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  • By Lisa Jevens

How and when to start seeds indoors

Those racks of bright, shiny seed packets start to appear in stores shortly after the holiday decorations vanish, offering hope for spring.

The advantage to starting seeds indoors is that you get a jump on the growing season by planting a seedling and not a seed. That means you get to eat that fresh tomato a few weeks earlier. Or you can stagger your harvests. An established seedling also has a greater chance of survival than a seed planted in the ground.

While it's OK to buy seeds and seed-starting tools in the winter, it is probably too early to start seeds indoors if you live in the Midwest, says Richard Hentschel of the University of Illinois Extension.

"The most typical mistake is starting too early," Hentschel says. "Plants get spindly and you run out of space for them as you repot and they get larger in your house, waiting for conditions outside to warm up.

"Determine the right time to start seeds indoors by reading the back of the seed packet. It should tell you when to plant outdoors. Start the seeds indoors a few weeks – not months – before that date.

For example, in the Chicago area you would not plant most seeds before mid to late April or May, as frost in April is common. The average date of the last frost is your guide for when the outdoor planting season potentially begins.

"Cool-season plants such as lettuce and radishes tolerate wet, cold spring ground but warm-season plants such as squash and cucumbers do not," Hentschel says.

What do you need to start seeds indoors? First, you need seeds. For novices, Hentschel recommends larger seeds that are easier to handle, such as pumpkins, marigolds and beans. Larger seeds have more stored energy in them, and better tolerate mistakes with temperature, water, and light.

The second most important thing to buy is a lightweight soil mixture. The medium should be loose, well-drained and fine in texture. Though most seed-starting mixes will do the trick, you can create your own mix by combining peat moss, perlite and vermiculite.


A plastic tray with small receptacles is necessary too. These are called cell flats, and hold the planting medium. They have drainage holes in the bottom and sit in a tray.

Hentschel recommends using new containers every year. "If you are going to reuse your seedling tray, make sure you clean it very thoroughly with bleach and water or soap and water," he says.


Follow the planting depth exactly as written on the seed packet. Make a small trough for the larger seeds. The tiny seeds get sown on the surface. Crumble a little bit of sprouting medium on the surface over them. The location of your seed farm is important. Strong, indirect light is best. Avoid an east or north window, and avoid a windowsill, as they can be cold and drafty. If you are unsure of a seed's requirements, contact the seed company or visit its website.

If you do not have a good location to start your seed, you can modify a room by purchasing warming mats that sit under the seed trays and grow lights. This might work if you want to start seeds in a cool (not cold) basement with low natural light. Hentschel says that grow lights are not necessary to start seeds indoors, if you have sufficient sunlight.

In fact, light has nothing to do with a seed's initial sprouting. It's all about the seed receiving water. The right amount of water is critical for good results. Tiny seeds sown on the surface with a small sprinkling of sprouting medium should be misted with a mister to avoid rotting. Seeds should not need extra water until they sprout.

One way to tell if your seeds have the right amount of water is by simply picking up the flat, Hentschel says. "If the seed flat is too dry, it will be extremely lightweight when you pick it up. If so, it needs water. If you touch the growing media and it is cold and damp, it doesn't need water."

Transplanting is necessary as seedlings quickly outgrow the small cells. They can be transferred to bigger pots with potting soil.

"Don't use dirt out of the backyard. It's too heavy, too wet, and doesn't drain well," Hentschel says.

Those small, brown biodegradable pots are good for transplanting. They can be easily peeled away and composted when it's time to plant the seedlings outdoors.

Recording the dates and results of your seed-starting endeavor is a good idea. An easy way to do this is to keep each seed packet and tape it to a piece of paper in a folder or album. Write down where you bought the seeds, when you planted them, how often and how much you watered them, when they sprouted, when you transplanted them, when they matured, when you harvested the vegetables or saw flowers, and the size of the harvest.

Print a picture of your results. This will give you a good idea of what to buy or avoid next year, and help fine-tune your green thumb.

This story was originally published in the Chicago Tribune "From House to Home" section, and on on February 2, 2015.

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