Boxwoods turning yellow often suffer from root rot caused by poor drainage or fungal pathogens. If you have noticed your once vibrant green shrubs looking sickly and pale, you are probably worried and looking for answers. The good news is that most causes of yellowing boxwoods are treatable if you catch them early enough.
In this guide, we will walk you through every possible reason for this discoloration. You will learn how to diagnose the exact problem and, more importantly, how to fix it so your shrubs can recover their lush color. We will cover everything from watering mistakes to winter damage and nutrient deficiencies.
Boxwoods Turning Yellow
When you see your boxwoods turning yellow, it is easy to panic. However, you need to stay calm and look at the pattern of the yellowing. Is the whole plant yellow, or just certain branches? Are the leaves crispy or mushy? These clues will tell you a lot about what is going on underground.
We will break down the most common culprits so you can match your symptoms to the right solution. Remember that boxwoods are tough plants, but they do have specific needs that must be met.
Root Rot Is The Primary Suspect
Root rot is the number one reason for boxwoods turning yellow in many landscapes. This condition happens when the roots sit in waterlogged soil for too long. Without oxygen, the roots begin to die, and they cannot transport water or nutrients to the leaves.
There are two main types of root rot that affect boxwoods: Phytophthora and Volutella. Both are fungal pathogens that thrive in wet conditions. You can often spot this issue if the yellowing starts at the base of the plant and works its way up.
Check the soil around your shrubs. If it feels soggy or smells musty, you likely have a drainage problem. You can also dig down a few inches and look at the roots. Healthy roots are white and firm, while rotting roots are brown or black and mushy.
How To Fix Poor Drainage
Fixing drainage is not always easy, but it is necessary. If your boxwoods are planted in a low spot where water collects, you might need to dig them up and replant them in a raised bed. Alternatively, you can amend the soil with compost to improve its structure.
For potted boxwoods, make sure the container has drainage holes. You should also avoid using saucers that hold water under the pot. If the soil is compacted, use a garden fork to poke holes around the drip line of the shrub to aerate it.
Volutella Canker And Blight
Volutella is a specific fungus that causes boxwoods turning yellow, followed by dieback. You will notice that the leaves turn a light green or yellow, and then the stems develop pink or orange spore masses in humid weather. This disease often attacks plants that are already stressed.
Unlike root rot, Volutella usually affects the upper parts of the plant first. You might see individual branches dying while the rest of the shrub looks okay. The key here is to prune out the infected wood immediately.
Always sterilize your pruning shears with rubbing alcohol between cuts. This prevents you from spreading the fungus to healthy parts of the plant. Dispose of the infected branches in the trash, not the compost pile.
Pruning Techniques For Diseased Wood
When you prune for Volutella, you need to cut back to healthy wood. Look at the cross-section of the stem. If the center is dark or hollow, you need to cut further down. Make clean cuts at a 45-degree angle to help water run off.
After pruning, apply a fungicide that contains copper or chlorothalonil. Follow the label instructions carefully. You will likely need to reapply the fungicide every 10 to 14 days during wet weather to keep the fungus at bay.
Winter Damage And Dehydration
Boxwoods are evergreen, which means they keep their leaves all winter. However, they still lose water through their leaves during the cold months. If the ground is frozen, the roots cannot replace that lost moisture. This leads to a condition called winter burn, which causes the leaves to turn yellow or bronze.
This is especially common on the side of the plant that faces the wind or the winter sun. The leaves might look scorched or crispy. While this is not a disease, it is still a shock to the plant system and can make it more vulnerable to pests.
To prevent this, you should water your boxwoods deeply in the late fall before the ground freezes. This gives them a reserve of moisture to draw from. You can also spray an anti-desiccant on the leaves to create a protective waxy coating.
Recovering From Winter Burn
If your boxwoods are already showing signs of winter burn, do not prune immediately. Wait until spring when new growth begins. This will help you see which branches are truly dead and which ones are just dormant.
Once new growth appears, you can gently scratch the bark on the yellow branches. If the tissue underneath is green, the branch is alive. If it is brown, you can cut it back. The plant will often push out new leaves from the base to replace the damaged ones.
Keep the soil consistently moist during the recovery period. Do not fertilize a stressed plant, as this can cause more harm than good. Give it time and it should bounce back by mid-summer.
Nutrient Deficiencies In Boxwoods
Sometimes, boxwoods turning yellow is a simple case of hunger. Boxwoods prefer slightly acidic soil with a pH between 6.5 and 7.0. If the soil is too alkaline, the roots cannot absorb iron and manganese, even if those nutrients are present in the soil.
This condition is called iron chlorosis. You will see the leaves turn yellow, but the veins will remain green. This gives the leaf a striped or netted appearance. Nitrogen deficiency, on the other hand, causes the older leaves at the bottom to yellow first.
You should test your soil before adding any amendments. A simple soil test kit from a garden center will tell you the pH and nutrient levels. This saves you from guessing and potentially making the problem worse.
How To Correct Soil Imbalance
If your soil is too alkaline, you can add elemental sulfur or a fertilizer formulated for acid-loving plants. Follow the application rates on the package. It is better to apply less and re-test than to overdo it and shock the roots.
For a quick fix, you can apply a foliar spray of chelated iron. This is absorbed directly through the leaves and will green them up within a week or two. However, this is a temporary fix, and you will need to address the soil pH for a long-term solution.
Use a balanced fertilizer like 10-10-10 in the early spring. Avoid high-nitrogen fertilizers in the fall, as this can stimulate new growth that will be killed by frost.
