Herbculinary herbSome care needed

Basil

Ocimum basilicum

A tropical plant treated as a summer annual, and the herb most often killed by being left outdoors too early. Basil wants warmth, light and shelter, and sulks below about 10 °C — which makes it a windowsill and greenhouse herb in Britain rather than a border one. Pinched regularly it bushes out; left to flower it stops producing leaves.

Position: Full sun
Water: moderate demand
Drainage: Free-draining, Moisture-retentive
Grows to: 30–60 cm × 25–30 cm
Hardiness: H1C
Harvest: June to September
Difficulty: Some care needed

Described view

A basil plant with one tier of small cupped puckered leaves and normal leaves above and below it

August

Harvest

Basil’s year

Resolved for United Kingdom (general). Every window is stored against a climate event rather than a date, so a late frost pocket runs later than the band shows. What else August calls for.

Activity	F	M	A	M	J	J	A	S
Sow under cover	February.	March.	April.	May.	June.
Plant out				May.	June.
Harvest					June.	July.	August.	September.

Timing that travels

The band above resolves this plant's windows into months for one region. These are the windows themselves, stored against a climate event rather than a date — which is the form that survives being carried to a colder garden, a frost pocket, or next year.

Sow under cover
from 8 weeks before to 0 weeks after your last spring frost, successionally, every four weeks for a continuous supply
source
Sourced guidancehigh confidence
- Royal Horticultural Society: Basil — sowing
Checked 2026-08-13
Plant out
3–6 weeks after your last spring frost
source
Sourced guidancehigh confidence
- Royal Horticultural Society: Basil — planting out
Checked 2026-08-13
Later than almost anything else. Basil put out at the same time as tomatoes usually checks and never recovers.

What kind of herb this is

Herbs are a kitchen grouping rather than a botanical one, and the plants in it want opposite things. This is the one distinction that decides how to treat it.

Warm-season tender herb

Growing regime

source

Sourced guidancehigh confidence

Royal Horticultural Society: Basil — growing

Checked 2026-08-13

Does nothing below about 10 °C and sulks in a cold wet spring. Warmth and shelter matter more than feeding, and outdoors in Britain is usually the wrong place until midsummer.

Treated the same way: shiso, thai basil. The herb bed, split by regime

Indoors: Indoors spring to autumn

Where the indoor assessment comes from

IndoorsSourced guidancemoderate confidence: Royal Horticultural Society: Basil — growing indoors
Checked 2026-08-13

Almost any herb will sit on a windowsill in July. This is about whether it is still there in March, which is the part a pot on a supermarket shelf does not tell you.

What happens when it flowers

On a herb this is rarely a problem and rarely nothing. It is the point at which the plant stops being what you grew it for — by a lot, a little, or not at all.

Leaves coarsen

source

Sourced guidancehigh confidence

Royal Horticultural Society: Basil — harvesting

Checked 2026-08-13

Pinch out the flowering tip back to the next pair of leaves as soon as you see buds. Basil recovers from this completely and bushes out, which is the whole reason regular picking keeps a plant productive — this is not a one-way change like coriander bolting.

source

Sourced guidancehigh confidence

Royal Horticultural Society: Basil — pinching out

Checked 2026-08-13

Conditions it needs

Light: Full sun
Direct sun: 6 hours a day or more
Frost: Frost tender
Hardiness rating: H1c (RHS)
Survives down to: 10–12 °CSourced guidanceDepends on conditions
Grows best at: 20–30 °C
Germinates at: 18–30 °C
Soil: Peat-free compost, Loam
Soil pH: 6–7.5
Drainage: Free-draining, Moisture-retentive
Water needs: moderate
Drought: poor tolerance
Waterlogging: poor tolerance
Heat: good tolerance
Wind and exposure: poor tolerance

Where these figures come from

LightSourced guidancehigh confidence

Royal Horticultural Society: Grow your own: basil

Checked 2026-08-13

Direct sunHorticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

FrostSourced guidancehigh confidence

Royal Horticultural Society: Basil — hardiness

Checked 2026-08-13

Hardiness ratingSourced guidancehigh confidence

Royal Horticultural Society: RHS hardiness ratings

Checked 2026-08-13

Survives down toSourced guidanceDepends on conditionshigh confidence

Applies when: Below roughly 10 °C basil stops growing and the leaves blacken at the edges; it does not need an actual frost to be ruined.

