Spring onions tend to be treated as an afterthought by most gardening books yet they are a popular crop and very useful, possibly because they are really easy to grow. Salad onions, also properly called scallions are not just easily grown, they can provide a useful substitute for bulb onions if stocks are low as you await the new crop.
Feeding Spring Onions
They like a rich well drained soil but being a useful crop to fill into gaps in the summer, they tend to get what they are given. It’s a good idea to give some general purpose fertiliser a week before and rake the soil into a fine tilth before sowing them.
Cultivating Spring Onions
Conventionally spring onions are grown in rows 6" (15cm) apart but they can more easily just be thinly scattered in a patch and either raked in or covered with half an inch (1.5cm) of fine soil.
They do not need a great depth of soil and a winter crop can be grown in the greenhouse in an ordinary seed tray filled with compost. Salad onions are ideal for container growing and even if you have a vegetable patch or an allotment, growing some salad crops by the back door where they'll be handy is always a good idea.
Successionally sow each week or two from early March for a continuous supply throughout the summer.
You can over-winter spring onions outdoors as well. Late sowings in August, September and a fine October will provide an early crop by late spring. Always use a winter hardy variety for this.