High Altitude Gardening
Getting Results From A Short Growing Season
Gardening at elevations of 5,000 feet and higher in America’s mountainous west presents unique challenges. The high country gardener must pay careful attention to the weather and its effect on growth to be successful. A little knowledge regarding climate and growing seasons, soil conditions, moisture and pest control — knowledge that all gardeners should posses no matter where they garden — will result in minimal failures and maximum success.
My own high altitude gardening knowledge came hard. Back when all of us wannabe hippies soured on the urban commune and decided it was time to get back to nature we, of course, struck out for the hills. The high, mountainous country of the American West, as it had for generations of Americans, represented freedom, a fresh start and a return to nature. Live off the land! Grow your own vegetables! Become self-sufficient!
Our desire for a life in concert with the land was superseded only by our ignorance. Even those of us who’d had farm experience in the Midwest and had raised vegetables with our parents and grandparents had no idea of the growing challenges at high altitude. We soon found out.
What was different from our warm, humid and lengthy summers in farm country? Plenty. The growing season was measured in weeks, rather than months, and infrequently interrupted by July hail storms and August frosts. Complications included scarce rainfall, searing sunlight, rocky alkaline soils, or forest-shaded acidic soils and, depending on our location, hoards of marauding deer, raccoons and rabbits.
Over the years, with plenty of trial-and-error experience and savvy advice from old hands, we eventually produced bumper crops of delicate greens despite the frosts, delicious, organic broccoli, Brussels sprouts and cabbages despite the waves of August insects, and straight-and-true root vegetables despite the poor soil. Keeping it all from the deer and raccoons? That’s another story.
Altitude affects every facet of climate; temperature, humidity and precipitation are all affected by changes of elevation. Sunlight-suffocating cloud cover can be common on one slope, absent, along with rain, on its opposite side.
The high-altitude gardener’s main concern is the length of the growing season. Attempting to raise a winter squash that requires 90 or 100 days to mature in a zone that provides only 70 to 80 frost-free days (or less) is a recipe for disappointment. Yet with wise planning, preparation and attention the high altitude gardener can grow such squash as well as a myriad of other vegetables, including tomatoes, eggplant, beans and peppers. Choosing the right vegetables to grow for your conditions, starting seeds indoors, protecting plants at the beginning and end of the growing season as well as doing everything possible to encourage quick, healthy growth will reward the high altitude gardener with results to rival his flatland counterparts.
Start by finding your area’s climate zone. Climate zone and plant hardiness maps will give you a general idea of your area’s growing season and which plants will thrive there. But zone designations can only help so much and may not be detailed enough to show variations between locations only a few miles apart. In Colorado, frost-free days range from over 150 in places including Boulder and Grand Junction but less than 50 in mountain towns including Steamboat Springs and Crested Butte. (Fraser, CO, elevation 8,560 feet, has an average yearly growing season of just 10 days). Entering my home zip code from Santa Fe, New Mexico (elevation 7,200 feet) into the zone finder yields a 5a result. But my growing conditions a few hundred feet above the city center on a west-facing slope are actually closer to zone 4 conditions. Recording incidence of frost and minimum night-time temperatures in a gardening journal will yield useful information for the years to come. And remember that the zone designations consider only days without frost and minimum low temperatures, They overlook other important growing factors. Consider that cloudy, wet, sea-level Seattle, WA with its acid soils shares a zone 8 designation with high, dry and sunny Tucson, AZ with its alkaline soils.
High-country gardeners must take into account the slope of their land and its exposure to the sun. Is it sloping to the east, getting morning sun only, a quick warm up followed by an early, cool evening? Is it sloping to the west which means it’s slow to heat up in the mornings but blessed by warm afternoon temperatures that carry into the evening? Do you have south-facing property, rich in sunlight all day long? Or is it north facing, shaded all day and basically unsuitable for most vegetables?
