By Harris Seeds Guest Growing Partner, Tom Stokes Harlow
Onions are one of those crops that seem humble, but they carry enormous value: consistent market demand, a relatively straightforward growing cycle, and flexible production methods that can work in greenhouses, pots, or open fields. I’ve been growing onions for decades, and I still find myself marveling at how versatile they are—not to mention how satisfying it is to pull a well-cured bulb from the soil.
For new growers, it can be a bit intimidating to sort through all the methods: growing in pots versus ground, seed versus sets, cuttings versus water. Don’t worry—onions aren’t out to make you cry (well, at least not until harvest time in the packing shed). Let’s break it down step by step so you can start strong and feel confident adding onions to your professional lineup.
Getting Started: What to Do When Your Onion Sets or Transplants Arrive
If you order onion sets or onion transplants, you might be alarmed when you open the box. They often arrive looking dry, with slightly yellowed tips. Don’t panic—that’s perfectly normal. Onion transplants are shipped dormant, and the plant can survive just fine off the energy in its bulb for about three weeks.
Here’s what to do when they arrive:
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Remove sets/transplants from the box immediately to prevent fungal growth.
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Place them in a cool, well-ventilated area away from direct sunlight, soil, or moisture.
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Plant them as soon as possible for best results (within three weeks maximum).
Timing is key: plant onions 4–6 weeks before your last average frost date. This gives them a strong start before the heat of summer sets in.
Soil Preparation: Giving Onions the Right Home
Onions thrive in full sun and well-draining soil. Raised beds or rows at least 4 inches high and 20 inches wide are ideal, since they encourage good drainage and airflow. Growing onions in raised beds improves soil temperature control and makes soil amendment management easier.
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Soil type: Loose, crumbly soil is best. If you’re working with heavy clay, amend with compost or sand to improve aeration.
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pH levels: Onions prefer slightly acidic to neutral soil, with a pH between 6.2 and 6.8. Too acidic? Add ground limestone. Too alkaline? Incorporate peat moss.
Pro tip: Before planting, rake in a pre-emergent herbicide like corn gluten meal into the top inch of soil. These soil amendments won’t harm your onion roots, but they will reduce weeds for up to six weeks—a must-do since onions don’t compete well with weeds.
How to Grow Onions in Pots
If you’re testing the crop or want to maximize small spaces, onions can be grown in pots.
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Use containers at least 10–12 inches deep.
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Space bulbs or seedlings 3–4 inches apart.
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Keep the soil moist (but never soggy).
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Fertilize lightly every 2–3 weeks until bulbs form.
Container onions are great for market displays and “urban-friendly” offerings. Just be prepared to water more frequently than in-ground crops.
How to Grow Onions in the Ground
For professional-scale production, in-ground planting is where onions shine.
Spacing:
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For full-sized bulbs: 4 inches apart in rows 16 inches apart.
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For green onions: plant closer, about 2 inches apart. (You can harvest every other one early for bunching onions, and let the rest grow to maturity.)
Fertilizing:
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At planting: use a fertilizer with a higher middle number (like 10-20-10) to support root growth. Apply it in a trench 4 inches deep, then cover with 2 inches of soil before planting sets 6 inches away from the trench.
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During growth: fertilize every 2–3 weeks with ammonium sulfate (21-0-0) in alkaline soils or calcium nitrate (15.5-0-0) in acidic soils. Stop once bulbs begin to form, since too much nitrogen at that stage can reduce bulb quality.
Watering:
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Onions need about 1 inch of water per week.
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Water thoroughly after planting and adjust as bulbs grow (more water closer to maturity).
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Stop watering once onion tops fall over—this helps the bulbs cure properly.
Weed control:
Onions hate competition. Keep beds weed-free pre-, or mulch lightly with straw (but pull it back once bulbs start forming).

How to Grow Onions from Seed
Seeds offer the greatest variety and flexibility for specialty growers.
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Start indoors 8–10 weeks before the last frost.
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Sow in shallow trays with seed-starting mix, ¼ inch deep.
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Provide 12–14 hours of light daily.
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Harden seedlings off before transplanting.
This route requires more labor but allows you to grow unique varieties—reds, sweets, or storage types—that can set your business apart at market.

How to Grow Onions at Home Without Seeds
For beginners or demonstrations, onions can be grown from sets or even grocery store onions:
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From sets: Quick, reliable, and straightforward—just plant them pointy side up.
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From sprouted bulbs: Plant the root end in soil for green shoots (not large bulbs).
This is an easy way to engage hobby gardeners or offer “instant gratification” products alongside your commercial program.
How Many Onions Grow from One Bulb?
Here’s a question I get all the time: “If I plant one onion bulb, how many onions will I get?
The answer: one bulb produces one mature onion. That’s just the way their biology works. However, you will get multiple green shoots (scallion-like greens) from a single bulb if you plant it as a cutting. Some growers initially expect onions to multiply underground like garlic, but they don’t. Each bulb is its own finale act—one seed, one bulb. The trick is spacing and succession planting to maximize yield.

How to Grow Onions from Cuttings
If you slice off the base of an onion (the root end), you can regrow it into greens or smaller bulbs.
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Place the base in moist soil or shallow water.
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Once shoots and roots appear, transplant to soil.
This method won’t produce storage-quality bulbs, but it’s fun for sustainability demos and small “green onion” harvests.
How to Grow Onions in Water
For an easy kitchen project, onions can sprout in a shallow dish of water.
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Keep roots submerged and bulb above the waterline.
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Replace water every few days.
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Harvest green shoots like scallions.
This is more novelty than production, but it’s a great educational tool for engaging customers.

Growing Healthy Onions: Pest, Disease & Maintenance Tips
Like all crops, onions have their challenges:
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Fungal issues (blight, purple blotch) thrive in high moisture. Prevent with good spacing, proper ventilation, and a fungicide application every two weeks if needed.
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Thrips cause silvery blotches and leaf damage. Reduce weeds (their overwintering spots) and treat with Neem oil or insecticides if infestations appear.
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Yellowing leaves may signal overwatering.
Knowing how to prevent onion root rot is crucial for a successful harvest. Think of onions like Goldilocks—they don’t like it too wet or too dry.
Harvesting, Curing & Storage
When onion tops turn yellow and flop over, it’s harvest time. Proper curing is essential, and knowing how to store harvested onions correctly will help to ensure a long shelf life.
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Harvest on a dry morning.
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Cure outdoors by laying onions in two rows, tops overlapping to prevent sunscald.
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If curing indoors, ensure excellent ventilation.
Curing test: the neck and skin should be dry and papery before storage. Using the proper tools, trim roots and cut tops back to 1 inch, or braid tops for rustic presentation.
Storage:
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Ideal temp: just above freezing (32–35°F).
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Humidity: 65–70%.
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Storage method: mesh bags or netting with good airflow.
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Pro tip: pungent onions store longer than sweet ones—use the sweets first.
