Hey Garden Bestie,
Today we’re digging into one of the most versatile crops you can grow: onions. Whether you’re brand-new to gardening or just looking to refine your onion-growing skills, this guide will walk you through the basics (and beyond) to set you up for success. Let’s roll up our sleeves and make those onion beds thrive!
Onion Types and Hardiness Zones
Onions fall into three main categories: long-day, short-day, and intermediate (day-neutral). Choosing the right type for your region makes all the difference in how well your onions grow and bulb up.
Long-Day Onions (Zones 3–7):
Grow best in northern areas where summer days stretch 14+ hours.
Popular varieties include Yellow Spanish and Walla Walla.
Require long daylight hours to trigger bulb formation, which leads to large, hearty onions.
Typically planted in early spring and harvested mid-to-late summer.
Flavor: stronger, more pungent — great for cooking, storing, and caramelizing.
Short-Day Onions (Zones 8–11):
Thrive in southern regions with winter planting and shorter day lengths (12 hours or less).
Notable varieties include Vidalia and Texas Supersweet.
Begin forming bulbs earlier, making them perfect for areas with mild winters.
Usually planted in late fall to early winter and harvested late spring to early summer.
Flavor: milder, sweeter — excellent for fresh eating, salads, grilling, or pickling.
Intermediate/Day-Neutral Onions (Zones 5–9):
Adaptable to a wide range of climates, making them a good option for gardeners who fall between northern and southern zones.
Start forming bulbs once daylight hits about 12–14 hours, so they’re less sensitive to extreme day length.
Common varieties include Candy, Super Star, and Red Burgundy.
Can be planted in both spring and fall depending on your region, with harvest usually in summer.
Flavor: balanced between pungent and sweet, often with good storage ability.
Starting Onions: Seeds vs. Sets
You’ve got two main options for planting onions:
Seeds: Offer the widest variety and can produce larger bulbs when transplanted carefully. Start them indoors 8–10 weeks before your last frost date, or direct sow if your climate allows. I’ve done both methods, and while direct sowing worked well, transplanting seedlings gives you more control over spacing (and bigger onions).
Sets: These are small, pre-grown onion bulbs that you pop straight into the ground. They’re fast and easy, perfect for beginners or for using as companion plants in other beds. Plant them in early spring, spacing 4–6 inches apart.
Click the hyperlinks below to purchase onion sets (available seasonally)
Fertilizing Onions
Onions are heavy feeders and need consistent nutrition:
At Planting: Work compost or aged manure into your soil.
4–6 Weeks After Planting: Apply a balanced fertilizer around your onion rows.
Mid-Season (Bulb Formation): Use a nitrogen-rich fertilizer to encourage strong leaf growth, which supports bigger bulbs.
1 Month Before Harvest: Stop fertilizing to let onions mature and develop flavor.
Timing: When to Plant and Harvest
Starting Indoors: Late winter/early spring is ideal for beginning onion seeds.
Transplanting Outdoors: Move seedlings once soil is workable (crumbly, not soggy).
Companion Planting with Onions
Onions are some of the best multitaskers in the garden. Not only do they add flavor to your meals, but they also help protect their plant neighbors by repelling pests with their strong scent. Adding onions into your planting plan is an easy way to boost the health and productivity of your garden.
Here are some of the best pairings:
Collards and Cabbage Companion Planted with Onions
Carrots: Onions and carrots are classic companions. The onion’s strong smell confuses and repels carrot flies, while carrots help maximize bed space since their roots grow deeper without competing with onions.
Spinach & Lettuce: These leafy greens thrive next to onions. Their shallow root systems won’t compete with onion bulbs, and in turn, they help keep the soil cool and shaded, which benefits onion roots. Plus, quick-growing greens make great use of garden space while onions take their time.
Collards, Cabbage & Kale: Members of the brassica family (like collards, cabbage, and kale) love being planted with onions. Onions act as a natural defense against common brassica pests such as cabbage worms and aphids. While your collards or kale are busy producing leafy harvests, onions quietly grow alongside them without crowding.
Beets & Chard: These root crops coexist well with onions since they don’t compete heavily for nutrients, and onions help deter insect pests that might otherwise damage tender beet greens.
Tomatoes & Peppers: Onions can also be tucked in near fruiting crops like tomatoes and peppers. Their scent helps repel aphids, spider mites, and other common pests, creating a healthier growing environment.
*Tap on each crop name to explore seed options.*
What to Avoid
While onions are fantastic companions for many crops, there are a few plants they just don’t get along with. Onions belong to the allium family (along with garlic, leeks, and chives), and they release compounds into the soil that can interfere with the growth of certain vegetables.
Beans & Peas (Legumes): Onions can stunt the growth of legumes by affecting the nitrogen-fixing bacteria that peas and beans rely on. Since legumes enrich the soil with nitrogen, pairing them with onions creates competition rather than cooperation. It’s best to keep your onions in a separate bed away from your beans and peas.
Asparagus: Onions and asparagus are also considered poor companions. Onions can inhibit asparagus growth and reduce yields over time. Since asparagus is perennial and likes its own dedicated space, keep onions out of that bed altogether.
Harvesting Onions
One of the most exciting parts of growing onions is knowing when it’s time to pull them from the soil. Onions give you a few clear signs that they’re ready:
Short Day Onions Ready for Harvest
Watch the Tops: When the green tops start to yellow, bend over, and eventually fall, that’s the plant’s way of signaling it’s finished growing and the bulb is mature.
Check Bulb Size: Gently brush back some soil around the bulb. If it looks plump and close to the expected size for the variety, it’s harvest time.
Timing: Depending on the variety and planting method, onions are usually ready anywhere from late spring through mid-summer.
How to Harvest:
Short Day Onions at Time of Harvest
Use a garden fork or your hands to gently loosen the soil and lift the bulbs out—avoid pulling by the tops, as this can cause breakage.
Handle carefully to prevent bruising, which shortens storage life.
Curing for Storage:
After harvesting, lay onions in a single layer in a warm, dry, well-ventilated area (like a porch, shed, or garage) for 2–3 weeks.
Once the outer skins are papery and the necks are fully dry, trim the tops back to about 1 inch and snip the roots.
Storage Tips:
Store onions in mesh bags, crates, or braided bunches in a cool, dark, and dry place with good air circulation.
Avoid storing them in plastic bags (they’ll hold moisture and encourage rot).
Sweet varieties usually keep for a few weeks to a couple of months, while pungent storage onions can last for several months when cured properly.
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