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It's Time to Start Some Seeds
First published on garden.org on February 26, 2009, by Suzanne DeJohn
It's that time of year, when the gray skies and frozen tundra outside start wearing on my nerves. I know it's spring somewhere and I just can't wait to get in the garden. When this feeling begins to overwhelm me, I know it's time to start some seeds indoors.
What a Seed Needs
Whether you are new at seed-starting or an old hand, it's helpful to understand the science behind seed germination.
First of all, a seed needs water to germinate. Water softens the protective seed coat, then is absorbed into the internal tissues. There, it causes chemical changes within the seed, and soon the tiny embryo, which had been laying dormant, begins to grow. A seed also needs oxygen. Just like animals, plants respire -- that is, they consume oxygen as they metabolize food to create energy for growth. Because germinating seeds are so small and growing so quickly, they require an abundant, consistent supply of oxygen.
When starting seeds indoors, you need to keep the soil (or seed-starting medium) evenly moist but never soggy. Both water and oxygen must be available at all times. (Think of your soil as a damp sponge that contains both water and air.) Make sure the containers have drainage holes and that excess water can drain freely. On the other hand, don't let the soil dry out or the germinating seeds' tiny roots will quickly dehydrate. Use a plant mister to apply water to tiny seedlings, or fill a waterproof tray with water and let the pots sit in it until the soil is moist, then immediately allow to drain. Pouring water on the top of the soil can wash away or uncover the seeds.
A seed uses the energy from its food storage structure, the cotyledon, to fuel its initial growth. Seeds must germinate, send out roots and shoots, and produce their first photosynthetic (green) tissues before the food runs out. That's why planting depth is so important. If you plant a seed too deeply it will use up all its energy reserves before it has a chance to develop leaves. Different seeds have different food reserves. Consider the seeds we consume: beans, peas, and corn have large food reserves; tiny poppy seeds have very little.
Planting depth is listed on seed packets; however, a rule of thumb is to plant seeds two or three times as deep as they are wide. Tiny seeds should be barely covered by soil mix, while large bean seeds should be sown an inch or so deep. (Note that some seeds need light to germinate, and should not be covered with soil but merely pressed into the soil surface. The seed packet will tell you this.)
Since a germinating seed relies on stored food, there is no need to add fertilizer to the germinating mix or to fertilize newly emerged seedlings. Wait to begin fertilizing until the seedling has two sets of leaves. Then fertilize with a soluble fertilizer, diluted to half the recommended dilution rate. Too much fertilizer -- especially an improperly diluted non-organic fertilizer -- can damage plant roots. I like to use a dilute seaweed/fish emulsion mixture, but be sure to look for one described as "odorless!"
Let There Be Warmth...and Light
Many seeds germinate best in warm soil. Some gardeners put newly planted seeds on top of the refrigerator or use a special heated germination mat. However, it's vital to check the containers daily, and as soon as you see a sprout emerge, move the container to a place with bright light so it can develop the green chlorophyll it needs for photosynthesis. If the light is insufficient, the seedling will put its energy into growing a long, thin stem stretching toward the light, exhausting its food reserves and either dying or giving you a weak, spindly plant. Ideally, use supplemental fluorescent lights suspended just an inch or two over the tops of the plants. Raise the lights (or lower the containers) as the plants grow.
Once they're up and growing, most plants grow best in slightly cooler temperatures, about 65 to 68 degrees F (cool room temperature). Warmer than that and the plants will grow quickly, but weakly. You're aiming for stocky, sturdy plants with thick stems and lush foliage. Small but healthy seedlings will transplant and grow better in the garden than tall, lanky ones.
Damping off. If tiny seedlings look fine one day, then flop over the next (and you're sure they aren't wilted from dry soil) then you may be seeing what's called "damping off." This is a disease problem caused by several soil-borne fungi. They attack seedlings at the soil line, constricting the stems and causing seedlings to topple over. Once a seedling is affected, there's nothing you can do to save it. Prevent damping off by using a sterile soilless seed-starting mix and sanitizing used containers in a 10 percent bleach solution. Some gardeners sprinkle a layer of "play" sand -- sand that's been sterilized for use in sandboxes -- on the soil surface of their seed-starting flats. Since sand doesn't hold water the soil surface stays dry, making it inhospitable to the damping off fungi. A fan set on low blowing in the room, but not directly on plants, will keep air circulating and minimize disease problems. (And the moving air may strengthen plant stems, too.)
Poor germination rate. Some seeds have naturally low germination rates; sometimes the seed packet will tell you to "sow thickly." However, if you're having trouble with tomatoes, peppers, zinnias, basil, and other reliable germinators, then something is wrong. Too cool or overly moist soil can cause seeds to rot. Allowing the soil to dry out even once can kill tiny root hairs. Planting seeds too deeply is another possible cause.
Spindly seedlings. This can be caused by a number of factors but it's usually a result of too little light. Too warm a room is another possibility.
Pale leaves. Too little light can cause this, but lack of nutrients is a likely culprit, too. Feed seedlings with a weak soluble fertilizer every two weeks or so.
Easiest Seeds to Start Indoors
In my experience, the easiest vegetables to grow from seed include broccoli, cabbage, cauliflower, eggplant, kale, peppers, and tomatoes. It's easy to start lettuce, squash, melons, and pumpkins but I find that seeds sown directly in the garden often catch up to ones I grow inside and transplant. Sow root crops like beets, carrots and turnips; beans; corn; and peas directly into the garden, since they don't like to be transplanted.
The easiest flowers include cosmos, marigold, and zinnia. You can start morning glory and other annual vines indoors but I find the vines quickly become entangled, making transplanting a chore. Some common annuals grow so slowly that I always purchase them as transplants; these include impatiens, pansies, snapdragons, and viola. Sow poppies, nasturtium, and sunflowers directly in the garden.
Try, Try Again
As they say, "If at first you don't succeed ..." All gardeners experience problems with seed starting, so don't get discouraged if some of your seeds don't thrive. Always plant some extras, and if an entire crop succumbs, you can usually purchase replacement seedlings.