February: Starting your garden from seed: how and when
It is easy to grow your own plants from seed. By starting your own seedlings you can choose from hundreds of varieties that are not available in garden centers. The cost of plants will be far less than those sold in nurseries. You can also have transplants ready to go into the garden at any time you choose.
Some plants are easy to start from seed. If you are new to seed starting, here’s a list of flowers and vegetables that are very easy to start from seed:
Flowers: alyssum, cosmos, marigolds, Shasta daisies, and zinnias.
Vegetables: broccoli, Brussels sprouts, cabbage, leeks, lettuce, onions, peppers, and tomatoes.
Here are the essentials for starting seeds indoors: containers, seed-starting mix (not soil), light source, heat source, water, labels and markers.
Containers: Choose from plastic seed-starting kits (bottom trays, divided plastic containers, sometimes called six-packs, and clear plastic humidity dome covers), undivided shallow wooden or plastic trays, called flats, peat or coir pots, Jiffy pellets, egg cartons, yogurt cups or cottage cheese and butter tubs (be sure to cut drainage holes in the bottom of plastic containers), or paper pots.
Germination mix: Prepackaged soil-free seed-starting mix or a homemade mix of 1 part fine sphagnum peat moss and 1 part vermiculite or perlite (1:1 ratio). A soil-free mix should be sterile (pathogen free), light, and loose to avoid compaction, and should absorb water easily but allow excess moisture to drain away quickly. When seedlings are ready to be transferred to a larger pot, switch to a potting soil.
Labels and markers: Wooden or plastic labels, permanent markers, pencils, crayons, or grease markers.
Light source: Grow lights, cool white bulbs in fluorescent light fixtures, south- or south-east-facing window. Because few windowsills get enough light to grow seedlings, your best choice is to use two 4-foot-long fluorescent tubes (“shop lites”) – one “warm white” and one “cool white” tube suspended in an adjustable fixture that will allow the lights to be suspended two-inches above the seed-starting mix and later above the growing seedlings.
Heat source: Germination heat mat. Most seedlings germinate quickest in warm soil (70° to 75°F/21° to 24°C); set your containers on top of the heating mat or cables and use a thermostat to switch the heat on and off automatically.
Water: Use spring water, non-chlorinated tap water, or rainwater. Use a rigid clear plastic dome or clear plastic bag to maintain high humidity before germination. Use a watering can with small-holed sprinkling head or use a spray bottle or spray wand that delivers fine droplets of water. Don’t spray directly with a hose.
Fertilizer: Seedlings growing in a soil-free starting mix or lean potting mix will need a small amount of plant food when the first true leaves develop. For the first three weeks after true leaves develop, feed young seedlings once a week using a half-strength solution of fish or seaweed fertilizer, compost tea, or a liquid organic fertilizer specially formulated for seedlings.
When to start seedsTo know when to start the seeds for your garden, you first have to know the date of the last expected frost in your garden. On average, the last frost in the Sonoma Valley comes in early May each year. After the 15th of May you can reasonably expect that frost will not hit your garden and kill young plants.
From May 15 you can count backward, using the seed-to-transplant time given on your seed packets or in seed catalogs to know when to start seeds indoors. For example, young tomato plants should not go into your garden unprotected until after the last frost and most seed companies recommend that seedlings be eight weeks old when they are transplanted into the garden; therefore, counting back from May 15 eight weeks, sow tomato seeds indoors about March 15.
It’s that simple!
If you decide to start plants from seed later in the year, you should know the date of the first frost in fall, so that your plants can mature before that date. On average the first frost in the Sonoma Valley comes about Nov. 15 each year. To enjoy annual flowers and vegetables later in the year, count back from Nov. 15 the number of weeks recommended on the seed packet and then add a couple of more weeks to compensate for slower growth late in the season.
Steve Albert is the author of The Kitchen Garden Grower’s Guide available at Amazon.com. He teaches in the landscape design program at the U.C. Berkeley Extension. He lives in Oakmont.