From our perspective as Grevillea plants, our growth rate and ultimate size are not predetermined but are a dynamic response to our environment. We are fundamentally opportunistic. In our native Australian landscapes, resources like water and nutrients are often scarce and unpredictable. Therefore, when conditions are favourable—ample sunlight, sufficient water, and well-drained soil—we grow with remarkable speed to establish ourselves, flower, and set seed quickly. This rapid juvenile growth allows us to capitalize on good seasons. However, this pace inevitably slows as we mature, redirecting energy from vertical expansion to flowering, root development, and strengthening our structure to withstand the harsh conditions we are adapted to.
Our genus exhibits incredible diversity in form, which directly dictates our potential size. This is a core part of our genetic blueprint. Some of us, like *Grevillea* ‘Poorinda Royal Mantle’, are prostrate groundcovers, sprawling horizontally to cover the earth, rarely exceeding 30 cm in height but spreading several metres wide. Others, such as many cultivars of *Grevillea rosmarinifolia*, are compact shrubs, naturally forming dense mounds between 1 and 2 metres in both height and spread. Then there are our larger cousins, like the magnificent *Grevillea robusta* (Silky Oak), which are true trees. From our seedling stage, we know our destiny is to reach for the canopy, growing rapidly to eventually become a towering specimen up to 35 metres tall.
While our genetics set the broad parameters, our immediate environment fine-tunes our final stature. Sunlight is our primary energy source. We will grow leggy, weak, and smaller than our potential if planted in deep shade. Full sun encourages dense, robust growth. Soil composition is equally critical. We possess specialised proteoid roots that are exceptionally efficient at nutrient uptake in poor soils. Consequently, rich, heavily fertilized soils, particularly those high in phosphorus, are toxic to us. They damage our root systems, stunting our growth, causing yellowing leaves, and ultimately leading to a much smaller, unhealthy plant. Perfect drainage is non-negotiable; waterlogged soil will swiftly kill our roots and halt all growth.
Your actions as gardeners significantly influence our shape and size. We respond very well to strategic pruning. Tip-pruning when we are young encourages us to branch out laterally, creating a much denser, more floriferous shrub and preventing us from becoming straggly. Even as mature plants, a hard prune after a main flowering flush can rejuvenate us, control our size, and prevent woody, unproductive growth. The selection of a cultivar suited to the space is the most important human decision. Planting a *Grevillea robusta* sapling next to a house will inevitably lead to conflict, as it will relentlessly pursue its genetic imperative to become a large tree, while a compact ‘Superb’ or ‘Moonlight’ would thrive in that space for years.
