By Carl Wilson and Mary Hartman, Extension Agents, Colorado State University Cooperative Extension
The annuals have faded and the turf has turned green again after a blistering-hot summer. It's Mother Nature's way of telling us to put the garden to bed for winter.
Take turf, for example. It will survive winter best and come back more vigorously in spring if you fertilize it this fall, when it's still green. Use a lawn fertilizer with a higher first number and lower second and third numbers--25-5-5, for example. This is particularly applicable to bluegrass, fescue and ryegrass. And as long as the lawn remains green, continue to mow it to a 2½ to 3-inch height. Don't scalp it by mowing short while it's still green. It's also a good idea to aerate the lawn and to continue watering until it turns brown. Even then, water once a month throughout winter, especially if the snow cover is scant.
The Vegetable Garden
Pull up old vines and vegetable plants. Insect pests that feed on these plants during summer and fall often lay eggs on the old plants. If the vines are left on the soil surface, insect eggs will survive the winter and hatch in the spring.
If they are not diseased, you can work the old plants back into the garden soil. This adds valuable organic matter to the soil and, at the same time, destroys insects and their eggs.
In addition to garden debris, other organic material may be added to the soil in fall. You can use well-rotted manure, compost, peat or leaves. Soil micro-organisms and beneficial soil insects will help incorporate these materials into the soil before the ground freezes and in the spring after it thaws.
You also can apply a light covering of ammonium sulfate (20-0-0) at the rate of a pound per 1,000 square feet of garden area. Spade or rototill all these materials into the soil, mixing well to a depth of 8 to 12 inches.
You'll want to leave one part of the garden intact. The area where you've planted root crops can be mulched instead of dug up and worked. To extend the digging season by weeks or even months, place a straw mulch over root crops such as carrots, beets, parsnips and Jerusalem artichokes. Parsnips turn sweeter after the ground cools. Jerusalem artichokes don't store well after they've been dug, so leaving them in the ground until you are ready to use them is the best storage method.
After a light frost nips their vines, harvest winter squash and pumpkins. Do this before a heavy frost damages the fruits. Cut from the vines leaving 3 to 4 inches of stem on the fruit.
Pull up spent vines and foliage of annual flowers and compost them or dig them into the garden. If the plants are diseased, however, discard them in the trash.
It doesn't matter where the weds are--the vegetable garden, flower beds or the lawn--this is a good time to get rid of them. Consider this: Weeds that are spread by seed produce thousands of seeds. Lambsquarter can bear up to 72,500 seeds per plant, curly dock can bear up to 30,000, purslane 52,000, and redroot pigweed 117,000. If even 50% of the pigweed seedlings germinated next spring, you'd have 58,000 pigweed plants to pull or otherwise get rid of.
Better to pull them this fall or, if weeds are in the lawn, to spot-spray a selective herbicide on the still-green perennial weeds. Perennial weeds, such as dandelion, thistle and bindweed, are more easily killed by fall sprays than by summer applications.
Tree and Shrubs
Shorter days and falling temperatures are prompting deciduous trees and shrubs to drop leaves and prepare for winter dormancy. Limit fertilization in fall, as nitrogen stimulates useless late-season growth and delays dormancy.
Do continue to water trees and shrubs through fall, sending them into winter with ample moisture. It also will be necessary to apply water every three to four weeks throughout the winter. Dry soil kills roots and puts stress on trees and shrubs. Water when temperatures are above freezing and when the soil is not frozen. Apply water early in the day so plants will have time to absorb moisture before soil might freeze at night.
By the first of November, wrap trunks of your deciduous trees with crepe-paper tree wrap. Begin at the base of the tree and wrap upward, overlapping about a third of the paper with each turn. Stop when you reach the first set of branches. Secure the top turn of the wrap with a piece of stretch tape. Wrapping trees and shrubs prevents sunscald injury, a conditions that develops when the warm winter sun is absorbed by the plant's bark. Remove wrap next April.
Cut back canes of fall-bearing raspberries to about ground level. Water the area during extended winter dry spells. Canes will regrow the following season and will bear fruit in August and September. Remove only older, thick canes of summer-bearing types so you can reap a harvest next year.
After temperatures hit freezing and the plants die back, cut the stems on most perennials to within an inch or two of the ground. Dispose of the cuttings; they can harbor diseases that could survive the winter and return to the plants in the spring. Some plants, such as Oriental poppies and iris, produce a cluster of green leaves in the fall. Leave these intact. Remove only the older, brown stems that remain form the spent flowers.
As the season progresses and the weather becomes colder, mulch the soil around the plants. This is generally done in mid-to late November. Mulch keeps roots cold. It doesn't protect them from the cold. A plant can be hardy in more northerly latitudes where winter temperatures are severe but can be injured here, where winter temperatures fluctuate considerably. The alternate freezing and thawing of exposed soil can damage roots and even heave them out of the ground.
Recommended mulching materials for perennials include hay or straw, evergreen boughs, pine needles, peat moss and cornstalks. These mulches are light and won't pack or suffocate roots. Apply to a depth of 4 to 6 inches. A few plants, however, such as peonies and bearded iris, don't require winter mulching and , in fact, do better without it. Mulching can cause their thick, fleshy roots to rot. As with other perennials, though, they require watering during dry winter conditions.
Photograph courtesy of Judy Sedbrook.
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010