The Clark Gardens Blog

Janice Ellis is the Clark Garden Garden Club President and shared with our Garden Club members information on how to plant onions.I asked Janice if I could share this information on the Clark Gardens blog and she kindly agreed.The following are her notes:

Growing Onions

The size of the onion bulb is dependent upon the number and size of the green leaves or tops at the time of bulb maturity. For each leaf there will be a ring of onion; the larger the leaf, the larger the ring will be. The onion will first form a top and then, depending on the onion variety and length of daylight, start to form the bulb. Onions are characterized by day length; "long-day" onion varieties will quit forming tops and begin to form bulbs when the daylength reaches 14 to 16 hours while "short-day" onions will start making bulbs much earlier in the year when there are only 10 to 12 hours of daylight. A general rule of them is that "long-day" onions do better in northern states (north of 36th parallel) while "short-day" onions do better in states south of that line.

Care Of Transplant Instructions

When you receive live plants, they should be planted as soon as possible. Should conditions exist that make you unable to plant these plants right away, remove the onion plants from the box and spread them out in a cool, dry area. The roots and tops may begin to dry out but do not be alarmed, the onion is a member of the lily family and as such will live for approximately three weeks off the bulb. The first thing that the onion will do after planting will be to shoot new roots.

Preparing the Soil

Onions are best grown in a raised bed. Onion growth and yield can be greatly enhanced by banding a fertilizer rich in phosphorous 3” below transplants at planting time. Make a trench 4” deep, distribute one Tablespoon per 1’of the fertilizer, cover the fertilizer with two inches of soil and plant the transplants 1” deep.

Planting

Set plants out approximately 1” deep with a 3” spacing. Should you want to harvest some of the onions during the growing season as green onions, you may plant the plants as close as two inches apart. Pull every other one, prior to them beginning to bulb, leaving some for larger onions. Transplants should be set out 4 weeks prior to the date of the predicted last average spring freeze (March 17 for Palo Pinto county).

Fertilization and Growing Tips

Onions require a high source of nitrogen. A nitrogen-based organic fertilizer (such as blood meal*) should be used. The first application should be about three weeks after planting and then continue with applications every 2 to 3 weeks. In my SFG, I use 1 Tablespoon of blood meal per square foot. Once the onion neck starts feeling soft do not apply any more fertilizer. This should occur approximately 4 weeks prior to harvest. Always water immediately after feeding. The closer to harvest the more water the onion will require. Unfortunately, there is not any organic 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.

Disease and Insect Control

The two major diseases that will affect onions are blight and purple blotch. Should the leaves turn pale-green, then yellow, blight has probably affected the plant. Purple blotch causes purple lesions on the leaves. Heavy dew and foggy weather favor their rapid spread, and when prolonged rainy spells occur in warm weather. The best cure is prevention: use only well-drained soil, run the rows in the same direction as prevailing wind and avoid windbreaks or other protection.

The insect that causes the most damage is the onion thrip. They feed by rasping the surface of the leaves and sucking the liberated juices. The thrips are light-brown in color and are approximately 1mm long…very small and hard to see.so look for the leaves curling in places and becoming distorted. For control use an organic plant based insecticidal soap*, biological insecticide* or pyrithrin based insecticide*. Always follow label instructions.

Flowering -- Abnormal For Onions; Normal For Garlic

Most folks want to grow onion bulbs NOT onion flowers! What causes bulb onions to send up flower stalks? Flowering of onions can be caused by several things but usually the most prevalent is temperature fluctuation. An onion is classed as a biennial which means it normally takes 2 years to go from seed to seed. Temperature is the controlling or triggering factor in this process. If an onion plant is exposed to alternating cold and warm temperatures resulting in the onion plant going dormant, resuming growth, going dormant and then resuming growth again, the onion bulbs prematurely flower or bolt. The onion is deceived into believing it has completed two growth cycles or years of growth in its biennial life cycle so it finalizes the cycle by blooming. Flowering can be controlled by planting the right variety (short day for zone III) at the right time. Planting too early in the spring in our area may not be the way to go because we tend to have cold then warm spells early in the spring. It may be better to wait later in the spring until temperatures are more consistent…not fluctuating between cold and warm so much. Use only transplants that are pencil-sized or smaller in diameter when planting in early spring or always plant seed, NEVER transplants, in early fall in Texas Zones III - V (USDA Zones 8 and 9).

DON'T plant garlic in the spring! Bulb formation in garlic occurs in response to the lengthening days of spring, and bulbing and maturity are considerably hastened if temperatures are high. In addition to these requirements, the dormant cloves (divisions of the large bulb) or young growing plants must be exposed to cold temperatures between 32 and 50 degrees F. for one or two months in order to initiate bulbing. Plants that are never exposed to temperatures below 65 degrees F. may fail to form bulbs. With fall plantings, the cold treatment is accomplished quite naturally throughout the winter, but a spring planting spells disaster for garlic in Texas Zones III - V (USDA Zones 8 and 9)

What To Do About Flowering?

Onions. What can one do if flower stalks appear? Should the flower stalks be removed from the onion plants? Suit yourself but once the onion plant has bolted, or sent up a flower stalk, there is nothing you can do to eliminate this problem. The onion bulbs will be edible but smaller. Use these onions as soon as possible because the green flower stalk which emerges through the center of the bulb will make storage almost impossible.

Garlic. Seedstalk formation (bolting) of garlic is not induced by exposure to fluctuating temperatures, as is the case with onions, which means that a wide range of fall planting dates is permissible for this crop. I plant garlic bulbs on the first day of winter. Seedstalk formation is also not damaging to garlic since the cloves are arranged around the seedstalk and will be removed from the dried seedstalk. When the tops become yellowish and partly dry, garlic is ready for harvest.

Harvesting And Storage

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. I usually store onions is in a nylon stocking. Place an onion in the leg of the stocking 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.

*For organice fertilizer and insecticide, go to  Organic Materials Review Institute and reference the products list

Notes: Much of this info came from TAMU and Plant Answers at TAMU and what I have learned from experience.