Basil is easy to buy and surprisingly easy to lose. A pot that looked lush on the supermarket shelf may become limp after one cold night outside, while several crowded stems can collapse from dampness long before you have harvested much. The trick is understanding what you're planting. Basil is a tender herb, and supermarket pots are often packed with many seedlings grown for quick kitchen use rather than long-term life in one small container.
For a longer harvest, move basil into a warm, sunny place with room for the roots and shelter from cold weather. There is no benefit in rushing it into an outdoor bed before early summer.
Choose the kind of basil you want
Sweet basil is familiar from pesto and tomato dishes. Thai basil has a distinctive aromatic flavour and a different growth habit. Purple-leaved cultivars bring colour as well as a useful culinary harvest.
Choose plants with firm stems and healthy leaves. Brown or black patches, collapsed stems and soggy compost are warning signs. A few yellow lower leaves may simply reflect overcrowding or ageing, but inspect the plant before deciding to keep it.
If buying a small plug plant, check whether it needs growing on indoors before going outside. A plug is not the same as a sturdy mature plant, even if both are sold as basil.
Wait for consistently warm weather
Basil dislikes frost and cold, wet conditions. The Royal Horticultural Society advises planting young basil outdoors in early summer, after hardening it off and once the chance of frost has passed.
If the nights are still cold, a sunny indoor windowsill or suitable greenhouse position is safer than an exposed patio. Frost can destroy basil quickly, and repeated chilly nights may stall growth.
Gradually introduce indoor-grown plants to the outdoors. Start with a sheltered position for a short period and increase exposure over several days. Bring them back inside when temperatures drop; the leaves need time to adjust to wind and stronger sunlight.
Give basil sunshine without excessive exposure
Basil likes warmth and good light. An outdoor pot in a sunny, sheltered spot often works well, particularly where you can move it under cover if a cold snap appears.
Avoid a dark, draughty corner. A kitchen windowsill can work, but a pane of glass may become very hot in midsummer sun or cold at night. Adjust the position if leaves scorch or stems become weak and leggy.
In the ground, use well-drained soil in a sheltered bed. A pot offers more flexibility, particularly in northern Britain, where temperatures can swing dramatically from one day to the next.
Divide an overcrowded supermarket pot carefully
Many supermarket basil pots contain dozens of young plants competing in a small volume of compost. You can sometimes extend their life by dividing the clump and repotting into several containers.
Water the old pot if it is very dry. Slide out the rootball and gently tease it into a few small groups, trying to keep as many roots attached as possible. Don't attempt to pull every seedling into a separate perfect plant if doing so tears all the roots apart.
Plant each group in a clean pot of peat-free multipurpose compost. Water in, allow excess to drain and keep the pots warm and sheltered while they recover. Expect a little pause in growth after dividing crowded plants.
Plant basil into a permanent pot
The RHS advises a container at least 20cm wide and deep for growing basil. Choose one with drainage holes and fill with suitable peat-free multipurpose compost.
Create a hole for the rootball and set the plant at roughly the same depth as it was in its previous container. Firm compost gently around the roots, leaving space below the rim for watering.
If using several plants in one larger container, give them sufficient room rather than repeating the supermarket overcrowding problem. Young basil raised from seed may be spaced around 7.5cm apart when being grown on indoors, with more room needed as plants develop.
Planting basil in an outdoor bed
Prepare a patch of fertile, free-draining soil. Remove weeds and loosen compacted ground before setting the plants into their positions.
Water the plants first if needed, then lift each rootball carefully. Place it into a hole matching the root depth, backfill and water around the base. Avoid burying lower leaves under damp soil.
Allow enough space for the mature plants to expand. Direct-sown basil may be thinned to about 10–20cm apart under RHS guidance; transplants should also be spaced according to variety and how large you intend to grow them.
Keep watering steady
Basil leaves wilt quickly when their roots dry out, especially in small containers. Water gently and thoroughly, allowing excess to escape through drainage holes. Avoid leaving the pot in standing water for days.
Check compost moisture with your finger. A pot in bright warmth may need attention more often than one on a cooler windowsill. Don't rely on a fixed schedule that ignores the weather.
Wet, stagnant conditions can also harm basil. If stems start blackening near the compost, investigate drainage, temperature and airflow rather than adding more water.
Harvest to encourage fresh shoots
Once the plant is growing well, pick suitable upper shoots rather than stripping every large leaf from the base. Cut just above a pair of leaves where side shoots can develop.
Frequent modest harvesting helps produce a bushier plant. If you're growing basil primarily for leaves, pinch out emerging flowerheads before they develop. Flowering can change the balance between fresh leaf growth and seed production.
Leave enough healthy foliage for the plant to recover. Taking half the plant away immediately after repotting may be too much for a small, stressed seedling.
What to do if your basil wilts
First check whether the compost is dry or soaking wet. Wilting is a symptom, not a diagnosis. A plant with very dry compost may revive after careful watering, while a cold, sodden pot needs drainage and warmth.
If outdoor leaves become dark and limp after a chilly night, cold exposure may be responsible. Bring suitable potted plants to a warm protected position and remove severely damaged growth once its extent becomes clear.
If leaves look pale and stems stretch, the plant may need better light. Move it gradually into a brighter location, rather than placing a shade-grown plant immediately in blazing midsummer sunlight.
Keep harvesting without wasting the crop
Several modest sowings or successive plants can provide a more dependable supply than relying on one ageing supermarket pot for the entire summer. Plan to harvest surplus leaves when growth is strong.
Fresh basil works well added near the end of cooking, when its aroma is most noticeable. You can preserve surplus basil by freezing prepared portions or incorporating it into suitable sauces.
In autumn, potted basil can sometimes keep going on a warm bright windowsill, but outdoor cold usually brings the summer crop to an end. Treat it as a warmth-loving herb rather than a winter-hardy garden perennial.