Arborvitae are popular landscape plants, valued for their evergreen foliage and dense growth, making them suitable for hedges and privacy screens. While generally low-maintenance, a common concern is when their foliage begins to turn light green. This article explores why arborvitae might lighten in color and how to address it.
Understanding Arborvitae Color Changes
Not every instance of lighter green foliage signals a serious problem. Fresh, new growth often emerges a lighter, brighter green. This tender foliage gradually darkens as it matures.
Additionally, arborvitae can exhibit slight color shifts with changing seasons. Some varieties may develop a bronze, yellow-green, or reddish tint during colder winter months as a normal response to low temperatures. This “winter bronzing” is not a sign of distress and the foliage returns to its vibrant green in spring.
Common Causes of Light Green Arborvitae
When light green foliage persists or appears alongside other symptoms, it often points to underlying issues. Various factors, from nutrient imbalances to pest activity, can contribute to this discoloration.
Nutrient deficiencies are frequent culprits. A lack of nitrogen, a macronutrient, can lead to uniform paling of older foliage, making the entire plant appear light green. Iron deficiency causes yellowing between the veins, with the veins remaining green. Soil pH also plays a significant role, as incorrect pH levels can make essential nutrients unavailable. Arborvitae prefer a slightly acidic to moderately alkaline soil pH, ranging from 6.5 to 8.0.
Water stress is another common factor impacting foliage color. Underwatering can cause the foliage to dry out, becoming stressed and appearing lighter, sometimes brittle. Conversely, overwatering or poor drainage can also be damaging. Waterlogged soil deprives roots of oxygen, leading to root rot, which impairs nutrient absorption, resulting in light green or yellowing. Arborvitae prefer moist, well-drained loamy soils and do not thrive in constantly soggy conditions.
Pests can also contribute to a lighter appearance. Spider mites feed by sucking sap from the plant’s needles. This feeding causes stippling, making the foliage look dull, dusty, and lighter green or bronzed. Heavily infested areas may develop fine webbing.
Environmental stressors, such as transplant shock, can temporarily cause yellowing or lightening as the plant adjusts. Extreme heat stress can also lead to foliage discoloration.
Problems with the plant’s root system, such as root girdling or physical root damage, can impede water and nutrient uptake. Arborvitae have shallow, fibrous root systems, extending 12 to 18 inches deep. Damage to these roots can manifest as light green foliage.
Diagnosing the Issue
Determining the specific cause of your arborvitae’s light green color involves a systematic examination. Begin with a thorough visual inspection. Observe the pattern of the lightening: is it uniform across the entire plant, patchy, or concentrated on new versus old growth? Look closely for pests. For spider mites, you can hold a white piece of paper under a branch and tap the branch sharply; tiny specks that begin to crawl on the paper indicate mites.
Next, assess soil moisture. Dig down a few inches near the base to feel the soil. If it feels dry and crumbly, underwatering might be the problem. If it feels soggy or appears muddy, overwatering and poor drainage could be at fault.
A professional soil test can provide accurate information about nutrient levels and soil pH. These tests analyze nitrogen, phosphorus, potassium, and pH, offering tailored recommendations.
Finally, consider recent conditions that might have stressed the plant. Reflect on recent weather patterns, such as prolonged drought or excessive rainfall. Recall any recent fertilization applications, noting the type and amount of fertilizer used. Think about whether the arborvitae was recently planted or transplanted, as this can induce temporary stress.
Effective Solutions and Prevention
Once the issue is diagnosed, appropriate solutions can restore the arborvitae’s health and prevent future problems. For nutrient deficiencies, fertilization is important. If a soil test confirms nitrogen deficiency, a slow-release, balanced fertilizer can provide a steady supply of nutrients. For iron chlorosis, iron chelate can be applied. If the soil pH is incorrect, amendments can adjust it; for example, pelletized limestone can raise pH, while soil sulfur can lower it.
Proper watering practices are important. Implement deep, infrequent watering to encourage a robust root system. Instead of frequent shallow watering, saturate the soil deeply, allowing it to dry out somewhat between waterings. Before watering, always check the soil moisture a few inches down. If poor drainage is an issue, consider improving soil structure with organic matter like compost, or creating raised beds to prevent waterlogging.
For spider mite infestations, horticultural oils or insecticidal soaps can be effective treatments. Always follow product label instructions carefully, and apply these during cooler parts of the day to prevent plant injury. Regular monitoring for early signs of pests can help prevent severe infestations.
General care and preventative measures contribute to long-term plant health. Applying a 1 to 3 inch layer of organic mulch around the base helps retain soil moisture, regulate soil temperature, and suppress weeds. Keep the mulch a few inches away from the trunk to prevent moisture buildup and potential disease. Proper planting techniques, including selecting a site with good drainage and planting the root ball at or slightly above ground level, are also important for establishment and growth. Routine inspection allows for early detection and intervention, ensuring healthy, vibrant plants.