Pests That Cause Yellowing
While diseases and environmental stress are common, you also need to consider pests. The boxwood leafminer is a tiny fly whose larvae burrow into the leaves. This causes blister-like spots that turn yellow and then brown.
Another pest is the boxwood mite. These are microscopic spider mites that suck the sap from the leaves. The damage looks like stippling or tiny yellow dots on the upper surface of the leaf. If the infestation is heavy, the entire leaf can turn yellow.
You can check for these pests by holding a piece of white paper under a branch and tapping it. If you see tiny specks moving around, you have mites. Leafminer damage is easier to spot because the leaves will have visible blisters.
Treatment Options For Pests
For leafminers, you need to apply a systemic insecticide in the spring when the adults are laying eggs. This is usually around the time the forsythia blooms. The insecticide is absorbed by the roots and kills the larvae as they feed.
For mites, you can use a horticultural oil or insecticidal soap. Make sure to spray the undersides of the leaves thoroughly, as this is where the mites live. You may need to repeat the application every 7 to 10 days to break the life cycle.
Encourage beneficial insects like ladybugs and lacewings in your garden. They are natural predators of mites and will help keep the population under control.
Improper Watering Practices
Overwatering is a huge problem for boxwoods, but so is underwatering. Boxwoods turning yellow can be a sign of drought stress, especially if you have sandy soil that drains too quickly. The leaves will look dry and wilted, and the soil will be dry to the touch.
On the flip side, if you water too frequently, you drown the roots. The leaves will turn yellow and then drop off. The soil will feel constantly wet, and you might see algae growing on the surface.
The goal is to provide deep, infrequent watering. You want to soak the soil to a depth of 6 to 8 inches, then let it dry out slightly before watering again. This encourages the roots to grow deep and strong.
Creating A Watering Schedule
During the first year after planting, boxwoods need regular watering to establish their root system. Water them deeply once a week if there is no rain. In hot, dry weather, you might need to water twice a week.
For established shrubs, water them every 2 to 3 weeks during dry spells. A layer of mulch around the base will help retain moisture and keep the soil temperature stable. Just make sure the mulch is not touching the trunk, as this can cause rot.
Use a soaker hose or drip irrigation to water slowly. This allows the water to penetrate deeply without running off. Avoid overhead watering, as this can splash fungal spores onto the leaves.
Environmental Stress And Sun Exposure
Boxwoods are versatile, but they do have preferences. They like partial shade, especially in the afternoon. If they are planted in full sun in a hot climate, the leaves can get sunburned, leading to a yellow or bleached appearance.
Conversely, if they are in too much deep shade, they might not photosynthesize properly, resulting in a pale, yellowish color. They also do not like strong winds, which can dry out the leaves and cause browning or yellowing.
If your boxwoods are in a harsh location, you might need to provide some protection. You can plant a windbreak or install a shade cloth during the hottest part of the summer. This will reduce stress and help the plant maintain its green color.
Adjusting The Planting Location
If your boxwoods are struggling due to location, the best long-term solution is to move them. This is best done in the early spring or fall when the weather is cool. Dig up as much of the root ball as possible and replant them in a more suitable spot.
When choosing a new location, look for a spot with well-draining soil and protection from the hot afternoon sun. Morning sun with afternoon shade is ideal. Also, make sure there is enough space for the shrub to grow to its full size without being crowded.
Water the transplanted shrubs deeply and keep the soil moist for the first few weeks. They will experience some transplant shock, but they should recover quickly if you give them the right conditions.
Frequently Asked Questions
Why are my boxwoods turning yellow in the middle?
Yellowing in the middle of the plant usually indicates poor air circulation and light penetration. The inner leaves are not getting enough sunlight, and they might be staying wet after rain. Thin out the branches to open up the center and allow light and air to flow.
Can yellow boxwoods turn green again?
Yes, if the cause is a nutrient deficiency or mild stress, the leaves can recover. However, if the leaves are already brown and crispy, they will not turn green again. You will need to wait for new growth to replace the damaged leaves.
How often should I water boxwoods?
Water deeply once a week during the growing season if there is no rainfall. In the winter, water them once a month if the ground is not frozen. Always check the soil moisture before watering to avoid overwatering.
Is it better to cut off yellow leaves?
You can remove yellow leaves if they are unsightly, but it is not necessary for the plant’s health. The plant will naturally drop these leaves. Focus on fixing the underlying issue instead of just removing the symptoms.
What is the best fertilizer for yellow boxwoods?
Use a slow-release fertilizer with a balanced ratio like 10-10-10. If the yellowing is due to iron chlorosis, use a fertilizer with chelated iron. Always water the fertilizer in well to prevent root burn.
Dealing with boxwoods turning yellow can be frustrating, but you now have a clear action plan. Start by inspecting the soil moisture and drainage, then look for signs of pests or disease. Test your soil to rule out nutrient issues, and adjust your watering habits accordingly.
Remember that boxwoods are resilient. With a little patience and the right care, they can recover and thrive. Do not give up on them too quickly. Monitor your plants weekly, and you will catch problems before they become severe.
If you have followed all these steps and your boxwoods are still struggling, consider consulting a local extension service. They can provide specific advice for your region and soil type. Sometimes a professional eye is needed to spot a rare disease or pest.
We hope this guide has given you the confidence to tackle this issue head-on. Your boxwoods can be green and healthy again. Just remember to be consistent with your care and observant of changes. Good luck with your shrubs, and do not hesitate to revisit this guide if you need a refresher.