How to grow basil from seed in the UK isn’t difficult, but it’s surprisingly easy to get wrong if you don’t know the small details that matter. Cold compost, weak light, the wrong watering technique, and basil dies fast. Get the basics right and a single £2 packet of seeds gives you basil plants producing fresh leaves for months — at a fraction of the cost of buying potted plants from a supermarket.
This guide covers exactly how to grow basil from seed in UK conditions. The right way to sow, the warmth and light it needs, how to pot seedlings on properly, and how to keep plants productive once they’re growing. Plus a few tricks (like propagating new plants from cuttings) that make basil one of the most rewarding herbs to grow at home.
Why Grow Basil From Seed?
You can buy a basil plant from a supermarket for £1.50 and have basil in the kitchen this afternoon. Why bother with seeds?
Three reasons. First, those supermarket plants are usually packed with 30 to 40 tiny seedlings competing for space in one small pot. They look full but they’re stressed and rarely last more than a few weeks. Second, a single packet of seeds gives you 50 to 100 plants for around £2. The economics are completely different. Third, the variety choice from seed is massive — Genovese, Greek, Thai, lemon, purple, lettuce-leaf — most of which you’ll never find as a bought plant.
Basil also responds beautifully to being grown properly. A plant raised from seed and given the conditions it actually wants will outproduce a supermarket plant tenfold and last all summer instead of all week. For when to sow and plant out, When to Plant Basil in the UK covers the timing in detail.
Choosing the Right Basil Variety
The basil you usually see in shops is sweet Genovese basil — the classic Italian variety with broad green leaves. It’s a good place to start and the most useful in the kitchen. But there are dozens of other varieties worth growing:
Genovese — the standard sweet basil. Best for pesto, tomato dishes, pizzas. Reliable and easy from seed.
Greek basil — small leaves, bushy compact growth, intensely aromatic. Perfect for windowsill growing and surprisingly tough.
Thai basil — anise/liquorice flavour, narrow leaves, purple stems. Essential for Asian cooking. Grows slower than Genovese but worth the effort.
Lemon basil — citrus undertone, good for fish, salads, and infusing oils. A nice change from regular basil.
Purple basil — deep purple leaves, milder flavour, looks stunning in salads. A bit fussier than green varieties but very satisfying to grow.
For a first attempt, Genovese is the easiest and most useful. Once you’ve succeeded with that, branch out into the others.
When to Sow Basil Seeds
Basil needs warmth more than almost any other common herb or vegetable. The seeds simply will not germinate properly in cool conditions. In the UK, the best window for sowing basil indoors is from late March through to early August.
For a full summer of basil, sow in April or May. For a windowsill plant year-round, you can sow every 6 to 8 weeks to keep fresh plants coming through. Don’t sow basil too early — February sowings on cold windowsills produce weak, leggy plants that rarely recover. The exception is if you have a heated propagator or grow lights, in which case earlier sowing works fine.
For detailed month-by-month timing, see When to Plant Basil in the UK.
How to Sow Basil Seeds Properly
This is where most basil growing goes wrong, so it’s worth taking the time to do it properly.
Use small pots or modules, around 7cm to 9cm. Fill with a good quality peat-free multipurpose compost or a dedicated seed compost. Best Compost for Vegetables in the UK covers what to look for. Don’t use garden soil — it’s too heavy and full of weed seeds.
Firm the compost gently and water it lightly before sowing. This way the seeds don’t get washed around when you water afterwards. Scatter 5 to 8 seeds across the surface of each pot. Cover with the thinnest possible layer of compost or vermiculite — basil seeds are tiny and need light to germinate well, so deep sowing kills them.
Mist the surface gently with a spray bottle to settle the seeds in. Cover with cling film or a clear plastic bag to keep humidity high. Put somewhere warm — basil germinates best at 18°C to 22°C. A propagator is ideal but a warm south-facing windowsill works.
Check daily. Seedlings should appear within 5 to 10 days at proper temperature. Remove the cover the moment you see green shoots — leave it on and they damp off (collapse from fungal disease at the base) within days.
Getting Light and Temperature Right
Once seedlings have emerged, light becomes the most important factor. Basil grown in low light goes tall, thin, and pale — what gardeners call “leggy” growth. Once a plant has gone leggy it never properly recovers. You need to get the light right from the start.
A south-facing windowsill is the best spot in spring and summer. If you only have north or east-facing windows, the seedlings will struggle, and a small grow light becomes a worthwhile investment. Why Tomato Seedlings Go Leggy in the UK covers this issue in more detail and applies just as much to basil.
