The thinking is changing on planting onions in the South. The original thinking in the deep South was that onions are best planted in the Fall and grow slowly over the winter. But the winter should not become so cold that the plant goes into dormancy, like it can in middle latitudes in Virginia and North Carolina. The best idea in those locales is to start seeds indoors and transplant when the ground can be worked, typically March 1st.
The key to this process is selecting Short-Day varieties. (Red Creole, Texas Early, White Bermuda). These varieties will develop all winter, establishing extensive roots, and beginning to bulb.
Long-day varieties require 14-16 hours of daylight. Virginia gets about 14 hours of daylight starting in May and running through August. (The Vernal equinox on March 21 theoretically has 12 hours of light and 12 hours of darkness) If you inadvertently plant long-day onions in September, you won't get much bulbing until May and they may be ready to harvest in June.
You may have to harvest them before they are ready, if the temperatures climb quickly. The heat may cause them to go to seed even before the bulb develops, and the stalks and leaves will begin to toughen. If that happens, harvest the rest of the crop and use the white and light green lower parts as if they were green onions.
Millenial Gardener:
1. Grow onions from seeds. (Not Sets).
Onion sets are started from seed, but then when they reach about 1" they are harvested and dried. Theoretically, when you plant the bulbs they resume growth. But often that period of dormancy fools the onion into thinking that they are in their second year, and will proceed directly to flowering without producing any bulb to speak of.
2 Use short-day onion seeds. This is not an area to experiment with. You have to carefully pair your variety to the latitude of where you live. As usual for the Hampton Roads geography we are on the border of two growing types. Southeastern Virginia is exactly on the line between Short Day and Intermediate Day varieties. But, because we live in the corner of the growing zone 8B that sticks up into Hampton Roads, we have warm enough temperatures in the winter to successfully start our seeds early.
Find the type that works in your area and always use it. Yellow Granex. Red Creole. Red amposta.
3. Work out the timing of seeding, planting, and harvest. Yellow Granex matures in 110 - 160 days, so we'll take an average of 140 days.
Harvest will be in mid-July. Lets take July 19th as the harvest day. 140 days before this date, will be March 1. This is when we want to plant our onion transplants into the garden. From seeding to transplant size is about 6 weeks, so we will start onion seeds indoors after January 15th.
4. Initially plant with high nitrogen fertilizer. Then, switch to a balanced fertilizer. You cut back on the nitrogen so that the plant will grow bulbs, not leaves. The restriction of the nitrogen is critical to a beautiful bulb.
4. Grow onions in loose and loamy soil. Not dense or compact. Mix in 2-3" of compost at the top of soil. Mulch heavily after planting.
5. When you transplant your onions Fertilize initially with a balanced fertilizer: 5-5-5, 10-10-10. They should establish in a few days. Once established, us a high-nitrogen fertilizer like Miracle-Gro to feed them. When they get ready to bulb, stop the high-nitrogen, and switch to a balanced fertilizer like the 10-10-10.
Onion Seed Schedule
January 15th. Start onion seeds indoors. Will need 6 weeks for germination and seedling growth. This will take us to March 1.
March 1st. Transplant onion seedlings into garden under low tunnels. Onion plants are hardy to 20 F, so planting out is safe. Plant seedlings 3" apart.
May 1st. Thin onions to 6" spacing. This will give you an early harvest as well as giving the remaining onion bulbs space to grow. Transplant pepper plants into the same bed to provide shade as the summer gets hotter.
June 1st. Trim onion leaves to 8". Spoon onions to give bulb room. You want the bulbs to be exposed, but not the roots.
July 10th - 20th. Plan to harvest your onions. The bulbs won't grow much bigger than this and may start to shrink in preparation for winter.
1870's Homestead
1. Grow onions from seed and transplant.
2. Top the onion leaves at 10 - 12 weeks to send growth down to the bulb. Trim the leaves back to 8". The trimmings are nutritious and should be used in the kitchen.
3. Spooning the onions. Lightly clear the soil away from the tops of the bulbs. This includes a bit of soil so that the tops of the bulb is exposed. Give that bulb room to expand. You want the bulb to be exposed, but not the roots. This allows the bulb to expand unhindered. Thin any onions that are growing too close, so that you have 4" between plants.
4. Onions are heavy feeders.
5. Intercrop with peppers
6. Shower watering to keep surface roots wet.
7. Stay on top of weeding, since onions don't shade out the surface of the soil.
Onion Harvest: In Virginia, we harvest alliums from late May through June, but harvest dates vary from year to year according to the weather, and also depend on if a crop is planted in the fall or spring.
Prior to harvest, the neck region of multipliers weakens and the green tops begin to fall down. Do not water them during this period. When approximately 50% of the tops have fallen, the crop has sufficiently ripened and is ready for harvesting. There is no advantage to breaking over the tops of onions still standing (in fact this may shorten the storage life of certain varieties). Not all the tops fall over at the same time. Harvest the mature onions every few days. Those with tops still standing after 7–10 days should be harvested and kept separate from the rest. Eat them first because they will not keep as well.
Perennial Onions are also planted in the fall as bulbs. This includes Walking onions, which are harvested for their greens, and Multiplier onions and shallots which produce multiple bulbs.
Plant bulbs from mid October to mid December, with early to mid November being optimal. After sprouting, cover with a 2" layer of mulch to overwinter.
Egyptian Walking Onions can be harvested for their fresh greens and bulbs from fall through spring. White multipliers are harvested in the spring.
