Growing Together: Spice up your yard, landscape with fall color

Don Kinzler
Forum News Service

Elephant jokes are timeless, and here’s a classic. How does an elephant get down from a tree? It sits on a leaf and waits until autumn.

Ask anyone to picture autumn, and colorful fall foliage probably come to mind. Autumn has a special ambience, and we can thank trees and shrubs for giving us a classic fall feature.

Why do leaves change color? When foliage starts its yearly transformation, we might assume cooler temperatures are responsible because they arrive about the same time. But temperature isn’t the first trigger of fall color — shorter days are. Plants sense the decreasing daylengths of autumn, and begin preparing for winter. Green chlorophyll in leaves breaks down, revealing pigments that were previously masked, mostly yellow and gold.

Besides the uncovering of yellow tones, which accounts for the golden fall color of some trees and shrubs, other species go a step further and produce red, orange and scarlet colors by their leaf chemistry. When night temperatures drop below about 45 degrees, sugars are trapped within these leaves and chemical reactions convert the sugars into red and purple pigments.

The most spectacular fall colors follow a succession of warm, sunny days and cool, crisp, non-freezing nights. Frost isn’t needed and does more harm than good because it makes leaves drop faster, ending the show.

For three seasons of color, plan new landscapes to include fall color favorites. Even established plantings usually have room to add shrubs, small-scale trees or perennial flowers that light up the yard in autumn.

The following are some well-adapted favorites.

Larger-scale trees

Dakota Pinnacle birch (yellow), Prairie Dream birch (yellow), Northern Tribute River birch (yellow), Northern Acclaim honey locust (yellow), Prairie Torch buckeye (orange-red), LavaBurst buckeye (orange-red), Autumn Splendor buckeye (orange-red), Prairie Stature oak (red), Prairie Expedition elm (yellow), Northern Flare sugar maple (orange red), Northern Red oak (red), Prairie Sky poplar (yellow), hackberry (light yellow), larch (golden yellow), Autumn Blaze maple (red) and Firefall maple (scarlet).

(Note: Autumn Blaze and Firefall maples are highly susceptible to iron deficiency chlorosis, and are often not the best choice for heavy clay soil.)

Smaller-scale trees

Flame Amur maple (red), Prairie Horizon alder (yellow), Prairie Radiance euonymus(red), Quaking aspen (yellow), Prairie Gold aspen (golden yellow), Canada Red cherry (purple in summer, red mix in fall), Juneberry (gold and scarlet) and Hot Wings Tatarian maple (scarlet).

Shrubs

Fireworks Amur maple (scarlet red), Carousel barberry (red), Rosy Glow barberry (purple in summer, red mix in fall), winged euonymus burning bush (bright scarlet), cotoneaster (orange red), Alaska viburnum (red), Gary viburnum (red), sumac (scarlet), gooseberry (copper orange), Siberian Pearls dogwood (purple red), Summer Wine ninebark (purple in summer, red mix in fall), Cotton Candy smokebush (scarlet) and Amber Jubilee ninebark (copper mix).

Perennial flowers for fall bloom

Chrysanthemums (Minn and Mammoth series), tall sedums (Autumn Joy, Neon, Pure Joy and Maestro), ornamental grasses, coneflower, rudbeckia, chelone, asters (Purple Dome and others) and ironweed.

Annuals for fall flowering

Alyssum, ornamental kale, dianthus, dusty miller, fountain grass, viola and pansy.

Fielding questions

Question: What’s growing on the trunk of my lilac tree? — Phyllis D.

Answer: Your photo shows mushrooms growing on the trunk, which are the visible, exterior “fruiting bodies” of fungi. Mushrooms generally live on dead or decaying organic material, and produce spores by which these fungi are spread.

Besides the visible mushrooms, these fungi have unseen rootlike structures, called mycelia, extending into the organic material on which the fungi are attached. When these mushrooms appear on tree trunks, mycelia are working internally in the trunk, and are usually a sign of dead or decaying tissue inside the tree.

Such fungi are normally secondary invaders, entering a trunk that was previously wounded by cracks, winter injury, pruning or other wood damage. I notice several cracks in the trunk and limbs, which might have led to injured tissue and moisture buildup — which was an invitation for secondary invading fungi to enter and begin the natural wood-rotting process.

There isn’t a good way to stop the fungi after they start their activity, because the underlying problem of damaged wood remains. It might be wise to scrape off the mushrooms as best you can, but the interior mycelium growth will still be there, living on the decaying or injured wood, and more mushrooms will eventually appear. If any rotten wood can be removed with a sharp knife, it might help. Fungicides are generally preventative, rather than curing fungal problems already entrenched.

Wood-rotting fungi are a part of the cycle of nature, helping to decompose dead wood, and when a tree enters this stage, reversal is rare. Trees can live with this condition for a time, and we see mushrooms growing on trees in forests. But it does signal a serious situation in which such trees likely won’t live to a ripe old age. I wish I had better news.

Q: Should I rototill my vegetable garden in the fall after it is cleaned out? — Darwyn S.

A: I think it’s a good idea to rototill the garden in the fall, but it’s somewhat of a personal preference. Autumn is a great time to add organic material like leaves, peat moss or compost, and turning the soil helps the material to decompose. Rototilling or spading the soil helps expose insects and disease organisms that might be trying to overwinter underground, and turning the soil exposes them to possible winterkill.

Fall tilling tends to make the soil more workable in the spring, especially if the soil is heavy. Some gardens are successful with a no-till type of operation, and that’s an increasingly successful trend. I still favor fall and spring tillage for my own garden, partly because I enjoy rototilling and the aroma of freshly turned soil.

Q: We planted a purpleleaf sand cherry bush about five or six years ago. I didn’t realize how fast and how much it grows every year. I’ve been trimming it back at least 12 to 18 inches every spring after it bloomed. It has all of the new growth on top and only a few new branches at the bottom. Is there anything I can do to force it to fill out at the bottom? I read that I can cut it back in the early spring, but can I do that since it’s been in the ground this long? — Yvonne R.

A: Your purpleleaf sand cherry will rejuvenate nicely, and can be done periodically even when it gets much older and needs occasional re-working. Even though it was planted five or six years ago, you can cut it all the way down to about 6 inches above ground level around April 1 before new growth begins. That’s the best time for such rejuvenation pruning.

Rejuvenation pruning will encourage vigorous new branches to sprout from the lower trunks, making the shrub fuller. Because these shrubs grow quickly, this rejuvenation can be done every four or five years, or whenever it looks “leggy.” Spring is the preferred time for this, rather than fall.

Annual alyssum and dianthus continue blooming even after frost.
Chelone, commonly called turtlehead, is a colorful fall blooming perennial.
Winter-hardy mums, like the Mammoth series, are spectacular fall blooming perennials.
A reader wonders what’s growing on the trunk of their lilac tree.