Temperature matters too. Basil seedlings want consistent warmth — at least 16°C, ideally 18°C to 22°C. They suffer in cold rooms, near draughty windows, or where temperatures drop sharply at night. If your seedlings stop growing or turn yellow, cold is usually the cause.
Turn pots every couple of days so seedlings don’t all lean towards the light.
Watering Basil Seedlings Without Killing Them
Overwatering is the single biggest killer of basil. The plants want consistent moisture but they absolutely hate sitting in wet compost. Get this balance wrong and the roots rot, the plant collapses, and there’s no coming back.
The simplest method is bottom watering. Sit pots in a tray with 1cm of water for 20 minutes, then remove. The compost soaks up exactly what it needs and the surface stays dry, which reduces fungal disease and keeps seedling stems healthy. Top watering from a heavy watering can knocks small seedlings flat.
Wait until the surface of the compost feels dry before watering again. Stick a finger in — if the compost feels damp 1cm down, leave it. How Often to Water Plants in the UK covers the general principles.
Never water late in the evening. Wet basil leaves overnight invite fungal problems that quickly kill plants.
Pricking Out and Potting On
Once your basil seedlings have two pairs of true leaves (not just the first round seed leaves), it’s time to thin them or pot them on.
You have two options. Either thin to leave 3 to 4 strong seedlings per pot and grow them on as a clump, or carefully separate them and pot up individually. Both work. Clumps fill out faster and look bushier. Individual plants grow larger eventually.
If pricking out individually, hold seedlings gently by a leaf (never the stem — bruise the stem and the plant dies) and use a pencil or chopstick to lift the roots out cleanly. Make a hole in fresh compost in a slightly bigger pot, drop the seedling in, firm gently, and water in.
Keep newly potted seedlings out of direct hot sun for a day or two while they settle. They’ll perk up quickly and start growing within a week.
Pinching Out to Get Bushy Plants
This is the single most useful trick in growing basil. The moment your plants have 4 to 6 pairs of true leaves, pinch out the very top growing tip. Just take the top two leaves off with your fingernails or scissors.
This stops the plant growing upward and forces it to send out two new side shoots from below the cut. A week or two later, pinch those out too. The plant becomes wider and bushier rather than tall and thin, and the total leaf production goes through the roof.
Keep pinching out tops and the plant keeps producing. Stop pinching and the plant tries to flower, leaf production slows, and the flavour goes bitter. Pinch out any flower buds as soon as you see them — basil flowers signal the plant is winding down.
Growing Basil Outdoors in the UK
Basil can go outside in the UK from June onwards, once nights are reliably above 10°C and frost risk has passed. Before that, leave it inside. Basil hates cold and never recovers from a single frosty night.
Harden plants off properly over a week before they go outside permanently. Start with a few hours in a sheltered spot, then build up time outdoors gradually. Plants moved straight from a windowsill to full outdoor conditions usually scorch and stall. How to Harden Off Plants in the UK covers the process.
The best outdoor spot is warm and sheltered. A south-facing wall or fence, a sunny patio, or a sheltered raised bed all work well. Avoid windy spots — basil leaves bruise easily in strong wind. UK Last Frost Date Checker helps you work out when it’s safe to plant out.
Even outdoors in summer, basil benefits from coming back inside on cold nights. A pot on the patio that comes onto a kitchen windowsill when the forecast turns chilly will outproduce one that’s left to take its chances.
Growing Basil in Pots
Basil is one of the best herbs for container growing. Use pots at least 15cm to 20cm wide and deep — basil has more roots than people expect. Smaller pots dry out too fast and limit plant size.
A good peat-free multipurpose compost is fine. Add a handful of garden compost or worm castings if you have them. Make sure pots have drainage holes — sealed decorative pots are death for basil.
Water when the surface is dry but don’t let pots stand in saucers of water. Feed every 2 to 3 weeks with a balanced liquid feed once plants are established. Basil in pots benefits from regular feeding because compost runs out of nutrients faster than open soil. Can You Grow Vegetables in Pots in the UK? covers container growing in general.
Move pots around through the season to find the best light. Basil loves a sunny morning windowsill but appreciates being shifted to a cooler spot in extreme afternoon heat.
Growing Free Basil From Cuttings
One of the most satisfying tricks in basil growing: you can produce unlimited free new plants from cuttings.
Take a healthy stem about 10cm long, cut just below a leaf joint. Strip the lower leaves off so you have a bare stem and a tuft of leaves at the top. Put the stem in a glass of water on a sunny windowsill. Within 1 to 2 weeks you’ll see white roots forming. Once roots are about 3cm long, pot the cutting into compost and treat as a normal plant.
This works with both garden-grown basil and supermarket basil. One supermarket pot can become 6 to 10 healthy long-lived plants this way. It’s a brilliant way to extend the basil season at almost no cost.
