To trim or not to trim onion seedlings before planting? Ask an Extension expert

Gardening season is starting to wind down, but there’s some things still do, and you may have questions. To ask one, simply go to the OSU Extension website, type it in and include the county where you live. A photo is very helpful.

Q: Is it advisable, or bad to trim onion seedling roots and tops prior to transplanting?

I like to get a jump on spring planting by starting seeds indoors. Often the weather here in Douglas County is warm enough to get started in the garden but the ground is too wet to work. When I get a day or two of dry weather I can poke seedlings into the garden with little trouble, especially if I use old planks to disperse weight but it is still too wet to work the soil with a shovel and rake to plant seeds. I know if I wait too long and start from seed, I do get smaller bulbs. Several web sites encourage trimming of onion seedlings as they grow and then trimming roots at planting. Others discourage it or claim it does not help or can reduce the overall size of the bulbs.

Can I improve my onion seedling survival if I trim? Would seed do better to overwinter in the ground? What is your advice for preparing/planting onion seedlings? How do most market farmers plant onions here in Oregon, from seed or seedling? – Douglas County

A: You can grow your own transplants by seeding in pots and transplant your onions in the spring when the plants are about 6 inches tall and soils have warmed up. This method allows you to choose from many different varieties, produces the best bulbs for storage and is the cheapest method of all. Start your onion seedlings indoors in February or March. Fill a container nearly to the top with a seed starting mix and then make two furrows, about 1/2-inch deep, for the onion seeds. Sprinkle seeds in the furrows and cover them lightly with more soil mix. Label the container with the name of the onion variety. Keep the container in a warm place.

Once the onion seeds germinate, keep the young plants in a sunny south window or greenhouse. You may need to trim the tops to keep them at about 6-8 inches. Do not trim the roots when transplanting.

The varieties of onions that grow best in our area are: Long-day varieties include Walla Walla (not good for long-term storage), Redwing, Ailsa Craig, Ruby Ring, Copra, Patterson, Cortland, Talon and Red Bull.

Onions grow best in full sunlight and well-drained soil. Before planting incorporate 4-6 inches of well-composted organic matter and an all-purpose fertilizer to a depth of 6-8 inches. Use a liquid fertilizer every couple of weeks during the growing season. Onions require regular watering. Watering once a week usually is enough in the spring, but you may need to water more often during dry weather. Water your onions slowly and deeply to help grow strong, healthy roots. Stop watering when the plants begin to mature to help the curing process. Organic mulches help conserve water, supply extra nutrients and reduce weeding.

Onions vary in their maturity times. Green onions may be harvested as early as 50 days after seeding. Bulb onions generally require 100-120 days to mature. Leave bulb onions in the ground until the tops fall over. Once the tops fall over, lift the bulbs but let them dry or cure for another two to three weeks before placing them into storage. – Chris Rusch, OSU Extension Master Gardener