How to sow vegetable seeds successfully: a complete guide

Growing vegetables from seed gives you access to a far wider choice of varieties. You decide exactly what to grow, how many plants you need and when to start them. It also allows you to follow the whole process from a tiny seed to a productive plant.

Successful seed sowing is not particularly complicated. The key is to provide the right balance of moisture, temperature, oxygen and light for each crop.

If you are unsure when to begin, consult our vegetable sowing calendar to see what you can sow each month in a temperate European climate.

Why grow vegetables from seed?

Growing your own seedlings has many advantages:

• A much wider choice of varieties.
• Access to traditional, regional and unusual crops.
• The possibility of growing organic, open-pollinated seeds.
• Control over the number of plants you raise.
• A lower cost per plant.
• Seedlings gradually adapted to your own growing conditions.
• The possibility of saving seed from open-pollinated varieties.
• The satisfaction of following every stage of the plant’s development.

You do not need a large greenhouse or professional equipment. For many crops, clean containers, suitable seed compost, good light and regular care are enough.

The four essentials for successful germination

A seed contains the reserves it needs to begin growing. To germinate, it mainly needs water, oxygen and a suitable temperature. Once the seedling emerges, light becomes essential.

Consistent moisture without waterlogging

Water activates the seed and starts the germination process. Seed compost should remain moist but never saturated.

Dry compost may interrupt germination. Constantly wet compost contains too little oxygen and increases the risk of rotting and damping-off.

After sowing:

• Water gently with a mister or fine rose.
• Avoid a strong stream that could displace small seeds.
• Keep the compost lightly moist until emergence.
• Do not leave containers standing in water.
• Ventilate propagators and transparent covers regularly.

Remove or open the cover as soon as the first seedlings appear.

The right germination temperature

Different vegetables need different temperatures.

Crop group	Indicative germination temperature
Lettuce, spinach and peas	10–18°C
Cabbages, onions and leeks	15–20°C
Carrots, beetroot and radishes	15–22°C
Tomatoes	20–25°C
Aubergines and peppers	22–28°C
Squash, courgettes and cucumbers	20–25°C

These temperatures are mainly important during germination. Once seedlings emerge, slightly cooler conditions generally produce sturdier, more compact plants.

A heated propagator or heat mat can help with aubergines and peppers. Remove the extra heat after emergence and provide plenty of light.

Oxygen around the seed

Seeds also need oxygen. Use fine, open and well-drained seed compost rather than dense or waterlogged soil.

Do not press the compost down too firmly. Gentle pressure is enough to create contact between the seed and the growing medium.

Plenty of light after emergence

Once seedlings appear, they need as much light as possible. Insufficient light produces tall, thin and pale seedlings, often described as leggy.

Place seedlings:

• Beside a very bright window.
• In a well-lit greenhouse.
• Beneath a suitable grow light when sowing particularly early.

In January and February, waiting a little longer is often better than raising weak plants in poor light.

Which compost should you use?

Good seed compost should be:

• Fine enough to surround small seeds.
• Light and well aerated.
• Able to retain moisture without becoming waterlogged.
• Low to moderately fertile.
• Free from large pieces of wood and other coarse material.

Very rich compost does not improve germination. During its earliest development, the seedling mainly uses the reserves stored inside the seed.

For very small seeds, sieve the upper layer to create a fine, even surface.

How deeply should seeds be sown?

As a general rule, cover a seed with compost to approximately two or three times its own thickness.

• Very fine lettuce and celery seeds are left on or very close to the surface.
• Medium-sized tomato, cabbage and radish seeds are lightly covered.
• Large bean, pea and squash seeds can be sown more deeply.

Seeds sown too deeply may exhaust their reserves before reaching the surface. Seeds sown too shallowly can dry out rapidly.

Always follow the guidance provided for the individual variety.

Sow at the right time

Work backwards from the likely outdoor planting date.

Tomatoes, aubergines and peppers need a long growing period and are started relatively early in warm conditions. Courgettes, cucumbers and squash develop much faster and generally only need to be sown three or four weeks before planting out.

