Arborvitae are evergreen shrubs and trees frequently used in landscapes for dense screening and privacy hedges. While generally robust and low-maintenance, supplemental nutrition can enhance their health, promote denser foliage, and maintain their characteristic deep green color. Fertilization acts as a targeted supplement when native soil lacks sufficient nutrients to support optimal growth. Understanding when and how to apply these supplements ensures the plant receives proper support without causing damage.
Assessing If Your Arborvitae Needs Fertilizer
Fertilization is not required for every arborvitae. The need for fertilizer is typically indicated by specific visual symptoms pointing to a nutrient deficiency. Signs such as stunted annual growth, sparse foliage, or smaller than normal needles suggest the plant is lacking essential resources.
The most common visual sign is a change in the rich green color, such as yellowing or browning of the tips, which can indicate a nitrogen or magnesium deficiency. Before applying any product, performing a soil test is recommended; this analysis provides a clear picture of the soil’s existing nutrient levels and pH, allowing for a precise treatment plan. If the plant displays severe browning or dieback, a deeper problem like improper watering, pest infestation, or disease is more likely the cause, which fertilizer will not fix and may even worsen.
Choosing the Appropriate Fertilizer Formula
Arborvitae benefits most from a fertilizer containing a balanced or slightly higher percentage of nitrogen (N) compared to phosphorus (P) and potassium (K). A balanced NPK ratio like 10-10-10 is suitable, but a nitrogen-heavy formula such as 15-5-10 or 20-15-15 encourages more vigorous, dark green foliage growth. Nitrogen is a fundamental component of chlorophyll, making it important for maintaining the plant’s deep color.
The physical form of the fertilizer is as important as the nutrient ratio. It is recommended to use a slow-release granular product, as this formulation dissolves gradually over several months. This slow delivery prevents the sudden surge of salts that can cause root burn. Specialized products labeled as “Evergreen Fertilizer” are acceptable options, provided they are slow-release and adhere to a suitable NPK balance.
Proper Timing and Application Methods
The timing of fertilizer application is important. The ideal time to fertilize established arborvitae is in the early spring, just before the plant begins its new flush of growth. This timing ensures nutrients are immediately available to support the season’s new shoots and foliage development. A single application of a slow-release product in the spring is often sufficient for the entire growing season.
Alternatively, some gardeners opt for a dormant feeding in the late fall after the plant has stopped growing and the foliage has hardened off for winter. Applying fertilizer in mid-summer or late fall before the first hard frost should be avoided. Fertilizing during these times can stimulate soft, tender new growth that is susceptible to winter damage.
When applying granular fertilizer, the product must be spread across the root zone, which extends out to the plant’s drip line. The majority of the plant’s feeder roots reside in this zone, not directly next to the trunk. Spread the recommended amount of granular fertilizer evenly over this entire area, ensuring the granules do not pile up against the trunk, which can cause localized burning. After application, the area must be thoroughly watered to help the fertilizer begin dissolving and move the nutrients down into the root zone.
Fertilization Guidelines for Newly Planted Arborvitae
For newly planted arborvitae, withhold chemical fertilizer for the first year after planting. The delicate feeder roots of a transplanted tree are focused on establishing themselves in the new soil, and introducing a strong chemical fertilizer can easily burn them. This root damage inhibits the plant’s ability to absorb water and nutrients.
If the planting location has poor soil, a mild, organic approach should be favored over chemical fertilizers. Instead of a strong NPK product, incorporate well-aged compost or a root stimulator solution into the soil outside the immediate root ball area at planting. These materials offer gentle support and encourage root development without the high salt content that causes root tip injury.