Throgmorton: Autumn is Coming

Folks living in the mountains know fall is coming. It was chilly this past week.

Summers go fast in the high country. The last frosts can happen in mid-June. The first fall frosts come as early as mid-August. That is as little as sixty frost free days. Warm season vegetables like tomatoes and peppers don’t grow well in that short of a season. Some annual flowers are just starting to bloom in sixty days.

Cool season vegetables do great in the high country. Broccoli, cabbage, lettuce and salad greens prefer cool temperatures. Try sowing spinach now.  It will germinate in a few weeks. The seedling plants stay dormant through the cold winter. As the temperatures warm next spring the plants grow quickly. They’re ready for an early spring harvest.

Annual flowers seem to glow in mountain plantings. Old stand-bys like petunias, marigolds and zinnias are a blast of color until the first hard frosts. Pansies, snapdragons and dianthus are great for cutting and tolerate frosts. Ageratum, alyssum, lobelia and violas are great cool season accents.

Folks growing shrubs at elevations above 8,500 feet should look for natives. Native birch and alder are large garden accents. Snowberry and thimbleberry are medium sized shrubs. Non-natives to try are the Canadian shrub roses. These roses are on their own root so if they freeze to the ground, the same plant will come back and bloom the next season. With an insulating cover of snow, the roses usually don’t die-back. But watch for mold and rot on the plant as the snow slowly melts in the spring.

Native trees like aspen, spruce and pine are high country mainstays. Crabapples, hawthorns and chokecherries are non-natives to add to the landscape.

This time of year woody plants need to be prepared for fall. If they keep growing, their soft new growth can be nipped in the first freezes. Don’t fertilize trees and shrubs after mid-July. That goes for the lowlands too. Fertilizer pushes soft, new growth. Limit pruning. Pruning stimulates growth. Cut back on water. Less water means less new growth to get nipped. Once trees, shrubs and perennials go dormant keep them moist until the soil freezes.

Summer zips by especially in the high country. Picking the right plants keeps mountain gardens blooming.

Tom Throgmorton, of Throgmorton Plant Management, can be heard on KUNC, 91.5 FM, every Saturday morning at 7:35 and 9:35 a.m.

Originally published on September 23rd, 2011.