Whyizzit that the owner of a hedge of failing evergreen trees is the last one to see...
... that the trees no longer serve their intended purpose?
Maybe it's related to the ghost-image effect, when the shape of a long-viewed item remains visible even after closing one's eyes. In that case, the image of those trees when they were young, dense and relatively short may be burned indelibly into the mind's eye of the person who planted them. It overrides reality.
Then again, it may not be a failure to see but the offshoot of the gardener's never-say-die attitude: These were perfect once, I can rejuvenate them!
Whatever the reason, it's a problem. It's common enough that we frequently hear these two questions:
"Help us figure how to incorporate understory shrubs where the lower branches of 20 year old spruce trees have died off."
"What can we do to make these trees dense again?"
Here's our answer, in two parts.
First, try to see that it's usually better to remove trees that are no longer screening the view. Look at old photos, compare them to the current view. Ask friends for honest appraisal.
If the trees are Colorado spruces (Picea pungens, whether green or blue) and more than 20 years old, start planning to replace them, and/or get the replacements started if you can. This species is not well suited to the landscape outside its native area -- scattered pockets in the Rockies.
If you are interested in native trees and shrubs, you should have Gary Hightshoe's masterpiece, Native Trees, Shrubs and Vines for Urban and Rural America. Ours is so worn we always keep an eye out for a replacement at used book stores.
Even in a good site (full sun, well drained soil, no competition from lawn in a very wide ring beyond the widest branches) they start succumbing to problems and thinning after 20 years.
People tend to make it worse by pruning back lower limbs, leaving those branches to starve with nothing but needles in the shade of upper limbs and increasing with every cut the whole tree's susceptibility to fungal infection. Those limbs thin even more, until the gardener cuts them off from the trunk. This leaves the tree's root system much more exposed than is good for that species.
Even without human pruning, Colorado spruces in the landscape lose lower limbs to shade and competition. They age, suffer from exposure of the root zone, run out of free root space, and become weaker. Growth slows, foliage thins and the tree's resistance to disease is reduced. Canker infections move upward and higher branches die. (Youth and vigorous growth is the best defense against this canker. Don't waste money on fungicide applications; put your cash into water, fertilizer and then a replacement tree.)
That big 50-year old spruce we just showed you has been in decline for 30 years. It's unstoppable but gradual enough to escape notice, at first.
An expanding root system keeps a Colorado spruce tree young. Youthful Colorado spruces are distinctive for density and growth that's fast enough to stay ahead of the fungal canker that kills branches on older, weaker trees. These trees did not evolve with bluegrass and the roots do not compete well with lawn; their roots might even be incapable of growing under lawn. When the root system stops expanding, the tree's growth slows and it begins to decline.
There are other spruces called upon for hedge work, such as Norway spruce and white spruce. They may have a longer useful life.
If they are in full sun and still relatively young (not yet much over 15 feet) you might be able to keep them small and improve their density. See Reduce a Spruce in What's Coming Up #176 for keeping them small. Watch our "Big Mistake" department for an upcoming illustration of keeping them dense.
However, if they've limbed themselves up or been limbed up, write them off. Spruces don't grow new branches from the trunk or from anywhere that the wood is leafless (needle-less).
We don't have much encouragement to offer if the failing trees are pines, either. It's in the nature of most pines to limb themselves up as they age. They're genetically predisposed to configure themselves like the gardener-pruned Colorado spruce. All of them can eventually earn the title, "Michigan palms."
Eastern white pines (Pinus strobus) probably have a better chance of retaining lower limbs than other common pines (Scots or Austrian) but only if they are grown in full sun and there is no competition -- not even from other white pines.
Second, recognize that it is tricky to plant and not easy to maintain plantings under established evergreen trees:
No matter how many lower limbs have been removed to make headroom, even species that will grow in that shade (See Spruce understory in Growing Concerns #647) will grow more slowly and be less dense than they would in sun.
Watering is critical but tough to do with overhead sprinklers. The need for supplemental water is both year-round and never-ending.
There is the trees' own reaction to understory neighbors to consider. The trees lose roots and vigor to the digging within their root zones. Their decline and thinning accelerate.
Removing trees can net an additional advantage, as the ground beneath old evergreens may be particularly good for growing because the trees kept it fallow for so long. Versile and Judy Fraleigh, founders of Fraleigh's Nursery in Ann Arbor, Michigan, commented recently on this effect: "We took down 10 spruce trees that had limbed themselves 'way up. We just broke the surface with a drain spade, put down maybe 3 inches of compost (then planted shrubs and) perennials... Oh how they grew!"
So you probably see why we love to hear questions like this from A.V.:
We have a line of old spruce trees, some of which are half dead, that need to be cut down. We're looking for replacement ideas, but something that provides us with some privacy.
It's our pleasure to point those people directly to Great big hedge plants.
When people balk at such a big change, we suggest starting replacement plantings in front or behind the failing evergreens, and letting them grow on for a time -- pruning away the spruces over the years to avoid deforming the newcomers. Then take down the declining old evergreens.
If expense is the primary issue, we suggest phased-in replacement or do-it-yourself work-arounds. See the diagrams and photos below for phasing in a new set of screen-ery.
Do-it-yourself work-arounds to reduce tree removal cost include removing only the branches and very top of each evergreen. Leave the trunks; each can support a vine such as climbing hydrangea (H. anomala petiolaris) or evergreen euonymus (E. fortunei) that will eventually develop a trunk thick enough to stand alone.
What you need is room if you must start replacement plants while the old hedge remains. Plant the replacements out in the sun beyond the trees. Here you see Ward's yews in the foreground. Although they would grow in shade closer to the big trees, they must be in sun to grow quickly and remain this dense.
Here's a replacement story, early stages. When the gardeners first met their Colorado spruce they were new in the house. The tree was over 30 and had beaten the averages, keeping its good looks. It probably owed that to moist well drained soil, full sun and having more room to root out than a spruce near a building or driveway. It may also have been in its favor that its competition was only utility turf -- lawn best described as field mowed short -- rather than a bluegrass monoculture. Colorado spruces do not fare well in competition with grass of any kind but they seem particularly sensitive to bluegrass lawn or the culture devoted to keeping bluegrass in good shape.
Aware that the tree was not likely to last much longer, the gardeners kept an eye on it and five years later started its replacement. It was a decision made easy by comparing then-and-now photos for relative thinness, and noticing that the tree's top had died back.
The replacement is a dawn redwood (Metasequoia glyptostroboides) -- not an evergreen, since it was determined that evergreen wasn't necessary. What mattered more to these gardeners: Dawn redwoods are well suited to the water's edge, fast growing (18" a year), have a strong pyramidal shape all their lives and have great fall color.