From the garden
It is time to get those onion transplants into the garden.
Onions have an optimum temperature range of 55° to 75° for ideal growth and bulb development. In mid-March day temperatures are normally in the 70s, while night temperatures are still cool. It is the night temperatures that give the advantage in rapid growth. Cool temperatures are critical to developing a strong root system since rooting in onion is enhanced at lower temperatures; shoot growth is enhanced at slightly higher temperatures of 68° to 75°.
Light freezes can still be expected in March, but onion transplants and sets are frost tolerant and can withstand 28°. If a harder freeze is expected, it is wise to protect newly planted sets by covering them.
Onions are a long-season crop, about 180 days for mature bulb development when started from seed. Establishing a bulb crop from transplants or from sets eliminates about 90 days, allowing the gardener to plant a set in March and harvest a bulb in June or July.
An onion bulb crop can be established from transplants or from sets. Both are available now in nurseries and garden centers. A set is a tiny bulblet that was dug at a young age when immature, then packaged for sale. These are usually more expensive than seedling transplants that are sold in bundles of 25 or 50.
The ideal size of an onion transplant is the diameter of a pencil. Trim leaves to about 4 inches for ease in handling and minimizing transpiration. Sets are larger than seedling transplants and root systems take longer to become established.
Planting transplants and sets: Prepare the planting bed by deep tilling soil to a depth of 12 inches to loosen soil; amend with organic matter and a light application of nitrogen. Allow for uniform bulb development by spacing properly. Place the basal plate of transplants at 1-inch depth, if planting sets cover them with 1” of soil. Place transplants 4 inches apart – closer than that and bulbs will be misshapen, further apart is wasted space. The number of bulbs in an area can be maximized by planting two adjacent to each other in the row, forming a ‘z’ pattern. Spacing between rows is 12 inches. Firm soil around the transplants. Water well. Keep moist; do not let them dry out.
Ellen Peffley Harp, a retired professor of horticulture at Texas Tech University, writes about gardening for several Texas newspapers.
