Basil seeds: how to sow and pair them?

In this article 9 ⌄

Basil is the best-selling and most frequently lost culinary herb. We buy it in a pot at the supermarket, and it withers within ten days; we sow it in March, and it fails to emerge. Both failures have the same cause: it is a tropical plant, and we treat it like a plant from our gardens.

Native to South Asia, basil tolerates neither cold, fluctuations, nor excess water. Once these three points are understood, it becomes easy—and generous for six months.

Sowing: warmth above all

When

Basil germinates from 18–20 °C soil temperature, with the optimum around 22–25 °C. Below 15 °C, germination is erratic and slow, and often fails altogether.

• Under cover—from March onward, on a warm windowsill or with a heating mat.
• In the ground—not before mid-May in most regions, and only once the soil has reached 18 °C. Sowing earlier gains nothing.
• Indoors—all year round, provided there is enough light.

How

1. Fine, moist seed-starting compost, in pots or a seed tray.
2. Cover only lightly—3 to 5 mm. The seed is small and light promotes germination: do not bury it.
3. Mist rather than water, so as not to displace the seeds.
4. Cover with film until emergence—5 to 10 days at the right temperature.
5. As soon as they emerge, remove the film and give them maximum light. Otherwise, the seedlings become leggy and will not recover.

One useful peculiarity: basil seeds become mucilaginous when they come into contact with water—they become surrounded by a translucent gel. This is normal, and even a good sign of freshness. Simply avoid soaking them before sowing, as they would become impossible to handle.

Transplanting and planting

Transplant at the two-true-leaf stage into individual pots. Wait until all risk of frost has passed before planting out permanently: basil exposed to 5 °C turns black and does not recover. Space plants 25 to 30 cm apart in the ground.

The gesture that changes everything: pinching out

This is what separates a lanky basil plant from a bushy one, and almost no one does it.

Basil naturally grows on a single stem that rises, flowers, and then stops. By cutting the tip above a pair of leaves, you remove apical dominance: the plant then produces two lateral stems instead of one. Repeat on each new shoot, and you will get a bush instead of a single stem.

• First pinch at 4 or 6 true leaves, just above the second pair.
• Always harvest from the top, never by removing the lower leaves — they are the ones that feed the plant.
• Remove the flower buds as soon as they appear. Flowering signals to the plant that its cycle is ending: the leaves become smaller, tougher, and more bitter.
• You can let one or two plants flower at the end of the season — for pollinators and to collect your seeds.

Watering and feeding

• At the base, never on the foliage — wet leaves turn black and attract fungal diseases.
• In the morning preferably, so everything has dried by evening.
• Regularly but not excessively — basil dislikes both drought and waterlogged roots. In pots, let the top centimeter of soil dry out between waterings.
• No nitrogen fertilizer. Excess nitrogen produces large, soft, bland leaves: the essential oils responsible for the aroma become concentrated in a slightly stressed plant. A generous amount of mature compost at planting is more than enough.

The varieties

• Sweet basil (Ocimum basilicum) — the classic, the one used for pesto and tomato salad. Broad leaves, a bold aroma. Start with this one.
• Thai basil (var. thyrsiflora) — anise and licorice notes, with purple stems. Essential in Asian cuisine, and it holds up better during cooking than sweet basil.
• Lemon basil (var. citriodorum) — highly aromatic, excellent with fish, summer fruit, and as an infusion.
• Purple basil (‘Purpurascens’) — very decorative dark foliage, with a stronger, slightly clove-like flavor. Superb as a border around the vegetable garden.
• Holy basil Tulsi (Ocimum tenuiflorum) — a distinct species, traditionally used as an herbal infusion. Hardier than other varieties and perennial in mild climates.

The whole selection can be found in our culinary and medicinal herb seeds.

Pairing basil

With tomatoes: what is true and what is not

This is the most famous pairing in the vegetable garden, and the most poorly explained. Two claims are commonly made:

• “Basil improves the taste of tomatoes” — no study establishes this. It is probably an extrapolation from their pairing in cooking.
• “Basil keeps pests away” — here, the mechanism does exist: basil's essential oils disrupt the olfactory detection of certain insects, particularly whiteflies. The effect is real but partial, and it requires immediate proximity — basil two meters away is useless.

There is also a rarely mentioned benefit: the two plants have the same needs — warmth, sun, regular watering at the base — and different root levels. That is the real reason for their compatibility. Allow one basil plant for every two tomato plants.

We discuss this topic in Pairing tomatoes and basil: myth or reality?.

Other good pairings

• Peppers and eggplants — the same requirements, the same aromatic effect.
• Zucchini — basil occupies the space before the foliage closes in.
• Asparagus — a traditional pairing, against asparagus beetles.
• At the edge of the bed — basil left to flower attracts bees and hoverflies, whose larvae feed on aphids.

To avoid

Common rue and cucumber, traditionally discouraged. Above all, do not plant it in the shade of a tall crop: this is the leading cause of decline in the vegetable garden.

Common problems

Symptom	Cause	Correction
Blackened leaves	Cold, or water on the foliage	Bring indoors or protect; water strictly at the base
Plant growing into a single stem	Never pinched	Pinch above a pair of leaves
Small, bitter leaves	Flowering in progress	Remove the flower buds
Soft, bland leaves	Excess nitrogen or lack of light	Do not fertilize; move it into the sun
Store-bought plant that is declining	Twenty crowded seedlings in a tiny pot	Divide the root ball into three or four sections and repot separately
Small holes in the leaves	Slugs or flea beetles	Dry barrier, evening harvest

Harvest, preserve, reseed

• Harvest in the morning, when the concentration of essential oils is highest.
• Basil dries poorly — it loses most of its fragrance. Freezing is preferable: whole leaves in a bag, or chopped in an ice cube tray with a little olive oil.
• Pesto freezes very well, and it is the best way to use up a large harvest.
• Taking cuttings — a 10 cm stem in a glass of water will root in one to ten days. The simplest way to propagate a plant you like, or to extend the season indoors.
• Harvesting the seeds — basil is self-pollinating: let one plant flower, wait until the calyces turn brown, then rub them over a bowl. See How to store your seeds.

Frequently asked questions

Why does my supermarket basil always die?

Because it is not one plant but around twenty seedlings crowded into a pot that is too small, forced to grow quickly for sale. They compete with and exhaust one another. The solution: remove the root ball from the pot, divide it into three or four sections, and repot them separately in a well-draining substrate.

Can basil be grown in winter?

Indoors, yes, provided it has a very bright window or supplemental lighting. Without enough light, it becomes leggy. Sacred basil, Tulsi, is the most tolerant of relatively low light.

Does it need to be watered every day?

In a pot and in summer, often yes. In mulched ground, two to three times a week is enough. The test is still whether the soil feels dry 2 cm below the surface.

How many plants should you grow?

Three to four plants, properly maintained, meet a household’s fresh needs. Plan on twice as many if you make pesto to freeze.

Is basil perennial?

It is perennial in the tropics and annual in our climates — the first frost kills it. Only sacred basil, Tulsi, can survive winter in very mild climates or in a conservatory.

Key points

Warm to germinate, bright to grow, pinched to become bushy, watered at the base and never fertilized. Treat it like the tropical plant it is, and a May sowing will provide for you until the first cool weather in October.

To go further

• Growing tomatoes and basil together: myth or reality?
• Heirloom tomato seeds: varieties, sowing, care
• Balcony vegetable garden: suitable techniques and varieties
• The month-by-month sowing calendar

Discover our five basils and all our culinary and medicinal seeds — all open-pollinated.