The selection of an appropriate pot size is fundamental to the success of a container-grown Grevillea, as it directly dictates the development and health of its root system. Grevilleas possess a vigorous, spreading root structure that resents being overly confined or disturbed. A pot that is too small will quickly become root-bound, leading to stress, moisture stress (drying out too quickly or holding too much water), and ultimately, root rot or plant death. Conversely, a pot that is excessively large holds a vast volume of soil that stays wet for prolonged periods, far beyond the needs of a small root system, creating anaerobic conditions that are fatal to these plants.
For most small to medium shrub varieties, begin with a pot that is at least 40-50cm (16-20 inches) in both diameter and depth. Larger, tree-type Grevilleas will require a substantially larger container, such as a half-wine barrel or similar. The key is to choose a size that allows for two to three years of growth before needing an upgrade. When repotting, typically necessary every 2-3 years, move up to a pot only one size larger to avoid the pitfalls of overpotting.
From the plant's perspective, excellent drainage is not merely preferred; it is an absolute necessity for survival. Grevilleas are quintessential Mediterranean-climate plants, adapted to well-drained, often sandy or rocky, soils. Their roots are highly susceptible to phytophthora and other fungal root rot diseases that thrive in waterlogged, oxygen-deprived conditions. The entire container system must be designed to facilitate the immediate escape of excess water.
This begins with an abundance of drainage holes. A pot must have several large holes in its base; a single small hole is wholly inadequate. The construction material also plays a role; porous materials like terracotta or unglazed ceramic allow the soil to "breathe" and dry out more evenly than non-porous plastic or glazed ceramic pots, though the latter are acceptable if their drainage is exceptional.
The choice of pot material interacts significantly with the soil medium to create the root environment. A porous terracotta pot will wick moisture from the soil, aiding aeration but also increasing the watering frequency required. A plastic pot retains moisture for longer, making the composition of the potting mix even more critical. Regardless of material, the soil medium must be exceptionally free-draining. A standard potting mix is too moisture-retentive and requires amendment.
An ideal mix mimics the Grevillea's native, nutrient-poor habitat. A perfect recipe would be a base of premium native plant potting mix, further amended with coarse sharp sand (or poultry grit) and perlite (or pumice) at a ratio of approximately 3 parts potting mix to 1 part drainage material. This creates an open, friable structure that allows water to drain rapidly while still holding enough moisture and air around the roots.
The final setup is crucial. Ensure the drainage holes are clear and never block them with rocks or pot shards; this反而 traps water and raises the water table within the pot. Instead, place a single piece of flywire mesh or a porous weed mat over the holes to prevent soil wash-out. Elevate the pot off the ground using "pot feet" or bricks to ensure the drainage holes are never sitting in a saucer of stagnant water. While a saucer can be used to protect surfaces, any water collected in it must be emptied shortly after watering concludes.
