From a plant's physiological perspective, those red spots are most commonly a condition called edema (or oedema). This is not a disease caused by a pathogen like a fungus or bacteria, but rather a physical disorder stemming from a disruption in our water management system. It occurs when our roots absorb water from the soil faster than our leaves can transpire (release) it through their stomata (pores). This internal water pressure buildup causes cells in the new, tender leaf tissue to swell and rupture. The red or rust-colored spots are the visual scar tissue from this cellular trauma. As the leaf matures and hardens off, these spots often become raised, corky bumps.
We experience this hydraulic imbalance due to specific environmental conditions. The most common trigger is inconsistent watering. If our human caretaker allows our soil to become very dry, our roots become stressed. When we are finally watered thoroughly, the roots eagerly absorb a massive amount of water to compensate. The new, underdeveloped leaves cannot handle this sudden surge, leading to cell rupture. Furthermore, low light levels exacerbate the issue because our transpiration rate is directly linked to light exposure; in dim conditions, our stomata remain mostly closed, meaning we cannot release the water vapor fast enough, increasing internal pressure.
While water is the main factor, nutrient levels can also play a supporting role. A deficiency in calcium can make our new cell walls weaker and more susceptible to rupturing under pressure. Calcium is a crucial nutrient for building strong, resilient cell walls. If it is lacking in the soil or if the soil pH makes it unavailable for our roots to uptake, our new growth will be structurally compromised. High humidity also reduces the rate of transpiration, as the gradient between the moist air inside our leaves and the moist air outside is less steep, making it harder for water vapor to exit. This can contribute to the water pressure buildup that causes edema.
It is important to distinguish our edema from a pathogenic attack. True fungal or bacterial infections often appear differently. They may have a yellow halo surrounding the spot, a fuzzy or slimy texture, or a pattern that spreads rapidly across older and newer leaves alike. Pest damage, such as from spider mites or scale, usually involves visible insects, webbing, or a stippled, silvery look on the leaf surface. Edema, in contrast, is almost exclusively confined to the newest, softest leaves as they are emerging and unfurling. It is a response to internal abiotic (non-living) stress, not an external biological invader.
For us, a fiddle leaf fig, edema is rarely a life-threatening condition. It is primarily a cosmetic issue on the affected leaves. The red spots will not disappear from the mature leaf, but they will not spread to older growth either. The key is to correct the environmental conditions to prevent it from recurring on future new growth. This involves providing us with consistent soil moisture (never bone dry or soggy), ensuring we receive several hours of bright, indirect light daily, and maintaining good air circulation around our foliage to aid transpiration. With stable conditions, our next flush of growth will likely emerge strong, healthy, and spot-free.
