If your arborvitae plant turns brown and begins to wither, it isn't always a cause for worry. Even though arborvitae trees are treasured for their staggering height and lush green foliage, some browning is normal and natural. To prevent browning from disease or illness, watch for over- or underwatering and be alert for pests.
During the winter months, your arborvitae will turn brown in the center, close to the stalk of the plant. The tips will stay green. If your arborvitae looks like this in the wintertime, you don't need to do anything at all. Your plant will look just fine when spring rolls around. If your plant is turning brown from the top of the plant, or the brown spots spread to the tips, no matter what time of year, it's likely that your plant is getting too much or too little water. Dig a small trench around your plant and feel the soil with your finger. If the soil is soggy, transplant your arborvitae to a new location. If the soil is dry, apply water directly to the root system of your plants with a soaker hose. To prevent this damage, water your arborvitae weekly with a soaker hose, but do not let the plant sit in pools of water.
On occasion, mites and other pests can infect arborvitae plants and cause browning and leaf death. Place a white piece of paper underneath your plant's branches and give the branch a good shake. Look for black spots that scurry off the page. If you find these mites, ask your gardening center for advice on pesticides to use. Similarly, if you find other pests on your plant, take them to your gardening center for advice. Do not spray your arborvitae with chemicals unless you have seen and identified the pests you're fighting. Spraying your trees indiscriminately can cause damage, including browning.