How to grow basil outdoors in England (and when not to)

To grow basil outdoors in England, sow it indoors in spring, harden it off and plant it into the bed in June once nights stay above about 10°C, in the warmest, sunniest and most sheltered spot you have. Be realistic, though: the RHS says basil is not hardy and only does well outdoors in a warm, sunny, sheltered position, and in cooler areas a greenhouse or windowsill is best.

This guide covers when to sow and plant basil, how to give it the best chance outdoors in a raised bed, how to pick it so it keeps going, and when you are better off growing it inside.

Basil at a glance

Can you grow basil outdoors in England?

Sometimes, and it is worth being honest about this. The RHS says basil is not hardy in the UK and needs warmth. It recommends growing it outdoors only in a warm, sunny, sheltered spot, and says a greenhouse is best in cooler areas.

For that reason, Sowstory treats outdoor basil as a lower-confidence crop. It plans basil into the bed only in June, requires at least six hours of direct sun, and assumes you have chosen a sheltered position. A seed supplier, Mr Fothergill's, lists outdoor sowing from March, but that conflicts with the RHS guidance and Sowstory does not use it.

As a rough guide:

• Good outdoor prospects: a sheltered, sunny bed in the south of England, near a warm wall or fence, in a decent summer.
• Poorer prospects: exposed, windy or shady gardens, the north and high ground, and frost pockets. Here, grow basil in a greenhouse, cold frame or on a sunny windowsill instead, and use the raised bed for hardier crops.

When to sow basil

The RHS sows basil indoors from March to July, at a temperature of about 20°C. Suttons notes that March sowings need a heated greenhouse or a warm windowsill. Mr Fothergill's gives 7–14 days for seed to come up at 15–20°C, and suggests sowing every two to three weeks for continuity.

Outdoors, the RHS says to sow only in early summer, once nights stay above 10°C. Sowstory's plan follows that: sow indoors from March to May, or sow direct only from early summer. See what to sow in March for the other crops started indoors at the same time.

How to sow basil indoors

1. Fill small pots or a module tray with fresh seed compost and water it before sowing, so you do not need to soak the seeds afterwards.
2. Sow thinly and cover the seed lightly with compost.
3. Keep them warm, at about 20°C, on a bright windowsill or in a propagator.
4. Water sparingly from then on, in the morning, keeping the compost just moist.
5. Pot on into individual pots once the seedlings are big enough to handle, and keep them indoors until June.
6. Harden off before planting out, by standing the plants outside by day and bringing them in at night, so they adjust gradually to outdoor conditions.

Watch for damping off

Basil seedlings are prone to damping off, which the RHS and Suttons both link to overwatering. Water sparingly, ideally in the morning, and do not leave seedlings standing in wet compost.

When to plant basil outside in the UK

Plant basil out only after the last frost, once nights stay above about 10°C, and harden the plants off first. In much of England that means June, and Sowstory plans basil into the bed in June only.

The south and coasts warm up first; the north, inland areas, high ground and frost pockets are later, and some summers never get warm enough for outdoor basil to thrive. Sowstory's months are England-wide rather than adjusted to your postcode, so check the forecast before planting out. Our guide to last frost dates explains how to judge it, and what to sow in June lists what else goes into the bed that month.

Growing basil in raised beds

Where to put it

Basil wants the same conditions as tomatoes: warmth, full sun and shelter from wind. It is short, about 20–50 cm, so in a raised bed it goes towards the front (south side), where taller crops on the north edge will not shade it. Suttons suggests a sunny spot with some relief from the strongest midday sun.

A raised bed helps basil in one way: it drains well, and the RHS says basil roots should not sit wet overnight.

Basil spacing

The RHS says to space basil at least 10 cm apart. Mr Fothergill's gives 20 cm, and Sowstory uses that wider figure, allowing a 20 × 20 cm square per plant and planning between two and eight plants per bed. The vegetable spacing chart lists the crops you might grow alongside.

Basil with tomatoes

Basil is the classic partner for tomatoes. Gardeners' World suggests herbs at the base of tomatoes may help confuse pests, though there is no trial evidence and the RHS basil guide does not mention it. The practical reason to pair them is that both like the same warm, sunny spot. Our guide to companion planting tomatoes explains the evidence, and how to grow tomatoes covers its partner.

If you want basil fitted in front of your tomatoes and the rest of the bed planned around it, Sowstory lays out the bed to scale, places tall crops on the north edge and gives a month-by-month plan. It is coming soon to the App Store, and your first bed plan is free.

How to care for basil

Watering

The RHS advises watering basil in the morning and keeping water off the leaves. Do not let the roots sit wet overnight. On the other hand, dry conditions push basil into flowering earlier, so aim for evenly moist, well-drained soil.

Feeding

Go carefully with feed. The RHS specifically warns against high-potassium feeds such as tomato feed, because they encourage flowering. That matters if you grow basil next to tomatoes: feed the tomatoes at their roots and keep tomato feed off the basil.

Pinching and removing flowers

Pinch out the shoot tips regularly to keep plants bushy. The RHS says basil usually flowers from mid to late summer; remove the flower stems as soon as they appear so the plant keeps putting its energy into leaves.

Harvesting basil

Outdoor basil can be picked from June to October. Suttons recommends picking young leaves regularly. Take whole shoot tips rather than single leaves from the bottom of the stem: that is the same job as pinching out, so harvesting and keeping the plant bushy go together.

Sowstory reserves the bed space for about 15 weeks from June planting, which covers the June to October picking season.

A basil year in England

Growing basil indoors instead

If your garden is cool, exposed or shady, grow basil inside. The RHS says a greenhouse is best in cooler areas, and Mr Fothergill's offers a windowsill as an alternative. Indoor basil follows the same rules: warmth, light, morning watering, no wet roots overnight and regular pinching. A pot on a sunny windowsill also keeps this tender herb away from the cold nights the RHS warns about, as long as it gets plenty of light. Sowstory plans outdoor raised beds only, so indoor basil sits outside the plan; use the bed space for a crop that suits your conditions, such as coriander, which tolerates more shade.

Sources

• RHS: How to grow basil
• Suttons: How to grow herbs
• Mr Fothergill's: Basil Sweet seeds
• BBC Gardeners' World: How to grow tomatoes
• Sowstory knowledge base, release v1.4