Gardening Articles: Care :: Soil, Water, & Fertilizer

Soil Prep for Alliums (page 2 of 2)

by National Gardening Association Editors

Side-Dressing

While your onions are growing you'll want to side-dress them. A side-dressing is simply an extra ration of nutrients; it can be additional compost, dried manure or commercial fertilizer. Onions like a steady supply of nutrients all season long, but they need a little more fertilizer once the bulbs start forming than they do at the beginning. That's because they use a lot of energy making bulbs.

The best time to apply a side-dressing is when the bulbs begin to swell. A pound and a half of 5-10-10 fertilizer or a few shovelfuls of composted manure will nourish a 15-inch-wide, 20-foot-long row; if your onions are in a narrow, straight-line row, this amount will be good for a row 100 feet long.

There are a couple of easy ways to apply a side-dressing. If you plant a single row, you can make a shallow furrow down both sides of the row, two to three inches from the plants and sprinkle the fertilizer in the furrow as you go down the row. Then cover it with soil.

If you plant in wide rows you can sprinkle fertilizer a few inches from the bulbs. If you use commercial fertilizer, be careful not to get any on the top green leaves because it might "burn" them. There's no danger of burning if you sprinkle good compost around the bulbs. In either case, the next rain or watering will start carrying the fertilizer or compost toward the onion roots.

If you have a very sandy, porous soil, your fertilizer will tend to leach straight down instead of spreading out to all the roots. Really sandy soils don't hold water and nutrients very well -- they drain away too fast. You may have to side-dress more often in sandy soil than you would with a clay or loam soil.

Deficiency Signs

Here are the signs that onions need more nutrients:

* Pale yellow or greenish yellow leaves indicate that onions could lack nitrogen. (Leaves can yellow after long, wet periods of weather because a lot of rain washes nitrogen from the soil.)

Before you plant onions, take care of your garden soil. Plants that grow slowly and with many thick-neck bulbs suggest that your onions may lack phosphorus (thick-neck bulbs won't keep as well).

Before you plant onions, take care of your garden soil Onions that develop thick necks, bulbs that are soft with thin skins or tips of leaves that turn brown may signify a lack of potassium.

Important: It's difficult to over-fertilize onions. They require quite a lot of nutrients.

Caution: Don't fertilize onions once the tops start to fall over. Fertilizer isn't needed that late in the season. In fact, the extra boost of energy could cause the onions to sprout new leaves at harvesttime. New growth at the neck of an onion will keep it from completely drying out, and may cause it to rot in storage.

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