Starting Onions from Seed in My Greenhouse

February 21, 2017

Starting Onions from Seed in My Greenhouse

Here at my Bedford, New York farm, patches of snow still cover the ground, but inside my greenhouse, there is a flurry of spring activity - my gardeners, Ryan and Wilmer, are busy repotting, transplanting, and starting vegetables from seed in preparation for the coming growing season.

Starting onions from seed isn’t difficult. They can be planted closely together in seed starting trays, and because they are shallow-rooted, they can be pulled apart easily when ready for transplanting outdoors. Many of our seed trays and supplies are from Johnny’s Selected Seeds - we've been using Johnny's for years. Over the last few weeks, our onion seeds have grown about four or five inches tall. They’ll remain in the greenhouse for a several more weeks until they’re planted in my vegetable garden. And by mid-summer, we will have lots and lots of beautiful, fat bulbs to harvest.

Enjoy these photos…

: Johnny’s Selected Seeds, in Albion, Maine, carries hundreds of varieties of certified organic vegetable, herb, flower, and fruit seeds. We chose several onion varieties. http://www.johnnyseeds.com/

: Seed starting trays come in all different sizes and depths. We use trays with shallow compartments for planting onion seeds.

: Ryan fills the seed starting tray with mix and pats it down lightly into each compartment. The mix should be level with the top of the tray.

: It’s best to use a pre-made seed starting mix that contains the proper amounts of vermiculite, perlite and peat moss. Seed starting mixes are available at garden supply stores.

: Ryan labels the seed markers and keeps them together with the matching packets.

: To create a quarter-inch deep furrow in the middle of each compartment, Ryan places one tray over another and presses down lightly, so the bottom of one tray makes indentations in the soil-filled compartments of the other.

: You can see the small indentations in each compartment – this is where the seeds will be planted. This is a great method when planting multiple trays.

: These onion seeds were started in early February, which is about two months before the last frost in this area.

: Using a hand seed sower, such as this one from Johnny’s Selected Seeds, pour a generous amount of seeds into the center dish.

: Ryan screws the plastic top onto the hand seed sower and adjusts the amount of seeds that will be released at one time.

: Ryan begins to drop onion seeds evenly into each compartment.

: It is good to start larger onions from seed, so they can be harvested the same year. Smaller onions can be planted directly into the ground.

: Red Hawk onions are medium to large in size with a bold red color.

: Great Western onions have brown skin and firm bulbs that are quite large.

: Cortland onions are large, blocky-round with thin necks that will dry well. They also have thick, rich brown skin for good storability.

: One to two seeds are dropped into each compartment and will be selectively thinned in a few weeks. This process eliminates the weaker sprout and prevents overcrowding, so seedlings don’t have any competition for soil nutrients or room to mature.

: Once the seeds are dropped, Ryan adds an additional light layer of soil mix, so the seeds are completely covered. Be sure to insert the appropriate labels, so there’s no confusion later.

: Ryan does this carefully, so as not to move any of the seeds in the tray.

: When possible, prepare several trays in an assembly-line fashion, and then drop all the seeds. Doing this saves time and simplifies the process.

: Fortunately, my greenhouse is large and can accommodate lots of seed starting.

: Here we panted white onions – the White Castle have excellent color and disease resistance. They are jumbo, globe-shaped bulbs with bright white skins. Wooden markers or popsicle sticks work well for labeling trays. Write the onion variety on one side and the date they were sown on the other.

: Once the seed trays are done, Ryan takes them to the greenhouse where they will get ample light and heat.

: We love these heat mats. Heat mats increase germination rates and allow temperature control.

: Ryan gives them a good drink of water.

: And then covers them with plastic humidity domes. The humidity dome remains positioned over the seed tray until germination begins.

: Keep seed starting trays moist and in a warm, sunny place. Here is how the onion seeds look a couple weeks after planting.

: Here are some other seedlings more than a month after planting. These seedlings will remain in the greenhouse for another four to six weeks until they are ready to be separated and transplanted into the ground.