Why Are My Arborvitae Turning Brown in the Summer?
Arborvitae turning brown in summer is usually a sign of stress from transplant shock, underwatering, pest infestations, or fungal disease rather than a normal seasonal change. The key is identifying the specific cause quickly so you can save the affected branches and prevent the browning from spreading. Below you will find the most common reasons for summer browning in arborvitae and the exact steps to diagnose and fix each one.
Is Summer Browning Always a Sign of Disease?
No. In fact, many cases of summer browning in arborvitae are caused by environmental stress, not disease. While fungal infections can turn foliage brown, drought stress and heat stress are far more common triggers during hot months. Arborvitae have shallow root systems that dry out fast, and when the soil moisture drops too low, the plant redirects water away from outer foliage, causing it to brown.
Disease-related browning often looks different. It tends to start on inner or lower branches and spreads upward, while environmental browning usually appears first on the side exposed to the afternoon sun or wind. Knowing this difference helps you rule out problems quickly without unnecessary treatments.
What Are the Most Common Causes of Arborvitae Turning Brown?
Several factors can cause arborvitae to turn brown in summer, and sometimes more than one is at work. Here are the most frequent culprits.
Drought and Underwatering
Arborvitae need consistent moisture, especially during the first two years after planting. When summer temperatures climb and rainfall is scarce, the soil dries out faster than the roots can compensate. The result is foliar browning that often starts at the tips of branches and works inward. If you press the brown needles, they feel dry and brittle rather than soft or mushy.
Heat Stress and Sun Scald
On very hot days, intense sun can literally burn the foliage, especially on young or recently transplanted arborvitae. This is called sun scald. It shows up as brown or bleached patches on the side facing the sun, typically the south or southwest side. Unlike drought browning, the soil may still be moist when you check it.
Transplant Shock
If you planted your arborvitae within the last year or two, transplant shock is a likely suspect. Moving disturbs the root system, and until the roots re-establish, the plant cannot take up enough water to support all its foliage. Brown patches often appear within a few weeks of planting, even with regular watering.
Fungal Diseases
Several fungi attack arborvitae during warm, humid weather. Tip blight (caused by Phomopsis or Kabatina) turns branch tips brown while the base stays green. Needle blight causes browning that starts on lower inner needles and moves outward. Look for tiny black fruiting bodies on dead needles as a sign of fungal infection.
Winter Damage Showing Up Late
Sometimes what looks like summer browning is actually winter burn that only becomes visible when the plant starts actively growing in spring and summer. Cold winds and frozen soil cause moisture loss from needles, and the damaged tissue turns brown months later. This is more common on the windward side of the plant.
Pest Infestations
Pests like spider mites and bagworms can cause significant browning during summer. Spider mites are tiny and hard to see, but you may notice fine webbing between branches. Bagworms create small, cone-shaped bags made of silk and foliage, and they feed on needles until branches turn brown.
How Do I Know if My Arborvitae Is Dying or Just Stressed?
Not all browning means the plant is dying. The table below shows how to tell the difference.
| Sign | Stressed (Recoverable) | Dying (Likely Fatal) |
|---|---|---|
| Brown area | Less than 30% of the plant, usually on one side or tips | More than 50% of the plant, spreading from multiple sides |
| Branch flexibility | Branches still bend slightly before snapping | Branches snap cleanly and feel hollow or dry |
| Inner growth | Green needles still present near the trunk | No green anywhere on the plant |
| Bark condition | Bark intact and firm | Bark peeling or cracking, especially near the base |
| New growth | You see new green shoots at branch tips | No signs of new growth after several weeks of warm weather |
If most signs point to stress rather than death, you can usually save the plant with proper care. But if the plant is mostly brown with no green and the bark is cracking, replacement is usually the better option.
Can Pests Cause Arborvitae to Turn Brown in Summer?
Yes, pests are a significant cause of summer browning, and they are often overlooked until the damage is advanced. Spider mites thrive in hot, dry weather. They pierce individual needles and suck out moisture, giving the foliage a stippled or dusty look before it turns brown. To check for mites, hold a white sheet of paper under a branch and tap it. If tiny specks fall and start moving, you have mites.
Bagworms are easier to spot once you know what to look for. The bags are about one to two inches long and blend in with the needles. If you see brown branches with bags attached, remove them by hand or treat with an appropriate insecticide while the larvae are still feeding in early summer.