There are other growing-season factors to consider in mountain country. Your garden’s unique microclimate — how much shade it receives, if it’s in a gulch or a pocket that holds heat and cold and protects it from winds, if there’s sunlight reflection from nearby structures, the amount of rain it receives and your soil’s ability to hold moisture — all these factors will affect your plants. Heat is slower to build and quicker to dissipate at elevation (the thinner air means more distance between molecules, making it easier for heat to rise). With so many variables to consider, only experience with your property will reveal exactly what kind of conditions you’ll face. Again, a yearly journal that records weather conditions and gardening results can become an invaluable tool.
The Right Choice
Generally, you’ll choose vegetable seeds with the shortest “days-to-maturity” numbers for your garden. Leafy greens and root vegetables — carrots, turnips, parsnips, radishes and beets — are the best choices for high-altitude, short-season gardens. Beets and turnips are also a good source for tasty, early season greens. Though susceptible to frost damage, potatoes are a good, high-elevation crop if well mulched and covered during early, over-night freezes. Spinach, leaf lettuce, arugula, chicory, chard, most varieties of Asian greens (pak choi) and mustards (Osaka) can be sown right in the garden. Vegetables that require a growth stage before producing seeds and fruits (tomatoes, squash, peppers, green beans) require more time and therefore are more risky. Most of these vegetables can be given a jump by starting seeds indoors and planting them in the garden after all danger of frost has passed. (Though I’ve been able to transplant green beans started indoors using biodegradable cups, they seldom do better than those planted directly in the garden.) They can also be transplanted outside early with protection from a cold frame or in covered raised beds. Vegetables that need warm conditions to flourish — eggplant, peppers, tomatoes — may need to be sheltered during the entire growing season.
“Days-to-harvest” ratings should be considered when choosing among vegetable strains. A 58-day Blue Lake bush bean will be more likely to succeed in zone 4 than a 65-day Blue Lake pole bean. But remember that other factors will also influence days-to-harvest. Maturity ratings are relative to ideal conditions; it may take your 45-day crookneck squash a full two months or more to bear fruit in the cool mountain air. We tried a number of short-season, 60-plus day sweet corns when living in the foothills of Washington’s Olympic Mountains (not so high in elevation, but an extremely damp, sunlight-challenged environment) without success. Then a local gardener introduced us to an heirloom corn that germinated and grew well in cool, damp soils and suddenly… sweet corn, which made our raccoon neighbors especially happy. (Sorry, after several subsequent moves I’ve forgotten the name of that corn, proving how important a garden journal can be. The 68-day Precocious is one sweet corn that works well in cool soil temperatures.) Take advantage of local information sources to find which variety of seed from different vegetables works best in your area. Your county extension office, community gardening club and your gardening neighbors are valuable resources that can save you the frustration.
Don’t be afraid to try uncommon vegetables, such as sorrel, that grow well in cool climates. And don’t forget herbs. Starting basil, parsley, mint and cilantro indoors, in their own pots or for transplant, will spice up your kitchen as well as your garden. Chives over-winter well down to zone 4 in containers that are mulched or covered as will tarragon, lavender and thyme (mulch these heavily and be prepared for disappointment). Some perennial herbs including creeping and mountain thyme will return year after year as long as they are well-protected during winter’s coldest months.
Jump Start the Season
The best way to get a jump start on the growing season is to start your seed indoors well ahead of last frost. The chart here (PDF, scroll down) tells how far in advance of your last expected frost to plant. Vegetables that are easy to start indoors and transplant include broccoli, cabbage, Brussels sprouts, lettuce and tomatoes. Vegetables suitable for starting indoors but with slower root development include cauliflower, onion, celery, peppers and onions (these last two will probably require additional protection once set outdoors). Cucumbers, pumpkins, squash, muskmelons and watermelons, even if they’re to be placed in covered raised beds, often won’t survive transplanting. To avoid disturbing their fragile root systems, start them in biodegradable containers, such as peat pots, that can be transplanted directly into the garden soil. Or you can make your own from recycled newspaper.
When you set plants out can be a gamble. Statistics give us planting schedules for zone 3 and 4 based on averages. But mountain climates seldom follow averages. Be alert to weather changes and prepared to cover plants and emerging seedling from extremely late, unexpected frosts and other weather events like hail.
