From a botanical perspective, not all Grevillea species are equally suited for hedge formation. The genus is incredibly diverse, with growth habits ranging from prostrate groundcovers to large trees. For an effective hedge, you must select species or cultivars that exhibit a dense, bushy growth habit and respond well to pruning. Key physiological traits to look for include small to medium leaf size (the "toothbrush" or "pinnatisect" leaf forms are excellent), strong lateral branching from the base, and a vigorous growth rate. Botanically ideal candidates include Grevillea rosmarinifolia (Rosemary Grevillea), Grevillea 'Robyn Gordon', and Grevillea 'Superb'. These plants possess a lignotuber or the ability to produce epicormic shoots, meaning they can regenerate new growth from buds beneath the bark when pruned, which is crucial for maintaining a thick, leafy screen.
The success of your Grevillea hedge begins with the planting process. Grevilleas are predominantly members of the Proteaceae family, which have evolved a unique root system known as proteoid roots. These dense clusters of short lateral roots are highly efficient at nutrient uptake but are also incredibly sensitive to high levels of phosphorus and disturbed soil. Therefore, planting should be done with care. Dig a hole twice as wide as the root ball but no deeper, to prevent settling. Amend the soil only with coarse sand or gravel if drainage is poor, avoiding rich composts and fertilizers. The spacing between individual plants is a critical decision based on their mature width and your desired hedge density. From a plant competition standpoint, spacing them at approximately 75% to 80% of their expected mature width (e.g., 1 - 1.5 meters apart for a plant that spreads 1.5 meters) encourages them to intertwine and form a solid barrier without being so crowded that they compete excessively for root space, water, and sunlight, which can lead to dieback in the lower canopy.
Establishing a robust root system is the primary goal after planting. While many Grevilleas are highly drought-tolerant once established, their proteoid roots require consistent moisture during the first summer to develop fully. A deep, infrequent watering schedule encourages the roots to grow downward, creating a more resilient plant. From a nutritional standpoint, these plants are adapted to nutrient-poor soils. Their physiology is intolerant of high phosphorus levels, which can be toxic, leading to chlorosis (yellowing leaves) and death. They require a fertilizer with a low phosphorus ratio, specifically formulated for native Australian plants. An annual, light application of a suitable, slow-release fertilizer in spring is sufficient to support the energetic demands of flowering and new growth without harming the root system.
Pruning is not merely about shaping; it is a physiological intervention that directs the plant's energy. To develop a dense hedge from the base, it is essential to begin tip-pruning or lightly shearing the plants when they are young, even before they reach the desired height. This practice, known as "pinching," removes the apical meristem (the dominant central growing tip), which encourages the growth of axillary buds lower down on the stem. This process, called apical dominance suppression, results in a bushier plant. Once the hedge is established, regular pruning after each major flowering flush is recommended. Make cuts just above a node where leaves are present, as Grevilleas often will not reshoot from old, bare wood. Consistent, light pruning is far better for the plant's health and structure than infrequent, heavy cutting back, which can expose leafless stems and stress the plant.
