edible gardening
How to grow basil UK — indoor & outdoor guide
Grow basil in the UK: sow indoors April, plant out late May or keep on a south-facing windowsill year-round. Pinching method + UK-specific climate tips.
How to grow basil in the UK — indoor + outdoor beginner guide
Basil (Ocimum basilicum, most often the Genovese sweet basil cultivar) is the most-grown culinary herb in UK kitchens — and one of the easiest IF you give it what it needs. The trick is heat: basil hates cold compost, cold air, and cold roots. UK weather makes this a real challenge — basil left outdoors before late May will sulk or die, and any temperature drop under 10°C stunts growth. Get the warmth right and the rest is just regular pinching.
Set basil reminders in Growli: Add your basil variety to the Growli app and the morning briefing tells you when to pinch, when to feed, and when a UK cold snap is on the way.
US gardeners — see the US version of this guide for zone-based outdoor planting.
When to plant basil in the UK
Basil is tender and frost-sensitive. Cold compost stunts growth and cold air kills seedlings. UK timing:
| UK region | Sow indoors | Plant out (sheltered, sunny) | Greenhouse / polytunnel |
|---|---|---|---|
| South of England | Mid- to late March | Late May | Mid-May |
| Midlands | Late March | Late May / early June | Mid- to late May |
| Northern England | Early April | Early June | Late May |
| Wales | Late March | Late May | Mid- to late May |
| Scotland (lowland) | Mid-April | Early June (only in sheltered south-facing spots) | Late May |
| Northern Ireland | Late March / early April | Late May / early June | Mid-May |
Soil temperature matters more than air temperature — basil germinates at 18°C+. Use a heated propagator or place seed trays on top of a warm radiator (with a tray underneath) for indoor seed-starting in cool British spring.
Three ways to start basil
1. Supermarket basil pot — fastest
The shortcut everybody overlooks. Tesco, Sainsbury's, Waitrose, and M&S all sell living basil for £1.50-£2.50. Each "plant" is actually 20-30 seedlings crammed into a tiny pot — they exhaust themselves within a fortnight in that configuration.
The split trick:
- Buy one supermarket basil pot.
- Tip it out and gently divide the root ball into 4-6 clumps of 3-5 plants each.
- Plant each clump into a 12-15 cm pot of fresh peat-free multipurpose compost (Westland New Horizon, Dalefoot).
- Water in and keep on the sunniest windowsill you have.
You will get 4-6 thriving basil plants from one £2 supermarket pot. They will outlast and outproduce seed-grown plants for the first 6-8 weeks.
2. Seed (cheaper, slower)
- Surface-sow seeds in moist seed-starting compost.
- Cover with a thin layer of vermiculite (basil needs light to germinate well).
- Keep at 18-24°C — heated propagator or warm radiator with a tray.
- Germination in 5-10 days.
- Pot up to 9-10 cm containers when first true leaves appear.
- Harden off for 7-10 days before transplanting outdoors after late May.
UK seed brands: Suttons, Thompson & Morgan, Mr Fothergill's, D.T. Brown, Dobies.
3. Garden centre transplant (easier, faster than seed)
Buy 3-4 starter plants from a garden centre in mid- to late May. One household needs 2-4 basil plants for steady summer supply. Look for stocky, dark green plants with no flower buds — leggy pale stretched plants struggle to recover.
Light requirements — the UK problem
Basil is a sun-lover, and UK light is the major constraint:
- Outdoors: 6+ hours direct sun. Only south- or south-west-facing positions reliably deliver this in the UK. Sheltered from wind — basil leaves are easily damaged.
- Indoors: The brightest window you have — south-facing windowsill minimum. North-facing rooms will not work without a grow light. A south-facing kitchen windowsill is the perfect UK basil home from May to September.
- Winter (October-March): Even a south-facing windowsill barely keeps basil alive. Use a grow light providing 12-14 hours/day, or accept seasonal basil and restart in spring.
Watering
Water when the top 2-3 cm of compost is dry — typically every 2-3 days in summer, longer in cooler weather. Basil signals thirst by dramatic wilting; water within an hour and the plant recovers fully.
- Water at the base, not on leaves — wet leaves invite downy mildew and grey mould, both major UK problems in wet summers.
- Mulch outdoor basil — retains moisture, suppresses weeds, keeps soil cool. Composted bark or grass clippings work well.
- Do not overwater — soggy compost rots basil roots fast. Container basil needs a drainage hole, full stop.
Pinching for bushy growth
This is the single most important basil skill. Every 2-3 weeks once the plant is 15 cm tall:
- Find a node where two side shoots are forming.
- Pinch the top growth just above that node — fingers work fine, or use clean snips.
- Two new branches grow from that node within a week.
Repeated pinching doubles the harvest. See the dedicated how to prune basil guide for the full method.
Flower removal
The moment basil shows flower buds, pinch them off. Once basil flowers, the plant shifts energy from leaves to seeds and the leaves turn bitter. Removing buds keeps the plant in leaf-production mode all summer. UK basil typically wants to flower from mid-July onwards — stay on top of it weekly.
Feeding
Light feeding only. Quarter-strength balanced liquid fertiliser (Westland Houseplant Feed or Baby Bio) every 2-3 weeks during active growth (May-September). Heavy feeding produces lush leafy plants with weaker flavour.
For pot-grown basil in compost over 2 months old, top-dress with fresh peat-free multipurpose to replenish nutrients without forcing soft growth.
