Transplants a grower’s own March madness

Posted Feb. 13, 2009, at 7:03 p.m.

March is almost upon us, the beginning of the gardening year for gardeners obsessed with growing their own seedlings of tomato, pepper, onion, sweet pea, nasturtium or any other variety not available as transplants at the local garden center. Growing your own is the only option.

But this madness — all of the effort associated with two months of indoor gardening, the watering, fertilizing, transplanting, adjusting lights, moving trays of plants to and from the porch, until finally the sturdy little transplants are set out into garden beds — may be more than a desire to try new varieties. When asked why we do it, Marjorie gives the only honest answer: You either start gardening in March or go insane.

Experience sets the schedule if you have been growing your own transplants for years. Newcomers should rely on the seed catalogs for planning information. For example, seeds of onions and peppers need a long time to germinate, so the seed catalog will tell you to sow onion seeds indoors in late February or early March, peppers eight weeks before transplanting outdoors. Producing sturdy tomato transplants, on the other hand, takes only five to six weeks.

Backward planning is the key. Identify the last frost date for your garden site and schedule the seed sowing based on the timing recommended by the seed catalog. Despite the incipient insanity, don’t start too early! The resulting pot-bound, leggy transplants will remain stunted after planting in the garden and produce poorly.

Here are some keys to success in growing your own:

— Seeds planted in cold, wet soils tend to germinate slowly if at all. Reduce germination time with bottom heat, maintaining a soil temperature between 65 and 70 degrees. Heating mats and soil thermometers are available from mail-order garden supply houses.

— Use a sterile growing mix with a starter nutrient charge and a wetting agent; I recommend Pro Mix. Wet the mix ahead of use to the moisture content of a wrung-out sponge.

— Use new or sterilized 2- to 3-inch peat pots or cell packs with similar size cells. Seeds and seedlings stay too wet for too long in larger pots.

— Sow two to three seeds per pot or cell, planning to thin to the sturdiest seedling after the first set of true leaves develop. Remove unwanted seedlings by cutting them at the soil surface rather than pulling them out.

— Sow the seeds on the surface of the growing mix and cover with a thin layer (about twice the diameter of the seed) of a fine-textured germinating mix such as Ready-Earth.

— After watering, cover the pots or cell packs with a loose layer of clear plastic (shrink wrap works well) to maintain uniform moisture.

— Once the seeds have germinated, remove the cover and the bottom heat. Optimum growing temperatures, both in the air and soil, are 65 degrees during the day, 60 degrees at night.

— Provide supplemental lighting as soon as the seedlings emerge; window light alone is too low in both duration and intensity. Standard fluorescent tubes are adequate. Keep the lights on for 14 hours each day, maintaining the tubes 2 to 4 inches above the growing seedlings.

— Water the pots gently and thoroughly as often as necessary to avoid excessive drying. Be careful, however, not to keep them too wet; let the surface of the soil dry between watering. When you do water, use a half-strength solution of water-soluble fertilizer to provide essential nutrients. Water from above to leach excess nutrients from the pot.

— Before transplanting your seedlings to the garden, they must be hardened off with a slow transition to outdoor conditions. Begin by setting them outside (temperature above 45 degrees) in partial shade for one or two hours per day, gradually increasing both the light and the length of exposure over a two-week period.

Additional tips and suggestions are contained in an online publication, Starting Seeds at Home, available at University of Maine Cooperative Extension’s Web site, http://extensionpubs.umext.maine.edu/.

Send queries to Gardening Questions, P.O. Box 418, Ellsworth 04605, or to rmanley@shead.org. Include name, address and telephone number.

PHOTO COURTESY OF NATIONAL GARDEN BUREAU

Growing your own sweet pea transplants results in earlier spring flowers.

March Madness: Growing Your Own Garden Transplants

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