Onions

Bulbing onions can be grown from ‘sets’ which are small bulbs sold in bags, ‘starts’ which are small pre-started onion plants, or from seed. Sets are easy to work with but they may not produce bulbs as large as onions grown from starts and seeds and may bolt prematurely. Starts are also easy to grow, however if you’re comfortable starting seeds indoors onion seeds are an economical and easy way to get started! Green onions are typically started from seed. Bulbing onions can be direct seeded in the garden but since they are slow-growing and germination can be spotty most gardeners prefer to start them indoors. Green onions can be direct seeded with greater success. Some gardeners like to start their bulbing onion seeds extremely early to get the largest possible bulbs. Onion seeds only remain viable for about 1-2 years; use fresh seed for greater success. After sowing the seeds, keep the seed starting mix consistently moist. A heat mat may be helpful for germination. Provide supplemental light as soon as seedlings emerge. Some growers trim the tops of the onion seedlings to around to 4-5 inches (10-12 cm) prior to hardening off to encourage stockier plants that are easier to transplant.

Onions prefer loamy, well-drained soil. Heavy clay soils can negatively impact bulb development in bulbing onions and soils that become waterlogged may lead to bulb rot. Work compost into the soil prior to planting. Onion sets can be planted as soon as the soil is workable in spring. Starts or seedlings can be transplanted after they are hardened off and once the risk of heavy frosts has passed. Young onions that are exposed to temperatures below 45°F (7°C) for an extended period of time may bolt prematurely.

Onions are heavy feeders, however with bulbing onions excessive nitrogen can delay maturity and negatively affect bulb quality. Fertilize regularly during the growing season with a balanced fertilizer. Stop watering and fertilizing bulbing onions when the plants start to mature (when the tops start to yellow and fall over)- about 1-2 weeks before harvesting.

Green onions are ready for harvest once they have reached the desired size- generally about 6-8" tall (15-20 cm). Green onions mature much more quickly than bulbing onions. Pull them out of the soil by holding near the base of the stalk. If you have clumps of green onions you can pull out more than one at a time. Trim the roots and peel off any dry or yellow outer leaves. Wash off loose dirt before storing.

Bulbing onions can be harvested and used at any stage of growth, but only fully mature onions can be cured and stored. If you see a flower head starting to form on an onion, harvest and use it right away as it will not keep. Onions are mature and ready to harvest when at least half of the tops are falling over and yellowed. Harvest when the soil is dry as harvesting on a wet day can prevent onions from curing properly. Pull onions out by their tops or if needed use a garden fork to carefully loosen the soil first without piercing the bulb. Onions should be harvested out once they have matured. Mature onions may spoil if left in the ground too long. Brush off any loose dirt from the roots.

Green onions can be stored in the fridge for up to several weeks or chopped and frozen in an airtight container or freezer-safe bag for up to several months. They can also be dehydrated for long-term storage.

Bulbing onions are usually cured for long-term storage. Some gardeners will cure onions by leaving them on the ground in warm, sunny conditions but if possible it's preferable to dry them indoors in a warm, dry, well-ventilated area. Ensure there is good airflow around each bulb. Bulbs are cured when the necks are completely dry; this will take about 2-4 weeks. Once cured the onion stems can be braided or cut off.

Cured onions can be stored in a cool, dark, dry place for up to several months. They should not be kept in the fridge unless they are cut or uncured. Use refrigerated onions within a week or two. Do not store onions in your basement if it is humid. Onions shouldn't be stored with potatoes (or other produce), as moisture and gases can be released that negatively impact self life. To freeze onions first peel and chop them then blanch them in boiling water. Cool the onions then freeze them in handy portion sizes in bags or airtight containers. Onions can be kept frozen for up to several months. Frozen onions are usually used in cooked dishes as they will not be as crisp as fresh onions. Onions can also be pickled.