Growing Basil

Basil is a light germinator, meaning you scatter the seeds on moist soil and press them down lightly, but don't cover them with earth. From mid-March you can start sowing indoors in seed trays or small pots on a windowsill. The germination temperature should be between 18 and 22 °C and not drop below 13 °C. After about two weeks the first seedlings appear. Keep the growing medium evenly moist but not wet, as too much moisture quickly causes damping off in the delicate seedlings.

After roughly four weeks you can prick out the seedlings and move them into a more nutrient-rich growing medium. In pots, a nutrient-rich compost works better than a lean herb mix. The sturdy young plants shouldn't go outdoors until after the last frost, so from mid to late May. Plant spacing should be about 20 cm within the row and 25 cm between rows. Direct sowing into the bed is possible from mid-May to June, once the last frosts have passed and soil temperatures are consistently warm enough.

Shop-bought supermarket pots usually contain far too many plants crammed into a small space. You can carefully divide the root ball and plant them out. In our experience, though, you need to acclimatise them to real light first.

Basil loves warmth and needs a sunny to partially shaded spot that is sheltered from wind. It thrives particularly well against a protected south-facing wall, in a raised bed, or in a greenhouse. At temperatures below 10 °C it stops growing and suffers damage.

The soil should be loose and well-drained. Before planting out, it's worth working in some compost. Waterlogging is this plant's worst enemy and almost inevitably leads to root rot and fungal problems.

The range of basil varieties is impressive. Classic Genovese basil with its large, soft leaves is the epitome of Italian cuisine and probably the most widely grown variety. There are also red-leaved varieties like 'Dark Opal' with dark purple foliage and a more intense flavour, compact globe types for small containers, and lettuce-leaved forms with a particularly mild aroma. Some varieties need more warmth than others — red basil, for example, requires plenty of heat to develop well.

Good to know: alongside the varieties of Ocimum basilicum, there are several distinct basil species with their own botanical names, sometimes sold under the general label "basil". Lemon basil (Ocimum americanum) with its fine citrus aroma is a separate annual species. Greek bush basil (Ocimum basilicum var. minimum) stays compact, has small leaves and is considered hardier. Thai basil Horapha (Ocimum basilicum var. thyrsiflorum) brings anise-like notes to Asian cooking. Holy basil or Tulsi (Ocimum tenuiflorum, also known as Ocimum sanctum) is highly valued in Indian healing traditions and is botanically a completely different species. African basil (Ocimum gratissimum) from Africa is another distinct species with a camphor-like aroma. These species differ from Ocimum basilicum not only in flavour but sometimes considerably in their care and growing requirements.

Because of its large leaf area, basil has a decent water requirement but can't tolerate waterlogging. Water at soil level so the leaves stay dry. Wet leaves in cool weather are an open invitation for fungal diseases.

For vigorous growth, basil needs a good supply of nitrogen.

Remove old leaves from the lower part of the plant regularly. This improves air circulation and helps prevent fungal problems. Overwintering Ocimum basilicum indoors generally doesn't work due to the lack of light, as the species is annual and dies after flowering.

The most common problems with basil are almost always linked to too much moisture. Damping off (caused by various fungi including Pythium) mainly affects young plants when the growing medium is too wet. The stems go soft at the base and the seedlings topple over. You can prevent this by watering sparingly and ensuring good drainage.

Septoria leaf spot causes brown patches that spread quickly and lead to the foliage drying out. The fungus has an easy time particularly in warm, humid weather. Alfalfa mosaic virus shows up as mosaic-like discolouration and distortion of the leaves and is often spread by aphids.

Aphids suck plant sap and leave behind sticky honeydew. With a heavy infestation, the leaves are no longer fit for eating. Leaf miners lay eggs in the leaves, and their larvae leave feeding tunnels in the tissue.

As a rule of thumb: if you ensure good air circulation, water at soil level and don't plant too closely together, you'll have avoided most problems before they start. Companion planting with tomatoes also helps, as the microclimate beneath tomato plants is often more favourable.