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. For the wider picture across all the kitchen herbs, see our guide to growing herbs.

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, and Best Vegetables to Grow in Pots in the UK covers which crops do well alongside basil in containers.

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

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.

This guide explains when to plant basil in the UK, why it struggles so often in British conditions, and how to grow it successfully whether you are starting from seed or working with a bought plant. For the full growing process from seed to harvest, see How to Grow Basil from Seed in the UK.

Quick Answer

In most UK gardens, basil is sown indoors from late March to May and moved outside only from June onwards once temperatures are reliably warm. Basil is extremely cold-sensitive — even a cool night can set it back significantly. It grows best as an indoor or sheltered outdoor herb through most of the UK summer.

Why Basil Is Difficult to Grow in the UK

Basil originates from tropical climates where temperatures are consistently warm and humidity is high. The UK offers almost the opposite — cool nights, unpredictable summers, and damp conditions that basil finds stressful.

This is why supermarket basil plants fail so often. They are grown in controlled glasshouse conditions and sold before the weather is warm enough to support them. Placed on a cold windowsill or outside too early, they deteriorate quickly.

Growing basil successfully in the UK means working with its needs rather than against them — starting it at the right time, keeping it warm, and understanding that it will always perform better in a warm, sheltered spot than in open garden beds. If you are new to growing herbs and vegetables, gardening for beginners in the UK covers the foundations that make growing easier across the board.

When to Sow Basil Seeds Indoors

Basil can be sown indoors from late March through to May. This is the most reliable way to grow it in the UK because it gives seeds the warm, stable conditions they need to germinate and establish properly before outdoor temperatures are consistently warm enough.

Basil seeds need warmth to germinate well — ideally above 18°C. A warm windowsill, propagator or greenhouse shelf all work. In cooler rooms germination is slow and uneven, and seedlings that do emerge often stay weak.

Sow seeds thinly into small pots or modules filled with good quality compost. Best compost for vegetables in the UK is worth reading if you are unsure which compost to use — the same principles apply for herbs. Cover seeds lightly and keep the compost moist but not waterlogged. Seedlings usually appear within one to two weeks in warm conditions.

Once seedlings have two pairs of leaves they can be thinned or potted on. Basil benefits from being grown in small groups rather than as single plants — this helps with bushier growth and keeps individual plants from becoming leggy.

When to Move Basil Outside

Basil should only be moved outside once night temperatures are consistently above 10°C — in most UK gardens this means June at the earliest. Even in a warm May, a cold night can cause leaves to blacken and plants to collapse very quickly.

Before moving basil outside it needs to be hardened off, just like any tender plant grown indoors. Basil is particularly sensitive to the transition between warm indoor air and cooler outdoor conditions. Read how to harden off plants in the UK before putting basil outside — a week of gradual acclimatisation makes a significant difference to how well it settles.

Even after hardening off, basil performs best in a warm, sheltered outdoor spot — against a south-facing wall, in a sheltered corner, or in a container that can be brought inside if a cold night is forecast. It is not a plant for open, exposed garden beds in the UK.

Checking UK last frost dates by postcode before moving basil outside is a sensible step — basil is one of the most frost-sensitive plants you are likely to grow.

Month-by-Month Guide to Basil

March

Late March is the earliest sensible time to sow basil indoors in most UK gardens. Conditions need to be genuinely warm — a cold spare room will not give good results. A propagator or warm south-facing windowsill is ideal at this time of year.

April

April is a good month for indoor sowing. Basil started in April will be well established by the time outdoor conditions are warm enough in June. Keep plants on the warmest windowsill available and away from cold draughts.

May

May is the last good month for sowing basil if you want plants ready for a full summer of use. Basil can still be sown in May and will establish quickly in warm conditions. Do not move plants outside yet — even warm May days can be followed by cold nights that damage basil badly. This is also the month to start hardening off April sowings ready for outdoor planting in June. If you are growing other tender crops this month too, what to sow in May in the UK and what to plant in May in the UK cover everything that can go outside this month.

June

June is when hardened-off basil can go outside in most UK gardens. Choose the warmest, most sheltered spot available. A container on a south-facing patio or against a warm wall works much better than an open bed. Keep an eye on the forecast and bring plants in if a cold night is expected.

July and August

The best growing months for basil in the UK. Plants established by now will grow strongly in warm weather and produce well if picked regularly. This is also the time to prevent flowering — pinching out flower heads as they appear keeps plants producing fresh leaves for longer.

September

Temperatures begin to drop in September and basil will start to deteriorate outdoors. Bring container plants inside before the first cold nights arrive. Plants left outside too long in autumn rarely recover. September is also a good time to take cuttings from healthy plants to overwinter on a warm windowsill indoors.

Where to Grow Basil in the UK

The best place to grow basil in most UK gardens is on a warm windowsill indoors or in a sheltered outdoor spot that gets full sun and is protected from cold wind. A south-facing windowsill in the kitchen is the classic choice and works very well because the warmth is consistent and picking is easy.

