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When its healthy, boxwood, otherwise known as buxus, brings a deep, glossy green to the garden. But sometimes the leaves can discolor, turning yellow or brown, which spoils the aesthetic.
There are a few reasons behind this – from environmental stress to pests. Most of them can be fixed with a little TLC, which means that your evergreen shrub may be able to be saved.
If you’ve seen leaves turning yellow, don’t worry—our simple guide tells you what could be causing it and how to get them back to their former glory.
Boxwood is a good choice for formal hedging around flower beds( credit: BROKER / Alamy Stock Photo)
According to the Royal Horticultural Society (the RHS), inclement winter weather can take its toll on boxwood.
Yellowing can be caused by waterlogged soil, they explain, particularly if it is clay. To treat the plants, they suggest digging them up and removing any rotting or dead roots. You should also cut back your boxwood to get rid of the damaged top growth. These hedge shears from Amazon are great for the job. After that, move it to a better spot (a place out of the wind is best) or plant it in new compost with grit added to help it drain. If your boxwood is in pots, you might want to water it less often and make sure the bottoms of the pots have drainage holes.
The tips of leaves can also turn yellow due to low temperatures, the RHS explains. And, frost damage can cause new, early-spring growth to turn pale brown and papery. In this case, you don’t need to replant the shrubs, but you can cut back the ones that got hurt in the spring. Applying a fertilizer afterward will help to revive them and encourage new, green growth.
Put down a thick layer of mulch around your boxwood next fall, but don’t let it touch the stem. This will help to protect it through the colder season.
Discolored leaves from winter damage can be pruned back in spring( credit: Bulavka / Alamy Stock Photo)
Box can also turn yellow or orange due to excessive heat and sunshine. Plants that have been around for a while can handle drought better, but they will still benefit from a little watering when it’s really dry.
Water box in container gardens and younger shrubs frequently, but avoid allowing the soil to become waterlogged.
If yellowing leaves are accompanied by dead, brown patches, your shrub may have succumbed to box blight. You may spot black streaks on the stems, too.
John has been writing about gardens for more than 50 years. In Amateur Gardening magazine, he often answers readers’ questions, many of which are about evergreen shrubs. He has also written four books and has delivered many talks over the years on horticulture.
Box blight, if unchecked, will destroy the whole bush, says the Amateur Gardening team. John Negus adds that two fungi are responsible (Cylindrocladium buxicola and Volutella Buxi) and they often occur together.
Cut back infected shoots to live, healthy tissue and bin or burn prunings, says the team. Then, they say to spray the plant with an ornamental plant fungicide, which should stop the disease from spreading. The evergreen shrub can also be nursed back to health by fertilizing it. John Negus suggests feeding it once a month with a sulfate of potash from mid-spring to fall. Simply sprinkle it over the root area and water it in.
The team also says, “If the steps above don’t stop the disease, I urge you to remove the bush, roots and all, along with the soil around the roots.”
A lot of people have box blight, but it can be fixed quickly (credit: Christopher Miles / Alamy Stock Photo).
As a gardener, you spend hours carefully tending to your boxwood shrubs, pruning and shaping them into perfect uniform hedges or ornamental forms. So when those emerald leaves start turning yellow, it can be concerning. Your first instinct may be to whip out the pruners and snip away the unsightly yellow foliage. But is that the right approach? Should you actually trim off yellow leaves on boxwoods?
The answer is not a simple yes or no There are a few factors to consider before taking pruners to yellow leaves Read on to learn more about the causes of yellowing boxwood leaves, when pruning is advisable, and how to restore your plants to their former vibrant glory.
Why Boxwood Leaves Turn Yellow
Before making any pruning decisions, it’s important to understand why your boxwoods have yellowing leaves in the first place Here are some of the most common culprits
Disease
Fungal diseases like boxwood blight or root rot can cause leaf yellowing. With boxwood blight, infected leaves often develop brown spots or streaks before turning yellow. Root rot may cause the entire shrub to look sickly and undernourished. Pruning won’t cure fungal diseases, so accurate diagnosis is essential.
Environmental Stress
Hot sun, drying winds, or inadequate water can stress boxwoods and cause yellowing. This type of discoloration usually starts at leaf edges and tips. Ensure proper siting and care to prevent environmental yellowing.
Winter Injury
In cold climates, boxwoods may turn yellow over winter. Leaves desiccate from exposure to sun and wind when the ground is frozen. Prevent this by spraying anti-desiccant or wrapping plants in winter.
Pest Damage
Hungry insects like mites, aphids, or leaf miners can distort growth and cause yellowing. Treat any infestations with appropriate organic pest control. Pruning won’t eliminate pests.
Poor Drainage
Soggy soil deprives roots of oxygen. Yellowing leaves can signal root rot due to excessive moisture. Improve drainage before pruning.
Dog Urine
Dog urine contains high nitrogen that can burn and yellow boxwood foliage. Use repellents or barriers to protect plants.
