Some seeds need steady, warm temperatures to germinate quickly. Daytime things may be fine, but at night they’ll suffer if it’s too cold in a greenhouse, outside or even on a draughty windowsill. The King Seeds catalogue gives very good information about the temperature seeds need to germinate. Tomato seeds and corn will germinate in less than a week thanks to sitting on a thermostatically controlled heat-pad, despite overnight frosts. It’s the type of heater mat that goes behind a heated mirror and uses about the same amount of power as an incandescent bulb. You can roll it up out of the way when it’s not needed. I use mine outside in a home-made ‘cold frame‘ resting on top of a slab of polystyrene. If your compost heap gets hot with plenty of spring lawn clippings, you can get the same effect for free, but in a less controlled way, by having a similar set up on top of your compost heap. Seeds that germinate slowly won’t do nearly as well in my experience as those that get up and get growing quickly and often germination rates are much lower. I think many of them rot before they get started.
If I’m sowing seeds in the ground at this time of year, I find covering them with a layer of frost cloth keeps them safe from birds, wind and heavy rain. It stops them drying out on a sunny day and I can water through the cloth if there’s not enough rain. You just have to remember to check when it’s time to take it off.
If you want to sow seeds in a easy, fun way amongst friends, come to a Spring Seed Sowing Session.