Arborvitae leafminer is another pest that can cause browning. The larvae tunnel inside the needles, causing them to turn brown and drop. Look for hollowed-out needles that feel papery.
What Should I Do When I Notice Brown Foliage?
Act quickly, but do not panic. Follow these steps in order to identify the cause and start the right treatment.
- Check soil moisture. Dig down three to four inches near the base. If the soil is dry, water deeply. If it is wet or muddy, you may have drainage issues or root rot.
- Inspect the brown pattern. Is it on one side only? That suggests sun or wind stress. Is it on inner branches? That leans toward fungal disease. Is it at the tips? That could be tip blight or drought.
- Look for pests. Examine branches with a magnifying lens if needed. Check for webbing, bags, or tiny moving specks.
- Snap a small branch. If it bends before breaking, the branch is still alive. If it snaps cleanly and is brown inside, that branch is dead.
- Prune dead or damaged branches. Use clean, sharp pruners to remove all brown foliage. Cut back to where green growth remains or to the main branch. Do not leave stubs.
- Apply water correctly. Water deeply and slowly at the base, not overhead. A soaker hose or drip system works best. Water once or twice a week during dry spells, aiming for about one inch of water per week.
- Mulch around the base. Apply two to three inches of organic mulch like wood chips or bark. Keep it pulled back a few inches from the trunk. Mulch keeps soil cool and moist.
If you suspect a fungal disease, apply a copper-based fungicide according to the label directions. For spider mites, use insecticidal soap or neem oil and repeat every five to seven days until the mites are gone.
How Can I Prevent Arborvitae from Turning Brown in Future Summers?
Prevention is much easier than fixing an established problem. A few simple habits can keep your arborvitae green through the hottest months.
Water Deeply, Not Often
Arborvitae develop deeper roots when you water slowly and deeply. A shallow sprinkle encourages surface roots that dry out fast. Use a soaker hose laid in a circle around the drip line. Water for about 30 to 45 minutes per session, once or twice a week depending on rainfall and temperature.
Apply Mulch Every Spring
Mulch is one of the cheapest and most effective tools for summer protection. It slows evaporation, keeps roots cool, and reduces weed competition. Replenish the layer each spring before the heat arrives. Avoid piling mulch against the trunk, which can lead to rot.
Prune for Airflow
Thick, crowded arborvitae trap humidity and create a perfect environment for fungal diseases. Thin out branches slightly in early spring to allow air to circulate. Prune only live wood and avoid cutting into old, bare wood where new growth rarely appears.
Choose the Right Location
Arborvitae planted in full sun with no afternoon shade are more prone to sun scald. If possible, plant them where they get some relief from the hottest afternoon rays. Also avoid planting in low spots where water pools after rain. Soggy roots lead to root rot.
Water During Winter Drought
Winter burn happens when the ground is frozen but the sun and wind continue to dry out needles. If you experience a dry winter, water your arborvitae on mild days when the soil is not frozen. This keeps the roots hydrated and reduces brown patches that show up later.
When Should I Call a Professional?
If you have followed all the steps above and the browning continues to spread, or if you see extensive branch dieback with no obvious cause, it is time to bring in a certified arborist. A professional can test for soil issues, identify advanced fungal infections, and recommend treatments beyond home remedies. Additionally, if more than half the plant is brown and you suspect a vascular disease like Phytophthora root rot, professional diagnosis can save you time and money. In many cases, replacing the plant is more cost-effective than treating advanced disease.
For routine care, a good pair of bypass pruners is essential. Look for a sharp, comfortable model like the Fiskars 15-inch Bypass Pruners for clean cuts that heal quickly. If you need to treat fungal issues, a copper fungicide spray is a reliable product to keep on hand. For pest control, neem oil works well and is safe for beneficial insects when applied correctly.
Why Are My Arborvitae Turning Brown in the Summer and How Do I Fix It for Good?
Summer browning in arborvitae is almost always a fixable problem if you catch it early. The most common causes are underwatering, heat stress, transplant shock, and fungal disease, and each has a straightforward treatment. Check soil moisture first, then inspect the pattern of browning and look for pests. Prune dead branches, water deeply, and mulch the base. For ongoing prevention, water consistently, avoid overhead watering, and thin branches for airflow. If your arborvitae is turning brown in the summer, act within a week of noticing the first signs, and you will give the plant the best chance of recovering and staying green through the rest of the season.