To avoid shocking your precious seedlings, be sure to harden off seedlings before transplanting to your garden. This can mean taking the pots outside for a few hours each day, preferably in a shady, protected spot, for a period of two weeks before putting them in the ground. Remember that the higher the elevation, the harsher the sunlight and the faster your plant’s soil will dry out. Putting seedlings in a vented cold frame is an ideal way to help them adjust.
You can give seeds that go directly in the garden a jump start by planting them under mulch. I’ve had success using this method with lettuce, peas, arugula, Asian greens, leafy cabbages, beets and turnips. Use only an inch or so of mulch and don’t plant more than two or three weeks ahead of the last frost date. The mulch should be enough to protect your seedlings from all but the hardest of frosts. Before germination, cover the mulch with black plastic to help heat the soil. Remove it when seeds begin to sprout. The mulch method works less well in very moist conditions.
You can also spread black plastic alone on top of your garden soil to help it warm ahead of sowing seeds. If your soil is particularly damp, plastic covers will slow the drying process. After germination and transplanting, using black plastic ground cover on either side of row crops raises soil temperature. (I prefer using natural, organic mulch over plastic.) But plastic or organic, the use of ground cover can give you a day or even a week’s edge over a short growing season. When summer conditions arrive in the high country — and they arrive suddenly, often skipping spring altogether — your seedlings will be ready to take full advantage. This may mean all the difference between a few sweet peas and a bountiful harvest.
Small efforts matter. Planting seed in troughs or depressions will help contain heat and keep your plants warmer during the short growing season. Making ridges between row crops protects them from drying winds and also helps hold heat.
If frost should hit your uncovered plants in early season, try watering them before the sun hits them. Don’t sprinkle leaves, of course, if temperatures remain below freezing. But a watering at the plant’s base may prevent otherwise fatal damage.
Many vegetables just won’t make it in zones 5, 4 and below without protective intervention. These measures can range from simple cloches, some filled with water to full-scale greenhouses (though be careful with these in the high country… I once saw a homestead tomato house blown away overnight by fierce mountain winds). Cold frames may be the simplest form of protection for your vegetables. Not only will they give you a head start with germination, but will encourage fast growth during the early days of the season. Most cold frames are fixed, but if built simply, they can be removed as plants mature and day-time temperatures rise. And they can be replaced on low-growing crops like lettuce and spinach when the first frost threatens. But be careful. The intense sunlight at high elevations means temperatures in your cold frame can quickly exceed what your plants can tolerate. Be sure to vent cold frames sufficiently during daylight hours to prevent wilting.
Fixed, raised beds have the advantage of warming up ahead of the ground, especially if PVC hoops are installed to support plastic. The plastic covering can easily be removed as temperatures rise during the summer or reapplied if temperatures fall. The hoops also provide support for netting which can keep out marauding birds and other unwanted garden visitors. There are as many ways to make covered raises beds as there are gardens. Get ideas here and here.
The “hoop house” idea can be adapted to cover entire rows of your garden. We’ve used this method to give all kinds of vegetables, including beans and tomatoes, a big advantage. Once we (carefully) transplanted cantaloupe vines we’d started indoors in a hoop-covered row and produced a few small melons, the first, according to our local gardening expert, ever grown in our particular mountain valley (that made them taste even better). You can build these hoop-row shelters wide enough to cover two or three rows. Work the soil where they will be used and plant seed before erecting the structure and covering. We’ve heard of gardeners who place a black 55-gallon barrel of water every 30 or so feet under their row house to collect heat and radiate it during the evening. This seemed to us to be too much work for our modest garden, crossing the line between intensive gardening practice and just plain crazy.
High country soil conditions demand soil testing. Colorado State Extension Service warns new gardeners that their soil may look fine, but have a pH of 8.5 and higher, too high for most plants. Mountain valleys may be too sandy and lacking in nutrients, east-facing slopes may be heavy with clay that will suffocate plant roots. And certain ground may give up more rocks than potatoes. Your soil may display characteristics of ample iron (the red color of dirt so common in parts of the West) but your plants may be iron deficient because of the high carbonate levels that prohibit plants from utilizing the mineral.
