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Several factors cause a boxwood to turn yellow, and it’s often a sign that something isn’t right with your shrub.
If your boxwood is turning yellow, you might be dealing with environmental stress, pests, or a nutrient problem.
Understanding what causes a boxwood to turn yellow is the first step to fixing the issue and bringing your shrub back to its lush green glory.
In this post, we’ll explore the main reasons behind a boxwood turning yellow and how to address each one effectively.
Let’s dig into the causes of boxwood yellowing so you can take action and restore your plant’s health.
I will guide you through each cause step by step to help you identify the problem quickly.
What Causes a Boxwood to Turn Yellow?
1. Overwatering or Poor Drainage
Overwatering is a common reason why a boxwood turns yellow.
Boxwoods need moist but well-drained soil, and when roots sit in water, they can’t get oxygen.
This leads to root rot, which causes the leaves to turn yellow and then brown.
If your boxwood is turning yellow and the soil feels soggy, drainage might be the issue.
You can improve drainage by amending the soil with organic matter or planting in raised beds.
Avoid watering too frequently, especially during rainy seasons.
Signs of root rot include a foul smell from the soil and mushy roots when dug up.
Check for standing water after rain to assess drainage.
2. Underwatering or Drought Stress
On the flip side, underwatering can also cause a boxwood to turn yellow.
When a boxwood doesn’t get enough water, the leaves may yellow and drop.
This is especially common during hot, dry spells or in sandy soils that drain quickly.
Checking soil moisture can help you determine if drought stress is causing the boxwood to turn yellow.
Water deeply once a week during dry periods to keep your boxwood hydrated.
Mulching around the base can also help retain moisture and regulate soil temperature.
Boxwoods in containers need more frequent watering than those in the ground.
A layer of organic mulch can conserve soil moisture.
3. Nutrient Deficiencies
Lack of essential nutrients like nitrogen or iron can cause a boxwood to turn yellow.
Yellowing leaves with green veins often indicate an iron deficiency.
Nitrogen deficiency typically causes older leaves to turn yellow first.
Soil testing can confirm if nutrient issues are behind your boxwood turning yellow.
Applying a balanced fertilizer formulated for evergreens can help correct deficiencies.
For iron deficiency, use an iron chelate supplement to green up the leaves.
Follow fertilizer instructions carefully to avoid overfeeding.
A soil test kit is inexpensive and easy to use.
4. Soil pH Imbalance
Soil pH that is too high or too low can cause a boxwood to turn yellow.
Boxwoods prefer slightly acidic soil with a pH between 6.0 and 7.0.
If the pH is off, nutrients become unavailable to the plant, leading to yellowing.
Testing your soil pH is easy with a home kit, and you can adjust it with lime or sulfur.
Maintaining proper pH helps prevent your boxwood from turning yellow.
Retest soil annually to keep pH in the ideal range.
Adjust pH gradually to avoid shocking the plant.
Environmental Factors That Cause Boxwood Yellowing
1. Winter Burn
Winter burn is a common cause of a boxwood turning yellow after cold months.
When the ground freezes, roots can’t take up water, but leaves still lose moisture through transpiration.
This desiccation leads to yellow or brown leaves on the outer parts of the shrub.
Providing winter protection like burlap screens can prevent your boxwood from turning yellow due to winter burn.
Watering well before the ground freezes also helps reduce winter burn risk.
Antidesiccant sprays can also be applied to protect leaves.
Choose winter-hardy boxwood varieties for your zone.
2. Too Much Sun or Wind
Boxwoods prefer partial shade, and too much direct sun can stress them.
Strong winds also dry out leaves, causing them to turn yellow and sometimes brown at the edges.
If your boxwood is turning yellow in a sunny, exposed spot, consider relocating it or providing shade with a row cover.
Windbreaks like fences or hedges can reduce wind damage.
Shade cloth can be used during the hottest part of the day.
Choose a sheltered planting site for new boxwoods.
Evergreen trees can provide natural shade.
3. Salt Damage from Road De-icers
Salt used on roads or walkways can cause a boxwood to turn yellow.
Salt spray or runoff can accumulate in the soil and burn the roots and leaves.
You may notice yellowing on the side of the boxwood facing the road.
Flushing the soil with plenty of water can help dilute salt levels.
Planting boxwoods away from salted areas prevents this cause of yellowing.
Use alternative de-icers like calcium chloride if boxwoods are nearby.
Replant boxwoods in a protected area if salt is an issue.
Pests and Diseases That Cause Boxwood to Turn Yellow
1. Boxwood Leafminer
The boxwood leafminer is a small pest that can cause a boxwood to turn yellow.
The larvae tunnel inside the leaves, creating yellow blisters or mines that are visible.
Infested leaves often drop early, and heavy infestations can weaken the shrub.
Proper pruning and removal of affected leaves can help manage this pest.
Insecticidal treatments containing spinosad or neem oil are effective if applied at the right time.
Encouraging beneficial insects also helps control leafminer populations.
Monitor your boxwood regularly for early signs of infestation.
Horticultural oil can smother leafminer eggs.
2. Boxwood Blight
Boxwood blight is a serious fungal disease that causes a boxwood to turn yellow and drop leaves rapidly.
It often starts with yellow spots on leaves and black lesions on stems, and it spreads quickly.
If you suspect boxwood blight, remove affected plants immediately to prevent spread to healthy ones.
This disease is a major reason why a boxwood turns yellow and dies, and there is no cure once infected.
Prevention through good sanitation and avoiding overhead watering is key.
Fungicides can be used as a preventive measure but are not effective after infection.
Space plants properly to improve air circulation.
Disinfect pruning tools between plants to reduce spread.
Cultural Care Mistakes That Cause Boxwood Yellowing
1. Improper Pruning
Pruning at the wrong time or too heavily can cause a boxwood to turn yellow.
Boxwoods should be pruned in late spring or early summer, not during fall.
Heavy pruning can stress the plant and lead to leaf yellowing.
Always use clean, sharp tools to make clean cuts.
Avoid pruning more than one-third of the plant at a time.
Thin out crowded branches to improve light penetration.
Shearing boxwoods into formal shapes requires careful technique.
2. Fertilizer Burn
Applying too much fertilizer, especially high-nitrogen types, can cause a boxwood to turn yellow.
Fertilizer burn damages roots and leads to yellowing or browning of leaf tips.
Always follow label instructions and water after fertilizing to dilute nutrients.
Using a slow-release fertilizer reduces the risk of burning.
If you suspect fertilizer burn, flush the soil with water.
Wait until the boxwood shows new growth before fertilizing again.
Organic fertilizers are less likely to cause burn.
So, What Causes a Boxwood to Turn Yellow?
Several factors cause a boxwood to turn yellow, including overwatering, underwatering, nutrient deficiencies, soil pH imbalance, environmental stress like winter burn and salt damage, pests like leafminer, diseases like blight, and cultural mistakes like improper pruning and fertilizer burn.
Identifying the specific cause of your boxwood turning yellow is crucial for effective treatment and recovery.
By understanding what causes a boxwood to turn yellow, you can take steps to restore its health and prevent future issues.
I hope this post has helped you pinpoint why your boxwood is turning yellow and how to fix it with confidence.
Remember, early intervention is key when you notice a boxwood turning yellow.
Check your boxwood regularly for signs of trouble.
With proper care, your boxwood can stay green and healthy.