How to grow BIG onions.

I hope this information helps you grow your biggest onions ever in the upcoming season.

Four Acre farm will be selling onion starts (seedlings) for two types of onions. Red Wethersfield and Alisa Craig. (pictured). Once you try this method you will never be satisfied by those mini onion sets again. Supplies will be limited as we test the demand for this product. Let's grow that green thumb together!

The frustration is real. We have all seen the pictures. A gardener standing there holding massive onions while ours are tiny in comparison. Then we ask ourselves why ours are so small? There are tips and tricks to having a huge onion harvest and I am going to lay them all out here in this post. Let's get growing shall we?

1. DON'T use onion sets. DO use onions starts.

Onion sets are tiny onion bulbs that come in a bag. These are actually second year onions that if left long enough or subjected to very high heat will bolt and go to seed. This is why they never get as big as from onion starts (seedlings). Most people do not have the time or the setup to grow onions from seed. Reason number one is you need to start them in January here in zone 3b. That is a very long time to have to care for them. Second is that you cannot just place them in a window as onions need bright direct light and our northern climate just does not fit that bill in the depth of winter. So you now need, containers, good soil, shelving and strong grow lights, all of which cost more money than the value of the onions themselves.

2. Choosing the WRONG TYPES of onions for your area.

Unlike most plants which we choose based on our growing zone, onions are rated for daylight hours. Here in zone 3b we need Long-Day onions. ALL of Canada needs Long-Day onions.

• Short-Day onions need 10-12 hours of daylight; best for southern zones (7+) planted in fall/winter.

• Intermediate-Day or Day-Neutral onions need 12-14 hours; ideal for central zones (5-6).

• Long-Day onions need 14-16+ hours; perfect for northern zones (6 and colder) planted in spring. 

Why it Matters:

• Bulb Formation: The correct day length triggers the onion bulb to swell; the wrong type might produce large tops but small bulbs, or fail to bulb at all.

• Climate Adaptation: This system allows onions to be grown from the tropics to subarctic regions by matching the onion's needs to the natural day length of the latitude.

3. Soil and Amendments matter.

Loose and crumbly (sandy loam or silt-loam) allows bulbs to swell far more easily while clay or compacted soil can restrict bulb formation.

Drainage is essential to prevent waterlogged ground, which hinders bulb formation and can cause rotting bulbs.

Prior to planting (I recommend at least two weeks prior to transplanting the seedlings or preferably in the previous fall), mix in plenty of compost or well-rotted manure for nutrients and structure.

Added nutrients: High nitrogen early on promotes leaf growth, leading to bigger bulbs; after that use a balanced fertilizer.

PH Level: Aim for slightly acidic, between 6.0 and 6.8.

Mulch: Apply straw or shredded leaves to retain moisture, suppress weeds, and add nutrients as it breaks down. You don't actually like weeding and watering do you? That being said, do not place mulch right up againt the seedling/bulb itself. As with most plants that can encourage rot and smaller yields.

Spooning: Not that kind. This is a gardening technique where you gently scrape soil away from the onion bulb as it grows, creating space for it to expand and form a larger, rounder bulb, rather than growing long and thin. It's done carefully with a spoon or fingers, leaving the roots covered, and helps the bulb swell out of the ground without soil resistance. This only takes me a few minutes once every couple weeks or after a particularly hard rain.

4. DON'T plant too deep.

Planting onion starts too deep is a common mistake that results in lots of green tops but small bulbs, as the bulb needs to sit partly above ground to form properly. To fix this, gently dig around deeply planted onions, expose the developing bulb, and backfill with soil just enough to keep them upright, ensuring the bulb (or most of it) sits near the soil surface, not buried, to encourage large, mature bulbs. 

5. Spacing is key.

I have learned that 6-8 inches apart is the absolute best to grow big onons. They need that space between or they will only grow to the space you give them. The same goes for all alliums including garlic. Personally I like to plant three lines 6-8 inches apart and then place them so the middle row seedlings are off-set between the two outside rows. More onions in less space that way and still within easy reach.

Raised beds are perfect for onions as they are fairly shallow rooted and adore the lighter soils mixes.

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