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Grow Your Own Transplants
by Dr. Vern Grubinger
March 7, 2004

Growing your own transplants gives you a jump on the joys of spring and is a lot thriftier than buying all those six-packs of tomatoes come Memorial Day. Of course, if you're like me, you'll grow some, then buy some more!

Transplants are great for getting the garden off to a fast start, making the most of a short growing season. Using transplants instead of direct seeding also is a good way to beat weeds and insects to the punch by starting with a larger plant.

By growing your own transplants at home, you can pick exactly which varieties you want from the array of seed packets that are offered in catalogs and at garden stores. However, to end up with healthy seedlings, you must give them the right soil, moisture, light, and temperature.

Do not start your transplants in ordinary garden soil. Most soils are too dense for good seedling root growth. Many contain fungal organisms that can lead to disease. The most common seedling disease is called damping off, which causes newly sprouted plants to rot at the soil line and keel over.

The best soil for starting plants is often called "potting mix." These mixes usually are a soil-less mix of peat moss, vermiculite, and perlite with a small amount of fertilizer added to help young plants along.

Peat consists of decomposed plants and generally is free of weed seeds and disease organisms, as are vermiculite and perlite, which are made up of minerals. There also are some high quality potting mixes made with compost, peat, and natural fertilizers that have been formulated for organic growers.

Both soil-less and compost-based potting mixes are available at garden stores. They are well aerated and better able to retain water than ordinary soil. They provide more nutrients for seedling growth, but to perform well they need to be properly managed once seeds have been sown.

Potting mix should be placed in containers that will allow for plenty of root growth before plants are set outside. If the container is too small, the seedlings will get root bound and growth may be stunted later. Before seeds are planted, the potting mix should be thoroughly wetted. This may require some mixing, especially with soil-less mixes.

After that, keep the mix from drying out, but take care not to overwater because potting mixes will not require watering as frequently as you might expect, especially while seedlings are small. Overwatering seedlings can lead to poor growth. Water only when the mix begins to feel dry to the touch beneath the surface.

Getting seeds to germinate requires warmth--about 75 degrees F is ideal for most seeds. Be sure to pre-warm your flats of soil mix before planting the seeds. Heating mats are available that will maintain the flats at a warm consistent temperature.

You also can use an electric heater with a thermostat to keep a small room consistently warm to promote seed germination. Or section off a "grow-room" from a larger room by hanging walls of plastic from the ceiling to save on heating costs. Avoid putting flats on radiators as they may dry out very quickly.

Seeds do not require light to germinate, but once the plants emerge from the soil, high light intensity is needed to keep them short and stocky. In early spring, because natural light intensity is low, supplemental lighting usually is required to keep plants, even those growing by a window, from getting leggy.

The most effective and inexpensive way to light your plants is with "shop lights" that contain 40-watt cool white fluorescent bulbs or a mix of cool white and warm bulbs. You don't need expensive grow lights. Regular incandescent light bulbs do not provide the best kind of light for plant growth.

If possible, hang the fixtures so their height can be adjusted by using a small chain or a wire that can easily be shortened up. Then position the lights about six inches above the tops of the plants. Use a simple household timer to turn the lights on and off. For best growth, plants require 14 to 16 hours of light per day.

Once your transplants have become well established, you may need to slow their growth, so they don't get too big before the weather is right for transplanting. Do this by lowering the temperature to 60 or 65 degrees F and holding back on water until just before the plants begin to wilt. Do not reduce light levels, as this will weaken the plants.

If your soil mix did not start out with adequate fertilizer, the lower leaves may begin to yellow as the plant grows. Correct this by adding a small amount of soluble plant food when watering. Do not overfertilize as too rapid growth may result.

Time the planting of seeds according to how fast the crops grow, and when they can be set out. Slow growers like celery, leeks, and onions take two months or more to get big enough to transplant. Fast-growing crops, including cucurbits, may be ready in a month.

Tomatoes, peppers, and broccoli take six to eight weeks from seeding to transplant size. However, these crops can be safely set out in the garden at different times due to the difference in their cold hardiness. In most of Vermont, crucifers, like broccoli, and other hardy crops, like lettuce, are safe to plant in early May, or even sooner in some spots. Tomatoes and other tender crops should not be set out until the end of May or shortly thereafter.


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