Starting plants from seed

Starting vegetable plants from seed is best done indoors under controlled conditions.

Many vegetable seeds do well sown directly into the garden, but results are often improved by starting seeds indoors.

Starting indoors has several advantages. Perhaps the most important is a controlled environment for fragile new seedlings. Indoors, you can protect them from damaging winds, heavy rains or hail. Tiny seeds can be more carefully sown in flats than in garden beds. Plants like tomatoes or peppers that require long growing seasons will not mature at all in northern climates unless started indoors.

Once you have selected your seeds, the important considerations for successful seed starting are starting medium, containers, temperature and light.

A light, porous starting mix will give you the best seed germination. Do not use garden soil. Though it may produce good results in your garden, it tends to contain weed seeds, insects and pathogens that should not be brought indoors. Most garden soil becomes crusty and does not drain well under indoor conditions. Commercial starting medium is a soilless mixture of vermiculite, perlite and sphagnum moss, with some amendments. This provides a good environment for germinating seeds.

If you want to try making your own mix, the basic recipe is two parts sphagnum moss, one part perlite and one part vermiculite. Amendments could include oyster shell, worm castings or compost in equal parts with sphagnum moss. Oyster shell will increase the pH of the mixture, counteracting the acidity of sphagnum moss. Worm castings and compost will add micronutrients, but they must be sterilized. Place moist worm castings or compost in an oven-proof container, cover it and place it in the oven at 250 degrees. Periodically check the temperature of the mixture with a candy thermometer. When it reaches 180 degrees, cook it for an additional 30 minutes.

A convenient container for seed starting is a plug flat with 72 cells, a tray sized to accommodate the flat and a clear plastic dome tray cover, available at many garden stores and nursery supply businesses. While this equipment is preferred by most gardeners, almost any container can be used as long as it drains, is deep enough for seedling root development and is clean and sanitary prior to use. It is best to grow seedlings in individual cells since it reduces root damage during transplanting.

When you are set up and ready to start, place one or more seeds in each cell. Plant them to the recommended depth — usually as deep as the seeds are wide. Label the cells clearly, then cover the flat with the dome cover to conserve moisture until the seeds germinate.

Most seeds germinate best when soil temperature is about 70 degrees Fahrenheit, so find a warm room for seed starting. Many garden supply stores sell heat mats that can be placed under the seedling tray. When plugged in, the mat will raise the temperature of the root zone 10 degrees to 20 degrees Fahrenheit above ambient room temperature.

Once seeds have germinated, remove the dome cover and unplug the mat. Too much humidity after germination can encourage certain fungal diseases, and too much heat can cause seedlings to become spindly. Keep the lights on them and watch them grow until it’s time to put them in the garden.

A WSU Master Gardeners of Chelan County column appears weekly in The Wenatchee World. Connie Mehmel is one of four columnists featured. To learn more, visit or call 667-6540.