You can start seeds indoors with a sunny window, a takeout container, and a bag of seed starting mix. Most of us add a few more pieces of gear over the years because they make the job easier and the seedlings stronger. This checklist covers the full setup. Start with the basics, then add the extras when you know you will use them.
You can start seeds in takeout containers on a windowsill, or in proper trays under lights. Both work. The supplies below make the job easier and the seedlings stronger.
The basics you need for any seed starting setup
Four things germinate a seed: moisture, warmth, air, and a bit of light once the sprout is up. Every supply on this list serves one of those four jobs.
Seeds
Fresh seed germinates faster and more evenly than old seed. Buy from a company that prints the packed-for year on the packet. My favourites are Botanical Interests, High Mowing Organic Seeds, and True Leaf Market. All three sell small packets, so you can try a few varieties without buying more than you can plant. See my full notes on the best seed companies and my winter sowing seed list for ideas on what to grow.
Seed starting mix
Seed starting mix is lighter and finer than potting soil. It holds water without packing down, so tiny roots can push through. Garden soil is too heavy and can carry fungus that causes damping off. Espoma organic seed starter mix and Burpee organic coconut coir seed starting mix are both reliable. One bag fills about four 72-cell trays. Moisten the mix in a bucket before you fill the cells. Dry mix repels water and floats the seeds out.
Trays and cells
Cell trays keep each seedling in its own plug of mix, so transplanting is quick and roots stay whole. A 72-cell seed starter tray with a humidity dome is the standard size and fits on most shelves and heat mats. If you want trays that last for years, Bootstrap Farmer 1020 trays are thick enough to carry with one hand when full and wet. Pair them with 6-cell inserts so you can pop out one six-pack at a time.
Reuse old trays after a wash in warm soapy water. A quick rinse in a 10 percent bleach solution kills any disease left from last year.
Labels and a marker
Label every tray the day you sow. Two trays of tomatoes look the same for six weeks. Plastic T-labels fit in a cell and wipe clean for next year. Use a Garden Marker pen rather than a regular permanent marker. Regular ink fades under grow lights and sun within a few weeks.
Water
A fine-mist spray bottle keeps the surface damp while seeds germinate without washing them out. Once seedlings are up, water from below. Set the cell tray in a solid tray with about half an inch (1 cm) of water and let the mix soak it up for 15 minutes. Bottom watering keeps leaves dry and cuts down on damping off.
Warmth: the supply that speeds everything up
Most vegetable seeds germinate fastest when the soil sits between 70°F and 80°F (21°C to 27°C). A cold basement floor can be 55°F (13°C). Peppers may take three weeks at that temperature and a week on a warm mat.
A seedling heat mat with a thermostat warms the tray from below. The thermostat matters. A mat without one can cook a tray on a warm day. Set it to 75°F (24°C), push the probe into a cell, and check it the first day. Take the tray off the mat once most seeds are up, because warm roots and cool air make leggy seedlings. My post on the best temperature to germinate seeds lists the ideal range for each crop.
Light: the supply most beginners skip
A south window gives seedlings a few hours of direct light in late winter. It is rarely enough. Seedlings that lean and stretch are telling you they want more light. A grow light fixes the problem for the cost of a few seed packets.
For one or two trays, a clip-on LED grow light or a SANSI full spectrum LED bulb in a desk lamp works. For a shelf of trays, Barrina 4-foot LED grow lights link together and hang on light chains. Keep the light 2 to 4 inches (5 to 10 cm) above the seedlings and run it 14 to 16 hours a day on an outlet timer. See my guide to the best grow lights for seedlings for a full comparison.
Air: the supply that prevents damping off
Still, damp air invites the fungus that topples seedlings at the soil line. A small clip fan set on low, pointed across the trays and not straight at them, keeps the air moving. It also thickens stems. Run it a few hours a day once the first true leaves show. Take the humidity dome off at the same time.
Nice-to-have supplies
These are not required. Each one solves a small problem.
A soil thermometer tells you the real temperature in the cells, which can be 10°F (6°C) off from the room. A soil blocker presses mix into free-standing cubes, so you skip plastic cells and roots air-prune on their own. A humidity dome kit with a built-in LED light bundles tray, dome, and light in one piece for a kitchen counter. A seed storage box keeps packets dry, sorted, and out of the sun between seasons. Small kraft envelopes hold seed you save from your own garden. My seed packet template prints labels for them.
A sample setup for a family garden
Here is a setup that handles about 300 seedlings. Two shelves, four 72-cell trays per shelf, two LED shop lights hung above each shelf, one heat mat shared between the tomato and pepper trays, a clip fan at the end of the shelf, and a timer that turns the lights on at 6 a.m. and off at 9 p.m. The whole setup fits in a closet.
Sow the slow crops first. Onions and leeks go in 10 to 12 weeks before the last frost. Peppers follow at 8 to 10 weeks. Tomatoes go in at 6 to 8 weeks. Squash and cucumbers want only 3 to 4 weeks, because they grow fast and sulk if root-bound. Read when to start seeds indoors for a full calendar, and how to harden off seedlings before they go outside.
What you can skip
Peat pots dry out fast and roots struggle to push through the walls. Egg cartons are too shallow for anything bigger than lettuce. Fertilizer in the first two weeks is wasted, because the seed feeds the sprout. Fancy pre-filled kits cost more per cell than a bag of mix and a tray. Spend the money on a good light instead.
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