You don’t need a huge garden to grow a proper onion crop. With the right variety and a smart layout, even a couple of grow bags or a corner of your raised bed can give you more onions than you’d think possible.
A lot of gardeners get stuck with small bulbs or floppy tops — but it’s usually down to a few small missteps: wrong type, poor spacing, or watering at the wrong time.
In this guide, I’ll show you how to fix all that. We’ll cover the best types of onions for small spaces, how to plant them properly, what to feed them (and when), and how to know exactly when they’re ready to harvest.
Choose the Right Onion Variety for Maximum Yields
Not all onions grow the same, and choosing the right variety is one of the most important steps in getting a big harvest in a small space.
Onions are classified into three main types—short-day, long-day, and intermediate-day—and picking the wrong one for your climate can lead to small bulbs or no bulbs at all.
Understanding Onion Types
- Short-day onions begin forming bulbs when daylight hours reach 10 to 12 hours. They are ideal for southern regions with mild winters, as they can be planted in fall and grown through winter.
- Long-day onions need 14 to 16 hours of daylight to start bulbing, making them best suited for northern climates with long summer days.
- Intermediate-day onions need about 12 to 14 hours of daylight, making them a great choice for mid-latitude regions where seasons are balanced.
Best Onion Varieties for Containers and Raised Beds
When growing onions in limited space, it is best to choose high-yielding, space-efficient varieties that mature quickly. Some of the best options include:
- Red Burgundy – A short-day variety that grows well in small spaces and has a sweet, mild flavor
- Yellow Granex – A classic sweet onion that thrives in containers and raised beds
- Walla Walla – A popular long-day variety known for its large, juicy bulbs
- Candy Onion – An intermediate-day onion that grows quickly and produces uniform bulbs
Should You Start from Seeds, Sets, or Transplants?
Onions can be grown from seeds, sets, or transplants, and each option has its pros and cons:
- Seeds – Take longer to mature but give you more control over variety and tend to produce the healthiest bulbs
- Sets (small onion bulbs) – The easiest and fastest method, but they often result in smaller onions because they were pre-grown the previous season
- Transplants – A good middle ground that allows for faster growth while still producing large bulbs
For the best results in a small space, using seeds or transplants will maximize bulb size and give you better control over spacing and growth.
Plant Onions the Smart Way for a Bigger Harvest
The biggest mistake many gardeners make is spacing onions too far apart or not using the right planting method.
With a few smart techniques, you can fit more onions in a single container or garden bed without sacrificing bulb size.
Spacing Techniques to Grow More Onions in Less Space
Onions need enough space for their bulbs to expand, but they do not require as much room as some gardeners think. Here are the best planting methods to grow a large harvest in a small area:
- Grid Planting – Instead of planting in long rows, plant onions in a grid pattern with bulbs spaced 4 inches apart in all directions. This allows for maximum use of space while still giving bulbs room to grow.
- Bunch Planting – For green onions or scallions, plant 5 to 7 onions close together in small bunches. This is perfect for containers and allows you to harvest multiple onions from one spot.
- Interplanting – Combine onions with companion plants like lettuce, carrots, or herbs to make the most of your space while also helping to deter pests.
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How Deep to Plant Onions for Best Growth
Seeds – Plant onion seeds about ¼ inch deep and thin them out once they sprout.
Sets – Place onion sets just below the soil surface, with the tip slightly exposed. Planting them too deep can prevent proper bulb formation.
Transplants – Set onion seedlings about 1 inch deep, making sure the roots are covered but the base of the stem is above soil level.
The Best Time to Plant Onions
- In warmer climates, plant onions in late fall or early winter for an early harvest.
- In colder climates, start onions indoors 8 to 10 weeks before the last frost or plant sets/transplants in early spring when the soil is workable.
The Perfect Soil Mix and Container Setup for Onions
The right soil and container setup is one of the biggest secrets to growing large, healthy onions in a small space. Onions have shallow root systems and need loose, nutrient-rich soil to develop properly.
The Best Soil for Growing Onions
Onions do best in light, well-draining soil with plenty of organic matter. Heavy or compacted soil will restrict bulb development, leading to small, misshapen onions.
- Use a loose, sandy loam soil that allows for easy root expansion
- Add compost or aged manure to enrich the soil with nutrients
- Maintain a soil pH between 6.0 and 7.0 for optimal growth
- Avoid heavy clay soil, which holds too much moisture and can cause rot
For container-grown onions, use a high-quality potting mix with added perlite or sand for better drainage.
Choosing the Right Container or Raised Bed
Onions do not require deep soil, but they do need plenty of space for bulbs to expand.
- Container size: A 6 to 8-inch deep container is ideal for onions. Choose wide containers or grow bags to fit more plants.
