Mountain West Planting Calendar

In the Mountain West a few hundred feet of elevation can change your growing season by weeks. A useful calendar starts with your own elevation, aspect and water supply.

Key points

Elevation, slope and cold-air drainage can matter more than latitude.
Check days to maturity against your own frost-free window.
Local irrigation rules shape planting plans.
Season extension helps but needs active management.

How does elevation change the planting calendar?

As elevation rises, temperatures drop, the frost-free season shortens and nights stay cold even in summer. Two sites in the same county can have very different frost dates. A valley floor may warm early but also collect cold air, while a bench or slope can shed cold air and warm up faster.

Because published averages often come from a town station, check how closely that station matches your elevation. Ask your extension office for local frost-date information and compare it with your own observations.

Neighbors at similar elevations are a good source of local knowledge, and growers who share frost dates and results build a better picture than any single record.

What do short seasons mean for crop choice?

Short seasons favor crops with quick maturity, cold tolerance and a good tolerance for cool nights. Check the days to maturity for each variety and compare them with your own frost-free window. Long-season crops may need transplants, season extension or a different variety.

Season extension tools such as low tunnels, row cover, cold frames and high tunnels can add weeks on both ends of the season. They also raise management needs, including venting on warm days and managing humidity.

Choose varieties with a shorter days-to-maturity
Start long-season crops indoors
Use covers to protect against cold nights

How do you judge when the soil is ready?

Cold soil holds spring back longer than air temperature suggests. Check soil temperature in the morning at seed depth. Snowmelt can leave soil wet and cold for weeks, and working it early can damage structure.

High-altitude sun is strong, and dry air pulls moisture out of seedbeds. Seeds placed at the right depth in moist soil do better than those placed in dry, sun-baked ground, so plan watering around emergence.

How does irrigation water fit the calendar?

Many Mountain West farms and gardens rely on irrigation water from ditches, canals or wells, with delivery dates and rules set locally. Water rights and schedules vary by state, district and ditch company, so check local rules before you plan a planting date.

Scheduling logic applies: water seedbeds to get stands, then irrigate based on soil moisture and crop stage rather than a fixed day of the week. Point-of-use checks, such as probing the soil with a trowel or soil probe, keep you honest.

What about frost, hail and late snow?

A frost in late spring or early fall is common at elevation, and a late snow can follow a warm stretch. Keep frost protection on hand through the average last frost date plus a margin, and watch National Weather Service forecasts for cold nights.

Hail can strike in summer. Hail netting and crop insurance are tools that growers use, and USDA RMA and a crop insurance agent can explain coverage concepts and reporting dates.

How do you build a Mountain West calendar?

For example, if your last spring frost usually falls in late May and your first fall frost in mid-September, you can count the days between them and compare that total with the days to maturity on each variety you want to grow. This example shows the method and is not a recommended date set.

Keep a simple weather log with last frost, first frost and low temperatures near planting dates. Over several seasons, you will learn how your site differs from nearby stations and how much season extension you need.

What mistakes cost Mountain West growers the most?

The usual mistakes are planting tender crops after a few warm days, forgetting that a late snow can follow, and using town-based frost dates for a site that is much higher or lower. A related error is choosing a variety that needs more days than the season offers.

Another is skipping hardening off. Mountain sun is intense, and transplants raised indoors can scorch or shock when moved outside too fast. Spend a week moving plants into the open for longer periods before setting them out, and protect them on cold nights.

High-elevation gardens also benefit from windbreaks, which reduce moisture loss and protect tender plants. Plant windbreaks with species recommended by your extension office, and give them time to establish before you rely on them. Note that wind patterns shift with the seasons, so observe your site before choosing where to put them.

Check the elevation of your weather station
Harden off transplants
Carry frost cover through the average last frost date plus a margin

When to get local help: Your county extension office, such as Colorado State, Montana State, Utah State or University of Idaho Extension, can give elevation-specific advice.

Sources and further reading

Last reviewed: November 2026. Educational information, ranges only. Confirm timing with your county extension office.

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