Choosing a potting mix
A good potting mix provides the right amount of water, air and nutrients to support healthy plants.
You should choose the right type of mix to suit your plants.
What your mix is made of
There are many different parts to a potting mix. Read below for a list of materials you will find in, or can add to, your mix.
Pine bark is often used in potting mix. It stops the mix from 'slumping' - sinking when wet - and mixes well with other components.
Bark chips trap air and water for use by your plants.
While bark chips are not easy to find in the Northern Territory, they are found in premium potting mixes that you can buy.
Sand is used in potting mixes for drainage but adds weight.
Medium to coarse sand grains are suitable for general mixes, while fine sand can be used in a seed-raising mix.
Look for sand that has been washed and sterilised, does not contain salts and is suitable for gardening - do not use paving sand.
Coir, or coir peat, is made from compressed fibres like coconut husk. It is good at trapping water for your plants.
A small brick of fine coir soaked in water will produce a full bucket of mix when wet.
Peat and peatmoss
Peat is partly decomposed organic matter that forms in cold, swampy areas. It can hold up to eight times its weight in water for your plants.
All peats are slightly acidic and break down quickly. Peat-based potting mixes will shrink when dry.
Soil is not widely used in commercial potting mix. It can be heavy and prone to waterlogging.
Soil used for potting mix needs to be sterilised to remove pests, diseases and seeds.
Vermiculite is a source of magnesium and some potassium for your plants.
Light and flaky, it is used to help seeds germinate. It is generally not found in potting mixes you can buy as it shrinks over time, causing drainage and aeration issues.
Perlite does not supply nutrients. It is made up of large, light particles that help with aeration and drainage.
Choose large particles if you need extra drainage.
There are many additives that you can use in your potting mix, including all of the following:
- water crystals, to help your mix hold more water
- wetting agents, to help water soak into your mix
- composts for added nutrients - use mature, high quality compost only
- worm castings
- polystyrene foam for drainage and aeration
- slow-release or animal fertilisers
- carbon extracts and micro-organisms.
Last updated: 04 March 2016
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