Outdoors, the ideal spot is against a south-facing wall or fence where the plant gets reflected warmth as well as direct sun. A patio or courtyard that traps heat works well. Open vegetable beds in exposed positions rarely give good results with basil in the UK — the combination of wind and cool nights is too much for it.

Containers work particularly well for basil because they can be moved — brought inside when cold nights are forecast and positioned to follow the sun through the day. If you are growing other vegetables in pots this summer, can you grow vegetables in pots in the UK covers how to manage containers through the season.

What Soil and Compost Basil Needs

Basil grows best in fertile, well-drained compost or soil. It does not like sitting in wet or waterlogged conditions — roots in cold, damp compost deteriorate quickly and the plant collapses from the base up.

For container growing, a good quality multipurpose compost works well. Make sure pots have adequate drainage holes and do not sit in standing water. Peat-free compost in the UK covers what to look for and what to avoid if you are choosing compost for containers this season.

In the ground, basil prefers light, open soil that warms quickly. If your soil is heavy or tends to stay wet after rain, growing basil in containers will always give better results than planting it directly into the ground. Why garden soil stays wet explains why some soils hold water for so long and what can be done about it.

How to Keep Basil Producing Through Summer

Regular picking is the single most important thing you can do to keep basil productive. Picking encourages bushy growth and delays flowering. Always pick from the top of each stem, removing the growing tip and leaving two pairs of leaves below. This causes the plant to branch and produce more stems rather than growing tall and straggly.

Once basil flowers, leaf production slows significantly and the flavour of remaining leaves diminishes. Pinch out any flower buds as soon as they appear — do not wait until they open. If plants do flower and you want to extend their useful life, remove the flower heads completely and the plant will often recover and put on fresh growth.

Watering needs some care. Basil needs consistent moisture but hates waterlogging. Water at the base of the plant rather than over the leaves, particularly indoors where wet foliage in low light leads to mould. Allow the surface of the compost to dry slightly between waterings. How often to water plants in the UK covers the principles that apply to herbs and vegetables alike.

Light feeding every two to three weeks with a balanced liquid feed helps keep plants productive through summer. Avoid overfeeding — too much nitrogen produces lush, soft leaves with less flavour. Feeding vegetables properly in the UK explains why restraint with feeding almost always produces better results than excess.

What to Do With Supermarket Basil Plants

Supermarket basil pots are usually packed with many seedlings grown very close together to look full and lush on the shelf. They are not intended to last — they are sold as a short-term product rather than a plant.

To get more from a supermarket basil plant, split it into three or four smaller clumps, pot each one into its own container with fresh compost, and keep them on a warm windowsill. Given a little space and proper conditions, each clump will often recover and produce well for months.

Do not put supermarket basil outside until June at the earliest. These plants have been grown in warm glasshouses and are even more sensitive to cold than garden-grown plants. Moving them outside too soon is the most common reason they fail so quickly.

Common Mistakes With Basil in the UK

Moving basil outside too early is the most common mistake by a significant margin. Even experienced gardeners underestimate how quickly basil reacts to cold nights. June is the safe month for outdoor planting across most of the UK — not May, regardless of how warm the days feel.

Overwatering is the second most common problem. Basil roots in cold, wet compost deteriorate quickly and the plant collapses in a way that looks like it needs more water, when in fact water is the problem. If basil wilts despite moist soil, the issue is usually root stress rather than drought. Why vegetable plants wilt in UK gardens explains this pattern in more detail.

Placing basil on a cold or draughty windowsill — even indoors — slows growth and weakens plants. North-facing windowsills, spots near doors, or positions where cold air comes in around window frames are all problematic. The warmest, brightest spot you have is always the right choice for basil.

Letting plants flower without pinching them out is another common mistake. Once basil runs to flower the plant puts its energy into seed production rather than leaf growth, and the flavour and quantity of leaves drops off quickly. For a broader look at what trips up beginners, common gardening mistakes beginners make is a useful read.

Basil Alongside Other Summer Crops

Basil is a natural companion to tomatoes in the kitchen and in the garden. It thrives in the same warm conditions that tomatoes need and is traditionally grown alongside them. If you are growing tomatoes this summer, the timing for both crops is similar — indoors now, outside in June once conditions are genuinely warm.

It also sits well alongside other warm-season crops like courgettes, cucumbers, sweetcorn and French beans — all of which share similar timing requirements and do best once the UK summer is properly underway. For the full picture of what to grow and when, the the vegetable sowing calendar and when to plant vegetables in the UK cover the whole season in one place.

Frequently Asked Questions

A Sensible Place to Start

Basil is not a difficult herb to grow in the UK once you stop fighting its needs and start working with them. Sow indoors in April or May, keep it warm, harden it off carefully, and do not rush it outside before June.

Give it your warmest spot, pick it regularly, and keep the flowers pinched out. Do those things consistently and basil will produce well from June right through to September — far better than anything you will ever find on a supermarket shelf.

If you are building out a full summer growing plan alongside basil, May gardening jobs in the UK covers everything that needs doing right now, and easy vegetables to grow in the UK is a good guide if you are deciding what else to grow this season.