Karline Jensen, High Rocks, Hillsboro, WV Many home gardeners have planted onions, only to be disappointed when they don’t get as big as the ones you can buy in the store. We interviewed one of our market gardeners who knows how to grow really big onions, to find out the key steps along the way. It turns out variety selection, quality seed stock, planting dates, weed prevention and watering are all very important!
When selecting varieties, take into consideration the difference between what are considered “short” and “long” day varieties. We all know that as spring turns into summer, the days gradually get longer. Onions use this change in day length to indicate the best time to start forming a bulb. Short day varieties will begin to bulb when day length reaches about 12 hours. Long day varieties will wait until day length reaches 14-16 hours. You need to plant your onions enough ahead of this trigger for them to get big before the bulbing happens. Luckily, you don’t have to do a bunch of complicated calculations for this all to work out. All you need to know is the latitude or distance from the equator of your garden. You can easily find this out by googling a nearby town. Here in Hillsboro, WV, we are about 38 degrees North. Then, when you select your varieties, make sure that your latitude falls within the range of latitudes the variety is suited for. If the company you want to buy your onion stock from does not list latitudes in the description, you might be able to find out by googling the name of the variety. If you want big storage onions and not just green onions, it’s not worth it to try and grow a variety if you’re not sure it is right for your latitude. Many stores sell the same onion sets year after year, and no one gets big onions from them, so just because it’s for sale at the local store doesn’t mean you can get storage onions from it.
Once you have your stock, the key is to get it in the ground as early as possible. Around here this means late March, early April at the latest. Waiting a week or two will result in significantly smaller onions, because they just won’t have time to grow enough before the day length changes. Storage onions are one crop that you don’t want to plan for succession plantings; it’s best to get them all in as soon as possible. Of course, they will store great, so you will be able to eat them all winter long. Sweeter onions have a slightly shorter storage life, so you will want to eat those first. The market gardener who we interviewed said that he always buys onion plants for his stock. If you want to grow your own plants from seed, you will have to get a really early start, like in February or earlier, so they will be big enough to set out in the field by the end of March. Sets can also work, but make sure to purchase them from a reliable company to avoid the problem of having all of them bolt. Onions are biennial, and once they have gone through a winter they are ready to flower. It is tricky to produce quality sets that don’t think winter has happened yet.
Onions will not grow well if there is any weed pressure. So make sure you cultivate them often. Get out there with your scuffle hoe any time you see the faintest hint of green between the rows; don’t wait until you can see from a distance that there are actual weeds growing. Or, try covering your onion bed with black plastic and cutting holes to plant your onions through it the way our market gardener friend does. But if you go this route, don’t forget to lay the irrigation tape under the plastic. Onions need a lot of water, two inches per week. It is best to water thoroughly once a week and then let the surface dry out a bit; keeping them soaked all the time could cause them to rot away. They need air too!
I hope this advice will help you to grow big onions too, and next summer you can be amazed by the size of your harvest.