Text 2. Seeding and transplanting.

The optimum temperature range for germination is 48 to 90°F. Planting normally begins as early as April 10 and continues until month's end. In Minnesota, onions are grown primarily on peat soils, although silt loam, or sandy loam soils are also suitable.

There are approximately 9,000 onion seeds per ounce. Most onions are direct seeded, although sets can also be used which are more expensive and can limit variety selection due to availability.When sets are used, about 800 lbs of 15/16 inch or smaller diameter sets, are needed per acre. The depth of transplant or set placement has an effect on onion shape (see following section).

Onions may be seeded as soon as the land can be made ready, but mid- April is considered ideal. If seeded too late, bulbs will be small since bulbing will begin before adequate vegetative growth occurs. Seeding should be completed by May l. It is recommended that onions be planted on raised beds (70" on center) in two sets of double rows (precision or broadcasted, depending on the planter) spaced approximately 4" apart with each set of double rows spaced approximately 18" apart. One of the most outstanding benefits from this type of culture is improved drainage. Onions do not grow well during extended wet periods which can contribute to root death, subsequent tip burn, and reduced plant vigor.With the described planting configuration, a seeding rate of 11 - 13 seeds\ft. 1/4" deep is recommended for maximum yield potential. With precision seeders (Stanhay® and Nibex®) 1.25 to 1.5 lbs. of raw seed are used per acre. These planters are also designed to accommodate pelleted seed. Higher seeding rates will generally result in significant increase in boiler size onions (<quot; dia.) and decrease in No. 1 size production.

If onions are to be planted without raised beds, it is recommended that the rows be spaced 12 - 14" with a seeding rate of 11 - 13 seeds/ft. Depth of seeding has an effect on bulb shape since the onion stem plate (the base of the onion bulb) forms at the point where the seed germinates. Shallow planting results in flatter bulbs, while deeper seed placement results in taller, and sometimes top-shaped bulbs.

Text 3. Fertilizer Recommendations.

Onions require a good supply of available nitrogen (N), one of the primary macronutrients; however, excess N applications can result in late maturity, large necks that are difficult to cure, soft bulbs, and poor storage quality. A higher percentage of fertilizer N is absorbed by the plant if the fertilizer is applied when the onion root system is well developed. Split applications of nitrogen are used more effectively by the plant than a single pre-plant broadcast application. Fertilizer N applied before planting should be incorporated into the plow layer or banded well away (6") from the seed on the furrow side of rows in two-row onion beds. Sidedressed nitrogen applications or nitrogen applied in irrigation water can be an effective means of providing supplemental nitrogen to the crop during the season. Nitrogens such as 28% N (Urea ammonium-nitrate) is a recommended form to use for fertigation.

Excessive rainfall and irrigation that cause nitrogen movement beyond the root system can reduce the amount of nitrogen available to the plants. Additional nitrogen may be required during the season under these conditions. Cool weather during the growing season can reduce nitrogen release from organic matter. Under these conditions, the nitrogen rates should be increased particularly on organic soils. Excessive nitrogen available to onions, particularly later in the season (mid-July), can delay onion maturity and make field curing of onions more difficult. Inadequate field curing before storage can result in greater losses due to rot. Onion varieties which differ markedly in yield potential can be expected to differ somewhat in their requirements for nitrogen. Higher yielding varieties may require slightly more nitrogen. Plant populations of lower than 4 plants per foot of row will require less nitrogen.

Phosphorus (P) is essential for vigorous early growth of seedlings. All phosphorus should be applied at planting, if necessary. P can be banded at planting 2" to the side and below the seed. All potassium (K) should be applied and worked into the seed bed before planting. Onions require medium levels of available soil potassium. The K soil test onions (dry) is based on K present in the surface soil (0-12").

The secondary macronutrients, calcium, magnesium, and sulfur, are generally not limiting to crop production in most Minnesota soils except under certain conditions.

Micronutrients include manganese (Mn), boron (B), zinc (Zn) and copper (Cu).