There are a whole range of vegetables that can be grown in winter

 Plant the likes of Cauliflower, Broccoli, and Cabbages in Mid March while the soil is still warm but follow up 4-6 weeks later with another planting. 

Apply Slug bait. Watch for the White butterflies and take action by applying vegetable dust or spraying with Mavrik which is very safe when used as directed. There is also a product containing the bacterium Bacillus theringiensis that kills caterpillars when applied as a spray.

April is a good time to plant brown, white and red onions. Tease the seedlings apart and plant individually to get the best results. This is also a good time to plant Broad Beans, Salad onions, Shallots and Lettuce, which enjoys the cooler conditions. Spacing all these seedling about a hoe's width apart makes for easy weeding when it is necessary to carry it out. About 2-3 weeks after planting apply a watering of the liquid fertiliser 'Harvest' which contains both nutrients and root stimulants.