Royal Horticultural Society: Basil — growing

Checked 2026-08-13

Grows best atHorticultural consensusmoderate confidence

Home and Garden Information Center — Clemson Cooperative Extension: Basil — culture

Checked 2026-08-13

Germinates atSourced guidancehigh confidence

OSU Extension Service — Oregon State University: Herb seed germination temperatures

Checked 2026-08-13

SoilHorticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

Soil pHSourced guidancehigh confidence

Plant Finder — Missouri Botanical Garden: Ocimum basilicum

Checked 2026-08-13

DrainageHorticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

Water needsHorticultural consensusmoderate confidence

Water in the morning so the compost is not cold and wet overnight.

No external citation — see the evidence type above.

Checked 2026-08-13

DroughtHorticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

WaterloggingHorticultural consensusmoderate confidence

Wet compost overnight in cool conditions is the classic way a supermarket basil pot dies.

No external citation — see the evidence type above.

Checked 2026-08-13

HeatHorticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

Wind and exposureHorticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

On your soil

Computed by comparing this plant's recorded requirements against each soil's recorded characteristics. A recorded horticultural fact overrides the comparison where GrowingHQ holds one.

Soil	Verdict	Why
Heavy clay	Works, with one condition	Basil will crop on heavy clay, but one thing has to be dealt with first. It needs ground that drains, and this soil holds water. For a crop lifted before winter the risk is not rot but the season: waterlogged ground is cold and unworkable in spring, so sowing is late and germination patchy.Improve the drainage before planting — a raised bed, or bulky organic matter worked in over several seasons. Do not add sand to clay in small quantities; it makes the problem worse.
Sandy	Works, with one condition	Basil will crop on sandy, but one thing has to be dealt with first. It has little drought tolerance and this soil dries out fast — it will check and bolt in the first dry spell without watering.Water and mulch will carry it through. On this soil the watering is not optional in a dry spell, which is the difference between a crop and a failure.
Chalky and alkaline	Works, with one condition	Basil will crop on chalky and alkaline, but one thing has to be dealt with first. It has little drought tolerance and this soil dries out fast — it will check and bolt in the first dry spell without watering.Water and mulch will carry it through. On this soil the watering is not optional in a dry spell, which is the difference between a crop and a failure.
Loam	Prefers this soil	Loam suits Basil as it stands: The pH suits it: it wants 6 to 7.5, and this soil is in that range. The free drainage is exactly what it wants. Loam is among the soils it is recorded as suiting. The soil holds moisture, which saves a great deal of watering.
Silty	Prefers this soil	Silty suits Basil as it stands: The pH suits it: it wants 6 to 7.5, and this soil is in that range. The free drainage is exactly what it wants. The soil holds moisture, which saves a great deal of watering.
Peaty and acid	Works, with one condition	Basil will crop on peaty and acid, but one thing has to be dealt with first. It needs ground that drains, and this soil holds water. For a crop lifted before winter the risk is not rot but the season: waterlogged ground is cold and unworkable in spring, so sowing is late and germination patchy.Improve the drainage before planting — a raised bed, or bulky organic matter worked in over several seasons. Do not add sand to clay in small quantities; it makes the problem worse.
Shallow over rock	Works, with one condition	Basil will crop on shallow over rock, but one thing has to be dealt with first. It has little drought tolerance and this soil dries out fast — it will check and bolt in the first dry spell without watering.Water and mulch will carry it through. On this soil the watering is not optional in a dry spell, which is the difference between a crop and a failure.
Made ground and urban soil	Works, with one condition	Basil will crop on made ground and urban soil, but one thing has to be dealt with first. It needs ground that drains, and this soil holds water. For a crop lifted before winter the risk is not rot but the season: waterlogged ground is cold and unworkable in spring, so sowing is late and germination patchy.Improve the drainage before planting — a raised bed, or bulky organic matter worked in over several seasons. Do not add sand to clay in small quantities; it makes the problem worse.

Not sure which you have? Four hand tests will settle it.

