Grow your own big, sweet onions

Q: Is it possible to grow large, sweet onions like I get from the grocery store?

A: Yes, it is possible -- and even relatively easy if you understand the secret of how onions grow.

Different varieties of bulb onions thrive in different areas. The difference has to do with light and day length, which triggers bulb development. There are short, intermediate and long-day varieties. In our area you want to choose a long-day variety.

A long-day onion plant will grow a top, or the green part that you see above the ground, until daylight is 12 to 14 hours long. Then the bulb will begin to swell. When bulbing begins, one layer or ring will form for every leaf on the top because the bulb tissue is simply an underground extension of the leaf. So, in simple terms, large tops translate into large bulbs.

Following are the essentials for growing large, sweet onions:

Grow your onions from seed and choose the right variety. Planting starts or sets is easy, however you may not get the large onions you want because you will be limited by the size of the start, the time of year it is available and the variety. Starting with seed can also minimize the possibility of introducing serious diseases such as white rot into your garden. If you do choose to use starts or sets, be certain that you purchase them from a reputable source and that they are certified disease-free.

Use fresh seeds every year because they are notoriously poor keepers. Obviously, you need to choose a variety that is sweet and large. Two great options are the famous Walla Walla onion and one called Ailsa Craig. If you are looking for size, try the latter. Both are available in various seed catalogs.

Start early. Order your onion seeds right away and start them indoors as soon as you get them. Even December is not too early to start onions. Sow about 20 seeds in an 8- or 10-inch pot filled with a good seed-starting mixture. This will give the roots room to grow. (When it comes time to plant them, you can dump out the whole pot and pull the plants apart.)

Set pot on a sunny windowsill or under artificial lights with a timer set to 10 hours per day -- any longer and you might confuse your day-length sensitive plants. Keep them watered, adding enough liquid fertilizer (fish works well if you can stand the smell) to keep them growing well. When tops get long, shear off a couple of inches and throw the clippings in your soup (you can do this repeatedly). Your goal is large, sturdy onion plants.

Set plants out in the garden in midspring. Harden off plants before transplanting, gradually exposing them to conditions outside over a two-week period. Onion plants tolerate light frosts but a hard frost can damage them. Space 3 to 4 inches apart, in fertile, well-drained soil.

Feed them well. For large onions you want your plants to grow quickly, so be sure to give them adequate fertilizer -- especially nitrogen. With their small, shallow root systems, onions are poor competitors for nutrients, so keep the bed free of weeds. One note of caution -- sulfur is the substance that gives onions their zing (and makes you cry when you cut them). Avoid using fertilizers such as ammonium sulfate that have sulfur in them unless you want your onions to bite you back!

Onions need lots of water to be sweet. Give them at least an inch a week (a nice long soaking). After bulbs have sized up and the tops begin to tip over, stop watering for a week or two before harvest.

These types of sweet onions are not good keepers, so you will have to use them up right away. Try slicing, frying and freezing them for use in soups, stir-fries and fajitas, or make and freeze French onion soup -- yum!

Northwest Flower and Garden Show

Check out the Web site for the Northwest Flower and Garden Show that will be in full swing Feb. 3 -7 in the Washington State Convention Center in Seattle: www.gardenshow.com/seattle/index/index.cfm

* Washington State University Extension Master Gardener Program is an organization of trained volunteers dedicated to horticulture and community service. Questions about gardening, landscaping or the program may be directed toward the Master Gardener Clinic by calling 509-574-1600 or visiting the WSU Extension office at 104 N. First St. in Yakima. New volunteers are welcome.