Boxwoods are pretty hardy plants and are not bothered by the elements. Be it cold winds, frost, direct sunlight, or infertile soil, these resilient plants can weather through it all.
The evergreen shrubs don’t lose their vibrant colors even in the bleak winter months. Staying green and glossy all year round.
But if for some reason your beloved Boxwoods have started losing their color and started turning brown, you should not take it lightly. Investigate the cause and start treatment ASAP!
Why are My Boxwoods Turning Brown?
A browning Boxwood shrub most usually looks like a case of Boxwood blight, a fungal disease that leads to significant leaf drop and bronzing. Other than that, Boxwood browning can be caused by winter damage, salt damage, over-fertilization, drought stress, Boxwood leafminer infestation, and more.
Boxwood blight is a fungal disease caused by the pathogen Calonectria pseudonaviculata. It is a relatively new plant disease that has spread across the US in recent years.
The first symptoms of blight are brown spots with dark brown edges on the foliage. These spots are accompanied by black streaks on the stems.
Soon after, considerable chunks of the foliage start turning brown, or bronze, and the dried leaves fall off the plant.
If not diagnosed earlier, the end symptoms of Boxwood blight look just like winter injury or drought stress and you will not have much success identifying the problem. A lab test will be able to help you identify whether it’s actually blight or not.
The disease is typically spread from plant to plant in nurseries. Blight is promoted in warm and humid conditions. But spores can stay active in the soil for up to 5 years!
If a new plant is planted in the place of a diseased one, the new plant will most likely contract the disease present in the soil. To use the soil again, you must get rid of blight in the soil first.
If you are able to identify blight in its early stages, remove the infected foliage right away and dispose of it by sealing it in a plastic bag.
Never let infected foliage fall to the ground or compost it.
A fungicidal spray containing chlorothalonil will prove helpful if you spray regularly every one or two weeks in the growing season.
Boxwoods are winter hardy plants can be grown outdoors all year round in USDA Hardiness zones as cools as zone 4-5. They can tolerate freezing temperatures down to -10°F(-23°C).
Tolerating such low temperatures is not a common plant trait and Boxwoods are unique for maintaining their green foliage year-round.
But these plants can still suffer winter injury when they are exposed to direct sun in cold weather.
The signs of winter damage start appearing on the outer foliage when the snow melts away. The foliage is injured when the plant tissue heats up too quickly in the sun.
This sort of winter injury can easily be identified by observing the foliage and noticing that the foliage beneath the snow line is still green and healthy, and only the outer foliage is affected.
Winter damage can also be caused when the leaves lose moisture, but the plant is not able to replenish its water reserves because the soil is too cold.
This can be prevented by adding a mulch layer. It will insulate the soil and maintain soil temperature to safe levels.
Boxwoods planted near sidewalks and roads are most affected by salt damage. The salt used for roads and sidewalks, when sprayed onto a Boxwood shrub has a drastic impact on the foliage.
Most foliage on one side of the plant turns brown and is killed. Similarly, if a lot of saltwater seeps into the soil, it will adversely alter the water absorption by the roots.
Salt damage can be identified by noticing that only one side of the plant has turned brown, or the pattern that Boxwoods planted near sidewalks or roads are most affected.
Boxwoods have a shallow root system that spreads laterally around the plant. Shallow roots are more susceptible to being over-fertilized than those growing deep in the ground.
When a plant is over-fertilized, the soil becomes excessively concentrated with salts and nutrients, which sucks water out of the roots into the soil.
This leads to a phenomenon called root tip burn. If too much fertilizer is added, one of the symptoms is bronzing of the foliage.
To prevent this, only use the best fertilizers for boxwoods, in mild, moderated amounts and at the right time.
Drought stress is most commonly spotted in newly planted or young Boxwood shrubs. Boxwoods are slow growers and take time to get established in the ground.
Even when they do get established, their roots cannot grow deep into the ground in search of water. This means they must be supplied with adequate soil moisture at all times.
Young Boxes or shrubs that are freshly transplanted show browning foliage as a sign of a lack of moisture and transplant shock.
Keep the soil well-irrigated until plants are at least 2 years old. Older plants can tolerate long dry spells but still need to be watered if it hasn’t rained in a long while.
Boxwood Leafminer Infestation
The Leafminer is a mosquito-like fly that lays eggs inside Boxwood leaves. The larvae develop by feeding on the leaf tissue and leave the leaf by creating a large hole.
Infested leaves get brown patches. Heavily infested plants look as if the foliage is browning and leaves start dropping in the fall and spring.
You can treat Leafminer infestation with timely treatment with special insecticides made for Boxwood Leafminer infestations.
Always keep an eye on your Boxwood foliage for browning foliage. If some brown leaves catch your eye, please don’t let it slide because it may just be the beginning of a devastating Boxwood disease.
Take special care of your Boxwood, and try to diagnose the problem as soon as you find it. Chances are it’s just the occasional dead stem or too much cold, but it can also be a severe problem such as blight.
Marcel runs the place around here. He has a deep passion for houseplants & gardening and is constantly on the lookout for yet another special plant to add to his arsenal of houseplants, succulents & cacti.
Marcel is also the founder of Iseli International Commerce, a sole proprietorship company that publishes a variety of websites and online magazines.