Start Sweet Peas from Seed: Your Guide to Early Indoor Sowing
Last spring, I started my sweet pea seeds on the windowsill in March. By May, I had armloads of fragrant flowers. My neighbor, who direct-sowed hers in April, got exactly five blooms before the summer heat killed them. That's when I learned: starting sweet peas indoors changes everything.
If you want sweet peas blooming from May through July instead of just a few weeks in June, you need to start early. And indoors is where that happens.
Why Indoor Starting Makes Sense
Sweet peas are weird. They actually prefer cool weather and will stop flowering when temperatures hit 80°F. That's why early indoor sowing gives you such an advantage. You're not coddling them - you're giving them the head start they need.
Starting seeds indoors gets you:
- 4-6 weeks more flowering time
- Stronger plants with better root systems
- Control over germination conditions
- Protection from birds and slugs that love the seeds
The seeds are big, like dried peas. Easy to handle, even for kids. They just take their sweet time germinating - sometimes 2-3 weeks. That's another reason to start inside where you can keep conditions steady.
When to Start Your Seeds
Count backward from your last frost date. Start seeds 4-6 weeks before that date.
Indoor Sowing Timeline
| Your Zone | Start Indoors | Transplant Out | First Blooms |
|---|---|---|---|
| 3-4 | Early March | Late April | Early June |
| 5-6 | Mid-February | Early April | Mid-May |
| 7-8 | Late January | Mid-March | Late April |
| 9-10 | December | February | March |
Southern gardeners can start in January or even fall-sow for winter blooms. The rest of us stick to late winter/early spring indoor sowing.
The Simple Sowing Process
Pick deep containers. Sweet peas have long roots. Use 4-inch pots minimum. I use old yogurt containers with drainage holes. Works great.
Plant two seeds per pot, 1 inch deep. Regular potting mix is fine. Some people soak seeds overnight first. I've tried both ways - doesn't make much difference.
Now here's where modern growing helps. A sunny windowsill works, but best rated LED grow lights keep your seedlings compact and healthy. Without enough light, seedlings stretch and get weak. Under grow lights for indoor plants, they develop properly with strong stems and roots. Keep lights 6 inches above seedlings, running 14 hours daily. The difference is huge - your seedlings will be sturdy and ready to thrive outdoors.
After germination, move them somewhere cool - 50-60°F is perfect. An unheated garage with grow lights, a cool window, whatever you have. This cool treatment makes them branch more and flower better.
The Pinching Secret
When seedlings reach 4-6 inches tall, pinch out the growing tip. Just squeeze it off with your fingers. This one simple action doubles your flower production. Don't skip it.
Transplanting and Support
Two weeks before your last frost, start hardening off. Days outside, nights inside for a week. Then leave them out if temperatures stay above 25°F.
Plant them 6 inches apart. Set up support before planting - sweet pea tendrils can only grab things 1/4 inch or smaller. String, netting, or chicken wire all work great.
Growth Speed by Temperature
| Temperature | Growth Rate | What Happens |
|---|---|---|
| 50-60°F | Steady, strong | Perfect growing conditions |
| 60-70°F | Fast growth | Peak flowering period |
| 70-80°F | Slowing down | Fewer flowers, prepare for end |
| Above 80°F | Stop | Plants shut down, season over |
Keep Them Blooming
Three things matter: water, picking, and temperature.
Never let them dry out completely. Pick flowers every 2-3 days - the more you cut, the more they bloom. When summer heat arrives, they're done. That's normal.
Some gardeners extend the season with afternoon shade once temperatures hit 75°F. Others start a second batch indoors under LED grow lights for fall greenhouse growing. You can even start super early - December or January - using indoor plant lights for the earliest outdoor blooms.
FAQs
What's the difference between windowsill and grow lights? Windowsill seedlings often stretch toward light and get leggy. Best rated LED grow lights keep seedlings compact and sturdy, especially important in February when natural light is weak.
Should I soak seeds first? Optional. Speeds germination by maybe 2 days. Room temperature water only.
How deep should I plant? One inch deep, no more, no less.
Can I save seeds from my flowers? Yes. Let pods dry completely on the vine first.
Why did my sweet peas die in July? Heat. They're cool-season flowers. Start earlier next year for a longer bloom period.
Seeds rotted? Too warm and wet. Keep under 70°F, don't overwater.
Tall, floppy seedlings? Need more light. Add a grow light or move closer to window.
Stopped flowering in June? Summer heat arrived. Normal for sweet peas.
The Bottom Line
Starting sweet peas from seed indoors isn't complicated. Plant deep in tall pots. Keep cool after sprouting. Pinch once. Transplant early.
This weekend, get some seeds and pots. Count back from your last frost date. Use grow lights if you have them, a sunny window if you don't.
By the time your neighbors are thinking about planting, you'll be cutting bouquets.
