Containers let you garden on concrete, move colour to wherever you sit, and grow plants your soil would never allow. They also concentrate every gardening mistake into a few litres of compost: a border forgives a missed watering, a pot does not. Getting the basics right — pot, compost, water, feed and winter protection — matters far more than which plants you choose.
Pot size: bigger is almost always better
The single most common container mistake is pots that are too small. A small pot holds little water and few nutrients, heats up and freezes faster, and blows over. As a working minimum, use 30 cm diameter for seasonal displays, 45 cm for permanent shrubs, and 60 cm or more for small trees and anything you want to leave in place for years. One large pot is easier to look after than five small ones, holds moisture through a hot weekend, and looks better too. If you garden on a balcony, check what the structure can bear before committing to very large planted pots, which can weigh well over 100 kg wet.
Materials, honestly compared
Every material is a trade-off between weight, cost, frost resistance and how it handles water:
| Material | Water behaviour | Pros | Cons |
|---|---|---|---|
| Terracotta | Porous — dries fast | Looks good, ages well, stable in wind, roots stay cool | Needs more watering; cheap pots crack in frost — buy frost-resistant |
| Glazed ceramic | Holds moisture | Colourfast, mostly frost-resistant, less watering than terracotta | Heavy, chips, quality varies |
| Plastic / resin | Holds moisture — can stay too wet | Cheap, light, frost-proof, good for thirsty plants | Easy to overwater in winter; light pots blow over; degrades in sun |
| Wood | Moderate | Insulates roots in winter and summer | Rots in time; line with plastic (with holes) to slow it |
| Metal | Holds moisture | Crisp looks, durable | Cooks roots in full sun and freezes hard in winter — insulate or keep out of extremes |
The practical upshot: terracotta suits Mediterranean plants, herbs and anything that hates winter wet; plastic and glazed pots suit thirsty summer bedding, hostas and vegetables. Match the material to the plant and you halve your problems. Whatever the material, the pot must have drainage holes — a container without them is a vase, and no plant survives one outdoors for long.
Peat-free compost, and how to work with it
Peat-free is now the norm for UK amateur gardeners, and the good brands are excellent — but they behave differently from the peat composts older advice was written around, and this catches people out. Most peat-free mixes are based on wood fibre, composted bark, coir and green compost. Three adjustments matter:
- Judge watering by weight and feel, not by the surface. Wood-fibre composts often look pale and dry on top while still moist underneath. Push a finger 3–5 cm in, or lift the pot to learn its light-versus-heavy feel, before watering. Watering on sight alone leads to chronic overwatering.
- Feed earlier and more often. The microbes breaking down woody material in peat-free mixes consume some nitrogen, and most bagged composts only carry four to six weeks of feed anyway. Start feeding container plants about four to six weeks after potting rather than waiting for pale leaves.
- Buy fresh and buy decent. Compost quality varies more between brands than between peat and peat-free. Avoid bags that have sat outside waterlogged, and use compost within the season — it is a biological product, not a shelf-stable one.
For permanent plantings — shrubs, trees, roses in pots — use a loam-based compost (John Innes No. 3 type, now available peat-free) or mix loam-based and multipurpose half and half. Loam holds nutrients and weight, keeping the pot stable and the plant fed over years in a way that fluffy multipurpose compost cannot. For acid-lovers such as camellias and blueberries, use a peat-free ericaceous mix and rainwater rather than tap water where you can.
The crocks myth
Generations of gardeners were taught to put a layer of broken pot, stones or polystyrene in the bottom of containers "for drainage". Controlled trials have repeatedly shown this does not improve drainage — water does not move readily from fine compost into a coarse layer, so a crock layer actually keeps the saturated zone higher in the pot, closer to the roots, while robbing rooting depth. All a pot needs is open drainage holes, kept unblocked. Cover a very large single hole with a piece of mesh or a single flat crock over-arched so compost cannot wash out, and stand the pot on pot feet so the holes can actually drain. Fill the rest of the container with compost, top to bottom.
