Q: We have utilized a lot of boxwood in our landscaping because the deer don’t eat them. Last year and currently, some of them are dying from some disease. I have talked to a number of “experts” and they all say there is nothing I can do about the problem. Your thoughts, please.
A: Since I have not seen your boxwood and do not know the amount of sunlight they receive per day and/or the condition of the soil they grow in, I will suggest several issues to consider:
- Phytophthora parasitica. This is a soil-borne fungus that starts to affect boxwood when the soil is wet and cool. It produces spores that move in a film of water in the soil, which means that boxwood growing in poorly draining soils will be among the first to exhibit stress. The disease advances with greater injury to the plant once temperatures rise between 75 and 85 degrees F.
This fungus can affect boxwood at any age. At first, leaves gradually turn yellow with ruffled edges, then the leaves change to a bright straw color but remain attached to the twigs. This may happen only in certain areas of the shrub or throughout the entire shrub.
The fungus can cause a partial or complete blockage of nutrients and water movement in the stems, which will turn dark brownish-black. The roots turn dull and dark brown. Healthy roots are normally a light tan.
If you suspect Phytophthora parasitica is the culprit, avoid replanting boxwood in the same space until soil drainage issues are corrected.
Boxwood should be routinely pruned and shaped for light penetration. A shaded interior makes for sparse foliage. Over time, insufficient foliage will render the plant unable to sustain itself through photosynthesis, and the shrub will ultimately decline and die. Photo courtesy of MetroCreative Connection
For more complete information about spider mites, consult HYG-2012-11, “Spider Mites and Their Control” at ohioline.osu.edu/hyg-fact/2000/pdf/2012.pdf.
- Desication: Boxwood lose moisture through leaves in winter. Since the soil moisture may be frozen, plant roots cannot absorb what is lost and the foliage desiccates, turns brown, and may drop. This can also be a serious issue with evergreen azalea, holly and rhododendron.
An anti-transpirant, also known as an anti-desiccant, can reduce transpiration that can, in turn, limit damage to the foliage. Make two applications per season, one in December and another in February, to protect your shrubs the entire winter. Most garden centers carry this product.
- General plant care: Are you routinely pruning and shaping the boxwood? Shrubs must be pruned for light penetration. A shaded interior makes for sparse foliage. Over time, insufficient foliage will render the plant unable to sustain itself through photosynthesis, which is the process in which plants produce their own food. Inadequate photosynthesis will result in the untimely decline and death of the plant.
- Soil and site conditions: Is the soil overall the same quality throughout the planting area? Is it uniformly a rich soil that is moist but well-draining? Are the shrubs that decline planted in an area that receives less moisture or stronger winter winds than the other shrubs?
- Service life: There is a term applied to shrubs and trees called “service life.” Service life refers generally to that period of time when the plant is in a healthy vibrant state, producing new growth, its presence complementing the surrounding landscape. Eventually the plant will surpass its service life and begin a decline. It may be that some of your boxwood are beginning to succumb naturally to a spent life. No plant lives forever and no plant lives in constant health during that lifetime.
Q: How are garden pots disinfected? I have pots with last year’s soil in which I planted impatiens, which were infected with fungus blight. I’ll of course dispose of that soil, but how do I clean and rid pots of any fungus before planting other annuals this year?
A: Scrub each container and disinfect it with a 10 percent chlorine bleach solution. Ideally, in succeeding seasons, you will want to do this during fall cleanup and store the containers in a shed or other area that will help to keep them clean through the winter.
For more horticultural information, call The Ohio State University Summit County Extension Hotline Tuesdays from 9 a.m. to noon at 330-928-4769, ext. 3, and request FactSheet HYG-1016-96, “Overwintering Plants in the Landscape.”
Dayle Davis is a freelance writer and avid perennial gardener, with a B.A. in communications and course work in botany, geology and wildflowers. Davis is a master gardener emeritus under The Ohio State University’s Horticultural Extension. Readers can send in questions regarding lawn and garden issues, which could be featured in a future edition, as well as about the OSU Master Gardener program. Questions can be emailed to firstname.lastname@example.org, faxed to 330-665-9590 or sent to Leader Publications, 3075 Smith Road, Suite 204, Akron, OH 44333. Please do not send any leaves, seeds or other organic material. Inquiries about area garden clubs or groups should be sent directly to the particular organization in question.
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