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High Altitude Gardening: Start planting your vegetables now with hoop houses, season extenders

Lori Russell
Daily Correspondent
Vail, CO Colorado

Global warming may wreck havoc on the rest of the country, but here in the mountains, you can’t help but revel in the unnatural warmth this spring. Warm springs and falls are a real boon to high-altitude gardeners. I already planted my garden in mid-April with spinach, bok choy, lettuce, peas, carrots, cabbage and beets. My spinach is already 1 inch high in Eagle. I should see my first harvest by May 1. But I also use the help of season extenders such as hoop houses and a greenhouse with frost covers. These season extenders help push the limits of our high-altitude growing season by protecting areas of the garden from the colder nights that slow down growth.

Greenhouses used to be the affluent gardener’s dream, often costing $4,000 or more. But with simple, plastic covers called hoop houses, you can create the same greenhouse protection for a fraction of the cost.

The first thing to know is which vegetables do well, or at least manage, at the cooler temperatures of the high altitude of central Colorado. Most leafy greens can grow well in daytime temps that are at least above 45 degrees and will survive nighttime temps down to 20. Ordering your seeds online from a grower that selects for cold-tolerant varieties, such as http://www.bestcoolseeds.com in Alaska, will greatly increase the seeds’ hardiness. Most big seed companies such as Burpee, (that you see at Home Depot) are bred in Indiana in a warmer climate.

With the right vegetable seeds, the objective is then to manage the temperatures in your garden area and maintain them near or above freezing at night and above 45 degrees in the daytime. This is done mainly with garden covers such as “frost covers” – a light cloth – and hoop houses, which are mini-greenhouses that anyone can set up in an hour. Hoop houses are cheap and easy to assemble. There are several kits available (see http://www.growerssupply.com), or the pieces are easy to put together from the hardware store. When combined with frost covers, they can maintain a garden area 5 to 10 degrees above the outside air temp. So even if the night gets down to 20 degrees, your garden will probably stay above freezing. As soon as the sun shines the next day, the hoop houses need to be vented because they can quickly warm up over 80 degrees, and your seeds will continue growing happily. As the season finally warms up and the last frost is past, (around June 1, depending on your elevation), you can remove the hoop house and frost cover, and the vegetables will be well on their way toward harvest.

Our local climates around central Colorado are strongly linked to your individual elevation. A garden in East Vail will have a somewhat different experience than a garden in Eagle, 2,000 feet lower and often 10 degrees warmer. So the problem becomes one of managing your own local micro-climate.

This system works with “cold tolerant” vegetable varieties but can also prewarm your garden for warm season veggies, such as beans and tomatoes. Most of the leafy greens are very cold tolerant, starting with spinach, chard, kale, bok choy, onion, radish, some lettuce and parsley. With some protection, these can be planted after April 1, when the nights are mostly above 20 degrees. As the nights get consistently above 25 or 30 degrees, you can plant carrots, peas, potatoes, beets, turnips and cabbage. When the nights are mostly above 40 degrees, you can remove all protection and these will grow fine with at least six to eight hours of sunlight per day (and plenty of water). The rest of the vegetables – the “warm season veggies” – must wait until after June 1 to plant, again depending on your elevation, when the nights are always above 40.

In higher elevations, you will probably need to employ garden covers for much of the summer for some of the warm veggies.

Lori Russell is a local gardener, professional landscaper and teacher of high-altitude techniques. She lives and gardens in Eagle.


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