The Complete Onion Growing Guide for Home Gardeners

The guide includes all the information you need to sow, care, grow, harvest, and store onions.

Onions are a versatile crop in any vegetable garden, coming in various colors for multiple culinary uses. They are a staple in different dishes worldwide, like soups, pickles, salads, tarts, and curries. All onion varieties are simple to grow and store well after harvest to enjoy home-grown onions all year.

If you’re wondering how to plant onions in your garden, how to care for them, and more about this must-grow vegetable, this growing onion guide is for you.

Recommended Onion Varieties

Many varieties of onions produce red, white, or yellow onions. Some are tangy and spicy, while others are mild and sweet. All varieties of onion fall into one of three groups: long-day (require 14-15 hours of light daily), short-day (require 10 hours of sunlight daily), and intermediate or day-neutral (require 12-14 hours of sunlight daily) varieties. The growing conditions of all varieties are the same, but the flavor varies from type to type.

Some of the recommended onion varieties are:

• Red Florence: Oblong shape, bright red

• Yellow Sweet Spanish: Round shape, large, yellow white

• Autumn Champion: Mildish flavor, sets in autumn.

• Red Stockton: Red ringed, large, white-fleshed bulbs

• Candy: Thick-fleshed, golden, stores well

• Snowball: White-fleshed, sets in autumn

• Setton: Easy to peel, strong & sweet flavor,

How to Grow Onions

You can grow onions from sets or seeds. Growing onions from sets is the most popular and more accessible method. A small onion set grows into a large onion. Onions love a sunny area and well-drenched and fertile soil. Keep the planting area moist in dry periods and weed-free.

Onion Seeds vs Sets

Onion sets are young bulbs with a diameter of 3/4 inch. Growing from sets is the fastest way to produce earlier crops. Plants developed from sets are less likely to be affected by disease. However, they’re more susceptible to bolting. So, choose heat-treated sets to lower the chance of bolting.

Onions take 90-100 days, around four months to mature from seed. However, onion sets are ready to harvest after 80 days or less than three months.

How to Grow Onion from Seeds Indoor

To grow onions from seeds, start sowing the seeds indoors in plug trays or pots before the last spring frost date and then transplant them as seedlings. Fill trays or pots with seed-starting potting mix and plant seeds half an inch deep and 1/2 inch apart. Trim the tops of grassy seedlings when they grow to encourage strong plants. Seedlings require 16 hours of light exposure daily, slightly moist soil, and fertilization with liquid organic fertilizer every 2-3 weeks.

When the resulting seedlings are small, transplant them to avoid upsetting the sensitive roots. Dig holes in prepared ground, plant seedlings about 4 inches apart, and then water the soil.

Sowing Onions Outdoor

Direct sowing outdoors can start in spring when the soil is suitable for plants and has warmed up. Level the ground and mark the location of seed drills that should be a foot apart and half an inch deep. Sow the seeds thinly, cover them, and run water along the rows. Covering sowings or transplants with row cover helps speed up growth at the beginning of the season and lessen the tendency to boult.

Some specific hardy onion varieties can also be sown in late summer to survive through winter and produce early crops in spring.

How to Grow Onions from Sets

Onion sets are partially grown onions that are best for quick produce and save time sowing. They don’t require soaking before planting. Plant sets in weed-free ground 10-15 cm apart, with 30 cm separating each row. In addition, plant them below the soil surface in moist and nutrient-rich soil, preferably with lots of well-rotted organic matter. Early autumn is also the best time to plant some sets to receive an early harvest next summer.

Watering Your Onions

Onions require well-draining soil and proper water to ensure the fullest bulbs. You will want to water your onions sufficiently after planting and then provide regular water afterward, watering your onions about once a week. They will generally need about an inch of water a week. Onions have shallow root systems, so do not let the soil at the base of your plants become dry and crack. Pay close attention, however, because overwatering can cause the onions to rot.

In sandy soil, the water will drain much faster than if you have loamy soil, so you may need to water more frequently. Onions do not grow well in clay soils as they hold too much moisture, and the onions will remain too wet.

Use Toro Aqua-Traxx Drip Tape or Netafim Streamline X at 8” spacing to ensure even water distribution through the irrigation system. Your soil type will determine the flow rate. At DripWorks, we have customer support available that can assist you with selecting your drip irrigation system.

Fertilizing Onions

Onion plants are heavy feeders and require constant nourishment to produce big bulbs. A balanced fertilizer (10-20-10) is required at planting for the onion to establish a healthy root system. Add fertilizer every 2-3 weeks with nitrogen (21-0-0) for the best results and big bulbs. Stop fertilizing when the onions push the soil away, and the bulbing process has started.

Apply fertilizer at the rate of one cup per twenty feet of row. You can apply fertilizer through your drip irrigation system with an EZ-FLO unit. The EZ-FLO fertilizer injector will connect in line with the drip irrigation and is compatible with water-soluble fertilizers.

How to Care for Onions

Fertilize autumn-planted bulbs in spring with nitrogen-rich content. During dry spells, water plants regularly to keep them moist and pull off any flower heads because they take the plant’s energy away from developing bulbs and producing seeds. The seedlings need to stay moist. Once they have matured, they will require just an inch of water a week. You’ll also need to ensure you are not overwatering or underwatering your plants.

Moreover, onions need full sun and 10-16 hours of light daily during bulb formation. Onions are shallow-rooted plants, so hand weed rather than using a hoe between rows. After being transplanted from plug trays, onions can be thinned out to produce large bulbs or left as is. The thinning’s are delicious, so that you can use them as green onions.

How to Harvest Onions

Once onions are big enough to use and most leaves have drooped or turned brown, harvest time is here. Usually, late summer is an ideal time to harvest onions. Mature and ready-to-harvest plants have yellow and drooping tops. Bulbs will swell in the next few weeks before nicely coloring up for harvest.

When they are ready, gently loosen the soil around the bulbs and lift the onions from the soil with a fork. Next, allow them to dry on a rack before storing. Avoid harvesting onions in wet conditions as they may rot during transportation and storage.

How to Use and Store Onions

After harvesting your onions, spread them on racks or newspapers to dry for a bit. When you feel rustle on their outer skins, it means they’re ready to use. Peel and chop onions to use in soups, sauces, pickles, and stews. Sweeter onion varieties like red onions are the best to use raw in salads.

Store onions in net bags or in a cardboard box in a single layer. Also, keep them in a cool and dry place. Make sure not to store them next to pears or apples. Onions are among the many vegetables whose flavor and storage are spoiled by the ethylene gas that fruit produces.

Visit our blog to learn more about planting vegetables, expert gardening & irrigation tips, and much more.

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