Simple Steps for Starting Seeds Indoors
Here's a beginner-friendly guide to starting vegetable seeds indoors, tailored for Illinois gardeners (USDA zones 5–6). These steps will get you off to a great start:
🌱 Step-by-Step Guide to Starting Seeds Indoors
1. Gather Your Supplies
You don’t need anything fancy—just these basics:
Seeds (choose varieties suited to Illinois—like tomatoes, peppers, broccoli, lettuce, etc.)
Seed trays or small pots (or reuse clean yogurt cups with holes punched in the bottom)
Seed-starting mix (lightweight and sterile—don’t use garden soil)
Humidity dome or plastic wrap (to retain moisture)
Grow lights (or a very sunny south-facing window)
Plant labels (you’ll forget what you planted—trust me!)
Spray bottle or gentle watering can
Heating mat (optional) – helps warm-loving seeds like tomatoes and peppers germinate faster
2. Timing: When to Start Seeds Indoors
Seed packets and seed catalogs generally include information on whether the seeds can be started indoors, as well as seed spacing, planting depth, days to germination (sprouting), and days to maturity (when the first flowers or fruits form).
Some seedlings can’t be placed outdoors until after the last frost-free date. In the Chicago area, that date generally is May 15. If you start your seeds too early, you could end up with spindly plants on your windowsills. If a seed packet says to “sow seeds three to four weeks before the last spring frost date,” count backwards from May 15 and sow the seeds indoors around April 23. Some packets of tomato seeds suggest sowing them six to eight weeks before the last frost date, and the sowing date would be March 15 or April 1. Six to eight weeks is a long time to spend on a windowsill. In that case, consider growing seedlings under lights, which will create stockier plants.
3. Planting Seeds
Moisten your seed-starting mix with water before filling trays (should feel like a wrung-out sponge).
Fill trays or pots, tamp down lightly.
Plant seeds at the depth listed on the packet (usually 2–3x the width of the seed).
Cover with plastic or a humidity dome to keep in moisture.
Place trays somewhere warm (65–75°F). Use a heat mat if needed.
4. Lighting & Growing
Once seeds sprout, remove covers and move under grow lights (or a sunny window).
Keep lights 2–4 inches above the plants and on for 14–16 hours/day.
Keep the soil moist but not soggy—bottom-watering is helpful.
5. Hardening Off
About 1–2 weeks before transplanting outdoors, slowly expose your seedlings to outdoor conditions:
Start with 1–2 hours outside in the shade, gradually increasing time and sunlight.
Bring them in if it gets cold or windy.
6. Transplanting to the Garden
Wait until after the danger of frost (usually around Mother’s Day in most of Illinois).
Choose a cloudy day or plant in the evening.
Gently pop plants out of trays, loosen roots, and plant at the same depth they were growing indoors (except tomatoes—you can bury deeper).
Are you a visual learner?
Check out this video. While her last frost date is earlier than Northern Illinois, you can just use a calendar and count backwards from May 15th. Do you need a heat mat? She used her radiator. In a video comment, it was suggested to place the tray on top of the refrigerator. Enjoy.