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Kinzler: Arborvitae injury, viburnums that won’t bloom and tomato rot

In today's "Fielding Questions" column, Don explains why a local shrub is growing well, but never seems to flower.

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A reader wonders what's causing this problem with their evergreen shrubs. Special to The Forum
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Q: I have a problem with my evergreen shrubs. I have no idea why they’re turning brown. I’d appreciate your thoughts. — Fargo.

A: The shrub is called globe arborvitae. Browning as shown in your photo has been fairly common this spring and summer. It’s not a disease or insect, so there are no sprays or other treatments that will make the brown foliage revert to normal green.

There are three common causes. First is rabbits, who often hide inside the shrub during winter or spring and gnaw on the bark of branches. Check inside the arborvitae, looking at the base of the branches whose foliage is brown.

Second, winter weather can cause browning of foliage, which is commonly only on one side. It might be on the south or west sides, caused by winter sunburn as the bright sunshine is reflected off the snow. It might be on the north side, caused by winter windburn.

Third, if the damage is next to a sidewalk, or facing a sidewalk or driveway where a snowblower is used, it might be damage from the force of the blown snow. Evergreens can't tolerate snow being shot directly at their foliage.

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A reader wonders what's causing this problem with their evergreen shrubs. Special to The Forum

What to do at this point? No matter what the cause, if the brown foliage and twigs are brittle when bent, and there is no sign of new growth, that area is likely dead. Scratch the twigs, looking for live green under the outer bark.

Damaged portions like the photo are often irreversibly dead, and the only choice is to prune them out. This often ruins the shape of the globe, because new growth doesn't rapidly fill the void. I'm afraid there isn't an easy fix.

Q: We’ve got two snowball viburnum shrubs that I planted together four years ago. It grows well but never flowers, except for a few at the bottom. I cut them back in late fall to about 3 feet. I can’t find any solutions online. Maybe planting the two together created some kind of incompatibility? It gets sun three-fourths of the day. — Mike, Fargo.

A: Viburnums can be planted in multiples, so that's fine. The failure to flower is caused by fall pruning.

Viburnums bloom on what is termed “old wood,” meaning during summer, the shrub is forming buds along the branches that will bloom the following year. By pruning in fall, you’re cutting off the flower buds that would have opened into next year’s bloom. The few flowers that you’ve seen on the lower part of the shrub have escaped the fall pruning.

Instead of autumn, pruning is best done right after flowering, after which the viburnum will produce flower buds along the branches for the following year’s bloom.

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Q: Once again this year, the bottom ends of my tomatoes are all black and sunken. Is it too late to do anything? The large green tomatoes still look OK. — Sandy, Horace, N.D.

A: The disorder is called blossom end rot, and it is caused by the tomato plant's inability to use calcium from the soil, so it sucks it out of the bottom of the developing fruit, leaving large, sunken black or brown lesions.

Most regional soils have abundant calcium, so adding more is counterproductive. To help the tomato plants access soil calcium, it's important to keep the soil moisture consistent, as the calcium must be dissolved in solution for the roots to absorb it. Preventing fluctuations in soil moisture helps greatly, and can be done by mulching the plants with straw, shredded bark, landscape fabric or grass clippings to which no herbicide has been added.

The first tomatoes are the most commonly affected, and plants often overcome the situation with later fruits.

ARCHIVE: Read more of Don Kinzler's Fielding Questions columns

If you have a gardening or lawn care question, email Don Kinzler, NDSU Extension-Cass County, at kinzlerd@casscountynd.gov or call 701-241-5707. Questions with broad appeal may be published, so please include your name, city and state for appropriate advice.

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Don Kinzler
Don Kinzler, Growing Together and Fielding Questions columnist. The Forum
Contributed / Special to The Forum

Don Kinzler
Don Kinzler, Growing Together and Fielding Questions columnist. The Forum
Contributed / Special to The Forum

Don Kinzler, a lifelong gardener, is the horticulturist with North Dakota State University Extension for Cass County. Readers can reach him at donald.kinzler@ndsu.edu.
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