Seed Starting Setup Desk: lights, heat, and trays for indoor seeds
Tell the desk about your shelf, light, and heat mat. It checks your hang height, shows how many trays fit, lists the soil temperature each crop wants, plans hardening off, and builds a shopping checklist you can download as a CSV. Your answers save on your device. No account needed.
Free seed starting setup planner. Check grow light hours and hang height, see how many trays fit your shelf, find the heat mat temperature for each crop, plan hardening off, and print a shopping checklist. Sourced from university extension.
How many hours of light
Run seedling lights 14 to 16 hours a day on an outlet timer. Iowa State, the University of Maryland, and Oklahoma State all give 14 to 16 hours. Minnesota says 12 to 16 and Clemson says 16 to 18. Do not leave lights on all day and night.
How far above the seedlings
| Light | Source | Distance |
|---|---|---|
| Fluorescent shop light | University of Minnesota Extension | No more than 4 in above seedling tops, as close as 2 in is ideal |
| Fluorescent shop light | Clemson Extension | 2 to 4 in, raised as plants grow |
| Fluorescent shop light | Iowa State Extension | 4 to 6 in |
| Fluorescent shop light | Nebraska Extension | No further than 4 to 6 in |
| Fluorescent plant grow tubes | Oklahoma State Extension | About 6 to 8 in |
| LED light | Iowa State Extension | About 8 to 12 in for many LED fixtures |
| LED light | University of Minnesota Extension | 4 to 6 in for seedlings |
| LED light | Nebraska Extension | 3 to 6 in above the leaves |
| LED light | University of Maryland Extension | 2 to 6 in for fluorescent and LED |
Raise the light as plants grow. Hang it from chains, or set trays on blocks you can remove. Watts measure the power a light uses, not the light plants get, so check the PPF number on the label. For LED, Oklahoma State and Nebraska Extension give 16 W per square foot of grow space for low light plants and 25 W for high light plants.
Heat mat temperature by crop
Crops with an ideal germination temperature of 70 F or higher sprout much faster with bottom heat from a seedling heat mat. Remove the heat once plants emerge. Temperatures are for the seed starting mix, not the room air.
| Crop | Heat mat | Mix temperature (F) | Days to sprout |
|---|---|---|---|
| Tomato | Likes bottom heat | 75 to 80 | 7 to 14 |
| Pepper | Likes bottom heat | 75 to 85 | 10 to 14 |
| Eggplant | Likes bottom heat | 75 to 90 | See the packet |
| Melon | Likes bottom heat | 80 to 85 | 5 to 10 |
| Squash | Likes bottom heat | 70 to 85 | 7 to 14 |
| Basil | Likes bottom heat | 70 to 85 | 4 to 10 |
| Marigold | Likes bottom heat | 70 to 85 | 5 to 8 |
| Zinnia | Likes bottom heat | 70 to 85 | 7 to 14 |
| Broccoli and cauliflower | Mat optional | 65 to 75 | 5 to 10 |
| Cabbage, kale, and collards | Mat optional | 65 to 75 | 5 to 10 |
| Celery | Mat optional | 65 to 75 | 10 to 18 |
| Lettuce | Mat optional | 65 to 70 | 7 to 10 |
| Onion, leek, and shallot | Mat optional | 65 to 70 | 10 to 14 |
| Parsley | Mat optional | 65 to 70 | 10 to 25 |
| Pansy | Mat optional | 60 to 65 | 14 to 21 |
Ranges are from University of Idaho Extension. Eggplant is from Oregon State Extension. Utah State suggests pairing a mat with a thermostat. Minnesota says the mix can run up to 5 F cooler than room air.
Water and airflow
Use a sterile seed starting mix and keep it moist, not soggy. Bottom water with 1 to 2 in of water for 3 to 10 minutes (Clemson). Run a small fan for airflow. Feed only after several true leaves show, at 1/4 strength once a week (Minnesota).
Hardening off
Iowa State says 7 to 10 days. Nebraska says 10 to 14 days. Minnesota says two weeks. Clemson says two to three weeks. Start in shade out of the wind, then give a little more sun each day.
Guides
Related
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Sources
- University of Minnesota Extension, Starting seeds indoors
- University of Minnesota Extension, Lighting for indoor plants and starting seeds
- Clemson Extension HGIC 1259, Starting Seeds Indoors
- Iowa State Extension, How do I set up supplemental lights for my seedlings?
- Iowa State Extension, Selecting, Hardening, and Planting Bedding Plants
- University of Maryland Extension, Starting Vegetable Seeds Indoors
- University of Idaho Extension, Start Seeds Indoors with Success
- Utah State University Extension, Starting Vegetable Seeds Indoors: Germination
- Oregon State University Extension, Soil temperature conditions for vegetable seed germination
- Oklahoma State University Extension, Lighting can be tricky when starting seeds indoors
- Oklahoma State University Extension, LED Grow Lights for Plant Production
- Nebraska Extension in Lancaster County, Using LED Lights for Houseplants and Transplants
- Nebraska Extension G1650, Growing Tomatoes in the Home Garden