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Growing from seed gives you access to a huge choice of vegetables, herbs and flowers, but successful seed sowing depends on more than simply putting seeds into compost. The right sowing time, temperature, moisture and depth all affect germination and the health of the young seedlings that follow.
Some seeds are best started indoors in warmth, while others can be sown directly into prepared soil. The seed packet should always be your first reference, as germination requirements vary considerably between plants. Our UK Sowing Calendar provides a month-by-month guide to when different flowers, vegetables and herbs can be sown.
Check the seed packet before deciding when and where to sow. It should tell you the recommended sowing period, whether the seed is suitable for indoor or outdoor sowing, the required depth and any particular temperature or light requirements.
It is also worth checking the age of stored seed. Seeds gradually lose viability, and the rate varies between species. An old packet may still germinate, but results can be less reliable.
For most indoor sowing you will need:
Recycled containers can also be used, provided they are clean and have adequate drainage.
Small seeds are often sown thinly across a seed tray. Once the seedlings are large enough to handle, they can be pricked out into individual pots or cells, giving them more room to grow.
Larger seeds are easier to handle and can often be sown individually into small pots or module trays, which are divided into separate cells for each seedling. This allows each plant to develop its own root system and makes it easier to transplant later with minimal root disturbance.
👉 Expert Tip: Label pots and trays as soon as you sow them. Include the plant variety and sowing date. Several trays of newly sown compost can look remarkably similar a few days later.
Indoor sowing is particularly useful for tender plants and crops that need a long growing season. Tomatoes, chillies, aubergines and many half-hardy annual flowers are commonly started under cover before outdoor conditions are warm enough for them.
A heated propagator can provide consistent warmth for seeds that require higher germination temperatures, but many seeds can be raised successfully on a suitable bright windowsill or in a greenhouse later in spring.
Fill the container with peat-free seed compost and gently firm it to create a level surface. Avoid heavily compacting the compost.
Then:
Seed compost should remain moist during germination, but it should not be saturated.
👉 Expert Tip: For very small seeds, watering the compost before sowing can make the job easier. You can then sow onto the damp surface without immediately disturbing the seed with water.
Direct sowing avoids the need to transplant seedlings and works well for many hardy flowers, vegetables and herbs. Carrots, parsnips, beetroot, radishes, peas, spinach, coriander and many hardy annual flowers can all be direct sown at suitable times.
Do not rely on the calendar alone. Cold, wet soil can delay germination and increase the risk of seeds rotting. In a late or cold spring, waiting for better conditions can produce stronger results than sowing simply because the packet gives a particular month.
Remove weeds, large stones and debris from the sowing area. Break up larger clods and rake the surface until the upper layer of soil is reasonably fine and level.
There are two main ways to sow directly.
A drill is simply a shallow channel made in the soil. It is commonly used for vegetables and other crops grown in rows.
Make the drill to the depth recommended on the packet, sow the seeds as evenly as possible and gently replace the soil. Water carefully afterwards.
Rows also make emerging seedlings easier to distinguish from weeds.
Broadcast sowing means scattering seed over a prepared area rather than placing it in rows. It is particularly useful for wildflower areas and some annual flower displays.
Distribute the seed as evenly as possible, then follow the packet instructions for covering or firming it into the soil.
👉 Expert Tip: Early outdoor sowings can sometimes be helped by warming the soil beforehand with a cloche. Protection can also shelter emerging seedlings while conditions remain cool.
Seeds need moisture to germinate, but excessively wet compost reduces the air available around them and can encourage rotting and seedling problems.
Aim for consistently moist rather than waterlogged compost.
When sowing in containers, use a fine spray or watering can with a fine rose so that small seeds are not washed together. Pots and trays can also be watered from below by standing them briefly in shallow water and allowing moisture to soak upwards through the drainage holes.
Once seedlings appear, continue to check the compost regularly. Do not leave young seedlings standing in permanently wet compost.
Warmth may be important for germination, but seedlings also need good light once they emerge.
Remove propagator lids or other clear covers when seedlings appear, unless the particular plant requires different treatment. Move seedlings into a bright position and avoid keeping them unnecessarily warm.
Seedlings receiving insufficient light often become thin and elongated as they stretch towards it. Turning pots on a windowsill can help prevent seedlings leaning strongly in one direction, although a brighter growing position is the better solution where available.
Seedlings eventually need enough room for their roots and leaves to develop without excessive competition.
Direct-sown seedlings may need thinning, which means removing some seedlings to leave the recommended spacing between those that remain.
Seedlings sown together in trays may instead need pricking out and transferring into individual pots or modules once they are large enough to handle.
When pricking out:
As seedlings continue growing, some may need moving into larger pots before they are ready for their final position.
Plants raised indoors or in protected conditions should not normally be moved straight into the garden. They need time to adjust to cooler temperatures, wind and the greater variation of outdoor conditions.
This gradual acclimatisation is known as hardening off.
Start by placing young plants outside in a sheltered position during suitable daytime weather, bringing them back under protection at night. Gradually increase their exposure to outdoor conditions over roughly two weeks.
Tender plants should only be planted permanently outside when conditions are suitable and the local risk of frost has passed.
👉 Expert Tip: Frost dates are not fixed. Gardens in exposed or colder locations can experience frost later than sheltered sites nearby, so use local conditions rather than a calendar date alone.
Poor germination and weak seedlings are often caused by growing conditions rather than the seed itself.
Nothing germinates: Check that the compost has not dried out and that the seed has been given the correct temperature. Also check the age of the seed and whether the variety has any special germination requirements.
Seedlings are tall and weak: They are often receiving insufficient light or being grown too warm after germination. Move them to a brighter position.
Seedlings collapse: Overcrowding, excessive moisture and poor airflow can encourage seedling diseases. Sow thinly, avoid waterlogged compost and provide ventilation once seedlings emerge.
Outdoor seedlings fail to appear: Soil may be too cold or wet, or seeds may have been eaten by birds, mice or other pests. Check the recommended sowing conditions before resowing.
Seedlings struggle after planting outside: They may have been planted out too early or without sufficient hardening off. Protect young plants if unexpectedly cold conditions are forecast.
Ready to start sowing? At Lyonshall Nurseries, you’ll find a wide range of flower, vegetable and herb seeds, along with seed compost, trays, pots and propagation equipment.
Visit us in Kington to pick up everything you need for seed sowing, with friendly advice from our team if you need help choosing what to grow.
