Bulb onions require full sun in order to maximize their crop production. Although some types in the onion family can survive in a little shade, 8 to 10 hours of sunlight per day helps keep pests and diseases away from your mature onions. When onions don’t get enough sun, or are planted at an incorrect soil temperature, they won’t produce a healthy vegetable.
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Can Onions Grow in Indirect Sunlight?
Although onions prefer plenty of sunlight, you can grow certain types of onion variety in partial sunlight. Scallions, also known as green onions, do well in indirect sunlight if they can receive at least five hours of sun. However, scallions harvested after exposure to indirect sunlight are often smaller than green onions cultivated in eight to 10 hours of sunlight. Although scallions flourish at temperatures between 65 and 75 degrees Fahrenheit, hotter temperatures require these onions to receive a few hours of afternoon shade to alleviate heat stress.
- Most onions need a lot of sunlight per day, but there are some varieties that can grow with some indirect sun.
- Scallions can get as little as 5 hours of direct sun per day.
- Too much shade can cause disease and fungi to grow on onions.
Also, be aware that too much shade can promote the development of fungal rot in both short and long-day onions.
Can Onions Be Grown in Shade?
Except for green onions, all other onions need plentiful sunshine to grow. Onion bulbs grown in shade likely won’t produce edible onions. They’ll also be more susceptible to onion maggots and bulb rot. Onion plants under stress due to lack of sunlight, exposure to extreme temperatures, or dry soil may also suffer from onion bolting or premature development of flower buds. Additionally, onions need ample sunshine because they contain rich amounts of flavonoids, a phytochemical that regulates onion plant tolerance to heat and cold.
What Happens if Onions Go Without Sunlight?
Common issues affecting onions that receive too much shade or partial sunlight include:
- Absence of bulbs accompanied by prolific leaf growth.
- Leaves develop white, gray, or yellow spots, especially if the weather is rainy, cloudy, and humid. A fungal disease called downy mildew will eventually cover onion leaves with purplish mold that can be difficult to eradicate.
- Bulbs appear normal in color but are too small, according to their variety. Planting onion types in incorrect growth zones or too late or too early in the wrong season will deprive onions of the sunlight they need.
- Lack of sufficient sunlight, combined with constantly wet soil and cool temperatures, may cause a fungal disease called damping-off in seedlings. The primary sign of damping-off is seedlings falling over due to loss of structural integrity.
Onions and other non-leafy vegetables should be planted in gardens that receive six or more hours (preferable 10 to 12 hours) of direct sunlight every day. Spinach, broccoli, and other leafy garden vegetables can be planted in partial shade without affecting their growth.
Can Onions Get Too Much Sun?
Onions really can’t receive too much sunlight, especially during the early stages of their growth. The problem with onions soaking in over eight hours of direct sunlight is the neutralization of compost fertilizer and soil becoming too dry.
- It’s difficult for onions to get too much sun.
- Dry conditions in the soil can affect bulbing onions.
- It’s important to properly plan your garden so other vegetables don’t shadow your onions.
In addition to sunlight, onions require a steady supply of fertilizer to provide gardeners with big, delicious bulbs. Lack of adequately moist soil not only hinders onion growth but prevents compost microorganisms from providing nutrients essential for enjoying a great onion harvest. To ensure onions get enough sunlight in a vegetable garden, make sure onions are not planted near vegetables or flowers that could shade onions with large leaves or flowers.
Do Onions Need Full Sun or Shade?
Onions need ample sunlight to grow properly. The only onion type that does well in both full and partial sunlight is the green onion (scallions). Although green onions only require about four or five hours of sunlight every day, they should be planted in loose, compost-rich soil at least one inch apart. Too much shade for other onion varieties can bring pests and rot to your crop.
Providing enough sunlight, fertilization, and water, are a few of the top things you can do to promote healthy onion bulbs.