I’m still seeing onion sets and transplants in the garden centers, so for this week’s tip I’m going to talk about the little peculiarities of growing onions. Onions are actually biennials, but they never make it to their second year unless we plan to save seed. They are grown as annuals and in our area, they are planted in the spring. Unlike garlic, which gets planted in the fall.
There are 3 ways to start onions: Sets (tiny bulbs), Transplants and Direct Seeding. Although planting onion sets is the most popular way to grow them, you’ll have better results transplanting seedlings. Direct sowing is out of the question for most onions, with our short growing season. Although you can start seed indoors. I start mine in February.
Sets are just tiny bulbs that were started from seed the year before and stored like any other bulb. As I mentioned, sets are the easiest way to plant onions, but young transplants actually offer better success and they store better.
If you do opt for sets, they should be about the size of a marble. Larger sets don’t always adjust well and could bolt or split. For similar reasons, don’t buy sets that have already sprouted. And as with all bulbs, onion sets should be firm and healthy looking.
Day Length Matters
Once you know how you plan to start your onions, you’ll have to decide what type of onions to grow. In some garden centers you don’t get a lot of choice. There are red onions and yellow onions.
But onions are categorized according to day length, in particular, how much day light there is when onions stop forming tops, or new green leaves, and start making bulbs. There are short day onions and long day onions.
Short day onions will begin forming bulbs when the day length is 10 to 12 hours. Sweet onions, like Vidalia and cipollini are short day onions. They don’t store especially well and they aren’t really sweet, just less pungent than long day onions. These tend to do better in the south and west.
Long day onions begin forming bulbs when the day length is 14 to 16 hours. They are a bit denser, with a higher sulfur content that gives them their kick. It also helps them store longer. Long day onions are a better choice for norther gardeners. If you don’t like strong onions, take heart, they mellow in storage. The popular Spanish onions are long day, as well as my favorites, ‘Italian Red Torpedo’.
Tops Down, Dig Up
You can harvest onions at any stage. Even the plants you thin out of a row can be used as green onions. The rule of thumb for harvesting onions is to dig them when the tops have fallen over. However as long as the tops are green, the bulbs will continue to plump up. So when is the ideal time to harvest them. That partly depends on the weather, as do so many things in the garden.
If you’re having a rainy season, onions can re-sprout, even after most of the tops have started turning brown. That may sound like a good thing, but re-sprouting will shorten their storage life. So if you’re growing a lot of onions to keep throughout the winter, don’t wait for the tops to brown.
Once you see ½ the tops are down, very gently coax the remaining leaves down, being careful not to snap them off the bulb. Then let the bulbs remain in the ground and cure for a couple of days before you lift them.
Dig don’t pull your onions. They have long roots and the tops will probably break off, requiring you to dig anyway. Plus they will store better with their tops in tact.
Once they’re up, brush off any loose soil, leave the leaves on, and put the bulbs somewhere dry to finish curing. Of course you can start eating them at any time now.
If you are going to store some, wait until the skins and neck start to shrivel. Then put them into mesh bags, so they’ll get good air flow, and store them in a cool, dry spot, like your basement. Onions keep longer in cool temperatures (35 – 40 degrees F.) but should not be allowed to freeze.