Space and spacing

Mature height: 30–60 cm
Mature spread: 25–30 cm
Rooting depth: 20 cm
Spacing: 20–25 cm apart

Where these figures come from

Mature heightHorticultural consensusmoderate confidence: No external citation — see the evidence type above.
Checked 2026-08-13
Mature spreadHorticultural consensusmoderate confidence: No external citation — see the evidence type above.
Checked 2026-08-13
Rooting depthHorticultural consensusmoderate confidence: No external citation — see the evidence type above.
Checked 2026-08-13
SpacingSourced guidancehigh confidence: Royal Horticultural Society: Basil — spacing
Checked 2026-08-13

Measured centre to centre. Plants set closer than this compete for light and water long before they look crowded, and the crowding cannot be undone once they are in.

In a container

Minimum volume: 3–5 litres
Minimum depth: 15 cm

Where the container figures come from

Minimum volumeSourced guidancehigh confidence

Per plant. A supermarket pot contains dozens of seedlings in a fraction of this and is why they collapse within a fortnight — splitting one into three or four pots saves it.

Royal Horticultural Society: Basil in containers

Checked 2026-08-13

Minimum depthHorticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

The classic windowsill pot herb, and the classic windowsill failure. Give it the brightest position available, water in the morning at the base, and never leave the pot standing in a saucer of water.

Where and how you can grow it

Each way of growing is assessed separately, and “not assessed” is a real answer rather than a gap we have filled in with a guess.

Method	Suitability	What it needs
Windowsill	Well suited source Sourced guidancehigh confidence Royal Horticultural Society: Basil indoors Checked 2026-08-13	A bright warm sill; Watering in the morning, not the eveningThe best indoor herb after chives: warm dry indoor air is exactly what basil wants and what most other herbs resent.
Greenhouse	Well suited source Sourced guidancehigh confidence Royal Horticultural Society: Basil under glass Checked 2026-08-13
Polytunnel	Well suited source Horticultural consensusmoderate confidence No external citation — see the evidence type above. Checked 2026-08-13
Container	Well suited source Sourced guidancehigh confidence Royal Horticultural Society: Basil in containers Checked 2026-08-13	A warm sheltered spot; 3–5 litres per plant
Hydroponics	Well suited source Sourced guidancehigh confidence Purdue Extension — Purdue University: Hydroponic herbs Checked 2026-08-13	Along with lettuce, one of the two crops soilless systems handle best, and grown this way commercially at scale.
Grow tent	Well suited source Horticultural consensusmoderate confidence No external citation — see the evidence type above. Checked 2026-08-13
Aquaponics	Well suited source Sourced guidancehigh confidence Purdue Extension — Purdue University: Aquaponic herbs Checked 2026-08-13
Raised bed	Workable source Horticultural consensusmoderate confidence No external citation — see the evidence type above. Checked 2026-08-13	A warm sheltered site, planted late
Indoor pot	Workable source Horticultural consensusmoderate confidence No external citation — see the evidence type above. Checked 2026-08-13	Supplementary lighting away from a window
Vertical growing	Workable source Horticultural consensusmoderate confidence No external citation — see the evidence type above. Checked 2026-08-13
Open ground	Marginal source GrowingHQ editorial positionmoderate confidence Outdoors in a British summer basil is slow, prone to slug damage and often blackened by the first cold night in September. It works in a hot year in the south and disappoints in most others. GrowingHQ editorial synthesis — GrowingHQ Checked 2026-08-13

Growing it

SowingSow on the surface of moist compost and cover very thinly, at 18 °C or more. Basil seedlings damp off readily, so sow thinly and keep the air moving.
PruningPinch out the growing tip above a pair of leaves once the plant has four or five pairs, and keep pinching. Each pinch produces two shoots, and a pinched plant yields several times what an unpinched one does.
HarvestingTake the tips rather than the lower leaves, and remove flower buds as they appear. Once basil flowers, leaf production effectively stops and the flavour changes.
WateringWater in the morning and from below where possible. Basil sitting in cold wet compost overnight is the most reliable way to lose it.
FeedingBasil in fresh compost needs no feed for the first several weeks. After that a dilute balanced liquid feed every fortnight keeps it in leaf. Water in the morning and at the base: basil left with wet leaves overnight in a cold spell is how most plants are lost, and that is a watering fault rather than a feeding one.
ProtectionBasil is not overwintered outdoors in Britain — it stops growing below about 10 °C and is blackened by the first frost. A plant brought onto a bright windowsill in September will carry on for a few weeks and then usually decline through the winter as light levels fall, so the more reliable approach is to take soft cuttings in late summer, root them in water and grow the young plants on somewhere bright and above 15 °C. Keep them on the dry side; cold wet compost in December kills more overwintered basil than cold alone.

