The Emerald Green Arborvitae (Thuja occidentalis ‘Smaragd’) is a highly valued landscape plant, recognized for its dense, naturally conical shape and vibrant, year-round foliage. Its consistent color and compact form make it a popular choice for privacy screens and hedges. Maintaining its deep color and promoting steady growth depends on providing the appropriate nutrients at the correct times.
Essential Nutritional Requirements for Emerald Green Arborvitae
The health and characteristic appearance of this evergreen relies on three primary macronutrients, often referred to by N-P-K. Nitrogen (N) is particularly important because it drives chlorophyll production, which maintains the deep green color and foliage density. A deficiency in nitrogen will quickly show as a general yellowing or paling of the entire plant.
Phosphorus (P) supports robust root system development, which is necessary for the tree to anchor itself and efficiently absorb water and nutrients. Potassium (K) helps regulate water movement within the plant, increasing its resistance to environmental stresses like drought, cold, and disease.
Beyond these major elements, arborvitae can suffer from micronutrient deficiencies, often manifesting as browning or yellowing on the foliage. Magnesium deficiency is a common problem, causing a specific pattern of yellowing between the veins of older foliage, known as interveinal chlorosis.
Choosing the Recommended Fertilizer Ratios
When selecting a product, the numbers on the label represent the percentage ratio of Nitrogen (N), Phosphorus (P), and Potassium (K) by weight. For established Emerald Green Arborvitae, a high-nitrogen formulation is recommended to maintain the signature deep green color and encourage dense foliage growth. Ratios that favor nitrogen, such as 3:1:2 (e.g., 12-4-8) or 2:1:1, are excellent choices.
A balanced fertilizer like 10-10-10 or 20-20-20 can also be effective, especially if the soil has not been tested. For the best results, look for a slow-release granular fertilizer formulated specifically for evergreens. These products release nutrients gradually over several months, providing a steady supply and reducing the risk of root burn compared to quick-release options.
The inclusion of secondary nutrients can be beneficial, particularly if browning is a recurring issue. Some evergreen fertilizers contain sulfur, which helps adjust soil pH to make other nutrients more available, or magnesium, which directly addresses the common chlorosis problem. Choosing a product labeled for evergreens ensures the nutrient balance is appropriate for this type of plant.
Establishing a Proper Fertilization Schedule
The most effective time to fertilize Emerald Green Arborvitae is in the early spring, just before the tree breaks dormancy and begins its new growth cycle. This timing allows the plant to immediately utilize the nutrients to fuel the burst of spring growth. If using a high-quality, slow-release granular fertilizer, a single application is often sufficient for the entire growing season.
A second, lighter application may be considered in early summer, but it is important to stop all fertilization by mid-summer, typically no later than mid-July. Fertilizing past this point stimulates tender new growth that does not have sufficient time to harden off before the first frost, making the plant susceptible to winter damage.
The application should focus on the area around the drip line, which is the zone beneath the outer edge of the branches where the feeder roots are most active. Granular fertilizer should be spread evenly across this root zone and not piled directly against the trunk, as this can damage the bark and encourage disease. After application, the area must be thoroughly watered to help the granules dissolve and move the nutrients into the soil, preventing fertilizer burn.