Most Brassicas can be sown indoor and outdoors, depending on variety and time of year.
Indoor – Brassicas can be grown in a greenhouse or a windowsill. Using either a shallow seed tray or one with individual modules, which does help with reducing root disturbance when potting on. Use a specific multipurpose seed sowing compost, as this will be of finer texture, have little nutrient and have an open structure. Refer to the individual seed packet for specific sowing instructions but generally sow the seed as evenly as you can, so they all have the same space between them, firm down and water. A good tip is to put the seed tray in a larger seed tray of water and let the water soak into the seed compost, rather than overhead watering which can cause the seeds to move or group together. Keep the temperature approx. 12- 20 degrees. Ensure these are hardened off before transplanting, by increasing their exposure to the outside temperature. The tray can be placed outside for an increasing amount of time each day until the seedlings are large enough to transplant.
Outdoors – You can sow in a trays similar to indoors but grow then outside. They will be slower but will naturally have hardening off before transplanting. Many can be sown in their final position and refer to the seed packet for specific conditions. Often you may have to thin seedlings out, removing any weak ones or ones that are not in their final spacings. Use a straight edge like a wooden plank to space out the plants correctly. Making a small v shaped trough in the soil, drop the seed in and then cover and water in.
Brassica Seeds - Transplanting
You can transplant the seedlings from indoor or outdoor seed trays, when several true leaves appear. The seedling leaves appears quickly but then the true leaves start to form from the growing tip. Plants should be about 10-15cm tall and will be 5- 6 weeks old. Using a dibber and trying to disturb the roots as least as possible, lift the seedlings by their true leaves and not the delicate stem. Make a deep hole and lower the roots until the lowest leaves are at ground level. Brassicas like to be firm, so planting them deep then firming the soil well around them, will benefit the growth of the plant. A good tip is to fill the hole with water and let the soil fill around the roots, then firm the soil around it.