Thursday, March 20, 2014

First Day of Spring: Starting Seeds Indoors

starting-seeds-indoorsEven while we remain snowbound, the days are growing longer and the sun is getting higher; robins are singing, and there’s a good chance spring will come sometime in 2014. For those who still believe in spring, late March is the time to start planting vegetable and flower seeds indoors.

Raising your own plants gives you the option to pick unusual varieties not available commercially in the spring, and it’s a lot cheaper than buying transplants. For kids it can be a fun activity, and for the rest of us it’s at least in part about seeds of change; a sign we believe growth and change are possible despite a bleak forecast.

Considerations for starting plants indoors are timing, containers, growing media, light, water and temperature. Seeds are helpful, of course, as are seed-packet instructions, which tell you how long before the last average frost date you should sow seeds indoors. The problem is that this varies from the average last frost date of May 3 in one area, but in another it’s May 30;  many old-timers still consider Memorial Day the time to set out plants. You can search by ZIP code for last frost dates online.

Any container at least three inches deep will work to start seeds if there are holes in the bottom for water drainage. Reusing commercial cell packs from garden centers is great, but it’s good to rinse them in a 10% bleach solution to reduce the incidence of damping-off and other diseases.

US_py_med_ml32Garden soils often harbor disease spores that can kill seedlings in an indoor environment, and a sterile “soil-less” growing medium from a garden center is a good investment. These mixes usually contain peat moss, minerals such as perlite and vermiculite for good aeration and water retention, and sometimes a slow-release fertilizer. Plant a few more seeds than you need in case not all germinate—you can always thin them later—and don’t forget to label each container or tray.

Because direct light is critical, even a large south-facing window is not really enough for indoor starts, which will become leggy and be prone to breakage without additional light. Ordinary 40-watt fluorescent tubes are just as good as expensive grow lights as long as you pair a cool-white tube with a warm-white tube in each fixture. Lights should be suspended between two and four inches above the foliage, and should be on for 12-16 hours a day.

Temperature is important, especially during germination when soil should be kept at 70-75F. Keep containers off windowsills during germination, as nighttime cold can lead to seed rot and poor germination.

Once the seedlings are up, cool-season plants like lettuce, onion and cabbage-family crops do better at 55-60 degrees, whereas warm-season plants like tomatoes, squash and marigolds prefer it 65-70F.

Pay attention to watering—small containers dry out quickly. The medium should be kept moist yet not waterlogged. Bottom-watering is best, but containers shouldn’t sit in water for over an hour.

After the first set of true leaves appear, you can add water-soluble fertilizer at half-strength every 2-3 weeks. When the second set of true leaves develop, you can transplant to larger containers. Then a couple of weeks before last frost, begin to harden off seedlings. Set them outside in a sheltered, partly shaded spot on calm warm days, starting with a few hours at first, and gradually work up to full days.

Take heart—it won’t be snow pea and iceberg lettuce weather for much longer. May the seeds of hope, whether figurative or literal, sprout and thrive in your home this late winter.


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Paul Hetzler has been an ISA Certified Arborist since 1996. His work has appeared in the medical journal The Lancet, as well as Highlights for Children Magazine.You can read more of his work at or by picking up a copy of his book Shady Characters: Plant Vampires, Caterpillar Soup, Leprechaun Trees and Other Hilarities of the Natural World

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