Common Problems With Basil
Seedlings collapse at the base. Damping off — a fungal disease caused by too much moisture and not enough air circulation. Remove covers as soon as seedlings emerge, water from the bottom, and ensure good airflow.
Tall, thin, pale plants. Leggy growth from lack of light. Move to a brighter spot, use a grow light, and pinch out the top to encourage bushier growth.
Yellow lower leaves. Usually overwatering. Let compost dry out more between waterings. If yellowing is widespread, the plant may also be cold — basil hates anything below 15°C.
Black spots on leaves after a cold night. Cold damage. Bring the plant indoors. The damaged leaves won’t recover but new growth will be fine if the plant warms up.
Flowers appearing instead of leaves. Plant is bolting — often because it’s been left to dry out, exposed to extreme heat, or simply matured. Pinch flowers off immediately and the plant may recover and produce more leaves.
Aphids on stems. Common in warm indoor conditions. Wipe off with damp cloth or wash plants under the tap. Spray with diluted washing-up liquid if persistent.
Sudden total collapse. Almost always root rot from overwatering. Once a basil plant collapses from root rot there’s no recovery — start fresh.
Harvesting Basil Properly
Pick basil correctly and a plant keeps producing for months. Pick it badly and you exhaust it in weeks.
The right method: take whole stem tips, cutting just above a pair of leaves on a stem. This encourages the plant to send out two new shoots from below the cut, doubling future leaf production. Never strip individual leaves from a stem — that weakens the plant and reduces yields.
Pick regularly even if you don’t need basil that day. The plant only produces more leaves if you keep harvesting. Leave it alone for too long and it starts flowering and slowing down. Frequent picking is the single best way to keep a plant productive.
Pick in the morning when oils are strongest and leaves are crispest. Basil wilts fast — get it into water or the fridge straight away if you’re not using it immediately.
Frequently Asked Questions
How long does it take to grow basil from seed?
Basil seeds germinate in 5 to 10 days at the right temperature (18°C to 22°C). From sowing to first harvest is around 6 to 8 weeks, depending on conditions. With regular picking and the right care, a plant produces for 4 to 6 months.
How deep should I plant basil seeds?
Very shallow. Basil seeds need light to germinate well, so just cover them with the thinnest possible layer of compost or vermiculite. Anything more than 5mm deep dramatically reduces germination.
How many basil seeds should I plant per pot?
5 to 8 seeds per small pot if you plan to thin or pot them on. 2 to 3 seeds per pot if you want to grow them as individual plants without disturbance. Basil seeds are cheap and germinate reliably, so don’t be too sparing.
Why are my basil seedlings tall and thin?
Lack of light. Basil seedlings stretch toward weak light sources and become leggy. Move them to a south-facing windowsill or use a grow light. Once a seedling is leggy, pinch out the top to encourage bushier growth.
Should I water basil from the top or bottom?
Bottom watering is best for seedlings and young plants. Sit pots in a shallow tray of water for 20 minutes, then remove. This keeps the surface dry, which reduces fungal disease, and ensures roots get consistent moisture without the plant being flattened by heavy watering.
Can I grow basil from a supermarket plant?
Yes. Either keep the original plant alive by separating it into smaller clumps and potting them on, or take cuttings from healthy stems and root them in water on a windowsill. One supermarket pot can become several long-lived plants this way.
How do I keep basil producing for longer?
Pinch out the top of every stem regularly to encourage bushy growth, remove any flower buds the moment they appear, water consistently without overwatering, feed every 2 to 3 weeks once established, and pick from the top of each stem rather than stripping individual leaves.
What is the easiest basil to grow from seed?
Genovese (sweet basil) is the easiest and most useful variety for beginners. It germinates reliably, grows quickly, tolerates UK indoor conditions well, and is the most useful in cooking. Greek basil is the next easiest if you want a smaller windowsill plant.
A Sensible Place to Start
If you’ve never grown basil from seed before, get a packet of Genovese, sow 5 seeds in a small pot of peat-free compost in April or May, keep it on the warmest sunny windowsill in the house, and water from below when the surface feels dry. That’s it. Within 8 weeks you’ll have a bushy basil plant producing fresh leaves whenever you want them.
Once you’ve succeeded once, basil becomes one of the easiest herbs to keep growing year-round. A few cuttings rooted in water over winter, a fresh sowing in spring, and a plant or two outside in summer keeps you in fresh basil from March to October at almost no cost.
For timing details, When to Plant Basil in the UK covers month-by-month sowing. And if you’re sorting out the rest of your garden alongside the basil, May Gardening Jobs in the UK and What to Plant in June in the UK cover everything else worth doing right now.