Hello. I am a hydrangea. From my perspective, the distress you see as "wilting" is my primary method of communicating a critical issue with my water balance. My large, soft leaves and abundant flower heads require a constant, careful flow of water to remain turgid and functional. When that flow is disrupted, I cannot support them, and I collapse. However, the cause—too much water or too little—creates two very different internal experiences for me.
This is the most direct and common reason I wilt. My extensive root system is designed to draw moisture from the soil to supply my vast foliage. On a hot, sunny day, I am transpiring water through my leaves faster than my roots can replace it. This creates a negative pressure, a literal vacuum, in my vascular system (my xylem). The water columns within me break, and air pockets form—a process called cavitation. My cells lose their internal water pressure, known as turgor pressure, which is what keeps my stems rigid and my leaves spread wide. I wilt as a deliberate survival strategy; by drooping, I reduce the surface area exposed to the sun, thereby slowing down further water loss. If you provide a deep, thorough drink, I can often recover my turgor within hours, as the water columns are re-established and my cells re-inflate.
This wilting is far more sinister and dangerous. It is not a lack of water, but a lack of *oxygen*. My roots are living organs that need to breathe. When I am sitting in saturated, waterlogged soil, all the air pockets in the soil are filled with water. My roots begin to suffocate and die from a lack of oxygen (anaerobic conditions). With a damaged and rotting root system, I am utterly unable to absorb water—even though it is abundantly available all around me. This creates a physiological drought *inside* me. Without a functioning root system to draw it up, water never reaches my leaves and blooms, and they wilt from a lack of hydration. This wilting will not improve with more water; it will only accelerate my root rot and eventual decline.
To understand which ailment I am suffering from, you must look beyond my drooping leaves and check my soil's story.
If I am underwatered, the soil will feel dry and crumbly to the touch several inches down. My leaves and flower heads will feel limp, thin, and papery. The wilting will likely be most pronounced during the heat of the day but may improve slightly in the cooler evening. My plea is simple: "I am thirsty."
If I am overwatered, the soil will feel consistently cold, soggy, and muddy days after watering. You might even detect a sour or musty odor from the soil, indicating root decay. My leaves, while wilted, may also begin to turn yellow, particularly the older ones, and feel soft and mushy. My stems might become soft and brown at the base. My cry is more desperate: "I am drowning; my roots are dying."