- Drainage: Ensure the container has good drainage holes to prevent waterlogging.
- Raised beds: A 10- to 12-inch deep raised bed is perfect for growing onions, providing excellent root space and drainage.
Adding the Right Nutrients for Maximum Growth
Onions need nitrogen early on to develop strong, healthy leaves, which in turn help fuel bulb growth. However, too much nitrogen late in the season can prevent proper bulb formation. Instead, you get lots of leaves.
- Early growth: Apply a nitrogen-rich fertilizer like blood meal or fish emulsion every 2 to 3 weeks.
- Bulb formation: Once onions begin forming bulbs, switch to a low-nitrogen, high-phosphorus fertilizer like bone meal to encourage strong bulb growth.
Watering and Feeding: The Trick to Big, Firm Onions
Many gardeners either overwater or underwater, both of which can lead to small, weak, or even rotting onions. By following the right schedule, you will ensure your onions develop strong roots and form large, firm bulbs.
How to Water Onions for Maximum Growth
Onions need consistent moisture, but the amount of water they require changes as they grow.
- Early growth stage (first 6–8 weeks) – Onions need regular watering to help develop strong leaves. Water deeply once or twice a week, keeping the soil evenly moist but not soggy.
- Bulbing stage – When bulbs begin forming, reduce watering slightly to prevent rot and encourage firm, well-shaped onions. Soil should be moist but not overly wet.
- Final few weeks before harvest – Once onion tops start yellowing and falling over, stop watering completely. This helps the bulbs cure properly and store longer after harvest.
The Best Fertilizer for Bigger Onions
Onions are heavy feeders, meaning they require regular nutrients to grow well. However, the type of fertilizer you use must change as the plant develops.
- Early stage – Use a nitrogen-rich fertilizer like blood meal, fish emulsion, or compost tea every 2–3 weeks. This promotes strong leaf growth, which is crucial for big bulbs.
- Bulbing stage – Once bulbs start forming, switch to a fertilizer high in phosphorus and potassium (such as bone meal or wood ash). Avoid high nitrogen at this stage, as it will result in too much leafy growth and small bulbs.
- Final stage – Stop fertilizing when the bulbs are close to full size to allow them to mature naturally.
The Final Step: Knowing When and How to Harvest for Maximum Size
Harvesting onions at the right time is just as important as planting and caring for them. Picking them too early can result in small, underdeveloped bulbs, while waiting too long can lead to split or rotting onions.
Signs Your Onions Are Ready to Harvest
Onions are ready to be harvested when they show clear signs of maturity:
- The tops begin to yellow and fall over naturally – This signals that the plant has stopped growing and the bulbs have reached their full size.
- The necks (stems) become soft and start to dry out – A firm, thick neck means the onion is still actively growing. Wait until it feels soft and pliable before harvesting.
- The outer layers of the bulb begin to dry – Mature onions will develop thin, papery skins that help protect them for long-term storage.
If a frost is approaching, harvest onions even if they are not fully mature, as exposure to frost can ruin the bulbs.
How to Harvest Onions Without Damaging Them
- Gently loosen the soil around the bulbs using a trowel or garden fork.
- Pull onions straight out of the ground by gripping them near the base of the stem. Avoid twisting or yanking too hard.
- Lay the onions on the soil surface for a few hours to dry in the sun (if the weather is dry).
Curing Onions for Long-Term Storage
Proper curing helps onions develop a strong outer skin, extending their shelf life and preventing rot.
- Place onions in a warm, dry, well-ventilated area (such as a covered patio or garage) for 2 to 3 weeks.
- Arrange them in a single layer on a wire rack, screen, or even a breathable surface like newspaper.
- Once the tops are completely dry and papery, cut them off about 1 inch above the bulb.
- Trim any loose roots, but do not remove the outer skins.
Best Way to Store Onions for Months
Store cured onions in a cool, dark, dry place like a basement, pantry, or root cellar.
Use mesh bags, wooden crates, or hanging bundles to allow airflow and prevent mold.
Avoid storing onions in plastic bags or sealed containers, as they need airflow to stay fresh.
Properly cured and stored onions can last up to 6 months—giving you a steady supply of homegrown onions long after harvest.
Growing onions is simple, fun, and incredibly rewarding—so grab some seeds, plant them smart, and enjoy a huge harvest right from your own space.
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See you in the garden,
—Tara 🌿
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Tara Cunningham is the green-thumbed half of Lawnmowerfixed.com, where she shares simple, no-fuss gardening tips for time-poor homeowners.
She’s a lifelong plant lover with a soft spot for cherry tomatoes, shady corners, and low-maintenance herbs.