Punch List: Mowing leaves into the lawn, cutting back perennials and more fall garden care

Saturday, 21 October 2017, 07:58:20 AM. This week, Betty Cahill offers gardening tips including fall lawn care, taking care of trees before winter hits, cutting back perennials before the freeze and more.

The high-country foliage color show is mostly over, but there’s still color on the Front Range. Take in the many shades of golden leaves on honeylocusts, elms and cottonwoods, the bright red of maples and purple ash, crabapples and ornamental pear trees. Shrubs such as chokecherries, currants and serviceberries are pulling their weight for the fall show, too.


Time to recall  from grade-school days the science behind leaves changing color each fall. Shorter days with less sunlight means a winter break from photosynthesis, when plants make their own food with help from sunlight, water and carbon dioxide.

The natural substances that make up leaf cells (pigments) become more noticeable each fall as chlorophyll production wanes. Both environmental and genetic factors affect the pigment and play an important role in color, intensity and duration of the fall splendor.

Many warm, sunny days and cool (but not freezing) nights allow the anthocyanins pigments to shine through with all those brilliant shades of crimson, purple and red.

Yellow, gold and orange leaves are fairly consistent from year to year due to carotenoid pigments that remain present in leaves despite the weather.

Fall moisture helps leaves stay colorful for a longer period of time. Drought conditions while leaves are losing chlorophyll pigment leads to brown leaves and early drop.

Rake leaves from the lawn as soon as the trees are bare. Leaves that remain during the winter can smother the lawn.

Dry leaves can be mowed into the lawn, adding back valuable organic matter to the soil. Set the mower height high and make several passes over the leaves.

Avoid blowing leaves into the street or tossing them in the garbage. Many municipalities have collection or drop off sites through early December. For information on leaf drop and post-Halloween pumpkin composting, call 311 or visit http://www.denvergov.org/content/denvergov/en/trash-and-recycling/composting/leafdrop.html

Water all plants, especially trees. We’ve only had one or two adequate water-producing storms so far this fall along the Front Range. Landscape plant roots need to be moist going into cold weather prior to the ground freezing. Dry plant roots coupled with lack of winter moisture can lead to root and branch death, less foliage, scorched foliage, no foliage or no tree next year. Water well so they enter winter with adequate soil moisture; trees need moisture to a depth of 12 inches.

In the landscape

It is a gardener’s choice whether to cut back perennials with dead foliage in the fall or spring. Plants receive additional insulation and protection from our frequent freeze/thaw winter cycles when foliage is left in place. Snow covered foliage can add interest during the winter months.

Any recent spring- or fall-planted perennials and shrubs should not be cut back in the fall. Birds appreciate seedheads and using the foliage for screening.

Do not cut back woody plants including butterfly bush, culinary sage, lavender and other late summer or fall-blooming plants.

Established perennials that had disease, harbored insects or may keep the crown too wet through the winter can be cut back in the fall, including bee balm, phlox, salvia, Japanese anemone and penstemo.

Continue putting in garlic planting stock and spring-flowering bulbs until the ground freezes. To deter critters like squirrels, voles and mice from bothering newly planted flowering bulbs, sprinkle or roll each bulb in an animal repellant powder during planting. Sprinkle more repellant or hot pepper flakes on top of the soil. Chicken wire can also be placed over the planting hole for additional protection.


Remove spent vegetables and foliage from the vegetable garden. Toss if diseased or add to the compost pile.

Root vegetables that are up and growing, including beets, carrots and parsnips and hardy spinach, can be thickly mulched (6-8 inches) and harvested through the cold months or until the ground freezes.


Keep watering the lawn each week if the weather is dry. Use hoses and sprinklers if automatic systems are turned off. Water mid-day when temperatures are over 40 degrees. Drain hoses after use.

Fertilize the lawn while it is green and the ground is not frozen. Use one half pound of actual nitrogen per 500 square feet. Fertilize after aeration.

Soil Test

Plants, fruits, vegetables and turf growing problems are often the result of soil issues. Soil may have too much or not enough nutrients, low or high organic matter or compacted or sandy soil that affects drainage. Soil testing is the first step in correcting what is wrong in your soil and getting a good start on planting or lawns next spring. The results will spell out how to fix nutrient and quality issues, which can be completed this fall or early next spring. Turnaround time is about two weeks.

Soil testing can be done on any area of the landscape, including turf, vegetable beds or borders. Avoid testing within 30 days of adding fertilizer, compost or manure.

The Colorado State University soil testing kit with sampling instructions can be found at your local extension office or independent garden center. The kits are free (or use your own bag); fees apply for testing.

Download the CSU soil test form with instructions, pricing and how to take samples from your garden at http://www.soiltestinglab.colostate.edu/documents/soilsample_horticulture.pdf  or call 970 491-5061.

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