If you are considering starting your own garden, you’ve probably wondered what to plant first. Should you go with beans or lettuce? Eggplants or asparagus? Growing what you love to cook with is a great idea. However, beginners should consider vegetables that are easy to grow from seeds. These plants require minimal care, are not picky about soil, are generally pest-resistant, and grow quickly.
Onions are among the most widely grown vegetables globally, cultivated in over 175 countries. Most of the world’s best savory dishes begin with a handful of diced onions.
- When to Plant Onions
- How to Prepare for Planting Onions
- How to Water Onions
- Do You Need to Fertilize Onions?
- How to Know When Onions Are Ready to Harvest
When to Plant Onions
Success in the garden starts with the right conditions. Onions are no exception. They need the right temperature, enough light, and proper timing, especially if you grow them from onion sets, which is the easiest option for beginners.
Onion sets are small bulbs grown from seed the previous season. They’re easy to handle, quick to mature, and forgiving of beginner mistakes. If you’re just starting your garden, this is your best bet.
Best Planting Time by Zone
When to plant onions depends on your USDA hardiness zone and local spring conditions. Here’s a guide to help you get it right.
- Zones 3–5. Plant in late April to early May, once the soil has thawed and daytime temperatures stay above 50°F (10°C). Choose a warm, sunny spot—raised beds work great.
- Zones 6–7. Plan for late March to early April. These zones warm up earlier, giving onions plenty of time to grow before summer heat kicks in.
- Zones 8–10. You can plant as early as late January to mid-February. Just make sure the soil isn’t too wet from winter rain.
- Zone 2 and colder. Outdoor onion growing is a challenge here due to the short season. Try containers, cold frames, or indoor setups if you’re determined.
Onions need a cool start, ideally around 60 to 64°F (16 to 18°C), with steady soil moisture. As the bulbs begin to form, they prefer drier air and warmer temperatures above 68°F (20°C).
Where to Plant Onions on Your Property
If you’re still setting up your first growing space or deciding where to place your garden beds, How to Start a Small Backyard Vegetable Garden offers clear guidance on layout, light, and soil planning for beginners.
In addition to timing, location on your property matters.
- In cooler zones (2–5), pick the sunniest, best-drained part of your garden, ideally with some shelter from strong winds. Avoid low-lying spots that stay wet or cold.
- In warmer zones (8–10), onions benefit from morning sun and light afternoon shade. This helps prevent heat stress and keeps the soil from drying out too quickly in early spring.
Whatever your zone, make sure your onions get at least 6 hours of full sun per day. Good light not only supports bulb formation but also helps prevent disease by drying out the foliage.
Also pay attention to day length. Some onion varieties need a specific number of daylight hours to form full sized bulbs. Choose short day, intermediate day, or long day varieties based on your zone. More details will come later.
How to Prepare for Planting Onions
Once you’ve picked the right time and location for planting, it’s time to gather your materials and get the bed ready. Onion sets are easy to work with, but a few key steps will help you get the most out of your harvest.
What You’ll Need
- Loose, well-draining soil (preferably a raised bed mix or compost blend)
- Onion sets (small pre-grown bulbs)
- Trowel or hand rake
- Mulch (straw, pine needles, or composted leaves)
- Watering can with warm water
Step 1: Choose the Right Soil
Onions need loose, fertile, well draining soil. Avoid heavy clay or soil that stays wet after rain. Onions do not tolerate soggy roots.
Tip for beginners: A pre-mixed raised bed soil from your local garden center is often the easiest and most reliable option. These blends are light, usually pH-balanced, and don’t need much amending.
Step 2: Set Up the Bed
Raised beds work especially well for onions. They warm up faster in spring, drain better, and give you more control over soil quality.
Choose a bed that’s at least 8 inches deep and ideally 4 feet wide. This gives you enough space for rows while keeping everything within reach, so you do not have to step on the soil.
Place the bed in a sunny spot, and make sure it’s not in a low area where water might pool.
Step 3: Prepare the Onion Sets
Most onion sets sold in the U.S. are ready to plant right out of the bag. No soaking or trimming is needed. It still helps to sort through them before planting.
Sort your sets: Discard any that are soft, moldy, or shriveled. Use only firm, healthy bulbs about the size of a marble.
No need to trim roots or tops. Unlike garlic, onion sets don’t require cutting before planting. Just plant them whole.
Some gardeners treat sets with an organic fungicide before planting, especially if the soil tends to stay damp. This step is optional and usually unnecessary with healthy sets and well-draining soil.
Note: There’s no need to protect the roots with powders or coatings. The set will sprout quickly on its own if planted properly.
Step 4: Planting the Onion Sets
- Create shallow furrows about 4–6 inches apart across your raised bed.
- Plant each onion set 1–1.5 inches deep, with the pointed end facing up. The top should just barely peek through the soil surface.
