Seed Starting 101
Master the art of starting seeds indoors. This comprehensive guide covers everything from equipment and timing to troubleshooting common problems.
Why Start Seeds Indoors?
Starting seeds indoors gives you a head start on the growing season, allows you to grow varieties not available as transplants at garden centers, and saves money compared to buying plants. It's also incredibly rewarding to nurture a plant from seed to harvest.
While some crops like beans, corn, and carrots prefer direct sowing, many vegetables benefit from indoor starting—especially warm-season crops like tomatoes, peppers, and eggplant that need a long growing season.
The Four Keys to Success
Temperature
Most seeds germinate best at 70-85°F. Use a heat mat to maintain consistent warmth. After sprouting, slightly cooler temps (60-70°F) produce sturdier seedlings.
Moisture
Seeds need consistent moisture to germinate—but not soggy conditions. Aim for soil that feels like a wrung-out sponge. Use humidity domes until seeds sprout.
Light
Seedlings need 14-16 hours of strong light daily. A sunny south-facing window often isn't enough—invest in grow lights for the best results.
Timing
Count back from your last frost date to determine when to start seeds. Starting too early leads to leggy, root-bound seedlings. Too late means missing valuable growing time.
Paper Towel Method
The paper towel method is a quick way to test seed viability or pre-germinate seeds before planting. It allows you to see exactly when seeds sprout and transplant only viable seeds.
- Testing old seed viability before planting
- Seeds that are slow or difficult to germinate
- Getting a head start on germination
- Seeds with hard coats (after scarification)
- Expensive or rare seeds where you want maximum success
- Label your bags with seed variety and date
- Check daily to catch seeds at the right stage
- Don't let roots grow too long—they become fragile
- Transplant root-side down into pre-moistened soil
- Keep transplanted seeds under humidity dome until established
Prepare Materials
Gather paper towels, a zip-lock bag or plastic container, spray bottle with water, and your seeds. Use plain white paper towels without dyes or patterns.
Moisten the Paper Towel
Dampen (not soak) a paper towel with water. It should be wet enough to stay moist but not dripping. Wring out excess water.
Arrange Seeds
Fold the paper towel in half or quarters. Place seeds on one half, spacing them so they don't touch. Fold the towel over to cover seeds.
Create a Mini Greenhouse
Place the folded towel in a zip-lock bag or plastic container. Leave bag slightly open or container lid cracked for air circulation.
Provide Warmth
Place in a warm location (70-85°F). Top of the refrigerator, on a heat mat, or in a warm cupboard works well. Avoid direct sunlight.
Check Daily
Open and check seeds daily. Mist if the towel starts to dry out. Most seeds will sprout within 3-14 days depending on variety.
Transplant Carefully
Once seeds show a root (radicle) about 1/4 to 1/2 inch long, carefully transplant to soil. Handle by the seed, not the delicate root.
Cold Stratification
Cold stratification mimics the natural winter conditions that many perennial seeds need to break dormancy. Without this cold period, these seeds may not germinate at all or will have poor germination rates.
| Plant | Weeks in Cold |
|---|---|
| Lavender | 2-4 |
| Echinacea/Coneflower | 4-6 |
| Milkweed | 4-8 |
| Black-eyed Susan | 2-4 |
| Baptisia (False Indigo) | 6-8 |
| Rhubarb | 2-4 |
| Asparagus | 3-4 |
| Many native grasses | 4-8 |
- Check seed packet—it will indicate if stratification is needed
- Don't skip stratification for seeds that require it—they simply won't grow
- Slightly moist, not wet—seeds can rot if too damp
- The refrigerator crisper drawer often provides ideal conditions
- Mark your calendar for when stratification ends
- Some seeds need both scarification AND stratification
Step-by-Step Guide
Before you start, make sure you have all the necessary equipment for successful seed starting.
- Seed trays or cell packs (with drainage holes)
- Seed starting mix (not regular potting soil)
- Plant labels and permanent marker
- Spray bottle for gentle watering
- Humidity dome or plastic wrap
- Heat mat (optional but recommended)
- Grow lights or sunny window
Use a sterile, fine-textured seed starting mix for best results. Never use garden soil.
- Moisten the mix before filling containers
- Mix should be damp like a wrung-out sponge
- Fill cells to the top and tap to settle
- Create a flat, even surface
Planting depth and spacing depend on the seed type. Check your seed packet for specifics.
- Sow 2-3 seeds per cell for insurance
- Plant at depth of 2x the seed diameter
- Very fine seeds: press into surface, don't cover
- Cover with thin layer of mix or vermiculite
- Label everything immediately
Most seeds need consistent warmth and moisture to germinate. Light requirements vary.
- Cover with humidity dome to retain moisture
- Maintain soil temp of 70-85°F for most seeds
- Use heat mat for warmth-loving crops
- Check moisture daily - mist as needed
- Remove dome once seeds sprout
Once seeds sprout, they need strong light and careful watering to grow into healthy transplants.
- Provide 14-16 hours of light daily
- Keep lights 2-4 inches above seedlings
- Water from below when possible
- Thin to strongest seedling per cell
- Begin fertilizing at 1/4 strength after true leaves
When to Start Seeds
| Crop | Weeks Before Last Frost | Days to Germinate |
|---|---|---|
| Tomatoes | 6-8 | 5-10 |
| Peppers | 8-10 | 7-14 |
| Eggplant | 8-10 | 7-14 |
| Broccoli | 4-6 | 5-10 |
| Cabbage | 4-6 | 5-10 |
| Lettuce | 4-6 | 2-10 |
| Basil | 4-6 | 5-10 |
| Cucumbers | 2-3 | 3-10 |
| Squash | 2-3 | 4-10 |
| Melons | 2-3 | 4-10 |
Use our Zone Finder to determine your last frost date, then count backwards to find your ideal seed starting date.