Container vs in-ground vs windowsill (UK)
| Setting | Pros | Cons |
|---|---|---|
| Indoor south-facing windowsill | Year-round potential, no slugs, no wind | Light is the limiter October-March |
| Container outdoors (15 cm+ pot) | Movable, brings indoors at first frost, easy to manage | Daily watering in summer, more feeding |
| In-ground in a sunny sheltered border | Lower maintenance, larger plants | Slugs and snails (significant UK threat), end-of-September frost |
| Greenhouse or polytunnel | Best UK results — heat + protection | Whitefly pressure, needs ventilation |
Indoor year-round basil rarely lasts past 3-4 months even with grow lights in UK winter conditions — plan to restart from cuttings or new seeds every season.
Common UK problems
- Yellowing leaves — overwatering, or compost depleted. Let compost dry; resume normal schedule; top-dress with fresh compost.
- Black spots and rapid leaf collapse — downy mildew, a major UK basil problem since 2010. Remove affected leaves immediately, improve air circulation, water at the base only, and consider downy-mildew-resistant cultivars like Prospera and Eleonora.
- Greyish fuzzy mould on stems and leaves — Botrytis (grey mould). Common in damp UK summers. Improve airflow, remove affected parts, water in the morning so plants dry by evening.
- Slug or snail damage outdoors — irregular holes overnight, slime trails. Use copper tape around pots, wool pellets (Slug Gone), or RHS-approved nematodes (Nemaslug).
- Leaves curling — heat stress (rare in UK) or transplant shock. Move to partial afternoon shade in extreme heat.
- Slow growth — compost too cold or insufficient light. Move to brighter and warmer spot.
- Flavour weakening — flowering. Pinch all buds immediately.
Companion planting
UK basil grows brilliantly alongside tomatoes — see growing tomatoes in the UK. The classic Mediterranean pairing also works in a UK greenhouse: basil under the tomato canopy gets the warmth it needs and helps deter whitefly.
Related articles
- How to grow tomatoes in the UK — basil's best companion plant
- Why are my plant leaves turning yellow? UK guide — diagnose basil leaf issues
- How to get rid of fungus gnats in the UK — common in seed-starting trays
- How to prune basil — the pinching method in detail
- UK hardiness ratings & last-frost dates — for timing transplants
Reviewed and updated by the Growli editorial team. For questions about anything here, open Growli and ask — or email hello@getgrowli.app.
Frequently asked questions
When should I plant basil in the UK?
Sow seeds indoors in late March, on a heated propagator or warm windowsill at 18°C+. Plant out in late May (south of England) to early June (Scotland and Northern England). Outdoor planting only works in a sheltered, sunny, south-facing position. The brightest south-facing kitchen windowsill is the most reliable UK basil home from May to September.
How long does basil take to grow?
From seed: 5-10 days to germinate, 4-6 weeks to first harvest, 8-12 weeks to a full bushy plant. From a supermarket pot (split into clumps): first harvest in 2 weeks. From a garden centre transplant: first harvest in 2-3 weeks. UK basil hits peak production in July-August on a sunny windowsill or in a greenhouse.
How to grow basil indoors in the UK?
Use the brightest spot you have — south-facing windowsill with at least 6 hours of direct sun, or a grow light for 12-14 hours daily. Water when the top 2-3 cm is dry, feed lightly every 2-3 weeks May-September, and pinch above leaf nodes every 2-3 weeks to keep bushy. Indoor basil in UK winter (November-February) usually struggles without a grow light — plan for 3-4 months of life before restarting.
How to grow basil from a supermarket pot?
Tip the pot out and gently divide the root ball into 4-6 clumps of 3-5 plants each. Plant each clump into a 12-15 cm pot of fresh peat-free multipurpose compost. Water in and keep on the sunniest windowsill. The crammed supermarket pot exhausts itself in days; split plants thrive for months and outproduce seed-grown basil for the first 6-8 weeks.
How to grow basil from seed in the UK?
Surface-sow seeds in moist seed-starting compost and cover with a thin layer of vermiculite. Basil needs light to germinate well. Keep compost at 18-24°C using a heated propagator or warm radiator. Germination happens in 5-10 days. Pot up to 9-10 cm containers when the first true leaves appear; transplant outdoors only after late May once nights stay above 10°C.
Why is my UK basil dying suddenly?
The two most common causes: downy mildew (black spots, leaves collapse fast — a major UK problem in wet summers) or cold-snap damage (overnight temperature drops below 10°C). For downy mildew, remove affected leaves, improve air flow, water at the base only, and switch to resistant cultivars (Prospera, Eleonora). For cold damage, move plants indoors and wait — basil under 10°C halts growth and often dies.
How to harvest basil so it keeps growing?
Always harvest by pinching whole stems above a node, not by picking individual leaves. Each pinched stem causes the plant to branch from the node below, doubling leaf production. Aim to remove the top 30-40% of growth at each harvest, every 2-3 weeks during active UK growing season (May-September).
What is the best basil variety for the UK?
Sweet Genovese is the all-rounder. Lemon basil and Thai basil are easy and add flavour variety. For downy mildew resistance — increasingly important in UK summers — try Prospera Compact or Eleonora. Greek basil (small-leaved) is bushy and decorative on a windowsill. UK seed suppliers: Suttons, Thompson & Morgan, Mr Fothergill's, D.T. Brown.
How does Growli help me grow basil?
Add your basil to Growli and the app sets pinching reminders every 2-3 weeks, watering reminders calibrated to your UK postcode weather, and frost warnings so you can bring container basil indoors before damage. Photograph any disease symptoms and Growli walks you through diagnosis and recovery — especially helpful for spotting downy mildew early.