Tips for germinating seeds yourself and growing healthy garden-starts
STORY BY JOSH VOLK
Now that winter is on its way out, and spring is on its way in, the days are getting longer, and any sun we see is higher in the sky, slowly warming the soil. For growers, it’s the time to switch from planning mode to planting mode. You’ve selected exciting seed varieties, now you need to plant them, and you want to do everything you can to get them off to a good start.
As a long-time market gardener, I’m constantly pushing the boundaries, and that has helped me learn more about what extremes seeds will germinate and thrive in, and how to shape the environment around them to set them up for success.
On the farm, we’re seeding pretty much every week from February through July, breaking up the work into small chunks, and constantly making adjustments based on what worked and what didn’t the week before. Seed a little every week or two, and you’ll get much better results than seeding all at once.
Most of that seeding is happening in a greenhouse, where we can better control the temperature, moisture, and soil. As a home gardener, you can let your local nursery do that seeding for you and then buy the starts, but starting your own ultimately gives you much more control over the varieties you grow — and when they’re ready to plant.
Pay attention to the soil temperature. Ideal soil temperatures for germination vary by seed type: Some prefer 60°–70°F, some like 70°–80°F, but in general, they’ll all germinate well around 70°F. Johnny’s Selected Seeds catalog has excellent graphs of optimal temperature ranges for seed germination by crop type, and it’s my go-to source for that information.
In the greenhouse, or even in your home, one of the simplest ways to get the right soil temperature is to use an electric heat mat, under your plug trays, combined with a thermostat that has a soil temperature probe. Set the thermostat to 70°F and stick the probe into the soil where you’re germinating the seed. The thermostat will turn the heat mat on to warm up the soil any time the soil temperature falls below 70. You can buy a quality, basic set-up that will last for years for less than $80. That might be a big investment if you’re only growing a few starts every year, but it is definitely worth the money if you’re serious about starting lots of seeds indoors.
Some seeds prefer to be sown outside. These are mostly roots, like carrots, beets, and salad turnips, but also baby salad greens and other thickly-sown crops. When sowing seeds outside, there are a few tricks to improving germination. One is paying close attention to the weather. In the cool, wet spring, I like to sow seeds at the beginning of a sunny, dry streak. Even a few days of sun helps warm the soil a bit as the seeds try to germinate, and the dry weather keeps the seeds from getting too saturated with water. In the summer, I look for the opposite: a streak of cloudy or drizzly days when the already-warmed soil will stay moist while the seeds are germinating.
Outdoors, it’s very hard to get the ideal soil temperature, but even small changes in soil temperature make a big difference. I can help influence the temperature with plastic film. Covering the soil with clear plastic in the early season warms up the soil significantly, protects it from rain, but keeps it moist – a good thing just before, and for a few days after, seeding. But make sure to remove the plastic before the seedlings poke through the soil surface. In the summer, covering with black plastic for a few days after seeding keeps the soil temperature cooler and moist all the way to the surface.
The simplest trick when seeding outside is to “firm the soil” in the freshly seeded row. Hand-propelled push seeders have a “press” wheel on the back to do this, but in the garden, I just do it with the back of my hoe or rake. This puts the soil in good contact with the seed, allowing it to transfer warmth and water more effectively. Conversely, loosening the soil surface inhibits germination, a good thing to do wherever you don’t want weed seeds germinating.
My last tip is to expect less than perfect germination. In the greenhouse, with excellent seed, sometimes we get germination rates in the 90%-plus range, but often we see trays with lower rates, and when you’re just starting out, 60% might not be that bad. In the field, I never expect much more than 50% of the seeds to germinate, and if I’m pushing the limits of early, cold soil, I expect as little as 25%, meaning I put down 4 times as many seeds as the number of plants I ultimately want. As with everything, practice makes perfect — or at least better — so get out there and seed regularly, pay attention to what works for you and what doesn’t, and have fun with it.
Once you get set up to grow indoors, it’s quite easy. But there is some initial investment required to prepare a proper space with the necessary conditions, and there is a bit of a learning curve when it comes to watering and plant care.
Containers: Plug trays are pretty standard on farms because they’re quick and easy, but any container will do as long as it has a bit of drainage and it holds enough soil. For just a few plants, paper pots are a nearly cost-free way to make your own containers of any size.
Soil: Buying an organic “potting mix” and mixing that with some balanced organic fertilizer (about 2 cups of something like a 7-3-5 with a 2 cubic-foot bag) is an easy way to get started. I’ve also used a mix of well-aged, sifted compost and garden soil with good results.
Watering: I really like a Haws watering rose that gives gentle overhead water, but there are many suitable cans and hose ends out there. What’s important is to not water too often, but to also never let the soil completely dry out. When you do water, make sure to soak the soil slowly so that all of the soil in the plug is saturated and just a little is starting to leak out the drain hole. Usually, watering once a day is enough, but sometimes a little more often or a little less, depending on the weather and the plant size.
Light: A common problem I see with homegrown starts is lack of light, which leads to elongated plants reaching for the light. A sunny window isn’t usually enough in our overcast climate. Use mirrors or foil-backed boards to reflect light back at the plants if they’re sitting in a window, or set up fluorescent bulbs as close as you can to the plants, within less than an inch! No need to buy special grow lights — simple shop lights will do.
Josh Volk is the author of the book Compact Farms. He writes from a desk that looks out over his garden, farms in Portland at Cully Neighborhood Farm, and travels around the country speaking to farmers and gardeners. You can find more about Josh at slowhandfarm.com.