Growing Basil in Pots Outdoors

Grown outdoors in a pot, basil asks for one thing above all: the warmest, most sheltered spot you have. It is a Mediterranean plant pretending to enjoy a British summer, so a sunny corner against a south-facing wall, on a patio or balcony, will always beat an exposed, breezy bed. Get the position right and a single 20cm pot will keep you in leaves from July through to the first chilly nights of autumn.

This guide focuses on the outdoor, in-a-pot version of growing basil. For the full picture — sowing, varieties and indoor growing — see the main basil growing guide, and for the wider skill of growing in containers, the guide to growing food in containers is worth a read alongside this one.

When it is safe to put basil out

Basil is frost-tender. Even a light frost will blacken and kill it overnight, and a cold, wet spell will check its growth so badly it may never recover. This is the single most common way UK gardeners lose their basil — putting it out too soon, full of spring optimism.

The safe window in most of the UK is June onwards, once nights are reliably above about 10°C. In the mild south and west you might risk late May in a warm year; in the north, Scotland, or anywhere prone to late frosts, hold your nerve until mid-June. Watching the overnight forecast matters more than the calendar — a cold snap can still arrive in early June.

If you have raised your own plants on a windowsill (or you are reviving a supermarket pot), they need to be eased outdoors gradually rather than dumped straight into the cold. This process is called hardening off: for about a week, stand the pots outside in a sheltered spot during the day and bring them back in at night, lengthening their time outdoors as they toughen up. Skipping this step shocks soft, indoor-grown leaves and stalls the plant for weeks.

Choosing pot, compost and position

The position does more for outdoor basil than anything you buy. Aim for:

• Sun: at least six hours of direct sun a day — the more the better. Basil grown in shade is leggy, pale and weak-flavoured.
• Shelter: out of the wind. Wind chills the leaves and dries the pot out fast. A corner, a wall, or tucking the pot among other containers all help.
• Warmth: a south- or west-facing wall is ideal. Brick and paving soak up the day's heat and release it overnight, giving basil exactly the warm-feet conditions it loves. A patio or balcony with a sun-trap corner is perfect.

For the pot itself, a 20cm (8 inch) container suits one or two plants, or three small seedlings if you want a fuller cluster sooner. There is no need to go much bigger for a single plant. Drainage holes are essential — basil hates sitting in cold, wet compost, so make sure water runs freely out of the bottom and stand the pot on feet or a couple of small stones if it is sitting on a flat surface.

Fill it with a good peat-free multipurpose compost. Fresh compost holds enough nutrients to carry the plant through the first few weeks, and its open structure drains well while still holding moisture. Avoid garden soil in pots — it compacts, drains poorly and brings weeds. If you are new to growing this way, the growing food in containers guide covers compost and pot choice in more depth.

Watering and feeding in a pot

Pots dry out far faster than open ground, and in a warm, sheltered spot — exactly where you want your basil — they can need watering every day in a hot spell. But basil is fussy about how it likes its water.

Water in the morning, at the base of the plant, not over the leaves. Morning watering means the compost is moist for the day's growth and the surface dries by evening, when cool damp foliage invites disease. Aim the can at the compost, keep the leaves dry where you can, and let the surface feel just-dry before you water again.

The thing to avoid is waterlogging. Basil sitting in cold, sodden compost is the fastest route to yellow leaves, collapse and root rot. Free-draining compost, a pot with good holes, and watering only when the top of the compost has dried out a touch will keep it happy. In short: consistent but never soggy.

After about four to six weeks the compost's own nutrients start to run low. A weekly feed with a balanced or general-purpose liquid feed, at half the strength on the bottle, keeps the leaves coming without forcing soft, floppy growth. Don't overdo it — over-fed basil grows lush but bland.

Pinching out and flower removal

Pinching out is what turns a single stem into a bushy, productive plant — and it is the most useful habit to get into. From when the plant has two or three pairs of true leaves, pinch out the growing tip just above a pair of leaves. The plant responds by sending out two new shoots from below the cut, and each of those can be pinched again. Do this regularly and one plant becomes a dense little bush.

Harvesting is pinching out: pick from the top, taking the tip and a set of leaves rather than stripping leaves from the bottom. The more you pick from the top, the bushier and more productive the plant becomes.

Keep an eye out for flower buds — small spikes forming at the tips. Once basil flowers it diverts its energy into seed, the leaves turn smaller and more bitter, and the plant begins to fade. Pinch flower spikes off the moment you spot them to keep the plant in leaf-producing mode for as long as possible. A plant kept pinched and de-flowered will crop for months; one left to flower is often finished in weeks.

Moving it under cover as autumn cools

Basil's season ends when the warmth does. From mid-September onwards, as nights cool and dews get heavy, growth slows and the plant becomes prone to mould and collapse. This is the time to either harvest in earnest or move the pot to shelter.

Because it is in a pot, you have the advantage of being able to move it. Bringing the container into a greenhouse, a porch, a cold conservatory or onto a bright kitchen windowsill can buy you several more weeks of picking as the outdoor weather turns. A pot on a warm windowsill indoors will often soldier on into October.

When the plant finally tires, harvest everything that is left. There is no point trying to overwinter basil outdoors in the UK — it is grown as an annual here and the first proper cold will see it off. Strip the remaining leaves and either use them fresh, freeze them (chopped into ice-cube trays with a little water or oil), or dry them. With a fresh sowing each spring you get a new, vigorous plant every year, which is far better than nursing a struggling old one through winter.

Growing alongside tomatoes

Basil and tomatoes are classic companions — on the plate and in the pot. They want exactly the same conditions: warmth, sun, shelter and steady watering, which makes them easy to grow side by side. If you are raising tomatoes in a warm, sheltered spot, tucking a basil plant into the same corner — or even the same large container — works well, and means you can pick both for the same summer salad.

Gardeners have long planted the two together in the belief that basil's scent helps deter some pests around tomatoes. Whether or not that holds up, the practical case is solid: they thrive in the same conditions, so a sunny patio or balcony that suits one suits the other. Just give each enough room and don't let the tomato shade the basil out as it grows tall.

For the full sowing, variety and care picture — including raising plants from seed and growing on a windowsill — head back to the main basil growing guide, the cornerstone of this little cluster.

With a warm, sheltered corner, free-draining compost and a habit of regular pinching, a couple of pots will give you more basil than you expect — fresh leaves on the patio all summer, and a freezer drawer's worth to see you through winter.