Plants that can be grown outside right now are lettuces, radishes, carrots, beetroots and spinach. Buy a few metres of horticultural fleece (I get mine from the 99p shops) and pin it over bent coat hangers as a simple cloche. This will add a few extra degrees of warmth and get them started faster.
Use the seed compost you bought for sowing indoors to make a line to sprinkle the seeds onto. Try some things you don’t see that often in the shops such as yellow beetroots, white radishes, purple carrots and other variants. But at the same time, do sow classic sturdy seeds you can trust to do well like Boltardy beetroot. Wet the compost before thinly sowing seeds, then sprinkle dry compost on top. Don’t water again at this point, as you will wash everything away.
The secret of a productive and useful salad bed is to sequentially plant. By planting some seeds every fourteen days you’ll keep a good supply rolling through and avoid gluts. Radishes grow surprisingly fast and they need to be eaten when small or they become too peppery and hot (and will eventually become hollow), so you don’t want to plant too many at a time.
As well as sowing single lettuces, buy a packet of ‘cut and come’ again lettuces. Sow a cigar-thick line and don’t thin them out as they grow, just give them a haircut with scissors when a few inches high. This will give you a nice mix of colours and flavours and the plants will happily carry on growing after their trim, letting you harvest at least four or more times over the coming weeks. Just make sure you water them well, as they hate drying out. Don’t forget that when you come to thin out your beetroots and carrots you can use the spare whole seedlings for the plate – providing you with your very own micro-herbs and vegetables.
As for pests and diseases, slugs and snails can be a problem. You’ll have to find your own solution here, but I confess to using a light dusting of slug pellets. Organic defences are available, but I’ve never found they really work. I did once try executing a snail a day with an airgun, to warn the others, but it never seemed to have any effect.