VARIETY AND ZONE: There are three essential facts to keep in mind about growing bulbing onions. FIRST: the bulb will be no bigger than the top. SECOND: the top completely stops growing when the bulb begins forming. So grow as big a top as you can as fast as you can. THIRD: grow a variety adapted to your zone. Change of day-length is what instructs or triggers the plant to change from growing top to making bulb while the lengths of day and night differ from North to South.
SHORT DAY ONIONS bulb formation with these varieties is triggered during the period of increasing day-length, such as we have during spring. Because days are still short at that time of year we call these “short day” onions even though they bulb when days are getting longer. Short Day varieties are grown commercially in the South where winters are mild enough to allow the plants to be directly seeded in fall. By spring when bulbing initiates, these overwintered onions have already produced large enough tops to make substantial. Short Day varieties make the large, sweet onion that Appears in our supermarkets from late April through midsummer. Short Day varieties must be grown in the South because no matter where you plant them they will stop growing tops and begin bulbing before summer.
INTERMEDIATE DAY VARIETIES are planted very early in spring and are adapted to day-lengths found in the intermediate Zones where the growing season is long and maximum day-lengths don’t get as extreme as they do in the North. Also, in most regions of the North, spring is too chilly and comes too late for Intermediate Day varieties to achieve enough size before they bulb. Unless of course you start in the North in spring with big transplants grown in the South – like the ones we sell.
LONG DAY VARIETIES are bred to grow in the North. These grow tops while the days are very long and begin bulbing only after day-lengths have decreased from their maximum on June 21st to about 14-15 hours. In the North, this happens from late July through early August. This timing works out so that the tops go down and the bulbs dry out well before summer is over. Long Day varieties do very poorly in the South, where the longest day on June 21st may not exceed 14 hours. They bulb way too soon, before they’ve achieved very much size at all.
Soil and Fertilizing
Onions demand light, loose soil and do their best in sandy loam. Amend heavier ground with compost or manure. This is usually best done the previous autumn. The important thing is to encourage them to grow tops as rapidly as possible. This means lots of fertilizer early on. Onions have coarse, small root systems. So place the fertilizer close to the plants and side-dress and/or foliar feed them. Once bulbing beings there is no point in fertilizing them anymore; the bulb’s size is already determined by the size of the top.
Onion seeding are quite hardy and can withstand 20° F frost. They should be set out 4-6 weeks prior to the last expected spring frost. When your plants arrive they should appear to be quite dry. DO NOT WET THEM NOR STICK THEIR ROOTS IN WATER. Unpack them and store them in a cool, dry place until it is time to plant. They should last about 3 weeks kept this way. Do not worry that your plants seem dry. They will “shoot” new roots and new, green tops as soon as they are planted. Be sure to specify on your order when you want your plants to arrive.
Onions have small, inefficient root system and need moist soil. Keep them constantly well-watered. But when the plants approach maturity their bulbs stop enlarging and begin to form skins. When this happens, withhold further irrigation and hope it does not rain much. Ideally, the bulbs will mature in very dry soil. This helps the skins to cure and makes your bulbs keep better.
Harvesting / Storage
After most of the tops have “gone down,” lift the bulbs. It may help to gently loosen them with a shovel first. Allow them to lie in the sun for a day or so, then cure and store them like garlic bulbs or shallots (see the growing directions for these vegetables).