If you’ve noticed your boxwood shrubs turning a rusty, reddish-brown, you’re likely seeing boxwood bronzing. This discoloration can be alarming, but it doesn’t always spell disaster. Understanding the cause is the first step to a solution, and the good news is that some varieties are naturally resistant to disease.
Boxwood Bronzing – Naturally Resistant To Disease
This specific heading points to a powerful strategy for gardeners. Instead of constantly treating problems, you can choose plants that avoid them from the start. Selecting a cultivar known for its toughness is the most effective way to prevent issues like winter bronzing and fungal diseases.
What Causes Boxwood Bronzing?
Bronzing isn’t a single disease. It’s a symptom with a few potential causes. Identifying the right one is crucial for proper care.
- Winter Burn: This is the most common cause. Cold, dry winds and frozen soil prevent the shrub from replacing water lost through its leaves. The foliage desiccates, turning bronze or tan, usually on the side facing the prevailing wind or sun.
- Boxwood Mite Damage: These tiny pests suck sap from the undersides of leaves. The damage appears as fine stippling that can give the entire plant a bronzed or dusty look. You might need a magnifying glass to spot the mites themselves.
- Nutrient Deficiency: A lack of certain nutrients, like potassium or nitrogen, can sometimes cause discoloration. Soil testing can confirm this.
- Fungal Diseases: While less common as a direct cause of bronzing, weak shrubs are more suseptible to diseases like Volutella blight or boxwood blight, which can cause browning and dieback.
The Champion Varieties: Naturally Resistant Boxwoods
Plant breeders have developed outstanding boxwoods that hold their green color beautifully. These varieties often have smaller, tighter leaves and denser growth, which helps them resist environmental stress and pests.
- ‘Green Gem’: A perfect mound-shaped cultivar that is exceptionally cold-hardy. It maintains a rich green color all winter with minimal bronzing.
- ‘Green Mountain’: This variety forms a conical shape naturally. It’s very resistant to winter burn and is a robust, reliable choice for hedges.
- ‘Green Velvet’: Known for its soft, lush foliage that retains a superb dark green hue through the coldest months. It’s a hybrid bred specifically for hardiness.
- ‘Winter Gem’ (Buxus microphylla var. japonica): As the name suggests, this one shines in winter. It’s a top performer for keeping its color when others fade.
- ‘Franklin’s Gem’: A newer introduction with a fine texture and a reputation for outstanding winter color retention and disease resistance.
How to Plant for Success and Resistance
Even resistant varieties need the right start. Proper planting sets the stage for a healthy, resilient shrub.
- Choose the Right Location: Avoid full winter sun and exposed, windy sites. Morning sun with afternoon shade, or dappled light, is ideal. Provide a windbreak if you can.
- Test and Amend Soil: Boxwoods prefer well-drained, slightly alkaline soil (pH 6.5-7.2). Amend heavy clay with compost to improve drainage.
- Dig a Proper Hole: Make it twice as wide as the root ball but no deeper. Planting too deep is a major cause of stress.
- Water Deeply: After planting, water thoroughly to settle the soil. Apply a 2-3 inch layer of mulch (like shredded bark) around the base, keeping it away from the stem.
Ongoing Care to Minimize Problems
Consistent, thoughtful care keeps your boxwoods strong and less likely to bronze or succumb to disease.
Watering Wisely
Deep, infrequent watering is better than frequent sprinkles. It encourages deep roots. Water well in late fall before the ground freezes to prevent winter desiccation. An soaker hose is a great tool for this.
Mulching Matters
Mulch is your best friend. It conserves soil moisture, moderates soil temperature, and prevents weeds. Just remember to keep it a few inches away from the main stems.
Pruning with Purpose
Prune in late spring after the new growth has emerged. Avoid heavy pruning in late summer or fall, as this can stimulate tender new growth that will be killed by frost. Always thin branches to improve air circulation inside the shrub, which helps prevent fungal diseases.
Fertilizing Carefully
Over-fertilizing can cause rapid, weak growth. Use a balanced, slow-release fertilizer in early spring, or simply top-dress with compost. If you suspect a nutrient deficiency, get a soil test first.
What to Do If You See Bronzing
Don’t panic. Assess the situation step-by-step.
- Inspect for Pests: Check the undersides of bronzed leaves with a magnifying glass for mites or their eggs.
- Review the Season: If the bronzing appeared in late winter or early spring, winter burn is the likely culprit.
- Check for Disease: Look for black streaks on stems, spotted leaves, or excessive leaf drop, which could indicate blight.
- For Winter Burn: Prune out dead branches in spring once new growth starts. The plant will often recover on its own with proper watering.
- For Mites: A strong spray of water from a hose can dislodge many mites. For severe infestations, use horticultural oil in summer, following label instructions.
Preventative Measures for a Healthy Garden
Beyond plant choice, a few garden-wide habits make a big difference.
- Clean Your Tools: Disinfect pruning shears with a bleach solution or rubbing alcohol between plants, especially if you suspect disease.
- Space Plants Properly: Good air flow is critical. Don’t crowd your boxwoods or plant them to close to walls or fences.
- Remove Debris: Clean up fallen leaves around the base of shrubs in fall to eliminate places where fungal spores can overwinter.
- Monitor Regularly: A quick weekly walk through your garden helps you spot problems early, when they are easiest to manage.
FAQ: Your Boxwood Bronzing Questions Answered
Q: Will a bronzed boxwood recover?
A: Yes, in most cases. If the cause is winter burn or mites, the plant will often push out new green growth in spring. Prune out any truly dead branches at that time.
Q: Are English boxwoods resistant?
A: Common English boxwood (Buxus sempervirens ‘Suffruticosa’) is actually quite prone to winter bronzing and several diseases. It’s better to choose the modern hybrid varieties listed above.
Q: Should I use anti-desiccant spray?
A> These sprays can help reduce winter moisture loss for evergreens. Apply in late fall on a dry, above-freezing day, and follow the product label carefully. They are a helpful tool for vulnerable plants in exposed locations.
Q: Is boxwood bronzing contagious?
A: No, the bronzing itself is not contagious. It’s a response to stress. However, if the stressed plant develops a fungal disease like boxwood blight, that disease can spread to other vulnerable boxwoods nearby.
Q: Can I prevent bronzing with more water in winter?
A> You cannot water when the ground is frozen. The key is deep watering in late fall before freeze-up and ensuring good soil moisture throughout the growing season so the plant enters winter well-hydrated.
Choosing a boxwood that is naturally resistant to disease and winter stress is the smartest first move you can make. By combining the right plant with proper planting site, consistent care, and smart preventative practices, you can enjoy lush, green boxwoods that maintain their beauty through every season. Your garden will thank you for the thoughtful approach.