Hello, human. It's me, your Grevillea. I'm trying to tell you something is wrong, and I'm communicating in the only way I can: by dropping my leaves. It's a distress signal. From my perspective, my home in Australia was tough, sunny, and had perfectly gritty, poor soil. Life here in the US is... different. Let's walk through what might be bothering me.
This is the most common reason I feel so unwell. In my native habitat, water drains away from my roots almost instantly. I am not built for dense, water-retentive clay soils or even overly rich potting mixes that stay wet. When my roots sit in soggy soil, they literally suffocate and rot. They can't breathe or take up nutrients, so my entire system goes into shock. The first thing I must do is shed leaves to conserve energy. Please, ensure I'm planted in a raised bed or a mound with a very coarse, sandy mix, and that water never pools around my base.
You might think you're helping with fertilizer, but you could be slowly killing me. I am a Proteaceae family member, and we have evolved in soils with incredibly low phosphorus. My root system is highly sensitive to it. Most common fertilizers in the US are far too high in phosphorus for my liking. It builds up in your soil and becomes toxic to me, burning my roots and preventing me from absorbing other crucial nutrients like iron. This quickly leads to yellowing leaves and leaf drop. If you must feed me, use a fertilizer specifically labeled for Australian natives or acid-loving plants that is low in phosphorus.
While some of my cousins are hardy, many popular Grevillea varieties are used to mild climates. A sudden frost or a prolonged period of cold weather is a profound shock. My cells can freeze and rupture, and the energy required to simply survive is immense. To make it through, I will jettison non-essential parts—my leaves—to focus everything on keeping my core alive. If you live in a zone that gets cold, please check my specific cold tolerance and provide protection if an unexpected freeze is coming.
I am drought-tolerant once established, but that doesn't mean I never need water. If I've been left completely dry for too long during a hot, windy spell, I will become severely stressed and drop leaves to reduce water loss. Conversely, frequent, shallow sprinklings encourage my roots to stay near the surface where they are vulnerable to heat and drought. I prefer a deep, thorough drink less often, which encourages my roots to grow deep and strong, just like back home.
This is a tougher issue to solve. I evolved in a climate with good air flow and relatively low humidity. In very humid parts of the US, the constant moisture on my foliage can make me susceptible to fungal diseases like root rot or leaf spot. These pathogens attack my systems, and my response is often to shed the compromised leaves. Ensuring excellent air circulation around me and watering at the base to keep my leaves dry can help me cope.
