Evergreen trees, typically conifers, retain their needles or leaves throughout the year, providing consistent structure and color to the landscape, especially in winter. Unlike deciduous trees that shed foliage annually, evergreens constantly maintain their green canopy. Because they retain foliage year-round, they are always actively respiring and require consistent care to remain vigorous. Understanding their specific, year-round needs is necessary for ensuring their health.
Essential Hydration and Soil Requirements
The foundation of a healthy evergreen begins with appropriate water management, which differs significantly from that of a lawn or garden bed. Evergreens prefer deep, infrequent watering that encourages a robust, far-reaching root system. Newly planted trees need soil moistened to a depth of six to eight inches during their first few seasons to establish themselves.
Evergreens are susceptible to root rot and cannot tolerate perpetually “wet feet,” making soil drainage a primary concern. Most coniferous evergreens prefer a slightly acidic soil pH, which optimizes the availability of necessary micronutrients. Applying a three-to-four-inch layer of organic mulch helps maintain consistent soil moisture and temperature. Keep the mulch several inches away from the trunk flare to prevent moisture buildup that can lead to rot and disease.
Because evergreens retain their needles, they continue to lose moisture through transpiration even when the ground is frozen. This requires a proactive approach to prevent desiccation, commonly known as winter burn. Deep watering in the late fall, before the ground freezes solid, ensures the root system is fully hydrated entering the colder months.
Strategic Feeding for Evergreen Vitality
Established evergreen trees often require minimal or no fertilization, especially if they are growing in good soil conditions. Over-fertilization can be detrimental, causing excessive, weak growth that is vulnerable to pests and environmental stress. A soil analysis can definitively determine if a nutrient deficiency exists, which is the ideal precursor to any feeding regimen.
When fertilization is necessary, slow-release granular formulations are preferable because they provide a steady supply of nutrients over an extended period. Evergreens generally benefit most from nitrogen, which supports foliage growth and color, often appearing as the highest number in a fertilizer’s N-P-K ratio. However, excessive phosphorus should be avoided because high concentrations can interfere with the beneficial mycorrhizal fungi that aid the tree in absorbing water and other micronutrients.
The optimal time for application is early spring, just before the emergence of new growth, or in late fall after the growth has hardened off. Fertilizing in mid-summer or late season should be avoided because it can stimulate a flush of tender, new growth. This soft tissue will not have time to harden before cold weather arrives, making it highly susceptible to winter injury and dieback.
Proper Pruning and Shaping Methods
Pruning is primarily done to maintain the natural shape of the tree, improve air circulation, and remove damaged wood. The best time for general shaping and maintenance is during the tree’s dormant season or in early spring before the new growth cycle begins. Dead, diseased, or broken branches should be removed immediately upon discovery, regardless of the time of year.
The technique for pruning evergreens is species-dependent, particularly concerning growth habits. On pines, new growth emerges as “candles,” which can be pinched or cut by up to two-thirds in the spring to encourage denser branching. Most evergreens, including spruce and fir, should only be cut back to a lateral bud or branch junction.
Avoid cutting into the “old wood” of many conifers, such as pines and junipers, because they lack the dormant buds needed to regenerate new growth from leafless sections. Pruning to enhance air circulation, especially in dense shrubs like boxwood, involves thinning the interior branches, which helps reduce humidity and the potential for fungal diseases.
Recognizing and Treating Common Ailments
Evergreens can show signs of distress from both living organisms and environmental stressors, often displaying symptoms that mimic each other. Pest infestations, such as spider mites, bark beetles, or scale insects, can cause yellowing, browning, or premature needle drop. Mites often leave fine webbing, while bark beetles create tiny entry and exit holes, sometimes surrounded by resin or “pitch tubes.”
Fungal diseases, including various needle cast and rusts, are frequently observed, especially in conditions of poor air circulation and high humidity. Needle cast, for example, typically causes older, interior needles to turn brown and drop prematurely, starting at the base of the tree and moving upward. Prevention is the first line of defense, which involves ensuring appropriate tree spacing and managing the canopy density to allow air movement.
Abiotic stresses, which are non-living causes of damage, can easily be confused with disease. Winter burn is one of the most common, appearing as browning on the tips or on the south and southwest-facing sides of the tree due to excessive moisture loss on sunny, windy winter days. Road salt damage is another concern, causing salt spray to desiccate needles or salt accumulation in the soil to inhibit water uptake. Mitigating salt damage involves applying physical barriers like burlap near roadways or leaching the soil with copious amounts of water in the spring to dilute the sodium concentration.