Part of the allure of fall foliage is color variation. There are trees that turn red, purple, yellow, orange and brown.


Part of the allure of fall foliage is color variation. There are trees that turn red, purple, yellow, orange and brown.
Specific plant pigments determine individual colors. Foliage derives its normal green color from chlorophyll, the substance that captures the energy of the sun.
Other pigments produce fall colors. Reds and purples are caused by anthocyanins, yellows by xanthophylls, and oranges by a combination of carotenes and xanthophylls.
Browns are the result of tannins present in the leaf. Most of these substances are present throughout the growing season but are masked by the green color produced by chlorophyll.
Anthocyanins are the exception and are produced after the chlorophyll is destroyed in the fall.  
If you have ever seen pictures of New England in the fall, you have probably wondered why trees in Kansas usually do not color as well.
This difference is partly because of the tree species prevalent in New England. Certain oaks and maples naturally produce good color.
Coloring also is influenced by the weather. Warm, sunny days and cool nights are ideal for good color. The sunny days encourage photosynthesis and, thus, sugar accumulation in the leaves.
As fall progresses, each leaf develops an abscission layer at the base of the petiole, or leaf stem, that prevents these sugars from being transported down the trunk to the roots for storage.
This high sugar content in the leaves produces more intense colors. Cloudy days and warm nights prevent some of the sugar accumulation in the leaves and results in less vibrant colors.
Weather during other parts of the growing season also can have an effect.
Heavy rains in the early spring or hot, dry weather during the summer can both have a deleterious effect on fall color.
The length of time a tree maintains fall color also depends on weather. Reds, yellows and oranges are short-lived when trees undergo frosts and freezes.
Should You Let Turf Grow Tall in the Fall?
Sometimes you will hear people say to let the grass grow tall right before winter sets in.
Their reasoning is that the extra foliage will insulate the crown of the plant from the extreme cold of winter.
Although this may sound reasonable, in practice it probably does little, if anything, to increase winter hardiness.
On the contrary, a canopy that is too high during the winter may lie over and become matted down, leading to an increased incidence of winter-diseases such as snow mold.
Turfgrass species vary genetically in their cold tolerance, with warm-season grasses being less cold tolerant than the cool-season types.
Given these differences, cold tolerance is improved by increasing the health of the plants going into the winter, and healthy plants are a result of a sound management program (fertilizing, watering and mowing) during the spring, summer and fall.
The lawn will benefit more from continuing to mow at the recommended height than from trying to gain some insulation against winter cold by allowing it to grow tall.
Here is a list of the recommended mowing height ranges (in inches) for home lawns in Kansas: Tall fescue 2.5-3.5 Kentucky bluegrass 2-3 Perennial ryegrass 2-3 Buffalograss 2-3 Bermudagrass 1-2 Zoysiagrass 1-2 (Note: Mowing at heights below 1.5 inches requires a reel mower).
There may be some benefits gained by adjusting mowing heights within the recommended range at times.
For example, it is a good practice to mow warm-season grasses at the higher end of recommended heights during late summer and early fall because this practice should help them store more carbohydrate reserves for the winter, and it may reduce the incidence of certain cool-weather diseases.
But the rule to remember is to stay within the recommended height range for your species.
Ornamental Grasses
As a rule, ornamental grasses should not be cut back while green because they need time to move the energy found in the foliage into the roots.
Even when browned by cold weather, most gardeners will leave the foliage until spring because of the interest it adds to winter landscapes.
Early March is the preferred time to cut back these plants. However, dry foliage is extremely flammable and should be removed in the fall from areas where it is a fire hazard.
Another question we often receive is whether we can divide ornamental grasses in the fall. Spring is the preferred time because divisions done in the fall may not root well enough to survive the winter.