The genus Eucalyptus, often called gum trees, encompasses a wide variety of species celebrated for their distinct, often silvery-blue, foliage and menthol-like aroma. These native Australian plants are popular ornamental additions across the globe, valued for their rapid growth and evergreen nature. Successfully cultivating these trees and shrubs outside their natural habitat requires understanding their specific needs. This guide provides practical instruction for maintaining the health and desired size of your eucalyptus plant.
Site Selection and Planting Preparation
Eucalyptus plants demand a location that receives full, direct sunlight for a minimum of six to eight hours each day. While they can endure partial shade in extremely hot climates, consistent light exposure is necessary for robust growth and dense foliage. The soil environment is equally important, as these plants require exceptionally well-draining conditions and will not tolerate standing water or waterlogged roots.
The ideal soil composition is generally slightly acidic to neutral, with a pH range between 5.5 and 7.5. If planting in the ground, dig a hole that is twice as wide as the root ball but no deeper than its height to prevent settling. Avoid enriching the planting hole with excessive compost or manure. Eucalyptus naturally prefers poor, unamended soil, and too many nutrients can encourage weak, overly rapid growth. Most species are reliably hardy only in USDA Zones 8 to 11. Those in colder regions must select cold-tolerant varieties or grow them in containers that can be moved indoors before the first hard frost.
Essential Watering and Nutrient Regimes
The watering strategy for eucalyptus shifts significantly as the plant matures. Newly planted or young eucalyptus requires consistent, deep watering to encourage a strong root system. The soil should be kept moderately moist, but never soggy, during the first few years, requiring watering during prolonged dry spells.
Once established in the ground, mature eucalyptus trees are drought-tolerant and rarely require supplemental irrigation. Container-grown plants need more frequent attention because the soil dries out faster. Water container plants thoroughly until it drains from the bottom of the pot. Fertilization is seldom necessary for in-ground plants, which are adapted to nutrient-poor soils and can be harmed by high-nitrogen products that encourage spindly growth. If growth seems stunted, a light application of a slow-release or balanced liquid fertilizer, perhaps at half-strength, can be applied to container plants during the spring and summer.
Controlling Growth Through Pruning Techniques
Managing the vigorous growth rate of eucalyptus is a primary concern for gardeners. Specific pruning methods allow for size control and the promotion of desirable juvenile foliage. The most aggressive technique is coppicing, which involves cutting the main trunk or stems back hard, typically to within 6 to 18 inches of the ground. This radical cut forces the plant to regrow from the base, producing multiple new shoots that feature the attractive, rounded, juvenile leaves. Coppicing is best performed in late winter or early spring just before new growth begins.
A different approach is pollarding, which establishes the plant’s height by cutting the main trunk back to a permanent structure of scaffold branches, usually between 6 to 10 feet above the ground. This method maintains a small, tree-like form with a rounded canopy of new growth emerging from the cut points. For general shape and density management, light tip pruning involves pinching or snipping the ends of new shoots, which encourages branching and a bushier habit.
Troubleshooting Pests and Environmental Stressors
Eucalyptus plants are generally resilient but can face issues when stressed by improper cultural conditions. The Eucalyptus longhorned borer is a serious pest attracted to stressed trees. Its larvae tunnel into the cambium layer, which can rapidly disrupt water flow and kill the tree. Keeping the plant healthy through correct watering and siting is the best defense against this and other insects.
Other common pests include psyllids, which secrete a sticky, white protective covering called a lerp and produce a sugary honeydew that can attract sooty mold. Horticultural oil or neem oil can be used as organic control methods for scale insects and psyllids. Environmental problems often manifest as leaf scorch, where leaf margins turn brown due to insufficient water during hot periods or exposure to high winds. Protecting container plants from cold is accomplished by moving them to a sheltered, cool location, such as an unheated garage or greenhouse, where temperatures remain above 45°F for winter rest.