Q: We have a row of evergreen trees that are all either dead or dying, as shown in the photo. What could be the cause, and is there anything that can be done? — Fargo.
A: Determining the cause of tree ailments often requires detective work and looking closely for clues. When trees die, or begin to decline, it’s often assumed they’re being attacked by some disease, for which a spray will bring remedy. Infectious diseases are not the most common causes of tree troubles, though.
In the row of trees in the photo, large old spruce and young small replacements are dead or dying. Although there are several diseases that attack spruce, it would be rare for small young spruce to have “caught” a disease so soon.
Instead, a rapid decline is more likely caused by something in the tree row’s environment. Did lawn herbicides drift onto the trees? Did snow-melting chemicals wash onto the rootzone from the nearby parking lot?
Then I noticed the probable cause. A newer-looking sidewalk runs along one side of the row; a large parking lot on the other. The tree row is located in a grassy strip that is lower than the surroundings. Water from both sides appears to drain toward the low-lying tree row. Spruce can be quickly killed in low areas into which water drains.
The tall old spruce likely achieved much of their growth in decades before the surrounding areas were raised, causing water to drain toward their sensitive rootzone, but once it did, they quickly succumbed. Spruce planted more recently are quickly showing ill effects.
It’s too late to save the tall, older spruce. There’s no way to bring them back. Several of the younger spruce might survive if the grade were changed to improve drainage. In the currant situation, replacing the spruce is futile until the drainage issue is resolved, or moisture-loving species are planted instead.
Q: Last year my lily-of-the-valley had three small, anemic leaf clusters. Now they’re spreading quickly, and I never dreamed they could come up like they did this year. I’ve been digging them out, but I know they will still be popping up. Will Roundup kill the sprouts? Or what else could I use? — Karen, Fargo.
A: Lily-of-the-valley is a pretty perennial that creeps outward from underground “pips.” Its small, bell-shaped white flowers are fragrant, and it grows nicely in the shade. But they are best planted in a spot where total containment is possible, such as the middle of a concrete island, unless you don’t mind them spreading outward with vigor.
They have been known to cross underneath sidewalks, and can certainly pass under most landscape edging. Besides digging, glyphosate (original Roundup) can be applied this time of year to the actively growing leaves, and again in September to sections that resprout. Because they regrow from such a tiny bit of root, persistence over a year or two is usually necessary.
Smothering can also be effective. You can even use cardboard covered with wood chips. The cardboard can be left in place, and will decompose into organic material.
Q: My fernleaf peonies are blooming beautifully, and my neighbor would like a division. When would be the best time? — Linda, Casselton, N.D.
A: Fernleaf peonies, with their finely cut foliage and rose-red flowers, bloom earlier than standard, old-fashioned peonies, which gained them the nickname “Memorial Day peonies.” The time to dig and divide fernleaf peonies is the same as other peonies: around Labor Day in September.
If your peony is currently healthy, well-filled with shoots and blooming nicely, it’s not necessary to dig and disturb the entire plant. Instead, in September dig a portion from the plant’s outer perimeter for your neighbor, leaving most of yours intact with less disruption.
If you have a gardening or lawn care question, email Don Kinzler, NDSU Extension-Cass County, at firstname.lastname@example.org or call 701-241-5707. Questions with broad appeal may be published, so please include your name, city and state for appropriate advice.