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Growing onions is a must for any garden! There are so many different varieties all with unique flavors that will come to life in your kitchen. Spring onions are sweet, mild, and great in salads. Bulbing onions of gold, yellow, and red can give your dishes complex flavors and aromas. In our kitchen, almost all recipes start with an onion! Onions are easy to grow if you know a few expert tips. You need to know what kind of onion to grow in your area if you want to succeed.
When to Grow Onions
Onions are a cool-season crop, meaning they like to grow in the cooler months of the year. For zones 9 and 10 you want to start your bulbing onions in the fall. Let them overwinter and harvest in late summer and fall. For spring onions, shallots, and other smaller onions, you can plant them in the spring and enjoy them as soon as they are the desired size.
Pro Southern California Tip
The most common mistake gardeners make with growing onions is they can’t get their onions to bulb. The most common reason why is because they planted a variety that is not appropriate for their region. Bulbing onions are daylight sensitive so you must grow the right kind in your area for success. Here are the three kinds.
Short Day Onions: 10-12 hours of sunlight required to form bulbs
Intermediate Day Onions: 12-14 hours of sunlight required to form bulbs
Long Day Onions: 14-16 hours of sunlight required to form bulbs
Those of us south of San Francisco should grow short-day onions.
There are lots of different varieties of onion available in seed. We specialize in short-day onions for southern growers. Gold coin onion is a tasty cipollini-style onion that does really well in Southern California. Red Burgundy is a classic red onion for southern states. Red Rock is a high-quality specialty red onion that does exceptionally well in southern states. For those in the north, we have tons of green and shallot-style onions that can be grown during any frost-free time of the year. Our Torpedo onion creates beautiful red shallots that are mild and tasty. They can be planted in spring for an early summer harvest. Then, of course, there are standard favorite varieties of onions like Toyko and Evergreen bunching onions.
Growing Onions from Seed
Onions are very easy to start from seed. You can choose to direct sow or transplant. If you choose to direct sow them in to the ground, you must make sure that you keep the soil moist the entire time the seeds are germinating to get good, even germination. This may mean watering 2-3 times a day when the soil dries out. You can, alternatively, easily start your seeds in trays or starter pots. Seeds should be planted in good seed starting soil and be kept moist until they germinate. For even germination, use finely sifted soil to cover your seeds.
Growing Onion Plants
Once your onion has sprouted, you need to get it growing! Your onion seedlings will need to be fertilized after about 2 weeks of growing. The best fertilizer for your baby plants is a liquid fertilizer with even numbers of nitrogen, phosphorus, and potassium. For example, a good product is a liquid fish emulsion with 2-2-2. Harsh chemical fertilizers can burn your plants, so use a natural or organic fertilizer if possible.
Onion Companion Plants
Onions are relatively fuss-free once you get them up and growing. You can leave them be until they are ready to be harvested. Beneficial flowers and companion plants can help keep your onions happy and healthy by bringing in beneficial insects. Plants like Nasturtium, Alyssum, Sunflowers, and Zinnias can grow very happily next to your onions.
Growing Onions in Containers or In-Ground
Onions can easily be grown in a container. What is great about growing them in a container is that you can move them around if needed. If you choose to grow onions in a container, make sure you use compost to help keep the soil in your container moist. You can mulch the top of the soil to help keep the soil cool and moist during warm months. If you choose to plant them in the ground, plant them in an area of your garden where they will not be in the way of other plants. Like in a corner where they can grow happily as you tend to the rest of your garden.
Knowing when to harvest your onions can be a tricky thing. Here are some pro tips. First, you need to know what kind of onion you are growing. If you are growing a bulbing variety, you need to wait until the plant has fully grown its bulb. This is usually in the fall. The tips of the onions turn brown and fall over, letting you know that they have completed their life cycle and are ready to be harvested. If you are growing spring onions, shallots, or green onions, you can harvest them at any point that they are large enough to use. Keep in mind onions like our Toyko variety can grow over 4” wide! That’s almost the size of a leek!