Think in threes: upright, trailing and foliage

A container that still looks generous in late August rarely happens by accident. The displays that hold their shape through heat, wind and the odd fortnight of neglect almost always follow the same formula: something tall to give the pot a spine, something that spills over the rim to soften it, and plenty of foliage to fill the gaps when the flowers inevitably pause.

For the upright element, think pelargoniums, upright salvias, cosmos, dahlias and standard fuchsias. These give height and a focal point, and most will keep going if you keep picking. For the trailing layer, choose bacopa, trailing lobelia, calibrachoa, bidens, trailing verbena or an ornamental sweet potato vine — anything that will cascade 30–45cm over the side. Then add foliage: a heuchera with deep burgundy leaves, a bronze carex, some silver-leaved helichrysum or a variegated coleus. Foliage is what carries the pot between flushes of flower, and it never needs deadheading.

Aim for roughly one upright plant per 30cm of pot diameter, three or four trailers spaced around the edge, and foliage tucked into whatever gaps remain.

Compost, drainage and the right-sized pot

Size matters more than most people expect. A 30cm pot is about the minimum for a mixed display that will look full by July; 40–50cm is far easier to keep going and dries out much more slowly. Terracotta looks lovely but wicks moisture away from the roots, so if you garden on a sunny patio, glazed ceramic or good-quality plastic will save you a lot of watering.

Always check for drainage holes, and raise pots onto feet so water can escape freely. Skip the old-fashioned layer of crocks in the base — it actually creates a saturated zone above the gravel. Instead, use a peat-free multipurpose compost mixed with about a quarter by volume of loam-based compost or garden soil. That extra weight stops tall plants toppling in a gust and holds moisture and nutrients far better than a light, airy mix alone.

Planting up: spacing, depth and a simple recipe

Fill the pot two-thirds full, firm it gently, then arrange your plants still in their pots before committing. Put uprights towards the back or centre, trailers near the rim, foliage wherever there is a hole. Once you are happy, knock them out, tease the roots apart slightly and plant at the same depth they were growing.

Leave a 3–5cm gap between the compost surface and the rim so you can actually get water in. Water thoroughly until it runs out of the drainage holes, then keep the pot in light shade for three or four days to settle before moving it into full sun.

A reliable combination for a sunny spot: a central upright salvia, three calibrachoas around the edge, a bronze carex and a couple of silver helichrysums. For shade, swap in a standard fuchsia, trailing lobelia, a heuchera and some ivy.

Feeding: slow-release first, liquid later

Compost nutrients are exhausted within about six weeks, which is precisely when your plants start flowering hard. Mix slow-release granules into the compost at planting time — a six-month formulation is ideal for a British growing season — and follow the packet rate rather than guessing.

From mid-June, start a weekly liquid feed at half strength, moving to full strength once the pot is packed with roots and flowers. A high-potash tomato feed suits flowering displays better than a general-purpose one, which tends to produce leaves at the expense of blooms. Stop feeding in early September, and never feed a dry pot: water first, then feed, or you risk scorching the roots.

Watering that keeps pots full, not frazzled

In high summer, a well-planted container can need water once a day and twice during a heatwave. Water in the morning if you can, and always until it runs freely from the base — a quick splash only wets the top inch and encourages weak surface rooting.

Two habits make a real difference. First, mulch the compost surface with 2cm of gravel or bark to cut evaporation. Second, group pots together so they shade one another and create their own humid microclimate. If you are away often, a reservoir pot or simple self-watering insert is worth the investment.

Deadheading and mid-season tweaks

Deadheading is the single most effective thing you can do to keep a pot looking full. Petunias, pelargoniums, cosmos, dahlias and nemesia all respond within days, pushing out fresh buds instead of pouring energy into seed. Pinch or snip just below the flower head, and remove any yellowing leaves at the same time.

Around mid-July, give straggly trailers a light haircut — take off a third of the growth — and they will branch and thicken. If a plant has gone completely over, pull it out and drop in a late-season replacement such as a small chrysanthemum or an autumn-flowering aster. Ten minutes of tidying a week is all it takes to carry the same pot from June right through to the first frosts.