Starting Seeds Indoors

In the Midwest the growing season is too short. Cool spring soil temperatures and cold weather can prevent seeds from germinating or kill young seedlings. If you wait until the weather warms, the plants get off to a late start only to be zapped by fall’s first frost; they don’t get a chance to bear a full crop or to put on a full floral display.

The home gardener can:

* Buy all of your vegetables and flowers as plant starts, once the weather warms.

* Extend the growing season outside with coldframes and rowcovers.

* Start your own seeds inside while the wintry weather lingers.

The first choice is best for beginning gardeners who are working on a small scale. The second option is for committed gardeners who want to test the limits. Starting from seed, however, is easy, is cheaper per plant and allows a greater variety of choice among both ornamentals and crops than buying nursery plants.


  • seeds
  • plastic tray (for seeds)
  • seed soil
  • seed starting greenhouse
  • 4 inch pots
  • gallon pots (for tomatoes)
  • plastic spoon (for scooping out seedlings from bio dome)
  • grow lights

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Clean your Equipment

The pots that will hold small plants, old seed trays, and flats need to be cleaned and disinfected. Scrape off old soil then clean with 1 part chlorine bleach to 10 parts water. This will kill microorganisms that are toxic to your seedlings.

When should I start my seeds?

In order to decide when to sow your seeds, you need to find the average last frost date for your region. In central Illinois the average last frost dates range from April 14 to April 21 based on the last 25 years. Based on my own experience, I now use May 15th. A few years ago I planted May 1 but had a frost the next few days though it was not forecasted. Dad says he has always used May 15th with success…your tomatoes can wait. I agree.

I start my tomato plants six or seven weeks before this date. Slow-to-germinate flowers get an eight-week head start. Squashes and cucumbers don’t transplant especially well, but I germinate them inside to protect them from marauding slugs. I move them outside two weeks later before they’ve developed much of a root system.

What should I plant indoors?

To determine what to plant indoors, read your seed packets. Many will list instructions for both inside and outdoor seed sowing. Knowing which to do will depend on your climate. With flowers, I often do both. I’ll start a limited number indoors for “insurance” and then sow the remainder of the packet directly in the garden once true Spring arrives.

Some crops should not be started indoors because they don’t transplant well or because they need an impractical amount of room. I would not recommend starting the following inside:

Not Recommended

  • beets
  • carrots
  • cabbage
  • chard
  • lettuce
  • onions
  • potatoes
  • radishes
  • spinach
  • turnips

These cool season plants can withstand planting directly outside even before the weather fully warms. Likewise, things you are going to plant in large numbers should wait until they can be sown into the garden soil. The following are usually grown in sizable quantities:

Plant Directly into Garden

  • beans
  • corn
  • peas
  • potatoes

If you are worried about your short growing season for crops like corn, look for varieties that have a short days-to-maturity period.


These are usually directly sowed, but can be started in peat pots so they are replanted without disturbing their root system. Start these about 3 weeks before the last frost.

  • cucumbers
  • pumpkins
  • zucchini


  • tomatoes
  • peppers
  • broccoli
  • eggplant
  • cauliflower
  • melons
  • squash
  • herbs
  • flowers

How do I start plants from seed?

The two most important factors for seed germination are temperature and humidity. The seed contains all the nutrients the plant needs to germinate, so it doesn’t need fertilizer or fertile soil.

Note: Fertilizer may actually prevent some seeds from sprouting. Generally, I avoid fertilizing until plants have grown their first set of “true leaves”, which look different than the first pair that emerges.

seed tray To start my seeds, I seed starting systems which contain little containers for each plant. The Hydrofarm germination station has a temperature-controlled pad to keep the seeds environment constant. The 6 pack seed containers are nice, too.

Seeds sprout best in a light soil; don’t use potting soil or garden dirt at this first stage! You can buy seed starting mix or make your own from peat moss, sand, and compost.

Note: Take care if using vermiculite; it can be a respiratory hazard. I prefer the little soil-less planting plugs because they’re mess free and they pop out easily for transplanting, doing minimal damage to the roots, but other methods work fine too.

Any device that keeps the environment moist and fairly warm will work. You can cover trays of soil with saran wrap or a dry-cleaning bag — poke plastic forks into the soil to hold the plastic layer up off the growing sprouts. Commercial peat pots, yogurt cups or milk cartons (poke drainage holes in the bottoms) all work fine, too.

Set your pots in a tray, tub or rimmed cookie sheet so you can water from the bottom, letting the moisture soak up through the soil. This helps keep the moisture level constant and prevents dislodging seeds with a fountain of water. Do not let the soil dry out! Little tiny seedling rootlets need constant moisture.

Seeds vary widely in size. I like to use tweezers to place them exactly where I want them. In general, seeds should be planted approximately four times deeper than their diameter. Some seeds need light to germinate and should be scattered just on the surface of the soil. Again, read those packets!

I usually put two seeds into each hole. I use three if I think the germination rate will be low. You can test your germination rate by placing ten seeds between layers of moist paper towels in putting them in a ziploc bag in a warm
place. This is a good idea if you have saved the seeds yourself or they are several years old. Do this 2-3 weeks before you want to actually start your seeds.

Taking notes

As you’re planting, take good notes! Make a planting diagram and jot down how many days it takes each type of seed to germinate. Some germination times are given as huge ranges (5-20 days). The happier the seed is (warm and wet), the speedier germination may be.