Where this guidance comes from

SowingSourced guidancehigh confidence: Royal Horticultural Society: Basil — sowing
Checked 2026-08-13
PruningSourced guidancehigh confidence: Royal Horticultural Society: Basil — pinching out
Checked 2026-08-13
HarvestingSourced guidancehigh confidence: Royal Horticultural Society: Basil — harvesting
Checked 2026-08-13
WateringSourced guidancehigh confidence: Royal Horticultural Society: Basil — care
Checked 2026-08-13
FeedingSourced guidancemoderate confidence: Royal Horticultural Society: Basil — cultivation
Checked 2026-08-13
ProtectionSourced guidancehigh confidence: Royal Horticultural Society: Basil — cultivation
Checked 2026-08-13

The bud you cut to becomes the new shoot, and it grows in the direction it points — which is why an outward-facing bud opens the plant up and an inward-facing one crosses the middle.

Is it worth putting under cover?

Whether it will grow there is on the methods table above. This is whether the space is well spent, which is a different question and usually the one being asked.

Structure	What protection is worth	What decides it
Greenhouse	Only possible under cover source GrowingHQ editorial positionmoderate confidence What protection is worth for this crop, judged against the same standard as every other record in this file. GrowingHQ editorial synthesis — GrowingHQ Checked 2026-08-13	Night temperature. Basil sulks below about 10 °C and a British night outdoors is below that well into June and again from September.The herb that most rewards a greenhouse, and the one most often killed by being planted out in May.
Polytunnel	Extends the season source GrowingHQ editorial positionmoderate confidence What protection is worth for this crop, judged against the same standard as every other record in this file. GrowingHQ editorial synthesis — GrowingHQ Checked 2026-08-13	Overnight temperature. Glass holds overnight heat that polythene loses, so a tunnel runs cooler at night than a greenhouse in the same garden. For a crop at the edge of its heat requirement that difference decides whether the fruit ripens.

On a windowsill

A few weeks, then replace

source

GrowingHQ editorial positionmoderate confidence

How long the crop is actually productive on an ordinary British windowsill without added light.

GrowingHQ editorial synthesis — GrowingHQ

Checked 2026-08-13

A supermarket pot or a sowing gives a few weeks of cutting and is then exhausted. That is what the crop is, not a failure to keep it alive. Light and night temperature. A summer sill grows it well; a bought pot is a dense plug of seedlings that exhausts itself in a few weeks whatever anybody does.Basil is the plant that most often convinces somebody they cannot grow herbs, and the reason is almost always the pot rather than the grower.

Growing it without soil

Nearly anything can be grown in a soilless system by somebody with enough equipment. The useful question is whether it is worth it, in which technique, and what goes wrong.

Well suited

An established soilless crop. Grown this way commercially or routinely by home growers, with predictable results.

source

Sourced guidancehigh confidence

Purdue Extension — Purdue University: Hydroponic herbs

Checked 2026-08-13

Along with lettuce, the crop most commonly grown hydroponically at commercial scale, and the easiest herb to start with.

Techniques that suit it

Nutrient film (NFT)A shallow stream of solution runs over bare roots in a sloped channel. Cheap and productive for small fast crops; a pump failure kills a crop within hours because there is no reservoir at the roots.
Deep water cultureRoots hang in aerated solution. Very productive and very unforgiving of solution temperature — warm solution holds less oxygen and root disease follows.
Drip-fed mediumSolution is dripped into an inert medium around each plant. The most forgiving technique and the one that suits large, long-season, heavy crops.
Ebb and flowA bed of inert medium floods and drains on a timer. The medium holds moisture between floods, which makes it far more tolerant of interruption than NFT.

source

Sourced guidancehigh confidence

Purdue Extension — Purdue University: Hydroponic herbs

Checked 2026-08-13

Root space: Modest. Basil is compact and fibrous-rooted and suits almost any technique.
Lighting: Needs supplementary light
Solution temperature: 20–24 °CSourced guidanceDepends on conditions
pH band: 5.5–6.5

Where these figures come from

Root spaceHorticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

LightingHorticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

Solution temperatureSourced guidanceDepends on conditionsmoderate confidence

Applies when: Basil wants a warmer solution than lettuce, which makes mixing the two in one reservoir a compromise.

