February 22, 2007 at 8:05 a.m.
Since onions are new to our plant sale this year, I thought I would share some information on them. Onions are members of the allium family and are cousins of garlic, chive, leeks and shallots. Onions are mostly biennial as they grow negligibly the first year then bloom the second year.
Onions are shipped bare root and dormant. The onion is a member of the lily family and will live off the bulb for about three weeks. The first thing the onion will do after being planted is establish new roots.
Onions can be planted early in the spring as soon as the ground is warm and fit for planting. Onions are similar to some other vegetables in that they don't like the cold, wet ground or cold weather.
Onions should be planted about one inch deep and about four to six inches apart. One reason for this is that onions will become quite large and need room to expand. Further, the onion needs room to keep the weeds out around the bulbs. It is a misconception that you should keep the onion bulb covered with dirt. By the time the onions are mature, most of the bulb should be above ground. About three weeks after planting, the onions may need some nitrogen. Stop fertilizing within three weeks of harvest when the necks begin to feel soft.
Water is very important to onions partly due to the shallow root system. If onions don't get enough water, it will not make a large bulb. When the necks start falling over and the onions mature, watering should be discontinued and the soil should be allowed to dry. Avoid over-head watering which may cause foliage diseases.
The two major diseases that will affect onions are blight and purple blotch. The first symptoms begin as small white spots surrounded by a greenish halo. Eventually, leaf death results and bulbs from infected plants may be small because growth is reduced by leaf loss. A good preventive fungicide spray program may be necessary if the problem becomes severe. As with many other vegetables, rotating crops and good air circulation helps reduce the potential for fungus problems.
Insects causing the most damage are the onion thrips. Thrips are light-brown in color and approximately 1 mm long. They feed by grasping the surface of the leaves and sucking the juices, causing deformed plants with silvery blotches. Thrips thrive over the winter in weeds, so reduce pest populations by keeping the garden clean. Another insect that affects onions is the onion maggot. Again, the best control is to rotate the crop on a three to four year rotation if the maggot becomes a problem.
We will be offering three kinds of onions. The yellow Sweet Spanish is a favorite onion in the northern states because it is a large sweet bulb. It matures in 100 days and stores from four to five months.
The Candy Onion is the most popular variety across the country because of its adaptability to all areas. It matures in 100 days and stores for three months.
The Copra Onion is the best storage onion on the market today. It is a medium sized bulb that matures in 110 days. It stores from 10-12 months and becomes sweeter the longer it is stored.
Saturday, March 3 is the date for our 9th annual Gardening Bonanza at the Abundant Life Church, just west of North Branch. You can take up to five classes that day for only $10! Registration brochures were mailed Feb. 5 to those on our mailing list. If you did not receive one, you can call or stop by the Extension office 651-674-4417.
You can also find the brochure and the plant order forms on our web page in the 'Hot Topics' box: http://www.extension.umn.edu/county/chisago.
Plus, Master Gardeners are volunteering to staff the booth at the Home Show, at Chisago Lakes High School.