Note: This article explains how to start onion seeds using a heat mat and shallow pots. To read about how to start seeds in deep pots, without heat mats, CLICK HERE).
|Onions going to seed.
- Sifted potting mix
- Sand (optional)
- Pots: We used to use rather large pots (4" x 6" deep - 25 seeds per pot) but have shifted to using tofu containers with holes drilled in the bottom (see picture below), or jumbo six-packs. These use less soil for the same amount of seeds.
- Seeds: start with fresh seeds each year; onion seeds lose viability within one or two years. If you wish to save seed, choose Heirloom/Open Pollinated varieties. Choose a variety appropriate to the length of your summer days.
- Greenhouse or grow-lights
- Heat mat (seeds will germinate better with a little bottom heat).
Pots: If you will need to wait more than 8-10 weeks, to transplant the seedlings into their permanent growing space, follow this guide for planting in 4"x 6" pots. This way you won't run the risk of the onions becoming root-bound before you transplant them.
Soil/Sand: Start with a good organic seed-starting mix. It doesn’t need to be a premium potting blend, in fact, if you start with too rich of a soil blend you can experience a condition referred to as ‘damping off’ which looks like algae or mold growing on the surface and which causes the young seedlings to rot as they emerge from the soil. One way to help eliminate this condition is to sprinkle a thin layer of sand over the seeds. By keeping the soil damp but not too wet and having good ventilation you shouldn’t have this problem.
|Onion seeds can be started in a variety of containers.
Seeds: You may want to actually count out the seeds the first time so that you can have an idea of what 25 - 35 seeds looks like because that is about how many would be optimal to sew in the tofu-containers or six-packs. You can adjust up or down depending on the size container you choose. The idea is to not have an overcrowded condition that would produce weak and unhealthy seedlings. Place the seeds in the palm of your hand and pinch out a few at a time. Gently drop them on the surface of the soil, distributing them as evenly as you can without becoming too concerned about accuracy. It’s OK if some seeds are touching each other. Sprinkle a sifted layer of starting mix or sand over the seeds at a depth of about an eighth to a quarter inch. Tamp it down again and water gently (a planter mister works great at this stage).
Watering: Keep the soil moist using either a small spray bottle or water them from below by putting water in trays and setting pots in them (light watering minimizes 'damping off' too). Tiny seeds, until established can be washed away with more aggressive watering techniques. Do not over-water! Soil should be damp but seedlings should never be in standing water.
|Teasing onion-roots apart before trimming.
First, dump the whole pot into the palm of your hand. Next, separate the clump into several sections (maybe 10-12 seedlings in each clump). Hold one clump by its 'greens' and gently tap the root ball until most of the soil has fallen away. Tease the seedlings apart and lay them back in your hand so that the small bulbs are in a line (see picture below). Using a scissors or hand pruner, cut away the tips of the roots, so they'll easily slip into the soil. Trim the tops to about the same length as the roots. Now set the clump into another shallow container with a little water in the bottom to keep them from drying out while you prepare the rest for transplanting. Prepare only as many as you are able to transplant in one session. If you end up with extras, surround their roots with some moist soil and keep them in the shade until you have time to get them in the ground.
|Trim roots and greens to same length.
Make holes: To make the holes you can fashion a planting stick called a ‘dibble’ from a smooth branch or a ¾ in dowel with a point or, just use a ‘Sharpie pen’, or even your finger to make the hole. Be systematic: make 5-10 holes and then go back and drop a single onion in each hole. Gently press the roots into the hole and pinch the soil around each one, making sure the part that was under the soil in the pot is covered when you transplant, leaving only the green top and a tiny bit of the bulb showing. Be sure that all the roots go in the hole and don't "J-root": with bits of the roots poking out from the soil; this will dry out the plant and force it to use extra energy in turning its roots back down into the soil. You’ll get the hang of it after a few tries and be able to transplant hundreds in no time at all!
|Onions in a wide bed.
If you have planted non-hybrid seeds, hold back a few onions to replant next spring to save seed. Onions are biennial meaning they don't produce seed till their second year. By collecting your own seeds you can begin the process all over again, and saving seeds, dear friends, is one big step toward greater food security!
Link to another post we wrote about onion-growing.