Autumn is glorious yet bittersweet in the Colorado garden. The intense summer heat is past; the air is cooler and crisp. Planting beds, mature and mellow, are now set against a brilliant backdrop of golden aspen. Native shrubs in autumn hues mingle with evergreens against the deep blue sky. Despite this time of breathtaking beauty, we know that the growing season is coming to an end and that months will pass before a new one begins.

There is much to do in the flower garden in fall. Transplanting, planting, cleaning out old beds, preparing spring beds, pruning and providing protection against the coming cold months are just a few of the tasks that can be done at this time of year. What you actually do and what you put off until spring is determined by your particular garden, your gardening style and how much time, enthusiasm and energy you have left for gardening activities as the season winds down.

FALL PLANTING

Autumn is a perfect for planting. The soil is still warm from the hot summer sun. This enables the roots of perennials that are planted now to continue to grow until the soil temperature reaches approximately 40°F. This gives the plants a head start on the next growing season. (This being said, there are some plants that should not be planted in our area in autumn because they need the long hot days of summer to establish. These include agastaches, many types of salvia and some penstemons.) An application of a mild granular fertilizer or compost to both new fall plantings and existing plants will allow the nutrients to sink down into the soil during the months ahead and be available for the plants to take up in early spring.

Whether you plant now or wait until spring, plan to use more late-season bloomers such as coneflower, coreopsis, gaillardia, aster, rubeckia and buddleia. Consider adding native shrubs such as Rocky Mountain maple, curl-leaf mountain mahogany, rabbit bush, red twig dogwood, chokecherry, golden current and rocky mountain thimbleberry. These late season perennials and native shrubs will ensure both vivid autumn blossoms and foliage next year. If you haven't already done so, add our native aspen to your landscape. Hard to establish in Colorado gardens at lower elevations, aspen, if provided with supplemental water during the first few growing seasons, will thrive in most Evergreen area gardens. Each autumn you will be rewarded, in brilliant gold, many times over for your efforts.

PLANTING BULBS

After the soil temperature drops to 60°F, plant bulbs for next spring and summer bloom. Try thinking beyond tulips (a preferred delicacy for deer and elk) and daffodils. Think galanthus, Siberian squill, chionodoxa, dwarf iris and fritillaria - all beautiful small bulbs that planted in abundance give a wildflower look to your Colorado garden. All are deer resistant, although some small rodents such as voles may find them tasty. To prevent bulbs from being eaten, plant them in groups enclosed in hardware cloth baskets that can be purchased commercially or make your own enclosures out of chicken wire. This does not protect the plant once it emerges, however. Although there are commercial or homemade rodent deterrents you can try, I find that the only sure way I can achieve abundant sweeps of color in my spring bulb beds is by over- planting. Bulbs -especially the small "wildflower" types- should be planted in the hundreds to look their best. Bulb fertilizer should be placed in each planting hole and added to the existing bulb beds at this time.

MULCHING, WATERING AND SOWING SEEDS

New perennials and bulbs should be mulched with a thin layer of organic material at the time of planting. After the first few inches of soil are frozen, a thicker layer of mulch should be put down. The additional mulch will serve to protect the plants against frost heaving. This extra layer of mulch needs to be removed in the spring in order allow the sun to warm the plants and to allow for the air circulation necessary for healthy new growth.

Fall is the season to slack off on watering, but not completely. Turf grass, shrubs and trees, especially young plants and those with shallow root systems, need to receive water throughout the winter. Lack of winter moisture is the demise of many trees and shrubs in our area. Monitor weather conditions and water during extended dry periods of approximately one month without snow cover. Water when the air temperature is above freezing and early in the day so that the water will have time to soak in before possible nighttime freezing.

Nature sows seeds in autumn and so should you. Wildflower and ornamental perennial seeds can be gathered when ready and sowed now or in the next few months. You can also let the seed heads remain on the plants to self-sow. Sowing seeds immediately before a heavy snowfall has worked well for me. Many of my perennial gardens and all of my native wildflower areas have been started from seed sown during fall and winter months.

WEEDING AND FALL CLEAN UP

One last weeding will help to improve the appearance of your garden throughout the remaining months of autumn. In addition, any weed that you can eliminate now will prevent possibly hundreds of weeds from sprouting in your garden next spring.

Gardeners have differing opinions on the subject of cutting back perennials at the end of the season. Some prefer to cut back in the fall favoring the neatness of a bare winter landscape or the fact that decaying plant material can cause mold and other fungal diseases. Plant matter also provides a safe harbor for over-wintering garden pests including meadow voles. Another valid reason to cut back plant material is to rid the area around your home of wildfire fuel during our often dry winter months.

Finally, cleaning up now will give you a head start on next spring's gardening chores. However, there are also reasons to let ornamental grasses and plants with sturdy stems and seed heads remain. Silhouetted against the snow, these dead plant materials can create magnificent winterscapes. More important than providing winter interest in our gardens however, many seed heads provide food for fall migrating and wintering birds. Not cutting back plants in the fall is also good for the health of the garden because the foliage will provide protection against desiccation and frost heave in the coming winter months. The old growth will also serve to shelter the succulent new growth from the frenzy of early spring feeding by deer, elk and other critters.

Another reason not to cut back until spring is that you may be just too darn tired at the end of the season or that Colorado winter activities seem more inviting right now.

PRUNING AND PROTECTING TREES AND SHRUBS

Pruning of dormant trees and shrubs can be done at anytime when the temperature is above 0° F. This means you can put off your pruning tasks until one of the many glorious warm winter days we are so fortunate to experience. Right now, however, is the time to protect the trunks of trees against winter scald and from antler rubbing by deer and elk. Tree wrap will help with both. For trees that are not subject to winter scald, either because they are planted in a northern, sheltered location or by their light trunk color (aspen), enclosing the trunk up to about six feet in heavy plastic netting or chicken wire will prevent damage by ungulates. I also place bird netting over young shrubs from October to May when deer and elk take up residence in my gardens. Older plantings that tend to be less tasty and that are in need of pruning anyway are fair browse for the herds

There are other flower garden chores to be accomplished during the months of autumn such as cleaning and storing garden tools and equipment, bringing in planters or décor that could be damaged by frost, draining hoses, cleaning out gutters, hardscape projects, ordering next year's plants and many more. No matter what garden tasks you decide to undertake, remember to take time to reflect on the satisfaction and joy that gardening provided this past year and to dream of the seasons yet to come.

Nan Spence is retired from a career in Environmental Science. She holds Rocky Mountain Gardener Certification through the Denver Botanic Gardens and Native Plant and Wildlife Master designation through Colorado State Extension Service. She is also a Habitat Steward with the National Wildlife Federation. You can, you can reach her at nmspence@att.net