Growing from seed is a simple and economical way of raising a whole host of plants for your garden. Sowing in a heated environment allows you to raise plants from seed in early spring - much earlier than if sowing directly outside.
What you will need
Quality seed compost. Seed compost has a fine particle size and is not as rich as potting compost. It is ideal for sowing seeds. We sell Klasmann Organic composts, for more information please see our blog post.
Modular Trays. These are rigid trays with varying numbers of cells, and a drainage hole at the bottom. Quick and easy to use; they come in a range of sizes and will last many years.
Plant pots. Chose strong rigid ones which will last several seasons.
Seeds. Always buy of a reputable supplier - preferably open pollinated. Don't forget to check the use by date. You can also save your own seed.
How to sow seeds
This is not rocket science - fill you chosen container with compost, level, firm gently and water well. Either scatter or place your seeds on top and then cover with a thin laver of compost. Label, lightly water again and cover with clear polythene or a sheet of glass, or place in a heated propagator with a lid. Maintain a temperature of around 15 - 18ºC unless seed packet states otherwise. Read the back of the seed packet before you start, as many seeds require specific sowing treatments, such as light-exclusion or scarification .
Small seeds can be sown into shallow seed trays and pricked out (transplanted) into larger pots while still very small. Alternatively, they can be sown into a modular plug tray, one seed per plug. This can be tedious but saves time in the long run as there is no need to pot on the young plants - they can be planted straight outside when big enough. Large seeds can be sown individually into 9cm pots. Seeds can also be sown outside once it is warm enough (end April onwards).
Optimum germination temperatures
Seeds can be divided into three groups. This is very general - always read the back of the seed packet.
Aubergine, Peppers, Tomatoes and Cucumbers germinate between 18 - 30°C
Corgettes, Pumpkins, Sweetcorn, Melon germinate between 15 - 25°C
Brassicas, Onions, Parsnip, Celery, Carrots, Lettuce, Beetroot, Spinach are more forgiving and will germinate between 5-15°C. Lettuce in particular does not like it too hot - be careful in a polytunnel/glasshouse as it can get very hot very quickly.
Hardening off and Planting out
Before you put your young plants outside you have to harden them off first. Hardening off allows plants to adapt from being in a protected, stable environment to changeable, harsher outdoor conditions. If suddenly placed outside, the shock can severely check a plant's growth. The effect of hardening off is to thicken and alter the plant's leaf structure and increase leaf waxiness. It will ensure that new growth is sturdy.
About two weeks before you intend to plant out your seedlings slowly move them to a cooler environment, eventually leaving them outside 'till quite late at night. The most common problem is damage from cold temperatures, or even a late frost. If this happens, cut out the damaged growth and continue to harden off.