HOW DO YOU PLANT OUT ONION SEEDLINGS?
Onion seedlings can be planted out anytime from mid-spring, so if you are living in an northern European climate you are looking at around the April/May time. If you are organised and have the foresight you can start preparing your onion seedbed in the autumn by digging in plenty of well-rotted farm manure. This will give the ground a chance to settle over the winter period and allow frosts to break down the soil clods. If you soil is too acidic – below pH 5.5 – you will need to add lime to it according to manufacturer's recommendations. In general, onions prefer a pH of between 6 and 7.5.
It is possible to grow good onions on heavy soil, but you must improve the drainage first before planting. Add plenty of horticultural grit and bulky organic matter to the soil and then create a ridge of soil 4 inches high to further reduce soil moisture.
Plant one onion seedlings every 4-5 inches. If you are planting more than one row then each row should be at least 9 inches apart. Remember to clear away any discarded, undersized seedlings so as not to attract onion fly.
You will need to keep a a particular eye on the newly planted onion seedlings as these will often attract the attention of inquisitive birds – particularly pigeons and blackbirds - who will lift your juvenile crop straight out of the seed beds for nothing more than a little mischievous fun. If you don't have some kind of protection in place you can end up loosing almost an entire crop!
Onions are not very good at suppressing weed growth, and if regular weeding is neglected they will easily be out competed for nutrients resulting in your crop becoming stunted. Try to leave enough space between the rows to get your hoe in for weeding, but always hand-weed any weeds close to your onions as they can be easily damaged by garden tools.
To maintain a good year-round supply of onions, you can make a second planting during the late summer which should be ready to harvest from June. However, this second planting isn't recommended if you have heavy, poorly drained soils. In general, onions should be given as long a growing season as possible to reach their maximum size.