Thin Air Harvest Practical gardening for the high, dry West

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Vegetable gardening at altitude

How to choose vegetable crops, dates, and covers for short seasons, cold nights, and windy, high-elevation gardens.

By the Thin Air Harvest editorial team. Updated November 1, 2026.

Vegetable gardening in this region is a calendar problem before it is a variety problem. The frost-free stretch at a Front Range bench can run five months on a median year and still lose a tomato crop to a cold June. A mountain garden at the elevation CSU Extension uses for its mountain fact sheet, above about 7,500 feet, may have fewer than 90 frost-free days. The Gilpin County office, at 9,300 feet, publishes June 10 and September 15 as its average last and first frosts. Those are different gardens. They should not share a planting week copied from a seed packet that was trialed in a warmer valley.

Start by writing down two dates for the station you actually match, using the method on the spring frost page and the numbers in the calendar section. The median last 32°F spring date is the middle of the historical record. The later date, often the 10 percent column in the NOAA occurrence tables, is the year that still freezes after most neighbors have planted. Hardy crops can go in before the median if the soil can be worked. Very tender crops, the ones CSU’s planting guide holds until summer-like days because a week under 55°F can stunt them, belong after the late date or under a cover you are willing to manage.

CSU splits the early crops by temperament. The planting guide’s hardy list includes broccoli, cabbage, kohlrabi, onions, lettuce, peas, radish, spinach, and turnips, and it allows them as soon as the soil is workable, often two to four weeks before the average last spring frost. The tender list in that guide includes beans, celery, corn, cucumbers, New Zealand spinach, and summer squash, sown around the average last frost when days are above about 55°F. The Colorado Vegetable Guide adds the mountain judgment on tomatoes in one line: they are very hard to grow unless the variety is short-season and grown under cover. Eggplant gets the same warning from the Gilpin summary. Peppers sit with them. If your frost-free window is under about 100 days, build the garden out of the hardy list and treat the tender list as a small, covered experiment.

Days-to-maturity need a translation, which the days-to-maturity article does in detail. For crops usually started indoors, seed companies count from transplanting, not from the day you sowed the tray. The Colorado Vegetable Guide says the number is not precise, and it tells mountain gardeners to leave a buffer because cool nights slow development. Gilpin County’s summary is more numeric: add about 20 days to the packet figure at that elevation. A 60-day bean is still a 60-day bean only where the summer matches the trial. Cool-season crops get more slack, because they survive a light frost and sometimes taste better after one. Warm-season crops with a long count simply do not finish unless the cover is doing real work.

Soil and siting decide whether the calendar you wrote is honest. Mountain soils often test under 1 percent organic matter, against a 5 percent figure CSU treats as a workable ideal. A south-facing gentle slope sheds cold air and catches spring sun. A flat creek bottom does the opposite, even when the map elevation looks favorable. University of Idaho’s short-season bulletins make the same point: the warm microclimate is usually a south or west wall, and a depression freezes first. Wind is not a side issue. The Colorado Vegetable Guide notes that high wind is common in spring and fall and that new transplants need protection. Put the detail with wind and raised beds, because a bed that dries out in a chinook is a water plan, not just a carpentry plan.

Season extension is a few degrees, repeated. The Colorado Vegetable Guide says air and soil under covers can run up to about 10°F warmer than outside. That is enough to establish brassicas in a cold May and to push a tomato through a September night on the Front Range. It is not enough to turn Climax, where the NOAA table’s median last 32°F spring date falls on July 7, into a sweet-corn town. Read cold frames, row covers, and the fabric and greenhouse comparison before you buy plastic. The raised-bed materials page prices a 4-by-8 bed in board feet and cubic yards, and the cold-frame and greenhouse page says which structure is worth building at your elevation. Solid plastic without a vent cooks a crop on the first bright day. Hail cloth is a different fabric with a different job, covered under hail.

A practical first garden at 5,000 to 6,500 feet is peas, lettuce, spinach, radishes, carrots, beets, a short cabbage, potatoes, and garlic planted the previous fall, plus one determinate tomato under cover if you want the ritual. A practical first garden above 8,000 feet drops the tomato until the cool-season beds are reliable, and it leans on the mountain list: greens, roots, peas, brassicas, and potatoes set two to three weeks before the last frost, pre-sprouted the way the CSU mountain sheet describes. The articles in this section follow that split. Pick the calendar for your state before you pick the cultivar.

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