High-elevation gardens take planning

By Kathy Hatfield
Gardening Columnist

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Gardening at elevations above 6,000 feet may seem almost impossible, but careful planning, the right choice of plants and a few season-extending tips will give you a colorful garden even in the high country.

While the average frost-free season at 5,000 feet is about 140 days, above 8,000 feet it is only 50 days. But elevation alone does not determine the length of a growing season. Low mountain valleys may trap cold air, higher elevations receive more intense sunlight and south-facing slopes warm more quickly, all factors that contribute to the length of a growing season.

It's often surprising to find that some higher communities, like Leadville at 10,000 feet, have a longer frost-free period than lower elevations. And "frost-free" is a term used loosely; at higher elevations, a killing frost can hit anytime during the growing season.

To get the most from the growing season, start by situating the garden in a protected area, if possible. Trees or buildings on the west, north or east side of the garden will help protect it from drying winds. A wall or building can reflect sunlight, warming the soil in spring more quickly. If you are lucky enough to have a south-facing slope, or can create one with raised beds, your plants will benefit from the warmer soil.

To extend the season, start flowers or vegetables in a cold frame, or place young plants in Walls of Water or cloches (hot caps). Most garden centers or garden supply catalogs have an assortment of season extenders. Protecting plants with a row cover, a polypropylene film stretched over wire hoops, not only keeps plants warmer, but also provides some protection from early insect damage. Mulches help protect plants from drying, but also delay soil warming and are best removed in early spring to allow the soil to warm.

Using containers to grow flowers and vegetables is another alternative where seasons are short. Plants can be started early and kept inside until temperatures warm sufficiently, then moved to outdoor locations. If you use containers, place large ones on wheels to make moving them easier. When temperatures drop, the containers can be moved temporarily indoors.

For any plants that are going to be grown outside, whether in containers or in the ground, be sure to acclimate them to the outdoors. Plants from a greenhouse or other indoor environment need a period of adjustment to their new environment. Allow about two weeks for the plants to adapt to the outdoors by gradually lengthening the amount of time that the plants are exposed to direct sunlight.

There are so many perennial and annual flowers that do well at higher elevations that it is impossible to list them all. Here are a few to get you started for a great-looking garden.

• Achillea sp. (yarrow) - easy to grow, fern-like foliage with flowers in white, yellow, pink and red
• Brassica oleracea (flowering cabbage or kale) - an annual that likes cool weather, has good fall color and is tolerant of mild frost
• Calendula spp. (calendula, pot marigold) - a self-sowing annual that is edible and a good cut flower
• Centaurea cyanus (cornflower) - a self-sowing annual that tolerates poor soil
• Centranthus ruber (red valerian) - a good plant for attracting butterflies and hummingbirds
• Dianthus barbatus (sweet William) - low mats of red, pink or white flowers with grass-like foliage
• Eschscholzia californica (California poppy) - bright yellow and orange flowers, self-sows
• Gaillardia x grandiflora 'Goblin' (blanket flower) - lots of red and yellow daisy-like flowers that bloom all summer
• Gypsophila paniculata (baby's breath) - dainty white or pink flowers; the classic filler for bouquets
• Iris germanica (bearded iris) - available in many different colors, does well in sunny, dry areas
• Nepeta x faassenii 'Walker's Low' (catmint) - lavender-blue flower spikes can be cut back after first flowering to encourage a second bloom.
• Oenothera macrocarpa (Ozark sundrops, Missouri evening primrose) - large yellow flowers that open in the afternoon and close the next morning
• Papaver nudicale (Iceland poppies) - blue-green foliage with bright, showy flowers
• Potentilla neumanniana (yellow creeping cinquefoil) - a low-growing groundcover that flowers in spring
• Sedum spurium (sedum, stonecrop) - low-growing rock garden plant, yellow or pink flowers
• Viola corsica (Corsican violet) - a short-lived perennial that self sows, purple flowers

E-mail your gardening questions to me at ocwildflowers@frii.com.