When to Start Each Vegetable (Weeks Before Last Frost)
| Vegetable | Weeks Before Last Frost | Germination Temp | Days to Sprout |
|---|---|---|---|
| Onions | 12 weeks | 70-80°F | 7-14 |
| Peppers (all types) | 10 weeks | 80-85°F | 10-21 |
| Eggplant | 10 weeks | 75-85°F | 7-14 |
| Broccoli / Cauliflower | 8 weeks | 65-75°F | 5-10 |
| Tomatoes | 6-8 weeks | 70-80°F | 5-10 |
| Kale / Cabbage | 6 weeks | 60-70°F | 5-8 |
| Lettuce | 6 weeks | 60-70°F | 3-7 |
| Basil | 6 weeks | 70-80°F | 5-10 |
| Cucumbers | 3-4 weeks | 70-80°F | 3-7 |
| Squash / Zucchini | 3-4 weeks | 70-85°F | 5-10 |
| Melons | 3-4 weeks | 75-85°F | 5-10 |
Find your last frost date: sunutri.com/planner/zone-finder
Supplies Checklist
Calculate Your Start Dates
Find your last frost date using your USDA hardiness zone at sunutri.com/planner/zone-finder. Then count backwards using the chart above. For example: if your last frost is April 15 and you're growing peppers (10 weeks), start seeds around February 4. Write all your dates on a calendar so you don't miss your planting windows.
Prepare Trays and Soil
Fill seed starting trays with pre-moistened seed starting mix — it should feel like a wrung-out sponge. Do NOT use garden soil (too heavy, not sterile, causes damping-off disease). Tap trays on a table to settle the mix. Leave 1/4 inch space at the top.
Plant Seeds at the Correct Depth
General rule: plant seeds 2x their width deep. Tiny seeds (lettuce, basil): press into surface, barely cover. Medium seeds (tomatoes, peppers): 1/4 inch. Large seeds (squash, beans): 1 inch. Plant 2 seeds per cell as insurance — thin to 1 later. Label every cell with variety and date!
Provide Warmth for Germination
Most seeds germinate best at 70-85°F soil temperature. Cover with humidity domes until sprouts appear. Use a heat mat for peppers, tomatoes, and eggplant (80-85°F). Cool-season crops germinate fine at room temperature. Remove covers immediately when you see sprouts — leaving domes on causes mold.
Set Up Grow Lights
Position grow lights 2-3 inches above seedlings for 14-16 hours daily. Raise lights as plants grow. LED shop lights from a hardware store ($15-25) work great. A sunny window alone is rarely enough — seedlings get leggy and weak. Use a $5 timer for consistent on/off.
Water Correctly
Bottom watering is best: place trays in shallow water for 10-15 minutes, then drain completely. This prevents damping-off disease (the #1 seedling killer) and builds stronger roots. If top-watering, use a gentle mist. Let soil surface dry slightly between waterings. Moist, not soggy.
Thin and Pot Up
At 2 true leaves: thin to 1 seedling per cell (snip the weaker one with scissors — don't pull). When seedlings are 3-4 inches tall with roots visible at bottom, pot up into 3-4" containers with potting mix. Start feeding with half-strength liquid fertilizer every 2 weeks.
Harden Off and Transplant
7-10 days before transplanting: gradually expose seedlings to outdoors. Day 1: 1 hour in shade. By day 7: full day in sun. Transplant on a cloudy day or in evening. Water deeply after planting. Mulch around transplants. Never skip hardening off — transplant shock can set plants back weeks or kill them.
Top 5 Seed Starting Mistakes (Avoid These!)
- Starting too early — follow the timing chart, not your excitement
- Using garden soil — always use sterile seed starting mix
- Not enough light — a window is rarely sufficient, get grow lights
- Overwatering — more seedlings die from too much water than too little
- Skipping hardening off — indoor plants need 7-10 days to adjust to outdoors
Quick Summary
Start vegetable seeds indoors 3-12 weeks before your last frost date (depending on the crop). Use sterile seed starting mix, not garden soil. Plant at the correct depth (2x seed width). Provide warmth (70-85°F) and 14-16 hours of light daily. Water from below to prevent disease. Thin to one seedling per cell. Pot up when 3-4 inches tall. Harden off for 7-10 days before transplanting outdoors. Find your planting dates at sunutri.com/planner/zone-finder.
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