Earlier sowing does not necessarily produce an earlier harvest. A younger plant raised in good light can quickly overtake an older seedling weakened by poor conditions.

Choosing the right sowing method

Method	Principle	Suitable crops
Seed tray	Several seeds in one tray, later transplanted	Lettuce, cabbages, leeks and tomatoes
Module tray	One or a few seeds in each cell	Lettuce, cabbages and herbs
Individual pots	Each plant grows separately	Tomatoes, aubergines, peppers and courgettes
Station sowing	Several seeds placed together	Beans, peas, squash and cucumbers
Row sowing	Seeds distributed along a shallow drill	Carrots, radishes, turnips and spinach
Broadcast sowing	Seeds scattered over a prepared surface	Green manures and some leafy vegetables
Direct sowing	Seeds sown where the plants will grow	Carrots, parsnips, radishes, peas and beans

Root vegetables such as carrots and parsnips are normally sown directly because transplanting can damage their main roots.

Useful seed-sowing equipment

Trays, modules and pots

Seed trays are practical for seedlings that will later be pricked out. Module trays keep roots separate and make transplanting easier. Individual pots suit fast-growing crops and plants that dislike repeated disturbance.

All containers must have drainage holes.

A propagator

A propagator or transparent cover maintains humidity and warmth during germination. Ventilate it daily and remove the lid after seedlings emerge.

A heat mat

Bottom heat is useful for tomatoes, aubergines and peppers. Once they have germinated, strong light becomes more important than continued high temperatures.

A soil blocker

A soil blocker creates free-standing blocks of compost, reducing the need for plastic pots and limiting root disturbance. Soil blocks dry out more quickly, so their moisture must be monitored carefully.

What should you do after germination?

Remove the cover

Remove the propagator lid as soon as seedlings appear. Prolonged warmth and humidity increase the risk of fungal diseases.

Provide maximum light

Move seedlings immediately to a bright position. Rotate containers regularly if the light comes from only one direction.

Thin overcrowded seedlings

Seedlings growing too closely together compete for light, water and nutrients. Keep the strongest and remove the surplus plants.

Prick out at the right stage

Seedlings grown together are generally ready to prick out when their first true leaves appear after the seed leaves.

Handle a young plant by a leaf rather than by its delicate stem. A damaged leaf can be replaced; a crushed stem usually cannot.

Tomatoes can be transplanted more deeply because their stems are able to form additional roots.

How can damping-off be prevented?

Damping-off causes young seedlings to collapse at soil level. Affected seedlings usually cannot be saved.

Reduce the risk by:

• Using clean containers.
• Choosing fresh, well-drained seed compost.
• Avoiding excessive watering.
• Not sowing too densely.
• Ventilating every day.
• Removing covers after emergence.
• Avoiding unnecessary heat after germination.

Why are my seeds not germinating?

Possible causes include:

• Temperatures that are too low or too high.
• Compost drying out during germination.
• Waterlogged compost causing seeds to rot.
• Seeds being sown too deeply.
• The normal germination period not yet being complete.
• Seeds requiring cold treatment or another preparation.
• Unsuitable seed-storage conditions.

Radishes may germinate within a few days, while parsley, parsnips and some herbs can take several weeks. Allow enough time before assuming that a sowing has failed.

Hardening seedlings off

Plants raised indoors are not immediately ready for full sun, wind and cold nights.

Begin approximately one or two weeks before planting:

1. Put the plants outdoors for a few hours in a sheltered position.
2. Avoid strong midday sunshine during the first few days.
3. Gradually increase their exposure to sun and wind.
4. Bring them inside when nights are too cold.
5. Do not allow the compost to dry out completely.

What does a healthy seedling look like?

A good seedling is not necessarily the tallest or earliest. Look for a plant that is:

• Compact and sturdy.
• Well rooted.
• Supported by a strong stem.
• Evenly green.
• Free from yellow or spotted leaves.
• Appropriately sized for its container.

A balanced young plant normally establishes more quickly than an oversized seedling raised in excessive warmth or insufficient light.

Choose your favourite varieties from our range of organic, open-pollinated vegetable seeds and start growing.