Not every seed wants to start inside. Some plants thrive when you baby them under grow lights for weeks before transplanting. Others absolutely hate being moved and would rather you just stick them straight in the ground. Here's how to figure out which ones do what, when to start them, and how to not murder them in the process.
Why Start Seeds Indoors?
Starting seeds indoors gives certain plants a head start on the growing season. This is especially important if you live in a cooler climate with a shorter growing season. Plants like tomatoes and peppers need a long, warm growing period — if you waited to plant them outside after your last frost, they might not have time to produce fruit before fall.
Indoor starting also gives you more control over moisture, temperature, and light during the most vulnerable stage of a plant's life.
Start These Indoors
These plants benefit from 4-8 weeks of indoor growing before being transplanted outside:
- Tomatoes — Start 6-8 weeks before your last frost date
- Peppers — Start 8-10 weeks before last frost (they're slow)
- Eggplant — Start 8-10 weeks before last frost
- Broccoli & cauliflower — Start 6-8 weeks before last frost
- Herbs (basil, parsley) — Start 6-8 weeks before last frost
- Kale & cabbage — Start 4-6 weeks before last frost
Direct Sow These Instead
These plants don't like their roots disturbed, grow fast enough to not need a head start, or just do better when planted directly in the garden:
- Carrots — Hate being transplanted. Always direct sow.
- Radishes — They grow so fast, starting indoors is pointless.
- Beans — Direct sow after last frost. They grow quickly.
- Peas — Direct sow in early spring. They like cool soil.
- Corn — Needs to be direct sown. It doesn't transplant well.
- Squash & melons — Can be started indoors but do great direct sown too. Their roots are sensitive.
- Lettuce & spinach — Can go either way, but direct sowing is easier and works great.
The Indoor Starting Setup
You don't need anything fancy. Here's the basic setup:
- Containers: Seed trays, peat pots, or even egg cartons with drainage holes.
- Seed starting mix: Use a light, sterile seed starting mix — not garden soil, which is too heavy and can harbor disease.
- Light: A sunny south-facing window can work, but a basic shop light or LED grow light hung 2-3 inches above seedlings is much more reliable.
- Water: Keep the mix consistently moist but not soggy. Bottom watering (sitting trays in water) is the easiest way to avoid overwatering.
- Warmth: Most seeds germinate best at 65-75°F. A heat mat can help if your house runs cold.
Hardening Off: The Step Everyone Skips
This is where most beginners lose their seedlings. "Hardening off" means gradually introducing indoor seedlings to outdoor conditions before planting them in the garden. If you skip this step and just plop them outside, the sun, wind, and temperature swings will shock and possibly kill them.
Here's the process:
- About 7-10 days before transplanting, start putting seedlings outside in a sheltered, shady spot for 1-2 hours.
- Each day, increase the time outside and gradually introduce more direct sunlight.
- By the end of the week, they should be outside all day (and overnight if temperatures allow).
- Then plant them in the garden. Water well.
Quick Reference Timing
Count backward from your last frost date:
- 10 weeks before: Peppers, eggplant
- 8 weeks before: Tomatoes
- 6 weeks before: Broccoli, basil, kale
- 4 weeks before: Lettuce, cucumbers (if starting indoors)
- After last frost: Direct sow beans, corn, squash, carrots, radishes
Track everything. Write down what you planted, when you planted it, and what happened. Next year, you'll have your own personal planting guide based on real data from your own garden. That's the power of keeping records — and that's exactly what the Plant Diary is for.