University of Wyoming Extension News

Landscaping Tips What annuals do best in Wyomings high altitudes?

By Karen Panter,
Extension horticulture specialist
UW Cooperative Extension Service

Dare we say summer is really here?

With that in mind, what sorts of herbaceous annual flowering plants should we think about for our gardens? Annuals are just one of several types of herbaceous plants. Others include perennials, grasses and bulbs.

Many of Wyoming’s communities are cool during the growing season due to high altitudes, especially at night. As a result, many annuals have a tough time reaching their true potential here simply because they prefer warmer day (and night) temperatures.

Some of these include marigolds, impatiens and flowering vinca as well as some vegetables like tomatoes, cucumbers and peppers. All of these will certainly grow in Wyoming’s “cooler” communities, but their size may be smaller than in a warmer climate, and their fruit will be smaller and may not fully mature before frost sets in, usually in early September.

If you’d like to try some of these warm-temperature crops, plant them in a sunny microclimate next to a house or rock. Often, these plants will thrive in the right niche.

Another method to try with these plants is to grow them in large pots or containers. Dwarf vegetable varieties (the plants are dwarf, but their fruits are not) abound these days, and many can be found in on-line or hard-copy catalogs from seed companies. Using containers, plants can be started earlier and can be moved around as the weather dictates.

Some annuals, like petunias, geraniums and pansies, are adaptable and readily thrive in many different types of temperatures and soil types. Pansies, in fact, are excellent as fall-planted ornamentals! Though usually sold as annuals, they are quite cold tolerant and often will bloom throughout the winter months, even in the state’s cooler climates.

So what annuals will do best in these climates? Among them are calendula (also called pot marigold), zinnia, gazania, verbena, dianthus (includes carnations and pinks), strawflower, California poppy, gladiolus and petunia. Hundreds of others are out there, so don’t be afraid to experiment.

Unfortunately, annuals are frequently perceived as being heavy water users. The truth is most annuals use no more water than many perennials, and some are very drought tolerant.

A garden planted with some annuals mixed in with other plant types will give you cheerful splashes of color all summer long.

The University of Wyoming Cooperative Extension Service has a number of bulletins on landscaping, gardens and lawns on its Web site at

Among them are B-1170, Landscaping: Flowering annuals for Wyoming; B-1146, Care of flowering potted plants; and B-1115, Gardening: Vegetables in Wyoming.

They can be downloaded free.

Copies also may be obtained by e-mailing the College of Agriculture’s Resource Center at, calling the center at (307) 766-2115, or writing to the University of Wyoming, College of Agriculture, Department 3313, 1000 E. University Ave., Laramie, WY 82071.



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