Potting Compost Ingredients

Potting Compost Ingredients


potting compost ingredients This must be good fibrous soil, ideally made by stacking turf in a covered heap for a year. It provides some nutrients as well as structure. Sterilizing the soil will kill weed seeds and release nutrients.

Garden compost

This must be well rotted, dark, and crumbly. It is a good source of nutrients and also helps to hold air and water. It may contain weed seeds and disease organisms, although the risk is less if the compost comes from a heap that has heated up.

Worm compost

This has a high nutrient value and also a very stable structure. It is excellent for adding to a base material such as leaf mould. If you feed your worms only on kitchen scraps and vegetable peelings, then the compost should be free of weed seeds.


Well-rotted strawy manure can also be used as a source of nutrients. It often needs chopping up and is best used in rough mixtures for large pots. It may contain weed seeds.


Peat forms the basis of most proprietary composts. It is a stable, sterile, consistent material, which is able to hold both air and water well and has little or no nutrient value. Also, it has a very low pH, so is suitable for acid-loving plants. However, it is not an easily renewable resource; it takes thousands of years to form and its extraction is threatening valuable wildlife habitats, so it is preferable to use a peat substitute.


Coir is a fibrous waste from the coconut industry, which is used as a peat substitute in some proprietary potting mixtures. It has good stability and holds water and air well. It has little nutrient value and a higher pH than peat. However, coir has to be shipped half-way across the world, so it is preferable to use ‘home-grown alternatives.

Leaf mould

This is a good home-made peat substitute. It is stable and holds air and water fairly well, although it tends to drain more quickly than peat. It has little nutrient value. For use in potting mixtures, it should be two to three years old so that it crumbles into smallish brown/black pieces. The older it is, the better it holds water.

Shredded bark

A percentage of fine grade bark (commonly up to 25 per cent) is used in some proprietary mixtures. Make sure that any bark you buy has been matured without added chemical nitrogen. It is useful for making mixtures more open, hence reducing water-logging. It has little nutrient value and tends to deplete nitrogen. Therefore, initially, you may need to add more nitrogen to mixtures — either with organic fertilizers or increased amounts of manure or compost. There is some evidence that bark can suppress diseases such as damping off.


The leaves of Russian comfrey (Symphytum x uplandicum) can provide nutrients for potting mixtures. Incorporate it by mixing the chopped leaves with, for example, an equal volume of leaf mould and leaving the mixture in a plastic sack until the comfrey has decomposed.

ANALYSIS OF COMFREY: Nitrogen 3.5%, phosphorus 0.5%, potassium 5.9%.

Limestone, dolomite lime, and calcified seaweed

Any of these materials can be used to increase the pH of the mixture. Calcified seaweed also provides trace elements.

Organic fertilizers

Mixtures of fertilizers such as bone meal, seaweed meal, and hoof and horn can be used to boost the nutrient content.


Bone meal: nitrogen 3.5%, phosphorus 20%, potassium 3.1%.

Hoof and horn: nitrogen 13%, phosphorus 0%, potassium 0%.

Seaweed meal: nitrogen 2.8%, phosphorus 0.2%, potassium 3.1%.

Coarse sand or grit

Small amounts of these can be used to increase drainage. They are preferable to perlite or vermiculite, which take a lot of energy to manufacture and do not decompose quickly when discarded.

28. November 2010 by Dave Pinkney
Categories: Garden Management, Greenhouse Gardening, Manures and Fertilisers, Soil Cultivation | Tags: , , | Comments Off on Potting Compost Ingredients


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