Seed starting 101: all you need to know to begin spring indoors

By Teresa Kolar

Houston County Master Gardener


Oh, the weather outside is frightful- looking at seed catalogs can be delightful!  It can also be overwhelming. Where do I start? If you’ve never grown vegetable plants indoors, try a few this year. You’ll get earlier harvests of many crops and give your long season crops more time to produce.

Some crops thrive in cool weather, while others only grow well when it is warmer. Keep the last spring frost date, soil temperature, air temperature and moisture all in mind. Rushing seeds into cold soil will not get you a head start on the season.

Here is a summary of which crops to plant early and which ones not to plant until after the last spring frost date (around May 15).

Very early spring (as soon as the ground can be worked):  Onions, peas and spinach.

Early spring: Lettuce, beets, carrots, radishes, dill, cilantro, cabbage, broccoli, celery, kale and potatoes.

After last frost date: Beans, corn, melons, cucumbers, squash, tomatoes, peppers, pumpkins, eggplant and basil.

Seed packets will list weeks from sowing seeds to garden size transplants. Take the last spring frost date and count backward for when to sow the seeds.

For example, a seed packet of tomatoes will indicate seeds need 6-8 weeks under lights before transplanting outside when all danger of frost is past. So the seeds could be started around the first week of April. The plants could be hardened off the last two weeks of May and planted into the garden the end of May.

You could sit with a calendar and figure all this out, or there is a great seed starting date calculator on Johnny’s Selected Seeds site at

At the top of the calculation sheet you enter the last spring frost-free date (05-15-2014) the sheet calculates it all for you in a nice chart. It lists crop, number of weeks to start seeds before setting out date, when to start seeds inside, safe time to set out plants relative to frost-free date and actual setting-out date into the garden.

Plastic seed starting containers and trays are reusable. Sterilize used containers by soaking in disinfectant solution such as 10 percent bleach (1 part bleach, 9 parts water.) Seed starting containers must have drainage holes at the bottom.

Commercial seed starting mixes are recommended for starting seeds. They’re sterile, lightweight and porous with a texture and PH suited to the needs of germinating seedlings. Commercial soil-less mix is readily available at garden stores. You can also make up a soil-less mix using 4 quarts vermiculite, 4 quarts peat moss and a couple tablespoons of lime. Don’t add fertilizer at this time.

Put the moistened soil mixture into the seed flat and pat down until surface is level and about ¼ inch from the brim of container.

Make shallow furrows one inch apart in the surface of the soil mix using a pencil or your finger: 1/8 inch deep for tiny seeds, ¼ inch deep for small seeds. Large seeds can just be poked down into the soil.

To cover the seeds, pinch the furrow closed. A rule of thumb is to make sure seeds are covered to twice their thickness. Retain the seed packets for information needed later. Some seeds need light to germinate and should not be covered at all with soil.

To water, place the flat in a pan, sink or bath tub of water at room temperature until the top of soil is moist. This is called bottom watering and helps prevent seeds from being washed away. Cover the flat with clear plastic – such as food wrap – or enclose in a plastic bag. This will keep it moist until the seedlings come up.

Germinating seeds must have steady warm temperature. Electric heating mats specifically for seed starting are available from garden centers. The seeds do not generally need light at this point, so you can place newspaper over the plastic wrap to insulate the flats and use the top of your refrigerator for warm even temperatures.

A windowsill is the worst place for seeds to germinate as the temperature fluctuates too much. Check the seeds daily. As soon as the first sprouts poke through the soil take off the newspaper and plastic cover.

It is much better to use fluorescent lights than to rely on natural light. Cool-white fluorescent bulbs work fine for vegetable seedlings. Hang lights from chains so they can be raised or lowered easily. Keep lights 1 or 2 inches from small plants. As the plants grow, raise the lights to stay ahead of them no more than 4 inches above the tips of seedlings. Plants will need 12-16 hours of light every day and 8 hours of lights out. A simple timer can be part of the set up.

Press the soil firmly with your fingertips; if it’s not moist, it’s time to water. Seedlings draw energy for germination from nutrients in the seed. They don’t need fertilizer until several sets of true leaves have emerged. Once the true leaves have emerged use a general purpose water-soluble fertilizer mixed ¼ strength once a week.

If you have planted several seeds to a pot, when the true leaves emerge use a scissor to cut off all but the strongest plant. If seedlings in a tray are overcrowded (touching each other) transplant some seedlings to another tray.

All seedlings need to spend a week or so outside before being transplanted into the garden. This is known as hardening off. Transplants must get used to the sun, wind and rain. About a week or two before setting out plants into the garden start cutting back on their water and fertilizer. On a mild day move the plants outdoors in partial shade and protected from the wind for just a few hours on the first day. Give them a little more time each day. It takes 3-4 days for the plants to become accustomed to direct sunlight. After a week or so the plants can stay out all night.

Please join us for the Fourth Annual Gardening Workshop in Caledonia on March 29. For more information, please email Cindy at [email protected] or call 507-725-5139.

Happy gardening!

  • Plantastico

    Great article! My favorite seeds to plant is the seeds of the Pet TickleMe Plant.
    The TickleMe will close its leaves and even lower its brahches when you Tickle it!