Plants in pots live in a world of their own. Out in the border, a root can wander a metre or more in search of moisture and nutrients, and the soil around it buffers everything from drought to downpour. In a container, the plant is stuck with whatever you tipped in at the start. There is no subsoil to fall back on, no worm population quietly improving things, and no reservoir of nutrients lurking below.
That changes what you should be looking for. A good container compost needs to hold water without staying soggy, drain freely without drying out in an afternoon, and supply enough nutrition to keep plants going for the first few weeks. Get that foundation right and everything else — watering, feeding, deadheading — becomes far more forgiving.
For the vast majority of pots, a good-quality peat-free multipurpose compost is the sensible starting point. Peat extraction is damaging to fragile habitats, and since the UK's move away from bagged peat, the peat-free options have improved enormously. A well-made mix based on bark, wood fibre, coir and green waste compost now performs every bit as well as the old peat blends, provided you buy a reputable brand and use it within a season.
What you are looking for is a compost that is loose and crumbly in the bag, smells earthy rather than sour, and holds together when you squeeze a handful without dripping water. Avoid anything that looks compacted, smells of ammonia, or has visible mould — that usually means it has been sitting somewhere damp for too long.
Multipurpose compost alone is fine for most plants, but some situations call for a little tailoring. Drainage is the issue that catches most people out, especially in a wet British summer when pots sit through weeks of drizzle.
Add grit or horticultural sand to the mix for anything that hates wet feet. Lavender, rosemary, thyme, olive, citrus, agapanthus and most Mediterranean herbs all prefer a leaner, sharper mix. A rough rule of thumb is one part grit to four or five parts compost by volume. Use horticultural grit rather than builder's sand, which can contain salts and clogs the mix rather than opening it up.
For large pots and long-term plantings, add a handful of bark chips or coarse composted bark to keep the structure open. This slows the collapse that happens as compost breaks down over a season, and it keeps air moving around the roots. If your pots sit on a hard surface in a rain trap, raise them onto feet or pot feet so surplus water can escape.
Even the richest bagged compost is running on empty by midsummer. Most multipurpose mixes include a starter fertiliser, but that charge fades after a few weeks of active growth. From roughly six weeks after planting, begin a regular liquid feed.
Tomato feed works well for flowering and fruiting plants. A general-purpose balanced feed suits foliage and leafy crops. For baskets and containers that get watered daily, feed at half strength every time you water rather than full strength once a week — it is gentler on the roots and keeps levels steadier. Slow-release granules mixed in at planting are a helpful top-up, but they work best alongside liquid feeding, not instead of it.
Watch the leaves for clues. Pale, yellowing foliage with green veins usually points to a nutrient shortage, while soft, dark, floppy growth suggests you have overdone the nitrogen.
Come March or April, most pots do not need tipping out and starting again. What they need is a top-up. Scrape away the top three to five centimetres of old compost, which will have crusted, grown weeds or collected fallen leaves, and replace it with fresh peat-free multipurpose. Work it in gently around the stems with your fingers, taking care not to disturb the roots.
This single job does three things at once. It removes any pests and weed seeds sheltering near the surface, it replenishes the nutrients the plant will draw on through spring, and it refreshes the structure so water soaks in rather than running off the crust. Add a slow-release feed at the same time and you have bought yourself a good few months of easy growing.
Every two or three years, larger specimens benefit from a proper repot into a container one size up, teasing out the rootball and trimming away any circling roots. Do it in early spring, before growth takes off, and water well afterwards.
Compost is not cheap, and a bit of care keeps every bag working harder. Store opened bags under cover, rolled shut, so they do not go soggy or blow about. Never reuse old compost for a new planting without refreshing it — spent compost has lost its structure and may carry disease. It can, however, be spread on the borders as a soil conditioner, or mixed into a new batch at no more than a third of the total volume.
Buy fresh each spring from a supplier who shifts stock quickly, and choose a bag that feels light and dry rather than heavy and compacted. A little attention at the till pays off all season.
Get the compost right and container gardening becomes what it should be: generous, abundant, and far less fuss than it looks.
The Seasonal Plot shares practical, down-to-earth guidance on british seasonal gardening and outdoor living for readers across the UK.
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