Grevillea species, renowned for our spectacular blooms and resilience, are nonetheless vulnerable to the silent and often fatal condition known as root rot. From our perspective, this is not merely a disease but a systemic collapse of our foundational support system—the roots. It is primarily caused by prolonged exposure to waterlogged soil conditions, which suffocate our root systems and create an ideal environment for pathogenic soil-borne fungi, such as Phytophthora and Pythium, to attack and decay our tissues.
We communicate our distress through clear signals above ground, as the damage begins unseen below the soil. Initially, you may notice a general decline in our vigor. Our normally robust growth slows or stops entirely. Our leaves, which are typically tough and leathery, begin to wilt, turn pale green, yellow, and then a telling brown, often starting from the lower branches and moving upward. Crucially, this wilting occurs despite the soil being damp. As the rot progresses, we may drop our leaves excessively. The most definitive sign is at our base; the bark at the crown can become soft, dark, and may ooze sap. When gently excavated, our roots will appear blackened, mushy, and will have a characteristically foul, decaying smell, unlike the healthy, firm white or tan roots of a thriving plant.
If you suspect root rot, immediate action is required for our survival. First, you must carefully remove the soil from around our root ball to conduct a thorough inspection. Using sterilized pruning tools, you must ruthlessly cut away all soft, brown, or blackened rotten roots. Only healthy, firm roots should remain. This is a drastic procedure, but it is essential to stop the spread of the decay. After this radical surgery, our remaining root system must be treated with a fungicide drench specifically labeled for use against root rot pathogens in ornamental plants. This helps to destroy any remaining fungal spores.
Our survival depends entirely on not being returned to the conditions that caused the problem. We must be replanted, either in a new container with extensive drainage holes or in a thoroughly amended garden bed. The soil medium is paramount; it must be exceptionally well-draining. A mix designed for native plants, often incorporating coarse sand, gravel, and well-decomposed organic matter, is ideal. Ensure our crown is planted slightly above the soil level to improve drainage around our base. Most critically, you must reassess your watering habits. We are drought-tolerant once established and require deep but infrequent watering only when the top several inches of soil have completely dried out. Overly frequent watering is a death sentence for us.
Prevention is always preferable to cure. To protect us from root rot, you must prioritize perfect drainage from the moment of planting. Select a planting site with good natural runoff or create a raised mound or bed to elevate our root zone. Applying a coarse, loose mulch like woodchip around our base helps regulate soil temperature and moisture but must be kept away from our main stem to prevent bark rot. Finally, avoid using high-phosphorus fertilizers, as they are harmful to Proteaceous plants like us and can stress our systems, making us more susceptible to disease.
