The Kousa dogwood (Cornus kousa) is a popular ornamental tree valued for its striking, star-like flowers and exfoliating bark. Like many landscape trees, the Kousa dogwood has specific nutrient requirements that must be met to ensure robust growth and prolific flowering. Proper fertilization requires understanding the tree’s natural environment and delivering nutrients in a way that the root system can effectively absorb them. A targeted feeding schedule provides the necessary building blocks to support the tree’s health throughout the growing season.
Soil Requirements and Readiness
The first step in nourishing a Kousa dogwood is ensuring the soil environment is conducive to nutrient uptake. This species performs best in a slightly acidic soil range, ideally with a pH between 5.5 and 6.5, which allows the tree to efficiently absorb micronutrients. Soil that is too alkaline can inhibit the uptake of elements like iron.
Beyond the chemical composition, the soil must be well-drained and rich in organic matter. Kousa dogwoods are sensitive to standing water, which can drown roots and hinder their ability to absorb nutrients and moisture. Incorporating compost or other natural amendments improves the soil structure, facilitating both drainage and the retention of moisture and nutrients. Performing a soil test before any application confirms the existing nutrient levels and pH, preventing unnecessary or counterproductive fertilization.
Selecting the Right Nutrient Blend
The best fertilizer provides a balanced nutrient profile. A balanced NPK (Nitrogen-Phosphorus-Potassium) ratio, such as 10-10-10 or 12-4-8, is recommended for established trees. Nitrogen promotes dense, green foliage, phosphorus aids root development and flowering, and potassium supports disease resistance and vigor.
A slow-release granular fertilizer or an organic option is preferable to quick-release synthetic products. Quick-release fertilizers deliver nitrogen rapidly, which can burn the shallow root system and encourage excessive, weak vegetative growth. Slow-release formulas, including organic materials like compost or aged manure, break down over time, providing a steady, gentle nutrient supply.
Micronutrients are important, especially when the soil pH is not in the ideal acidic range. In alkaline conditions, the Kousa dogwood struggles to take up iron and manganese, leading to visible deficiency symptoms. Selecting a fertilizer formulated for acid-loving plants, which may contain chelated forms of these micronutrients, helps keep them available for root absorption.
Timing and Application Methods
Proper timing ensures that the Kousa dogwood receives nutrients when its metabolism is active. The optimal time for fertilization is in the early spring, just before the tree begins its new seasonal growth. This application supports the development of new leaves and sets the stage for flower bud formation.
A light, secondary feeding can optionally be applied in early summer to sustain growth, but application should be avoided after mid-summer. Fertilizing late in the season stimulates tender new growth that lacks time to harden off before winter. Young trees should establish their roots for the first one to two years after planting before heavy feeding begins.
When applying granular fertilizer, scatter it evenly around the root zone, which extends out to the tree’s drip line. Dogwoods have a shallow, wide-spreading root system, and applying the product directly against the trunk can cause severe bark and root burn, so a buffer zone must be maintained. After broadcasting, water the area deeply to move the nutrients down into the soil.
Addressing Nutrient Deficiencies
Kousa dogwoods may exhibit symptoms indicating a nutrient deficiency despite a proactive feeding schedule. A common sign of distress is chlorosis, characterized by the yellowing of the leaf tissue while the veins remain green. This pattern often suggests an iron or manganese deficiency, which occurs when high soil pH locks these elements out of reach.
If the tree exhibits a general lack of vigor, stunted growth, or pale-green leaves, it may be suffering from nitrogen deficiency. Nitrogen is highly mobile, so the tree prioritizes new growth, causing older, lower leaves to show the symptoms first. Correcting a diagnosed micronutrient deficiency, such as iron chlorosis, may require applying a chelated iron supplement directly to the soil or as a foliar spray.
Addressing nutritional problems often involves adjusting the soil environment rather than just adding more fertilizer. If a soil test confirms high pH is causing chlorosis, applying sulfur or an acid-forming fertilizer can gradually lower the pH. Always confirm the specific deficiency with a soil test before applying targeted amendments to avoid creating a new nutrient imbalance.