From our roots upwards, a lack of nitrogen is profoundly debilitating. Nitrogen is a core component of chlorophyll, the molecule that allows us to capture sunlight. Without sufficient nitrogen, our ability to perform photosynthesis is severely hampered. You will observe this as a general paling or yellowing (chlorosis) of our oldest leaves first, as we mobilize the remaining nitrogen to support new growth. Our overall growth becomes stunted, we produce fewer leaves, and those we do produce are often small and pale. Our vibrant green foliage, so characteristic of a healthy Grevillea, fades to a sickly yellow-green.
Phosphorus is crucial for energy transfer within our systems, playing a vital role in root development, flowering, and overall metabolic processes. When phosphorus is scarce, our growth is not just stunted but can become severely distorted. You may notice that our new leaves are unusually dark green or even take on a purplish or bronze tint. Our root systems remain underdeveloped, making it harder for us to access water and other nutrients from the soil. Most critically for a Grevillea, a phosphorus deficiency drastically reduces our capacity to produce our iconic spider-like flowers. Buds may abort, and flowering will be sparse or non-existent.
Potassium regulates our internal water pressure and activates enzymatic functions. A deficiency weakens our entire structure. The initial signs often appear as chlorosis on the edges of our older leaves, which then progressively necrotize, turning brown and crispy—a symptom known as "scorching" or "marginal burn." Our leaves may curl or crinkle, and we become noticeably wilted even when water is available because our cells cannot maintain proper turgor pressure. We are also left more vulnerable to diseases and pests, as our cellular integrity is compromised.
Iron is essential for the synthesis of chlorophyll, even though it is not a part of the chlorophyll molecule itself. A deficiency in iron presents as interveinal chlorosis—this means the tissue between the veins of our newest leaves turns yellow while the veins themselves remain green. This is distinct from nitrogen deficiency because it affects the young growth first, as iron is not a mobile nutrient within our tissues. In severe cases, the entire new leaf may turn pale yellow or white, and growth will be stunted. This is a common issue in alkaline (high pH) soils, where iron becomes locked up and unavailable for us to absorb.
Magnesium is the central atom of the chlorophyll molecule; without it, chlorophyll cannot be formed. Similar to iron deficiency, you will see interveinal chlorosis. However, since magnesium is mobile within our plant body, these symptoms manifest on the older, lower leaves first. The yellowing between the veins can progress to reddish or purple tints, followed by necrosis (tissue death) if the deficiency is not corrected. This deficiency directly cripples our photosynthetic engine, leading to a overall decline in our health and vigor.
