Basil is one of the most popular herbs to grow in the UK, but it is also one of the most commonly killed by poor timing. Buy a supermarket pot in April, put it on a windowsill, and watch it slowly collapse. Grow it from seed at the right time with a little care and it produces abundantly through summer. The difference is almost always timing and temperature.
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.
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 UK vegetable planting calendar and when to plant vegetables in the UK cover the whole season in one place.
Frequently Asked Questions
When can I plant basil outside in the UK?
Basil can go outside from June onwards in most UK gardens, once night temperatures are consistently above 10°C and frost risk has passed. Moving it outside before June risks cold damage even on nights that do not feel particularly cold.
Can basil survive outside in the UK?
Yes, but only in warm, sheltered conditions during the summer months. Basil is not hardy and will not survive frost or prolonged cold. It grows best outdoors in the UK from June to early September in a warm, sunny, sheltered spot.
Why does my basil keep dying?
The most common reasons are cold temperatures, overwatering, and poor light. Basil is very sensitive to cold — even indoors on a draughty windowsill — and roots in wet compost deteriorate quickly. A warm, bright position and careful watering solve most basil problems.
When should I sow basil seeds in the UK?
Basil seeds can be sown indoors from late March through to May. They need warmth to germinate well — above 18°C is ideal. A propagator or warm south-facing windowsill works well.
Can I grow basil on a windowsill year round?
Yes. A warm, south-facing indoor windowsill can support basil through the year, though growth slows significantly in winter when light levels drop. A grow light can help extend the productive season indoors if needed.
How do I stop basil from flowering?
Pinch out flower buds as soon as they appear. Always pick from the top of stems to encourage bushy growth rather than letting plants grow tall. Regular harvesting is the most effective way to delay flowering and keep plants productive.
Is basil easy to grow in the UK?
Basil is straightforward once you understand its needs — warmth, good light, careful watering and protection from cold. The main difficulty in the UK is that our climate is cooler and more unpredictable than basil prefers, which makes timing and positioning more important than with hardier herbs.
What is the best place to grow basil in the UK?
A warm south-facing windowsill indoors is the most reliable option for most of the year. Outdoors, a sheltered south-facing spot against a wall or on a warm patio works well from June to early September.
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.