Last Frost Date Planting Calculator
Enter your last expected frost date and a crop, and get the exact dates to start seeds indoors, harden off transplants, and put them in the ground, no calendar math needed.
Calculate planting dates
Use your local last expected frost date, check your county extension office or the Old Farmer's Almanac if you don't know it.
Select a frost date and crop above
Results will appear here.
How to use this calculator
Enter your average last frost date in spring (not the last hard freeze, the last light frost). If you don't know it, the Old Farmer's Almanac, your local cooperative extension office, or a quick web search for "[your city] last frost date" will provide it. Select your crop and the calculator shows three key dates: when to start seeds indoors, when to begin hardening off transplants, and when it's safe to put plants in the ground.
Understanding the planting windows
- Start indoors: Count backwards from your transplant date by the crop's indoor growing period.
- Harden off: Begin the outdoor acclimation process 7–14 days before final transplant.
- Transplant / direct sow: The safe outdoor planting date relative to your frost date.
- Cold-hardy crops like peas, kale, and spinach can go out 4–6 weeks before frost date.
- Tender crops like tomatoes, peppers, and basil must wait until after the frost date.
FAQ
How do I find my last frost date?
The USDA Plant Hardiness Zone Map gives your zone, but for frost dates specifically, check the National Gardening Association's frost date database (garden.org) or your local cooperative extension office website. Many seed companies also provide frost date look-up tools by ZIP code.
What if I miss the indoor start date?
You can often still start indoors 1–2 weeks late, you'll get slightly younger transplants, but they usually catch up quickly once in warm soil. For crops like cucumbers and squash that grow fast and dislike root disturbance, it's often better to direct sow at the right time than to transplant a week-late indoor start.
What does hardening off mean?
Transplants grown indoors under artificial light are not acclimated to outdoor conditions, wind, temperature fluctuation, and UV intensity. Hardening off is a gradual exposure process: set plants outside for 1–2 hours on day one, increasing by 1–2 hours each day over 7–14 days until they're outside full-time. Skip this step and your transplants will suffer transplant shock or sunscald.
Can I use row covers to plant earlier?
Yes. A single layer of lightweight row cover fabric (1–1.5 oz weight) protects plants down to about 28°F (-2°C), effectively extending your season by 2–4 weeks. Heavy row cover (2–2.5 oz) can protect to 24°F (-4°C). Wall-o-Waters (water-filled plastic teepees) can extend the season even further for tomatoes and peppers.
What's the difference between direct sowing and transplanting?
Direct sowing means planting seeds directly in the garden bed. Transplanting means starting seeds indoors and moving the seedlings outside when conditions are right. Root vegetables (carrots, beets, radishes) must be direct sown, they don't tolerate root disturbance. Most other vegetables can go either way, though starting indoors gives you a head start on the season.