This page talks about growing onions, their benefits and what is meant by long day vs short day onions.
Onions are a delicious addition to any edible landscape! There are three basic categories that onions fall into: short day, intermediate day and long day. It’s very important that you select the right type of onion variety for your climate for the best growing experience. Onions grown in the wrong are may end up very small, or have other issues. When to plant onions is also determined by your climate. Areas with harsher winters will want to plant in early spring, when the ground becomes workable, and warmer, more moderate climates will want to plant in fall.
Short day onions will begin forming bulbs when there is 10 to 12 hours of daylight per day. The earlier you plant them, the bigger the bulb that will form. Most varieties are sweet. These should be grown in the south (zone 7 or warmer). They can be grown in the North, however, they won’t be nearly as big. Short day onions should be planted in the fall in the south take approximately 110 days to mature. If you plant them in the north, plant them in early spring. They will mature in 75 days. Harvest short day onions in late spring.
Intermediate day onions will begin forming bulbs when there is 12 to 14 hours of daylight. This onion works well in zones 5 and 6, but tends not to grow as well when you get as far south as Texas and Florida. Intermediate day onions should be planted in fall in milder climates and early spring, as soon as the ground is workable, in areas with harsher winters. They mature in about 100 days. Harvest them in mid to late summer in areas with harsher winters.
Long day onions will begin forming bulbs when there is 14 to 16 hours of daylight. They do best in colder areas (zone 6 and further north), from the Midwest to the Canadian border. If you plant them early, they will also do well in intermediate day areas. They mature in roughly 90 to 100 days. Sweet onions will mature a few weeks before storage onions, but they don’t keep as long.
After you’ve determined the best variety and best time to plant onions for your region, plant onions seeds indoors 6 weeks before you intend to transplant them into the garden (review notes above for best planting times for your region). Onion seeds do not keep for long periods, so it’s best to start with a fresh batch each year. Barely press the seeds into the soil. Keep the sees moist and use a grow light. Seeds should germinate in 4 to 5 days.
Once your growing onions are ready for transplanting, choose a sunny spot (full sun) in your garden with good drainage for planting. Onions do well in raised beds, but can also be planted directly into the soil so long as it is not too heavy (like clay). You can either mix compost into the soil, or a slow-release fertilizer.
Space onion plants 4 to 5 inches apart, with 12 to 18 inches between rows. Be very careful not to bury the whole plant. Only bury the seedlings about 1 inch into the soil to keep the leaves above ground and healthy. Onions grow short, shallow roots, so keep your plants well hydrated, particularly during the warmer months.
Try to keep soil and water from collecting on the leaves. Fertilize your growing onions periodically with nitrogen for bigger bulbs. After the bulbing process begins, the onions will burst through the soil. Do not recover them.
When your growing onions are nearly mature, their leaves will begin to yellow and die. Once most of your onion plants have yellowed and fallen over, go ahead and bend the remaining ones down. Wait 10 to 14 days for the onions to fully mature, then dig them up.
Do not wait any longer than 14 days to dig up your onion bulbs, as they may begin to rot or grow again. Once you’ve dug them up, cut the stems off. Store your onions in a cool (40 to 50 degrees), dry place.
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