizal)
- Soybean meal
- Alfalfa meal
- Kelp meal
- Soft rock phosphate
- Other plant-based slow-release fertiliser
It’s critical that your garden soil is a well-draining loam to ensure good drainage and aeration.
Add a handful each, or follow the manufacturer instructions, of the optional ingredients for extra nutrients so your plants will grow for longer before requiring fertiliser. If you can’t find all of the optional ingredients, just add what you can.
Thoroughly mix all the ingredients in a large bucket or wheelbarrow. Extra potting soil can be stored in a closed container.
The recipe can be adapted to you and your plant needs. The ‘parts’ can be any volume, or the recipe can be multiplied, based on how much soil you require. If you’re growing plants like succulents that need more drainage, just increase the amount of drainage material. For plants that like more moisture, add more coconut coir and/or aged compost to increase moisture retention.
Lastly, check the soil pH to make sure it’s appropriate for the plants you’re growing. If the pH is too high, add sulphur, or if it’s too low, add garden lime. By adding these last you can adjust your base mix according to your specific plant needs.