Oy!!! Choosing the Best Onion for Your Plant Hardiness Zone


“Hello Horticulturess, I am going to attempt to grow my own onions this year, but I need some help.I understand that there two types of onions but there are also hybrids. Will you please recommend one for my region, I live in zone 6. I need one that will store well also. I have read that you should plant as soon as the soil can be worked. I can work the soil here in the first of March, should I plant the seed then? Is the ground too cold for germation at that time? Your help will greatly appreciated. ~J.”

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Onions fit into three categories: short-day, intermediate-day and long-day varieties. Short-day onions will start making bulbs early in the year when day length is only 10-12 hours. They are often mild and soft-fleshed making them unsuitable for storage. The more pungent long-day onions will bulb up much later in the year, when day length reaches 14-16 hours.

Gardeners in plant hardiness Zone 7 and south will succeed best with short-day varieties. Zones 5 & 6 will probably be able to grow these varieties, too, if they are planted in late winter instead of in the fall. Intermediate-day varieties will work for most gardeners in Zones 5 & 6 while long-day varieties will succeed in Zone 6 and colder zones. There is obviously some overlap with varieties that require shorter days being adapted to climates where much longer days occur. The key factor here is whether these varieties have sufficient time to make enough growth before lengthening days signal the bulbing response, and of course, the days have to get long enough to signal the response.

As for how to plant, you have a few options.  For a March 1st planting date, I would recommend getting your seeds started as transplants as soon as possible.  Growing your own transplants requires at least 7 weeks so time your sowing date so that you transplant after your last hard frost.  Onion seeds do require some warmth to germinate so start them indoors at this time of the year. Choose either a sterile seed mix or make your own seed starting mix with compost, sand, and peat or coir. Seeds should be sown about 1/4″ deep either in individual cells or 6-8 seeds per 2-inch cell in the larger seed trays. Since the seed is so shallow, the soil needs to be kept moist so either cover the seed tray with a dome, saran wrap, or enclose in a plastic bag. Germination should occur in 7-14 days.  As the seedlings grow, provide supplemental light to keep the leaves healthy and short. Begin feeding the onions with dilute fish fertilizer every 2 weeks. Do not thin the onions or else you might disturb their shallow root system. However, to promote thicker stems, cut back to leaves to 3″ every couple of weeks.

As we are getting down on time here for a March 1 planting date, your other options are to purchase plants or sets.  Onion plants are just that — bare root seedlings that are about 3-4 inches in length.  These are transplanted into the ground like any other transplant.  Onion sets resemble dry, miniature onion bulbs.  They are planted in early spring (as soon as the soil can be worked) in rows marked at one foot apart and with the onion sets planted three inches apart and about one inch deep.

No matter which method you use for planting, onions require a high source of nitrogen. A nitrogen-based fertilizer (ammonium sulfate or ammonium nitrate) should be applied at the rate of one cup per twenty feet of row. The first application should be about three weeks after planting and then continue with applications every 2 to 3 weeks. Once the neck starts feeling soft do not apply any more fertilizer. This should occur approximately 4 weeks prior to harvest. Always water immediately after feeding and maintain moisture during the growing season. The closer to harvest the more water the onion will require. For weed control a pre-emergent herbicide (DACTHAL) should be applied prior to planting. This will provide weed control for approximately one month after planting. Other products such as GOAL and BUCTRIL, can assist in weed control during the growing season. Always follow label instructions. For organic gardeners a rich compost high in Nitrogen should be incorporated into the soil. Unfortunately, there is not any product available to assist in weed control so the only method will be cultivation. While cultivating be careful not to damage the onion bulb. As the onion begins to bulb the soil around the bulb should be loose so the onion is free to expand. Do not move dirt on top of the onion since this will prevent the onion from forming its natural bulb. Start early with cultivation practices.

Onions are fully mature when their tops have fallen over. After pulling from the ground allow the onion to dry, clip the roots and cut the tops back to one inch. The key to preserving onions and to prevent bruising is to keep them cool, dry and separated. In the refrigerator, wrapped separately in foil, onions can be preserved for as long as a year. The best way to store onions is in a mesh bag or nylon stocking. Place an onion in the bag and tie a knot or put a plastic tie between the onions and continue until the stocking is full. Loop the stocking over a rafter or nail in a cool dry building and when an onion is desired, simply clip off the bottom onion with a pair of scissors or remove the plastic tie. Another suggestion is to spread the onions out on a screen which will allow adequate ventilation, but remember to keep them from touching each other. As a general rule, the sweeter the onion, the higher the water content, and therefore the less shelf life. A more pungent onion will store longer so eat the sweet varieties first and save the more pungent onions for storage.

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© Mertie Mae Botanics LLC and Horticulture Talk!, 2010. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Mertie Mae Botanics LLC and Horticulture Talk! with appropriate and specific direction to the original content.

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4 thoughts on “Oy!!! Choosing the Best Onion for Your Plant Hardiness Zone

  1. Thinking about growing Copra onion and I live in Minnesota. Maybe Red Candy too. Would these be a good fit for my region?

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