Watering and feeding through the year
Watering is the whole game from May to September. A densely planted container in a sunny July spell needs checking daily and may need watering daily; peak-summer hanging baskets sometimes need it twice. Water thoroughly until it runs from the base — a surface splash wets nothing that matters — and water in the morning or evening rather than midday. If compost has dried to the point of shrinking from the pot sides, stand the whole pot in a tub of water for half an hour to re-wet it, because water poured on top will simply race down the gap and out. Grouping pots together, moving the thirstiest out of afternoon sun, and adding a simple drip irrigation kit on a timer for holidays all cut losses dramatically.
Feeding, once started four to six weeks after potting: a balanced liquid feed every one to two weeks for leafy growth, switching to a high-potassium feed (tomato feed is the cheap standard) weekly for anything grown for flowers or fruit — pelargoniums, petunias, tomatoes, chillies — from June to September. Permanent shrubs are simpler: a dose of controlled-release fertiliser worked into the surface each April carries them through the season. Stop feeding everything by late September so growth hardens before winter.
Seasonal displays versus permanent residents
It helps to run two mental categories. Seasonal pots are repotted twice a year: summer bedding, herbs and tender salvias planted out after the last frosts (mid-May in much of England, late May further north), then cleared in October for winter-and-spring plantings of wallflowers, violas, ivy and bulbs — tulips layered under violas in November is the classic. Compost from healthy seasonal pots can be refreshed rather than replaced wholesale: tip out, mix in a third of fresh compost plus feed, and reuse for the next display, sending the excess to the borders.
Permanent pots are long-term homes for shrubs and small trees that earn their keep year-round: Sarcococca, Skimmia japonica, dwarf pines, Acer palmatum (out of wind and afternoon sun), clipped bay and yew, hostas for shade, agapanthus for sun — agapanthus actually flowers better slightly root-bound. Olives and pittosporums are popular but genuinely borderline in cold inland winters. Permanent pots want the loam-based compost above, the biggest container you can manage, and the winter routine below.
Overwintering: the pot changes the maths
Hardiness ratings assume roots insulated by the open ground. In a pot, the root ball freezes from the sides as well as the top, so a plant's effective hardiness drops — treat a pot-grown plant as roughly one H-rating band more tender than its label. An H4 olive or shrubby salvia that shrugs off winter in a sheltered border can be killed in a pot on an exposed patio. The countermeasures, from November to March:
- Pot feet under everything. Winter losses in pots are caused by waterlogging and the freeze that follows more often than by cold air. Raising pots a couple of centimetres lets them drain and stops them sitting in a puddle.
- Move the vulnerable. Cluster pots against a house wall, which is measurably warmer and drier; move H2–H3 plants (pelargoniums, fuchsias, citrus) into a frost-free porch, greenhouse or bright shed before the first proper frosts, usually by late October or early November.
- Wrap the pot, not the plant. For hardy-but-borderline residents, wrap the container in bubble wrap or hessian to insulate the roots and slow freezing; leave the plant itself unwrapped unless it is genuinely tender, as trapped damp around foliage causes rot. Fleece is for short cold snaps, taken off again when they pass.
- Keep watering, barely. Evergreens in pots still lose water in winter and die of drought under a house wall as often as of frost — check monthly and water sparingly in mild spells.
Repotting and topdressing long-term plants
A shrub in a pot slowly eats its own compost. Every two or three years, in March or early April, either pot on into a container 5–10 cm wider, or — once the plant is in its final pot — root-prune and refresh: slide the plant out, saw or tease away 3–5 cm of the outer root ball, and return it with fresh loam-based compost around the sides. In the intervening years, topdress instead: scrape away the top 4–5 cm of tired compost in spring, replace with fresh mixed with controlled-release feed, and water in. Signs a plant is overdue for attention are water racing straight through, roots circling the surface or poking from the drainage holes, and growth stalling despite feeding. Done on this cycle, a yew, bay or Japanese maple can live happily in the same pot for decades.
Sources and further reading
- Royal Horticultural Society — container gardening, peat-free growing and plant hardiness ratings
- Garden Organic — peat-free composts and organic feeding
- Met Office — frost dates and seasonal forecasts for timing planting and protection