This article appeared in the May 2002 web issue of Horticulture Update,
edited by Dr. William C. Welch, and produced by Extension Horticulture,
Texas Cooperative Extension, The Texas A&M University System, College Station, Texas.
How to Start Seeds Indoors
Gardening is a wonderful pastime and filling your garden with plants you started yourself from seeds simply doubles the pleasure. If you think growing from seed is difficult and takes too much time and equipment, the steps and tips here will dispel those apprehensions.
Basically all you need to know about specific seeds is whether or not they require light to germinate and the number of days germination takes. With a fluorescent light or a very sunny window, a few containers – purchased or found – and a good germinating mix, you will be on your way.
The magic: watching a seedling push up above the soil surface creates a bond between you and your garden.
Materials You Need
Containers: any shallow receptacle that holds soil, such as flats with or without individual cells, peat or paper pots, egg carton bottoms or halved milk cartons. For transplanting seedlings, 2-1/2 to 4-inch diameter plastic, clay or peat pots. To ensure even moisture for seeds – and save yourself time – look for self-watering seed-starting kits.
Germinating mix: commercial or homemade.
DIY: Mix your own seed starter soil, with a 50-50 combination of fine sphagnum peat moss and vermiculite.
Transplanting mix: A good potting soil will do, but a mix specifically formulated for young seedlings is better. The latter usually contains a coarser grade of sphagnum peat moss than a germinating mix and often contains fertilizer.
Fertilizer: balanced all-purpose fertilizer. If you prefer to grow with organic rather than chemical fertilizers, use fish emulsion is very odoriferous but nutritious for plants.
Wet the germinating mix thoroughly and let it drain. It should be moist but not soggy.
Fill flats or individual pots with the mix to within about an inch of the top.
Make shallow row indentations with a ruler or your finger in the flats. It’s easier to separate seedlings when transplanting time comes if you sow in rows. Sow thinly so you do not waste seed. If using pots make shallow holes and set 3 to 4 seeds in each.
Check your seed packet to see if the seeds need light to germinate. If they do, press them lightly into the surface. If they require darkness, cover with l/4 to l/2 inch of mix or vermiculite and tamp it down.
Mist the surface with water to settle the seeds.
Cover the flats with a sheet of plastic wrap or set them in plastic bags. Set pots in plastic bags and close with twist ties. This keeps the mix from drying out while the seeds germinate, but check the mix occasionally and moisten if necessary by spritzing with water.
Place the flat in a warm, bright location or under a fluorescent light. Check the seed packet for specific soil temperatures for germination. Generally, seeds germinate with soil temperatures of 70-75 degrees F.
Hot peppers sometimes will not germinate until soil temperatures reach 80 to 85 degrees F.
When the seedlings emerge, remove the plastic covering. Seed packets give you an idea of germination time, usually 7 to 10 days, sometimes as long as 2 to 3 weeks.
Keep the mix evenly moist, not soggy. Water from the bottom by setting flats and pots in a sink filled with a couple of inches of water; remove them when you see moisture on the surface of the mix.
The first leaves on a seedling are cotyledons, not true leaves. Their shapes usually do not look like the plants familiar leaves. When seedlings in flats grow at least two sets of true leaves, transplant them into larger pots.
Moisten the transplanting mix and let it drain. If you use an all-purpose potting soil, add a handful of vermiculite for each quart of mix to lighten the texture.
Fill 2-1/4 inch pots about three-quarters full.
Use your fingers or a pencil to pick each seedling out of the flat, carefully holding each by the leaves not the stem (plants readily grow new leaves but not broken stems).
Set the transplant in the pot, filling in around the roots with more mix and firming the mix down.
Place pots on a sunny windowsill or under a fluorescent light.
Water transplants regularly from the bottom until they grow 3 to 4 inches tall. Then you can begin to water from the top.
Feed as you water by diluting a water-soluble fertilizer, such as fish emulsion, to half the strength recommended on the label. Or, feed at regular strength every week to 10 days.
You do not need to move most flowering plants into larger pots before setting them outdoors in the garden. Some vegetables, such as tomatoes, produce extensive root systems and grow quickly into lush plants; transplant them at least one more time into larger pots before the weather warms up enough to put them in the garden.
To encourage compact, bushy plants, occasionally pinch off the growing tips of herbs and most flowering plants.
Many seeds germinate best – more quickly and more abundantly – if you do not cover them with a mix when you sow.
Ageratum Lettuce Begonia
Nicotiana Coleus Petunia
Columbine Parsley Dill
Feverfew Savory Salvia
Gaillardia Impatiens Yarrow
A Few Do’s
Know the date of the average last spring frost in your area; you need to start most plants indoors a certain number of weeks before that date. Seed packets include that information.
Give pots on windowsills a quarter turn every week so plants grow straight instead of bending towards the light.
Opt for the easiest plants to start indoors if this is your first attempt.
These include basil, coreopsis, dianthus, gaillardia, gloriosa daily, marigold, oregano, yarrow and zinnia.
Label your seed containers as you sow.
A Few Don’t s
Combine different varieties of seeds in one flat unless they germinate in the same number of days.
Let seedlings in flats grow large before you transplant them. Their roots become too entwined, making them difficult to separate without damage.
Start root vegetables indoors.
Over water seedlings. Soggy soil promotes fungus and root rot.
Some plants resent being transplanted, but if your growing season is short, you can start them indoors in individual peat or paper pots, which biodegrade; set plant in its pot in the garden.
Annual Phlox Fennel Chervil
Lupine Cucumber Nasturtium