If you are using individual pots, mark them with labels or masking tape, unless you know for sure that you will recognize what the leaves of your young plants will look like. There’s nothing worse than getting your plants mixed up.
This is especially important if you are starting different varieties of the same crop! Free plant stakes can be made
simply by cutting up a plastic yogurt tub. Store your leftover seeds in a ziploc bag or glass jar in the refrigerator.

Now that the seeds are snug in their beds, cover them to retain moisture and put them in a warm place. A temperature of
70 degrees Fahrenheit (21 degrees Celsius) is ideal, but in March our house is nowhere near 70 degrees! I like to set my
mini-greenhouse on a heating pad (a wet/dry safe heating pad set on low) to maintain a more constant temperature, since
our thermostat drops to 54 degrees (12 Celsius) at night. Some people recommend putting the seed tray on top of the
refrigerator. If your house is more temperate, the heat source is unnecessary. I have often started seeds without a heat
source, but peppers and eggplants seem especially fussy about the temperature.

What happens after the seeds sprout?

Once the seeds have germinated, they’ll need light, nutrients and air. Give them some ventilation
and move them to a very sunny window, supplemented with artificial light. There is no need to buy an expensive grow
light or full spectrum light. For these purposes, a basic 48″ fluorescent shop light is all you need.

Tip: The type I own has two tubular bulbs per light; they’re available at home improvement stores for less than $20. The
critical thing is to hang them in such a way that they can be raised as the plants grow; I use a link-type chain that
can be doubled-up on itself to different lengths.

As your plants grow, keep the light about 6″ from their tops. If the light is too far away, the plants will grow spindly
as they stretch for it. This can be rather tricky if you are starting different types of seeds at the same time, because
they will grow at varied rates. You can lift the shorter ones with shoeboxes or phonebooks to alleviate this difficulty.
Once all the seeds in your tray have germinated, remove the cover completely. Too much humidity at this stage can
encourage mildew and harm the seedlings.

As you water, fertilize with a weak solution of water-soluble all-purpose fertilizer. I make mine about one-quarter the
strength called for. Watch out for crystallized salts forming on your soil surface — that’s a sign you’re
over-fertilizing and need to cut back. Turn the lights off for your plants at night (they need a dark cycle to grow
properly) but leave the heat on (temperature fluctuations can stunt them).

Time to Transplant to a Pot

empty plastic flower pot
When the seedlings first sprout, they will usually have a pair of first leaves that look nothing like the true leaves
that come later. (Many crops are dicots, but not all.) Watch closely, and soon after they have two sets of true leaves,
it’s time to move the teenage seedlings into their first real apartment. Water your seedlings thoroughly an hour or two
ahead of time, and then, working carefully and quickly, remove each seedling into its own pot.

At this point I generally use an all-purpose potting soil. Scooping them up from below, try your best to get all their
little roots, and handle their tops as little as possible, and always by the leaves, rather than the stem. A damaged
leaf can be replaced; a damaged stem often dooms a plant at this stage. A plastic spoon works well for scooping out plants.
Do not pull a plant by the stem.

Depending on how long your plants will be living inside, you may perform only one transplant, or you may need two. For
my tomatoes, I’ll move them into 4-inch plastic nursery pots first, then into gallon-sized pots before they go outside.
Everything else gets one transplant, then into the garden.

Hardening Plants

Once your seedlings are thriving, it’s tempting to treat them a bit too carelessly. Being started inside in a safe environment, they can’t stand the shock of an immediate change in their conditions. Expose them gradually to the out-of-doors by setting them outside on nice days for a few hours, being sure to bring them inside at night and making sure they don’t get sunburned or blown over. Some gardeners like to have a fan blow on their indoor starts, saying it strengthens the stems to withstand windy outdoor conditions. I can’t vouch for that, but I do think it helps prevent mildew. Putting the plants in a wagon makes it easy to move them around.

After Planting

milk jug greenhouseAfter the plants are in the garden they are fodder for rabbits and other animals. Flowers I do not do this. I protect them until they are two feet tall or so, past the stage of nibbling, with cut out 1 gallon milk jugs. The bottom
of the jug is cut off, creating a plastic greenhouse, then put into the ground around the plant.

Another idea that has worked well for me is surrounding the garden with a two foot wire fence. I take it down every year after harvest.

Make your own Seed Soil

Method 1

A good germinating medium is fine textured and free of pests, diseases and weed seeds. It should be low in fertility and soluble salts and capable of holding and moving moisture.

But beware: Soil straight from your backyard just won’t do the job, says Barb Fick, home horticulturist with the Oregon State University Extension Service.

Typical backyard soil is too compacted and full of weed seeds. Native soil may not drain as well as potting mixes, and it can develop a crust that prevents seedlings from pushing though the surface. And it is not pasteurized, which can cause diseases in seedlings.

Fick’s recipe for a good basic pasteurized soil for starting seedlings is a mixture of 1/3 pasteurized soil or finished compost, 1/3 sand or perlite and 1/3 peat moss.

You can use your oven to pasteurize a small quantity of seedling soil. Put slightly moist garden soil or compost in a heat-resistant pan and cover with a lid or foil. Place in a 250-degree oven with a food thermometer, to ensure that the mix reaches a temperature of 180 degrees for a full half-hour. Avoid overheating it, as the structure of the soil may be damaged.

Sand, peat moss and perlite are available at most nurseries and garden stores, and a mixture of 1/2 peat moss and 1/2 perlite or sand works well, too, according to Fick.

I tried backyard soil for one plant and it was a disaster. After a few waterings, the soil turned hard as a rock.

I also tried potting soil. It worked ok for most plants but it has a lot of debris (sticks) in it.

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