- Spacing: Leave about 3–4 inches between each bulb. If you want larger bulbs, give them more room—up to 6 inches apart.
- Cover gently with soil and firm it lightly with your palm.
- Water thoroughly with warm water after planting to help the soil settle around the bulbs.
Step 5: Mulch the Bed
Apply a thin layer of mulch (like straw or pine needles) to help retain moisture and suppress weeds. Don’t pile it too high—onions like air circulation.
Onions grown from sets are typically ready for harvest in about 80 days or just under three months.
Companion Plants: Who Grows Well Next to Onions?
Onions do more than grow well. They also help protect nearby plants from pests. Their strong scent repels many common garden insects, and they benefit from certain neighbors in return. Here are some of the best companion plants to grow alongside onions:
- Carrots. A classic pairing. Onions repel the carrot fly, while carrots help deter onion flies.
- Beets. These grow well in similar conditions and don’t compete heavily for nutrients.
- Lettuce. Quick to mature and shallow-rooted, lettuce doesn’t interfere with onion growth.
- Tomatoes: Onions can help repel aphids and spider mites from tomatoes.
- Strawberries. The onion scent helps keep some of the pests that bother strawberries away.
- Chamomile and summer savory. These herbs may improve onion flavor and support pollinators.
What Not to Plant Near Onions
Avoid planting onions near crops that are sensitive to their root chemicals or attract the same pests.
- Beans and peas. Onions can stunt the growth of legumes.
- Sage. May not thrive next to onions.
- Asparagus. Competes too much for nutrients and space.
How to Water Onions (Without Guesswork)
Onions do not need constant attention, but the way you water them matters. Proper timing can make the difference between full, sweet bulbs and small, bitter ones. Because the U.S. has many climate zones, there is no single schedule that fits everywhere. Here is a simple approach that works in most regions.
General Rules for Watering
- Water deeply, not often. Aim for the water to reach about 4–6 inches deep into the soil — that’s where the roots are.
- Use about 1 inch of water per week in the beginning (including rainfall). This equals about 2–3 gallons per 10 square feet.
- Always water at the base of the plant, not over the leaves. Soaker hoses or watering cans with a narrow spout work great.
Best time to water: Early morning. This allows the tops to dry during the day and reduces the risk of disease.
First Month After Planting
- Onions need steady moisture to grow strong roots and healthy tops.
- In cool or mild weather. Water once a week if it hasn’t rained.
- In warm, dry weather. Water every 4–5 days.
- In hot or windy weather. Check more often. If the soil looks dry and cracked, it’s time to water.
Optional tool: A moisture meter is a clean, $10–$15 tool that tells you when the soil is dry — no need to touch the dirt.
Bulb Formation Stage
Once the onion tops stop growing taller and thicker, the plant shifts its energy to growing the bulb. At this stage:
- Reduce watering to once every 10 days.
- Let the top inch of soil dry out between waterings.
- Keep water away from the bulbs. Maintain steady moisture, but do not let the soil stay soggy.
When to Stop Watering
As harvest time nears, overwatering can ruin your crop. Here’s how to know when to stop.
- The green tops begin to soften and bend over naturally.
- Lower leaves turn yellow.
- You’re about 2–3 weeks from harvest (check your variety’s timeline).
Once you see these signs.
- Stop watering completely.
- If rain is expected, cover the bed with plastic or a tarp to keep it dry.
Do You Need to Fertilize Onions?
If you use high quality bagged soil or a raised bed mix with compost, you likely do not need extra fertilizer. These mixes support plants for about 6 to 8 weeks, which covers the early growth stage for onions.
Onions are not demanding. Focus on steady sunlight and proper watering instead of extra feeding.
Quick tip. If the leaves start to lose color or growth slows down, apply a light dose of diluted liquid fertilizer for vegetables once, about 3 to 4 weeks after planting.
How to Know When Onions Are Ready to Harvest
Most onions grown from sets are ready in about 80 to 100 days, depending on the variety and growing conditions. But instead of watching the calendar, the best way to know they’re ready is to watch the tops.
Signs It’s Time to Harvest
- The green tops begin to fall over on their own. This is not from wind or damage, but a natural sign that the plant is finishing its life cycle.
- The lower leaves begin to yellow and dry out.
- The bulb feels firm and has pushed up slightly above the soil.
If only a few tops are down, wait another week or so. When about half to two-thirds of the tops have fallen, you can harvest the whole bed.
What Not to Do
- Do not pull onions while the tops are still green and upright. The bulbs may still be growing.
- Don’t water once the tops start to fall. Dry soil helps the bulbs finish and cure properly.
Finishing Strong: Storing Your Onion Harvest
If you want your onions to last through fall and winter, do not skip the final step of curing.
After harvesting, lay the onions in a dry, shaded, well ventilated area for 2 to 3 weeks. Let the tops dry completely, then trim them and store the bulbs in a cool, airy place such as a pantry or basement.
Done right, they will keep for months.
