When Should I Start Seeds Indoors? (How to Calculate From Your Frost Date)

Every January, gardeners start Googling "when to start tomato seeds indoors." They find a chart. The chart says "6-8 weeks before last frost." They look up their frost date. They count backwards on a calendar. And then they forget which weekend they were supposed to start, because they never wrote it down.

Or worse: they start too early, because the excitement is irresistible, and by April they have leggy, root-bound seedlings that take weeks to recover from transplant shock.

The timing math isn't hard. But doing it right — and actually remembering what happened — requires a little structure.

Your frost date is the only number that matters

Everything counts backwards from your last expected frost. Zone 7a? That's roughly mid-April. Zone 5? Late May. The USDA hardiness map gives you a regional estimate, but experienced gardeners know their yard is a microclimate. Maybe your south-facing raised bed is a week ahead of the neighbor's shady lot.

Once you know that number, the rest is subtraction:

• Peppers and eggplant: 8-10 weeks. These are slow. Start them first.
• Tomatoes: 6-8 weeks. The most common mistake is starting these with the peppers.
• Broccoli, cabbage, cauliflower: 6-8 weeks.
• Basil and parsley: 6-8 weeks (basil especially needs warmth to germinate).
• Lettuce and kale: 4-6 weeks.
• Squash, cucumbers, melons: 3-4 weeks. That's it. These grow fast and hate being transplanted late.

Starting too early is worse than starting late

This is the thing nobody tells you. A pepper plant that spent 12 weeks in a 3-inch pot is not "ahead" — it's stressed, root-bound, and will underperform a plant that spent 8 weeks and went out at the right time.

I've done this myself. The February enthusiasm is real. But the plants that did best in my garden were the ones I started on time, not the ones I started earliest.

If you're unsure, err a week late. A slightly smaller transplant in warm soil beats a big transplant in cold soil every time.

Don't forget the hardening-off gap

Between "ready to go outside" and "actually planted outside" there's a 7-10 day window where seedlings need to gradually adjust to outdoor conditions. Sun, wind, temperature swings — indoor plants haven't experienced any of it.

If you want to transplant by May 1, you need to start hardening off around April 20. That means seedlings need to be big enough by mid-April. Work backwards from there, and suddenly the math matters more than you thought.

Generic charts vs. your actual data

Here's what makes the second season easier than the first: you have real dates. Not "6-8 weeks before frost" from a chart, but "I started Cherokee Purple on March 3 and it was perfect" or "I started jalapenos on February 15 and they were way too leggy."

Those notes are worth more than any planting guide. Your garden, your windowsill, your conditions. The chart gets you in the ballpark. Your records get you to the right answer.

That's why we built MyVeggieGarden around the idea that task timing should come from your frost date and your experience — not just a generic table. You set your frost date once, and the app calculates start times for every plant. When you complete a "start seeds" task, it logs the date. Next January, you're not Googling — you're looking at what you actually did last year.

Keep reading

• What to Write in a Garden Journal — so you actually have useful data next year
• Starting Seeds Indoors (Guide) — the full walkthrough with milestone tracking
• Planning Your Garden From Last Year's Notes — turning records into a concrete plan