Basil (Ocimum) is a grown for its aromatic, peppery leaves. There are many kinds, from pungent sweet basil to spicy liquorice-infused Thai basil, as well as lemon, lime or cinnamon flavours. The deliciously fragrant leaves may be ruffled or smooth, large or tiny, and various shades of green, red or purple.
Basil is not hardy. It likes growing in warm conditions so it's best in a greenhouse or on a kitchen windowsill. It can be grown outside in a UK summer, but it needs a sheltered, warm and sunny spot, either in the ground or in containers. Basil makes an attractive addition to herb gardens and veg plots, and even flower borders and pot displays, especially the more decorative varieties.
It can be grown from seed sown or bought as young plants. It is usually treated as an annual and removed in autumn, as it won’t survive winter outdoors. Basil will eventually start to flower, which causes leaf quality to deteriorate. At this point plants can either be removed, or just enjoyed for their bee-friendly flowers in shades of white through to purple.
Basil is widely used to make pesto and often added to tomato-based pasta sauces and salads. You can even use this versatile herb in fruit sorbets and ice-creams.
Month by Month
There are many excellent varieties of basil, offering a feast of flavours, from sweet and aromatic to rich and spicy. Most form fairly compact plants, 30–50cm (12–20in) tall, with attractive foliage – take your pick from large or small leaves that are green through to dark purple, smooth, ruffled, glossy or hairy. If you grow several types, you can have an array of flavours, fragrances, textures and colours to enjoy all summer.
When choosing varieties, look for those with an RHS Award of Garden Merit (AGM), which shows they performed well in trials – see our list of AGM fruit, herbs and veg.
What and where to buy
You’ll get the widest choice of varieties if you grow from seed – many varieties are readily available in garden centres and from online retailers. Basil is also available as plug plants and potted plants from similar outlets, as well as from supermarkets, although the choice of varieties is usually more limited.
Basil seeds are usually sown indoors, for more reliable germination and protection from slugs and snails. Basil can also be sown outdoors, but dislikes cold, damp conditions, so wait until temperatures warm up in early summer.
It’s well worth sowing several batches, a month or so apart, so you have plenty of fresh tender leaves to hand all summer.
It’s best to start basil off indoors in warm conditions, to give a longer growing season. Sow several batches from late February through to mid-summer in small pots or seed trays, at a temperature of about 18°C (64°F). Cover the seeds with a thin layer of vermiculite, water gently and place in a propagator or cover with a clear plastic bag.
Once seedlings appear, remove from the propagator or take off the bag, place in a warm, bright spot, such as on a windowsill, and protect from hot midday sun. Water regularly, but avoid overwatering, as seedlings are prone to damping off disease.
When the seedlings have their first true leaves, transplant into their own 7.5cm (3in) pots filled with multi-purpose compost or plant several into a larger pot 7.5cm (3in) apart if you're intending to grow a group in a container.
You can also sow basil more densely in trays, for harvesting after only a few weeks.
Basil can be sown outdoors once temperatures warm up in early summer, at a minimum of 15°C (59°F). It needs a sheltered, warm, sunny sowing site, with free-draining soil. Seedlings must be protected from slugs and snails. Basil can also be sown in containers of multi-purpose compost.
Growing in containers is often more successful, as they provide the free-draining conditions basil needs, and plants are easier to protect from slugs and snails.
Sowing outdoors gives a shorter growing season than sowing indoors, and in colder regions basil may fare best if kept covered with cloches or grown indoors.
Once seedlings are large enough to handle, start thinning out gradually until plants are eventually 20cm (8in) apart – remove the weaker plants and add them to salads. Overcrowded plants tend to start flowering sooner, bringing leafy harvests to an end.
You can plant newly bought basil plants and indoor-sown plants outdoors in late spring or early summer, once there is no danger of frost and temperatures are consistently above 15°C (59°F). Harden plants off carefully for a couple of weeks first, to acclimatise them to outdoor conditions.
Choose a warm, sunny, sheltered planting site with rich, light, well-drained soil, or a container filled with multi-purpose compost. Space plants 20–30cm (8–12in) apart. You can plant several in a large container, or one per smaller pot, moving it into a slightly bigger container each time its roots show through the drainage holes – an established basil plant needs a pot at least 20cm (8in) wide. Overcrowded conditions can lead to premature premature flowering and an earlier end to harvests. But realistically, if you're growing the less bushy sweet basil in containers, space plants closer together to give a worthwhile crop and have another batch coming on successionally.
Basil thrives in a greenhouse, in pots, grow bags or a greenhouse border, where it enjoys the warmer temperatures and makes a good companion to tomatoes. This is usually a more successful option than growing outdoors, especially in colder locations.
Protect basil plants from slugs and snails. This can be tricky in the ground, so growing in containers is often a safer choice, as plants are usually less accessible.
Once established, basil is easy to look after – just keep it warm, protect it from slugs and snails and water regularly, especially when growing in a container. Keep plants bushy and productive by harvesting the shoot tips regularly.
Water basil regularly in hot weather, especially when growing in containers, which dry out quickly. Basil may start to flower sooner in dry conditions.
When watering, try to avoid splashing the leaves and water in the morning if possible, as basil hates having wet roots overnight.
You can give plants a boost with a balanced liquid fertiliser to encourage leafy growth – avoid potassium rich fertilisers like tomato feed, which encourage flowering.
Weed regularly around basil plants, so they don’t have to compete for light or water.
Basil usually starts to flower in mid- to late summer – you can delay this and maintain leaf quality for as long as possible by removing any flower stems as soon as you spot them. It’s worth letting plants bloom eventually though, as basil flowers are rich in nectar, providing food for bees and other insects.
Although basil is usually grown from seed, it’s easy to grow new plants from cuttings. Snip off a non-flowering shoot just below a leaf, remove the lower leaves and pinch out the tip, then stand the cutting in a jar of water. It will quickly form roots and can be planted in a pot of multi-purpose compost after just a few weeks.
Basil leaves can be harvested throughout the summer. Pick leaves as required on a cut-and-come-again basis taking a few leaves from each plant, or harvest entire plants if lots of leaves are needed to make pesto or sauce.
If you only want a few leaves, remove the tops of plants to encourage bushy growth.
Another option is to harvest basil seedlings after only a few weeks, when packed with flavour and nutrients.
Basil flowers are also edible, with a milder flavour than the leave.
Basil leaves are best used freshly picked, but you can stand sprigs in a pot of water in a cool place for a few days, if you change the water daily. Putting basil in the fridge can cause the leaves to deteriorate.
Add basil to salads or use sweet basil to make pesto. It also works well in all kinds of tomato-based dishes. Thai basil adds rich flavours to spicy dishes. Basil tends to lose its flavour if cooked, so fresh leaves are usually best sprinkled over hot dishes just before serving.
Basil is generally easy to grow, but take care to protect the seedlings from slugs and snails. Aphids can also be a problem.
Basil needs heat and sun to grow well, and can’t withstand frost. So keep young plants indoors until after the last frost, and at the end of the season bring plants indoors or cover with cloches if you want to keep them going into autumn.
When growing in a greenhouse, ventilate well to help reduce problems with fungal diseases such as powdery mildew, grey mould and damping off disease in seedlings.
To prolong the leafy harvests, remove any flowers that start to form.
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