How to Plant, Grow and Harvest Onions

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.  

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.  

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.

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.  

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:  

Fertilizing:  

Watering:  

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.  

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:  

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.  

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.  

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:  

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. 

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:  

Final Thoughts  

Adding onions to your program is a smart, steady move. They require careful planning but reward you with reliability, market demand, and customer loyalty. Whether you’re planting in pots, sowing seeds in trays, or curing a field’s worth of bulbs, onions are a crop that can elevate your lineup.