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Regional Calendars, Climate & DataElevation and Planting Dates
As you climb, the growing season usually gets shorter and cooler. Planting dates written for the valley floor often fail on the hillside, and the reverse can also be true.
Key points
- Higher sites usually run cooler with a shorter frost-free period.
- Valley floors can frost first because cold air drains downhill.
- Aspect can shift planting windows by days or weeks.
- Compare days to maturity with your own frost-free window.
How does elevation change the growing season?
Air generally gets cooler as elevation rises, so spring warms later and fall cools sooner at higher sites. The frost-free period gets shorter, and the number of warm days available for heat-loving crops shrinks. Nights can be cold even in midsummer at high elevation.
This means that a published frost date for a nearby town may not describe your farm if you sit hundreds of feet higher or lower. Ask your extension office whether the nearest station is close to your elevation, and adjust your expectations accordingly.
Check your state extension planting guide for the range for your area, because the size of the elevation effect depends on region and terrain.
Why can a valley bottom be colder than a slope?
Cold air is dense and flows downhill on clear, calm nights, pooling in low spots. A valley floor, a hollow or a field with a fence or hedge that blocks drainage can frost when a slope above it does not. This is called cold air drainage.
Growers sometimes call the warmer zone on a slope a thermal belt. Orchards and vineyards often use it to reduce frost risk. If you are choosing a site, walk it on a clear night after a cold day and note where frost forms first.
- Low spots collect cold air
- Obstacles can trap cold air above them
- Mid-slope sites often frost less than the valley floor
How does aspect matter?
South-facing slopes in the Northern Hemisphere receive more direct sun and warm earlier in spring. North-facing slopes stay cool, hold snow longer and warm slowly. East-facing sites get morning sun and dry out early, and west-facing sites collect afternoon heat.
Aspect can shift the planting window by days or weeks even within a single field. Use south-facing ground for early crops and heat-loving crops, and use cooler aspects for crops that dislike heat, such as lettuce and spinach in midsummer.
How should you adjust crop choice at higher elevation?
Choose crops and varieties with a shorter time to maturity, good cold tolerance and tolerance for cool nights. Compare the days to maturity on the seed packet with the days between your last spring frost and first fall frost, with a margin for slow growth in cool weather.
Long-season crops can still work with transplants, plastic mulch, row cover, low tunnels or high tunnels, but each adds management work. Ventilate on warm days and watch humidity.
Test small plantings before you commit a whole field. A short row of a new variety, started a week earlier or later than the rest, shows how it behaves on your own ground and costs very little.
What about soil, snow and water at elevation?
Snowmelt can keep soil cold and wet well into spring, and working it early can damage structure. Soils on slopes can be thin and prone to erosion, so contour planting, cover crops and residue help.
Many mountain growers depend on irrigation water governed by local rules and ditch schedules, which vary by state and district. Confirm delivery dates before setting your planting dates, and schedule watering by soil moisture.
Frost-prone sites can sometimes be improved by clearing barriers that trap cold air, such as dense hedges across a slope. Ask your extension office or NRCS conservation planner before changing a windbreak, because the same hedge may also protect the field from wind.
How do you tune your own elevation calendar?
Start with the nearest station's frost data and note its elevation. Then compare with your own thermometer log and adjust. For example, if a station in town reports a last spring frost in early May and your farm sits much higher, you might expect your last frost to run later, and plan tender crops accordingly. That is an example of the method, not a prediction for your farm.
Keep a simple log of last frost, first frost and low temperatures near planting. After a few seasons, you will know how much your elevation shifts the calendar.
What mistakes do growers make with elevation?
The first mistake is using the frost date of a valley town for a hillside farm, or the reverse. The second is planting the most tender crop in the lowest corner of the field, where cold air collects. The third is choosing a long-season variety with no plan for a cold, short year.
Another mistake is ignoring wind. Exposed ridges dry out soil, break stems and make covers hard to keep in place. Anchor row cover with soil or sandbags, stake tall crops early and plan windbreaks with help from your extension office.
- Check how close your station is in elevation
- Keep tender crops out of cold pockets
- Have a backup plan for a short season
Sources and further reading
Last reviewed: November 2026. Educational information, ranges only. Confirm timing with your county extension office.