Greetings, human cultivator. We, the Grevillea genus, speak for the roots and leaves of your cultivated specimens. To thrive in the landscapes of the United States, we require a very specific dietary approach. Our needs are not like those of your common roses or azaleas; in fact, their food can be our poison. To understand what nourishes us is to understand our very essence.
This is the single most important rule you must follow. We are Proteaceae, a family of plants that evolved in ancient, phosphorus-deficient soils of Australia. Our root systems are exceptionally efficient at scavenging this element. When you provide a standard, high-phosphorus fertilizer (the middle number on the bag, like 10-10-10 or 20-20-20), you are essentially force-feeding us. This causes a toxicity that burns our root tips, preventing us from taking up water and other vital nutrients. The result is our slow, yellowing, and eventual demise. You will see chlorosis, a yellowing between the veins of our leaves, which is a clear cry for help.
What does a suitable meal look like for us? We seek a fertilizer with a nutrient ratio where the phosphorus (P) number is the lowest of the three. Formulas labeled for "Australian Natives," "Camellias & Azaleas," or "Ericaceous Plants" are often suitable, but you must always check the label. An NPK ratio like 3-1-2, 6-4-8, or even 0-0-10 is far safer and more beneficial for us. We also have a particular fondness for trace elements like iron, manganese, and sulfur, which are crucial for maintaining our deep green foliage and supporting our vigorous blooming cycles. A fertilizer that includes these micronutrients is a complete meal.
From our perspective, slow and steady wins the race. We strongly prefer slow-release, organic fertilizers. A light application of a blood meal (for nitrogen) or a fish and seaweed emulsion provides a gentle, sustained release of nutrients that our roots can absorb at a natural pace. This mimics the nutrient availability in our native habitats. For a more immediate boost, especially if we show signs of hunger, a liquid fertilizer with a low-phosphorus formula can be applied, but it must be diluted as directed. Remember, it is always better to under-feed us than to over-feed us.
Before you even think about fertilizer, our foundation—the soil—must be correct. We demand exceptionally well-draining soil. Our roots are shallow and widespread, and they will rot if left sitting in water. Amend heavy clay soils with generous amounts of sand, gravel, and acidic organic matter like peat moss or pine bark. After planting, please provide us with a thick layer of an organic mulch like wood chips, leaf litter, or pine straw. This mulch is not just for moisture retention and weed suppression; as it breaks down, it provides a gentle, natural source of the exact nutrients we crave, all while keeping our sensitive root zone cool.
Our feeding cycle aligns with our growth and flowering peaks. The primary feeding should occur in our early spring, as we awaken and prepare for a major flush of growth and blooms. A second, lighter application can be made in the mid-summer to sustain us through the season. However, as autumn approaches and our growth slows, you must cease fertilization. Encouraging tender new growth at this time makes us vulnerable to frost damage in colder US regions. We need to harden off and prepare for our winter rest.
