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In the Garden: For onion success, opt for long-day types

Sun., March 23, 2014, midnight

This onion patch was grown with Big Daddy plant starts last year. (Susan Mulvihill)
This onion patch was grown with Big Daddy plant starts last year. (Susan Mulvihill)

If you use onions in your cooking as much as I do, it pays to grow your own. Onions are an easy-to-grow cool-season crop.

You can start them from seeds, small bulbs called “sets” or from plant starts. No matter what your preference is, be sure to select a long-day variety, which is well-suited for northern regions.

A few years ago, I didn’t know day length had a bearing on how successfully onions will grow here. A reader shared this information with me, and it’s made a huge difference in my harvests. It turns out there are short-, intermediate and long-day onion varieties, which are based on the hours of daylight a region gets during the summer months.

In the Spokane area, onions start developing bulbs once our day length hits 14 to 16 hours.

Seeds, plants or sets can be planted as soon as the ground can be worked. To determine this, grab a handful of your garden soil. Squeeze it into a ball. If your hand is wet and the soil feels sticky and clumpy, it’s too soon to do anything in your garden. If, however, you poke the ball with a finger and it crumbles, the soil is ready to be prepared.

Onions grow particularly well in raised beds. I like to add compost to the soil to provide nutrients and improve soil drainage. I also work in some bone meal since it is high in phosphorus, just what root crops need to grow.

To start them from seeds, make shallow furrows in your bed that are 8 inches apart. Sow the seeds 1/4-inch deep and 2 inches apart. Once seedlings are 4 inches tall, thin them to 4-inch spacing.

If you purchased onion sets, plant them about 2 inches deep and 4 inches apart. You will be amazed at how quickly they start growing.

I used to grow my onions from sets but switched to plant starts after seeing how well they grow. Plant them 1 inch deep and spaced 2 inches apart. During the growing season, pick every other one for use as a scallion. The remaining plants will now be 4 inches apart, which is enough room to form a nice bulb.

Water the onion bed regularly, preferably at ground level because overhead watering can cause fungal problems to develop.

If any flower stalks form, snap them off; eat those onions as soon as you can since they won’t keep well.

The nice thing about onion plants is that they tell you when they’re done growing. Once the stalks start falling over, it’s time to stop watering their bed. Pull the plants up out of the ground and let them dry for a few days. If rain is in the forecast, cover the bed or move the onions to a sheltered location.

Once they’re dry, you can snip off their roots and all but 1 inch of the tops. Store them in a cool, dry location.

Walla Walla Sweets don’t keep long in storage, so eat those first. The longer-keeping varieties are Copra (10 to 12 months), Big Daddy (4 to 6 months), Red River (3 to 5 months) and Yellow Sweet Spanish (4 months). Sources for plant starts include local garden centers and online at Dixondale Farms ( and Renee’s Garden (

Susan Mulvihill can be reached at her blog at susansinthegarden. and Facebook page at susansinthegarden for more gardening information.

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