Root Damage
Construction work, tilling, or transplanting too deep can damage boxwood roots and cause upper leaf yellowing. Pruning won’t help damaged roots.
When to Prune Yellow Leaves
If yellowing is due to environmental factors like sunburn or winter damage, pruning may improve appearance temporarily. But long-term health will depend on modifying care to prevent recurs.
Prune yellow leaves caused by dog urine or mechanical damage, since affected branches won’t recover. But again, address the underlying cause for a permanent solution.
Otherwise, hold off on pruning and address what’s stressing the plant instead. With disease or pests, infected branches often die back entirely, making it easy later to see what should be removed.
Sometimes it’s best to prune nothing and just let the plant grow out of minor or temporary yellowing. Radical pruning stresses boxwoods further, slowing recovery. Removing too much risks killing the shrub or destroying its shape.
Wait to prune until you’ve fixed underlying issues, and new growth looks normal. Then prune only dead or declining branches as needed to restore form. Avoid shearing off yellow parts of otherwise healthy leaves. Prune on a dry day to avoid spreading disease. Sterilize tools between cuts.
When to Remove Entire Plants
If despite your best efforts, a boxwood declines past recovery, replacement may be necessary. Signs of poor prognosis include:
- Most branches and roots dead
- Few surviving green leaves
- Plant collapsing or falling over
- Persistent yellowing over years
- Severe disease infection
Test questionable plants by scraping away a little bark. Green tissue means the branch is alive; brown is dead. If most of the shrub is dead, removal is likely your best option.
Caring for Yellowing Boxwoods
While pruning alone won’t cure sick boxwoods, providing optimal care can help recovery. Steps to nurse ailing plants back to health include:
- Improve drainage and ensure adequate irrigation
- Apply fertilizer to nourish distressed plants
- Protect from sun/wind damage
- Monitor for pests and treat promptly
- Remove deadwood and clear leaf debris
- Maintain proper siting and spacing
With time and TLC, mildly affected boxwoods can often regain their vibrant evergreen luster. But severe cases may only steadily decline. Know when to prune yellowing leaves versus when it’s kinder to replace struggling specimens.
A bit of yellow here or there doesn’t necessarily spell doom. But radical pruning is rarely the right solution. Consider why leaves are discolored, treat the underlying cause, and wait for plants to recover before taking pruners to yellowing boxwood foliage. Patience and attentive care is key to preserving the health, shape, and beauty of your boxwood investment.
Caterpillars and other pests
Caterpillars can invade box bushes and cause leaves to turn pale yellow or brown before dying.
John Negus says that the best way to get rid of this sneaky pest is to pick out the caterpillars by hand and set up at least one box tree moth trap. He says that these work because of pheromones that drive male moths to their deaths, leaving female eggs unfertilized.
Boxwood leafminer can also be a nuisance and cause yellow leaves and a blistered appearance. Some types of boxwood are stronger than others, and pesticides and spring pruning can help keep them from doing damage.
Q&A – What’s wrong with my boxwood? Some leaves are yellowing.
FAQ
What to do if your boxwoods turn yellow?
What do overwatered boxwoods look like?
How do I get my boxwoods green again?
What is the best fertilizer for yellowing boxwoods?
Can you cut boxwood in winter?
Do not trim boxwood in fall or winter. Trimming promotes new tender growth which won’t tolerate cold temperatures well. New growth produced by pruning in fall or winter is easily damaged. Can you hard prune boxwood?
How do you care for a boxwood plant?
Give your shrub a loamy soil that drains well. Locate it where it will be sheltered from winds. Boxwood roots are shallow, which can expose them to excessive heat. Put a layer of organic garden mulch, 3 inches thick, around your plant to give it protection from the heat.
Can boxwood be trimmed?
Boxwood is a popular staple in formal gardens, where it acts as a border and lines walkways. In more contemporary landscapes, it can be trimmed into shapes, including orbs, cones, and, in some cases, animal figures. Choosing a variety of boxwood already somewhat in the shape you want is a good first step in having a healthy plant.
Why is my boxwood turning yellow?
Serious infestations can result in boxwoods turning yellow. Faithfully inspect your plants for pests, particularly the undersides of the leaves. If you find any pest activity, spray with insecticides such as Neem oil. Perform “the scrape test” to see if your boxwood is dead. With a sharp knife, scrape off a bit of the bark on one of the branches.
When should boxwood be pruned?
Moderate spring temperatures followed by warm summer temperatures allow the new growth to mature before cold weather returns in fall. Boxwood shrubs that are pruned in late summer or fall are more likely to be damaged, sometimes to the point of death, during the winter. The tender new growth is vulnerable to freezing temperatures.
When should a box plant be pruned?
Discolored leaves from winter damage can be pruned back in spring 2. High temperatures Box can also turn yellow or orange due to excessive heat and sunshine. Established plants are more tolerant of drought, but will still appreciate a bit of watering in very dry spells.