Why your thuja are turning brown and how to save them

Thuja are popular garden shrubs which, despite their charm and ease of cultivation, often turn brown. Why does this happen? Here are some tips on how to save the plants when they start to lose their green colour.

Thuja is a popular choice because of its low price and ease of cultivation. They don’t require much attention or special treatments, and after a few years, they create a tall, dense hedge that provides privacy. To take care of Thuja, you need to regularly water and trim them, but also check if they have been attacked by fungal diseases.

One of the most dangerous diseases that threatens Thuja is phytophthora. This disease most frequently attacks Thuja in August due to high temperatures and high humidity caused by heavy rains or excessive watering.

Phytophthora in Thuja initially manifests as browning and drying out of the needles, starting from the lower parts and progressing upwards. The disease weakens the plant, slows its growth and causes the roots to rot. Brown spots on the roots and the base of the trunk are characteristic. In severe cases, it can lead to the complete death of the Thuja.

When you see that your Thuja are infected, you must take appropriate measures. Phytophthora can spread to other plants with similar requirements, such as rhododendrons or spruces. The pathogen can survive for a long time in the soil, so early detection and combating the disease is crucial.

Comprehensive measures are needed to save an infected Thuja. First and foremost, you should remove and destroy all diseased parts of the plant, including infected branches and roots. Then, improve soil conditions by loosening the soil around the Thuja to a depth of 4-6 inches and adding compost or manure for better drainage.

Mulching with pine bark or sawdust is recommended. Natural plant protection agents, such as extracts from garlic, grapefruit, nettle, or horsetail, can help battle the disease. Biofungicides containing Bacillus subtilis can also be effective. Correcting fertiliser application is important, too—you should reduce the use of nitrogen fertilisers in favour of potassium-phosphorus ones, especially in the second half of summer. These comprehensive actions can help combat the disease and strengthen the plant.