Once you know how, it is possible to have a constant supply of bunching onions (I prefer to avoid the term "spring" as it gives a wrong impression, as you have found).
Bunching onions on demand 365 days a year are one of the things my wife claims are why she loves me so
, along with a year-round supply of rocket, green salads and flat-leaf parsley.
Before I describe my method, I must admit to growing them in the polytunnel now, though the method worked perfectly well outdoors for ten years.
Firstly, there are two species of "spring" onions: Allium cepa
which is the same as normal western bulbing onions, andAllium fistulosum
which is the oriental "bunching" onion which never forms a bulb
Most of the onions with “western” names (e.g. White Lisbon) are Allium cepa
, the ones to look for are the ones with “oriental” names. Some very good varieties are:
Ishikura (widely available)
Long White Tokyo
I used to sow White Lisbon direct and get the sort of crop you describe. When I came across Japanese about 25 years ago, I decided this was a waste of rather more expensive seed. So module sowing was the answer – and so it was very good germination, no thinning, no loss due to overcrowding.
I use modules about an inch square and one and a half deep; fill with multipurpose compost, dib a hole in each about a third to half an inch deep and sow about six seeds in each module. When the onions are about four inches high (and it takes a good while to reach that size) I plant each module entire, without splitting, about four inches apart.
To get a year-round crop, I usually do three sowings: early-mid March; mid May; late August. The first sowing is rather slow to come to planting size, but is ready for eating in the summer, the last sowing is OK in the tunnel, but might suffer outdoors.
For outdoors I would suggest module sowing in March (under cover if possible), late April, June and/or July.
Another widely available Japanese variety is Summer Isle (despite its name)
A good cheaper variety is Cipollotto da mazzi (literally bunching onion) from Seeds of Italy.