Greenhouse crops can be started in earnest now, they will benefit from the longer, warmer days and higher light levels. Tomatoes, Cucumbers, Sweet Peppers, Chillies and Aubergines can be sown in a frost-free greenhouse. If you sowed them at the end of last month in a propagator, they will soon be ready for pricking out.
Wait until they have their first true leaves before you prick them out, pot on into 3 inch pots and do not allow them to dry out. Standing the pots in a seed tray or on capillary matting will help keep them moist, Shuttle Trays have 18 x 3 inch terracotta-coloured plastic pots specially made to fit securely inside the trays keep pots stable and make it easy to move plants around for maintenance and when planting out.
If you are a bit late with your sowing, a Heated Propagator can be a big asset. They are a really useful aid to germination, especially during a cold spring. Give seedlings some ventilation once they have germinated and grown a bit.
If you are gardening in the north of the country, bear in mind you may need to sow two or three weeks later, be led by the weather and the condition of your soil, not what it necessarily says on the packet. Do not be tempted to transplant your young plants outside too early. Harden them off well and do not leave outside overnight until you are sure the weather will not damage them.