close-up of growing onion plantation in the vegetable garden

There are 2 distinct ways to start growing onions; seeds or collections. Sow oignon seeds in January or February; mild winter areas will also be able to start planting in the autumn. Exotic youthful sets (also called seedlings or bulbs) outside in April or May or when soil temperatures reach a continuous 55F.

Onion Bulbs

The ability for the onion bulb to form is determined by the amount of day; longer, warmer days promote bulbing. Bulb development won’t occur in colder weather however long the day.

Types of blossoms


the best alternative for Northern gardeners. Longer summertime (15+ hours during the summer months) supply the required day length for bulb growth.


the best alternative for those gardening in the middle-section of america. 14 hours of daylight is required to induce bulbing.


best for Southern climates that only need 8-12 hours each day to activate bulbing.

Note: Your seed/set provider is a good source for other questions regarding onions on your region

Où planter

Onions grow best in full sun, although in the heat of the summer, a little shade is desired since it will delay the plant out of seeding too fast. Plant your onions behind a taller crop (berries are a great choice), since they can offer a shade on hot mid-summer days.

Préparation du sol

The fewer rocks on the soil, the better. Rocks cause deformities in the onion bulb’s development. To enhance heavy soil, loosen the soil at least 18″ down and mix in well rotted manure, compost, shredded leaves or other organic matter.

Preapare the soil

      • Onions prefer slightly acidic soil with a pH of 6.6-6.8.
      • Sandy loam soil is great when mineral material is high. Avoid planting in clay soil.
      • Soil needs to be non-crusting so bulbs do not”cement in” and stunt development. Keep your soil moist for best results.
      • If your soil is potassium deficient, your blossoms will store badly; if your soil is phosphorus deficient, your blossoms will have thick necks and smaller bulbs; and too much nitrogen will postpone the bulb’s growth, and stop supplementing nitrogen when the bulbs start to form.
      • For sweeter onions, prevent gypsum fertilizers (which contain sulfur)

Semences et germination

Growing onions from seed gives the most number but can take up to five months to grow and the plants are more prone to disease than sets.

Using fresh onion seeds is important; if not kept dry and cool, they lose viability quickly. Onion seed viability is about 1 year in cool, dry storage.

Germination occurs at temperatures 50-95F, with the optimum temperature around 75F for fastest germination.

Getting started indoors

      • (and transplanting). Start your seeds indoors AT LEAST 8 weeks before the last frost.
      • If indoor growing space is limited, plant seeds 1/4″ apart in apartments; leave onions in apartments until outside planting.
      • In the first growth phase, young plants grow best in cool temperatures around 60F
      • Keep temperatures below 70F during the day and about 50F at night.

Sowing and growing – Outdoors

      • Planting seeds directly into the backyard. Onion sets are easier to plant than seeds, and accessibility of varieties may be restricted
      • When planting in fall or spring, loosen the dirt well. Push bulbs to the soft dirt just far enough to fasten in place but do not cover the tops.
      • Early weed control is very important to the health and evolution of onion starts. Take care not to disturb the onion’s roots when pulling weeds. Pulling weeds too near the bulb can pull the onion start in the floor.
      • Consistent weeding is suggested to keep the weeds from growing big; if you discover a large pot, clip it at ground level if it is too near a bulb.
      • For direct-to-ground seeding, the most seed thickness shouldn’t exceed 1/2″ (1/4″ in heavy soil).
      • When planting in rows, thin the onions to 4″ apart.
      • As top spears become thick like chives, crop early shoots for green onions.
      • Another choice for growing onions would be to sow your transplants or sets in a grid formation with sufficient room for effortless farming (think of a tick-tack-toe grid).
      • While the day span remains consistent from year to year, soil and air temperature will be different. This might affect your crop quality.

On a Personal Note: I’ve successfully developed onion sets from the seeds of rare Italian varieties like Yellow of Parma, Red of Florence, and Bianca Di Maggio. Perpetuating these old world onions maintain a history and a taste well worth preserving!


Keep soil moist, but not soggy from planting through harvest. Once outside, onion plants require 1″ of water each day with occasional heavier applications throughout the entire year.

Growing onions are prone to disease when their tops are moist. If you can, use a soaker hose to keep the water onto the floor and away from the leaves.

If overhead watering is the only alternative, water in the morning so the leaves have enough time to dry out completely before day.

Plantation d'accompagnement/rotation

Onions planted among carrots are observed to repel carrot flies. Some anglers have reported an improved flavor in onions when planted with summer savory and chamomile.

Most problems with growing blossoms can be lessened (both pests and diseases) by 1) frequently rotating your harvest ( not planting in precisely the identical place as the previous year), 2) applying row covers immediately after planting to maintain onion maggots from getting plants, and 3) by controlling the weeds, which also lowers the breeding ground for insects.

Onions can be chosen early for green onions.

Harvesting mature onions

Once the tops of most of your onions start to fall over, mark the day in your calendar and stop all watering; following fourteen days, harvest your own onions.

Be careful not to bruise or hurt bulbs with your spade. It shortens the shelf-life of onions, causing them to rot more quickly (such as an apple or a peach would).