In almost every case, adding organic material to your ground will improve conditions, including adjusting soil pH. Extremely alkaline soils need careful application of sulfur and lots of organic material, preferably more acidic materials like wood chips, pine needles and leaves. Contacting your extension service for testing and remedial solutions is highly encouraged. Correcting high alkaline soils, including the removal of salts, can be an intensive process with results coming slowly. Adding agricultural gypsum to “break-up” clay soils is a mistake where soils are highly alkaline. Gypsum will only serve to increase already high pH readings. Again, adding organic material in the form of finished compost will allow clay soils to un-pack, making room for water drainage and root structure.
In the high country, insects, like the plants that feed them, come on strong and all at once. They also contend with the short growing season. Somehow, this doesn’t deter them. A grasshopper’s life cycle is about 90 days, the same as a butternut squash. Yet, grasshoppers manage to be more prolific than squash, even in places where harsh winters should kill their soil-buried eggs (grasshoppers benefit from mulch, too). Organic gardeners facing infestations can use Semaspore, a natural occurring pathogen carried by wheat bran that affects only grasshoppers, in and around their gardens.
High country gardeners must also deal with cabbageworm (hand pick from plants when in the caterpillar stage and release parasitic wasps into the garden) root maggots (put protective discs around each plant to prevent the maggot from burrowing down to the root; plastic row covers will also keep the flies from the plants), cut worms and aphids (use beneficial insects such as ladybugs and lacewings to control them). Your best defense against insect pests is to keep a clean garden, especially at the end of the growing season when insects will look for places to survive the winter in the remains of your plants. Organic means of pest control, including neem powders, garlic oil, horticultural oils and soaps can be used when needed.
Larger pests are a different story. Almost every organic gardening book I’ve seen recommends fences to keep out deer. But I’ve never seen a fence, even if eight feet high and electrified, to be completely effective. (I know of one gardener who had success attaching poles to the top of his deer fence and stringing crepe paper streamers between them.) Deer repellent is good for keeping deer from browsing your shrubbery during winter but not usually suitable (or effective) protecting vegetables.
Raccoons are even more persistent at penetrating fences, even electric ones, and will wipe out several rows of corn in a single night. Having an outdoor dog is a good deterrent but training one to maintain vigilance while not destroying the garden with relentless pacing (and keeping you awake with barking) is a challenge even the most accomplished dog whisperer would find frustrating. A friend used Havahart live traps and relocation to reduce his raccoon population, a great idea until he came out one morning and found a skunk in one of his traps.
The least frustrating approach might just be co-existence. Resign yourself to the fact that, despite your best efforts, the varmints will make off with some of your food. This technique usually involves planting more than you think you might need, thus covering your losses, and planting the edge of your garden with plants, like lettuce and herbs that will keep rabbits and others busy at the edges or discourage them altogether. You may even find their presence beneficial. Last summer, I had a rabbit who made itself at home in a patch of mixed lettuce. It stayed concealed there during the day, nibbling away and thinning out the mesclun, allowing room for other plants to mature. At night it moved out into the yard. Yes, I lost some lettuce. But I gained a gardening friend.
In a sense, my relationship with the rabbit stands as a symbol for high-country gardening. One must be ready for compromise and disappointment. You may not be able to grow the biggest Beefsteak tomato. But those Manitoba and Early Girl hybrids or Northern Light and Siletz heirlooms will be every bit as tasty; more so since you grew them yourself. There will be years when unexpected frost will wipe out your precious seedlings and you’ll be forced to plant again, years in which punishing hail storms claim all your lettuce, broccoli and zucchini plants, years with springs so cool and wet that you’ll get little more than peas and greens from your garden. But then will come a season with just enough rain, plenty of sunshine and frosts that wait well into September before getting serious. And my, how your garden will grow.