Based on the date you expect to eventually plant outside, the information on the seed packet can guide you when you need to start your seeds. For our area, May 5 has been the average frost-free date for many years. If we had an early spring, a few days earlier could work, but with our weather being so abnormal, May 5 may be a better date this year for planting those very hardy seeds and transplants. A later date may even be safer if you are concerned with our weather and the location of your garden in the yard.
Seeding four to six weeks ahead is pretty common, yet be sure you follow the label. After reading all the seed packets, you will see that starting all your seeds at the same time is not the thing to do! Those warm loving vegetables can be sown later so they will not be overgrown and leggy by the time you move them to the garden.
To avoid seed germination issues, use either clean or brand new seedling flats. Along with the seedling flats, use a soilless media to avoid soil borne diseases. Soilless media also will drain quickly while holding adequate moisture. While you are waiting to see the first signs of seedling emergence, make sure the soil media is moist but not overly wet. Emergence can be just a matter of a few days to 10 or more days, depending on what you're going to grow.
Some gardeners will lightly cover the seedling flats with a sheet of plastic or saran wrap to conserve moisture and retain a bit of heat that may help hasten germination. The seed packet may even suggest that for better success. Some seeds are happy to germinate in the dark while others require light. You may need to group those seeds in the same seed flat. Once the seedlings emerge, they all require light immediately. Light intensity drops off quickly the farther the light fixture is away from the flat. A bright indirect light from the sun in a window will work too. If the light source is too far away, the seedlings will stretch and end up with thin, long stems before it is time to take them to the garden or flower bed. Your seedlings also will stretch if the nighttime temperatures are high, so that cooler windowsill may be a better place.
Once you are getting closer to planting day, those transplants will need to be conditioned to the outdoors. Several days ahead of planting day, set them outdoors in a protected location a few minutes each day, extending the time outdoors each day. Try to pick a planting day where the weather is cooler and cloudy. This will be a better first day for the transplants than a sunny hot day. Watch them carefully to be sure the transplants do not wilt from lack of moisture. Their root systems have been limited to the transplant container and can easily dry out.
For questions, contact the Kendall County Master Gardener Help Desk at 630-553-5823 or learn more about vegetable gardening at https://extension.illinois.edu/veggies