For home gardeners, there may be nothing more satisfying than picking that first warm, ripe tomato off a plant you started yourself from a tiny seed. It seems like a kind of miracle.
If you’ve never started seeds, don’t be intimidated. Following these simple rules can guarantee success even for rookies:
1. Choose easy-to-start annuals like marigolds, zinnias and tomatoes.
2. Start with good materials like sterile soil and clean pots.
3. Buy a shop light to provide bright light for seedlings.
4. Follow directions on seed packets, don’t let your enthusiasm run away with you, and never, ever overwater!
Not only will you save money by starting your own seeds, but you can try uncommon plant varieties that are hard to find or expensive to buy in nurseries. And starting plants inside gives you a jump on the season.
Sterile soil is necessary to minimize disease problems. Seed-starting mixes are good; they are light enough to prevent the sogginess that can lead to disease. You’ll need small, clean pots with drainage holes (and trays to catch the water) or clean plastic trays at least 2 inches deep to hold your soil and plants.
You can make your own pots by poking drainage holes in plastic yogurt or sour cream containers. Make sure there are enough holes so water drains quickly. Before using, sterilize containers by soaking them in a water bath with 10 percent bleach.
Seedlings will need a bright spot in which to grow. A south window may work if it is well-insulated from spring chills, but a shop or plant light is more reliable. Most seeds want bottom warmth to germinate. If you don’t want to spend money on commercial heat mats, placing trays on top of a radiator or next to a heat register also works.
Now for the fun part: choosing seeds! Big seeds are usually easier to start. Annual seeds like marigolds, zinnias, bachelor’s buttons, cosmos, morning glory and cleome are easy to handle and can be planted in mid-March. Seeds with very hard outsides, like morning glories, benefit from being nicked with a knife and soaked in water for 24 hours before they’re planted, to aid sprouting. Among vegetables, tomatoes and broccoli can be started indoors in the next few weeks.
This is where you need to temper your enthusiasm and look to directions on the backs of seed packets for guidance. While we’re all eager to start gardening, planting seeds too early will leave you with spindly, weak plants instead of sturdy, vigorous seedlings. Information on the seed packets will tell you when to plant seeds, how deep to plant them and how long it will be before seedlings pop out of the soil. Packets often direct gardeners to plant seeds “eight weeks before last frost date” or something similar. In the Twin Cities area, that means counting backward from about May 10, so mid-March is a perfect time to get started.
I cover newly planted seed trays with clear plastic wrap to conserve moisture. When seeds germinate, the plastic comes off. Marigolds pop up in just a few days, while many other seeds take up to two weeks. Again, pay attention to the directions on seed packets. Once when I had bad luck starting annual gomphrena (globe amaranth), I realized that my seeds should have been in total darkness to aid germination. I replanted, covered the pots with sheets of cardboard and had better luck the second time around.
Once your seedlings are up, move the trays to a bright spot or under lights that can be raised and lowered. To grow sturdy plants, lights should be 2 to 4 inches from the tops of seedlings and raised as the plants grow. If lights are too far above plants, your seedlings will stretch for the light, and stems will be weak. Lights should be on about 16 hours a day. Many plants need darkness each day, so putting the lights on a timer helps.
Watering at this stage is critical. Overly wet soil and low temperatures can lead to rot and disease, including “damping off” where stems darken and seedlings keel over. Ideally, plants should be in a location where the temperature is between 60 and 70 degrees. The safest way to water tiny seedlings is from the bottom, pouring lukewarm water into the tray and letting the potted seedlings suck the moisture up from below. Pour off any remaining water after about 15 minutes.
It’s fascinating to watch the plants grow. The first pair of “baby” leaves, the cotyledons, usually look plump and rounded. Then the true leaves emerge, and you recognize little marigolds or tomatoes. Give your plants room to grow by thinning plants to one per pot or one every couple of inches by pulling the weakest seedlings or cutting them off at soil level with a scissors.
Watch the temperatures. When you’re preparing to plant, let your seedlings adjust to the outside in a protected spot like the side of a house or garage that offers shelter from burning sun and wind blasts. In a few days you’ll see your plants grow visibly sturdier and tougher-looking, and you can move them to a more exposed location to harden off some more.
Then comes the best part. Plant!
The University of Minnesota Extension Service has a good guide to starting seeds indoors.
Mary Jane Smetanka is a Minneapolis freelance writer and a Hennepin County Master Gardener.