The lovely thing about sowing annual flowers from seed is that there’s such as wide choice of colors and varieties. The sad thing is that in my Chicago climate, seeds sowed after the last average frost date, while the soil is still cool, will take weeks to sprout and get going. There isn’t enough time in the growing season for me to get all the color I feel entitled to.
The solution is to start the seeds indoors under lights or in a conservatory so they get a head start inside where it’s warm. Seeds sowed about six weeks before the last frost—about the first of April where I garden—should be ready to transplant outdoors in mid- to late May, about the same time as tomatoes.
I always use a soilless seed-starting mix. It’s like potting mix, but sifted for a finer texture, and sterilized to reduce the risk of fungal disease that can wipe out seedlings.
I like to use peat pots or make my own little seed-starting pots out of newspaper about 2 inches in diameter. I’ll be able to transplant the entire biodegradable pot without disturbing the seedlings’ delicate roots. If I poke some holes in the pot, the roots will find their way out and the pot will decay away.
Until the seeds sprout, I’ll use a spray bottle of water to keep the top of the growing medium moist. Then I’ll switch to watering from the bottom until transplant time, so it’s important to set the seeds in a waterproof tray before I plant any seeds.
When starting seeds under LED or fluorescent lights or in a conservatory, it’s important to make sure the light is distributed evenly, or the seedlings will stretch toward it. If I sow seeds in individual pots rather than trays, I have more control; I can rotate them or switch them around to make sure all the seedlings grow up straight.
The seeds of some species, such as cleome and alyssum, need to be exposed to light to germinate, so I can sow them right on top of moist seed-starting mix. Others are best covered about 1/4 inch deep, such as cosmos, zinnias, bachelor’s buttons and marigolds. Nasturtium seed are usually planted even deeper, up to an inch. Of course the seed packet is the final law on how to sow any seeds.
Globe amaranth will germinate better if you soak them in water for a couple of days before you sow them. The same is true of morning glories, but I’ve quit growingthem because they reseed too widely.
If I lived in a climate with a longer growing season, I’d be able to sow these seeds right into the soil in a careless array of color. Growing them indoors under lights is my way to pretend I have that kind of garden.