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How to grow basil in the UK
Basil loves warmth, and the British climate is only just warm enough. With a sunny windowsill or greenhouse, it is easy to grow.
Choosing a variety
For Italian cooking, sweet basil of the Genovese type is the classic choice for pesto and tomato dishes. Other kinds, such as purple or Thai basil, give different flavours. Seed packets will tell you the variety.
Sowing indoors
The RHS says to sow indoors from March to July in small pots or modular trays of damp, peat-free seed compost. Scatter the seeds thinly on the surface and cover with a propagator lid or clear plastic bag. Seeds germinate well at about 20°C. Sowing several small batches a few weeks apart gives a longer harvest.
Sowing outdoors
Outdoor sowing is less reliable and suits only warm locations. Wait until early summer, once night-time temperatures stay consistently above 10°C. Sow thinly in free-draining soil in a warm, sunny spot, then thin seedlings to 10 to 20cm apart, removing the weakest first.
Temperature
Basil is not hardy in the UK. Keep young plants indoors until after the last frost, harden them off, and plant out in early summer in a warm, sunny, sheltered spot. At the end of the season, bring plants indoors or cover them with cloches if you want them to continue into autumn.
Pots
Containers suit basil well because they give the free-draining conditions it needs and make it easier to protect from slugs and snails. Use a container at least 20cm wide and deep, filled with peat-free multi-purpose compost, and space plants at least 10cm apart. See the container guide.
Watering and feeding
Water regularly, especially in greenhouses and containers, and water in the morning to avoid wet roots overnight. Container plants can run short of nutrients, so use an organic-based, balanced liquid fertiliser. The RHS says to avoid potassium-rich feeds such as tomato feed, which encourage flowering.
Pinching out
Regularly pick the shoot tips to keep plants bushy and productive. Pinching also removes flower stems as soon as they appear, which helps extend leaf quality.
Supermarket pots
These are often overcrowded and prone to fungal disease or early flowering. The RHS advises dividing and repotting them promptly, and growing them indoors to limit biosecurity risks.
Problems
- Pests: slugs, snails and aphids.
- Diseases: damping off in seedlings, grey mould and powdery mildew. Ventilate greenhouses well.
In the kitchen
Add basil at the end of cooking. Pesto and caprese ideas are in cooking ideas, and sowing dates are in the sowing calendar.
Growing basil on a windowsill
A bright south-facing windowsill suits basil from spring to early autumn. Turn the pot regularly so growth stays even, and keep it away from cold glass at night. Don't stand pots in water, which rots roots. If you use the leaves heavily, sow a fresh pot every few weeks.
Using up a glut
Make pesto and freeze it in ice cube trays, or chop leaves into olive oil. Both preserve more flavour than drying.
Basil with tomatoes
Basil is traditionally grown near tomatoes in a greenhouse or on a patio, which suits both crops because they like similar warmth and watering. Use the same sheltered spot, and keep both off cold nights.
Frequently asked questions
When can I sow basil?
Indoors from March to July, according to the RHS. Outdoors only in early summer once nights stay above 10 degrees C, and only in warm places.
How do I make basil bushier?
Regularly pick the shoot tips. This also removes flower stems as soon as they appear.
Can I plant a supermarket basil pot?
Divide and repot it promptly and grow it indoors, advises the RHS, as supermarket pots are often overcrowded and prone to disease.