Compost for containers

Garden soil can be used for planting containers providing the plants are short term, such as annuals or pansies, and are replaced after a few months. But there are many disadvantages to using soil in pots, not least in that it will be full of weed seeds just waiting to germinate and choke the plants. There will probably be some pests such as chafer grubs. Vine weevils and leatherjackets, and spores of various fungal diseases. Garden centres and  stores are well stocked with a range of proprietary composts to suit every plant's needs, including soil-based kinds whose soil has been sterilized, and soil-less types using peat, coir (coconut fibre) or other additives to provide a suitable growing medium.

The one great advantage of soil-based compost is that it is more retentive of moisture and so less likely to shrink away from the edge of the pot as it dries out, making re-watering easy. Its disadvantage compared to soil-less compost is that it is heavier and a large container recently watered is not easily moved.

There are various specialist composts too, such as ericaceous composts for lime-hating plants and orchid mixes that provide a really open, free-draining material. Composts with built-in resistance to some pests are proving popular and every type of compost contains a fertilizer whose composition is consistent in every bag. There are composts containing slow-release fertilizer that gradually supplies nutrients to the plant roots over a period of anything from 6 months or even up to 14 months for shrubs in pots, but most others are exhausted of nutrients after about six weeks. Plants in pots need regular feeding during the growing period and should eventually be repotted into larger containers with fresh compost.