Purdue Extension — Purdue University: Warm-season crops in solution culture

Checked 2026-08-13

pH bandSourced guidancehigh confidence

Outside roughly this band, individual nutrients become unavailable even when they are present in the solution — which is why a crop can starve in a full reservoir.

Purdue Extension — Purdue University: Hydroponic solution management — pH

Checked 2026-08-13

What actually goes wrong

Cold. Basil stalls below about 10 °C and blackens at the leaf edges, and an unheated indoor system in winter is colder than it feels.
source
Sourced guidancehigh confidence
- Royal Horticultural Society: Basil — growing
Checked 2026-08-13
Pump or power failure. In nutrient film and aeroponics there is no reserve at the roots, so a crop can be lost within hours; medium-based systems hold moisture and are far more forgiving.
source
Sourced guidancehigh confidence
- Purdue Extension — Purdue University: Hydroponic system design — failure modes
Checked 2026-08-13

No nutrient recipes here

GrowingHQ records pH bands, which are measurable properties of nutrient availability, and deliberately records no EC or PPM targets and no mixing instructions. Published targets vary by cultivar, growth stage, water source and technique, and the figures that apply to your system are on the product you bought.

Harvesting

Time from sowing or planting: 8–10 weeks

source

Sourced guidancehigh confidence

Royal Horticultural Society: Basil — timing

Checked 2026-08-13

When it is readyPick from the point the plant has several pairs of leaves, and keep picking the tips.
How to pick itPinch or cut just above a leaf pair.
Keeping itDoes not keep. Refrigeration blackens the leaves; a cut stem stands better in water at room temperature. Freezing in oil or as pesto works far better than drying.

Where the harvest guidance comes from

When it is readyHorticultural consensusmoderate confidence: No external citation — see the evidence type above.
Checked 2026-08-13
How to pick itHorticultural consensusmoderate confidence: No external citation — see the evidence type above.
Checked 2026-08-13
Keeping itHorticultural consensusmoderate confidence: No external citation — see the evidence type above.
Checked 2026-08-13

Keep picking

Regular picking keeps this plant producing. Fruit or leaves left to mature signal it to slow down or stop.

What goes wrong

Problem	How often	Notes
Damping off	common source Sourced guidancehigh confidence Royal Horticultural Society: Damping off Checked 2026-08-13	Basil seedlings are unusually prone to it.
Slugs and snails	common source Sourced guidancehigh confidence Royal Horticultural Society: Slugs and snails Checked 2026-08-13	Outdoor plants are stripped overnight.
Aphids	occasional source Horticultural consensusmoderate confidence No external citation — see the evidence type above. Checked 2026-08-13

Start from what you can see

What to look for

Views that settle something a description cannot. Where the photograph has not been taken yet, the description of what it will show is here instead — which is the useful half of it either way.

Described view

The growing tip of a basil plant being pinched out just above a pair of leaves, with side shoots already breaking below

Each pinch turns one stem into two.

Grown with, grown after, grown instead

Every relationship states its mechanism. A pairing nobody can explain is a pairing nobody has checked, and it does not go in.

Grown togetherTomato
The most repeated companion pairing in gardening. What is well supported is that both are frost-tender crops wanting the same warm sheltered position, so they share a greenhouse or a sunny bed conveniently. Claims that basil repels tomato pests or improves tomato flavour are not supported by trial evidence.
Sourced guidanceDepends on conditionshigh confidence
Applies when: A shared-conditions relationship, not a pest or flavour one. Recorded this way deliberately: the pairing is sound advice for the wrong stated reason.
Royal Horticultural Society: Companion planting
Checked 2026-08-13

Sources for this page

GrowingHQ editorial synthesis · Home and Garden Information Center · OSU Extension Service · Plant Finder · Purdue Extension · Royal Horticultural Society

Each figure on this page carries its own citation, under the “where these figures come from” note in its section. Record last reviewed 2026-08-13.

If something is wrong with it

Dark or black spots on leaves — 2 causes GrowingHQ holds for basil
Plant wilting although the soil is moist — 2 causes GrowingHQ holds for basil
Lower leaves turning yellow — 3 causes GrowingHQ holds for basil

Something else? Work through it with the diagnostic tool.