From a plant's perspective, high summer temperatures present a multifaceted physiological challenge. For a genus like Ligularia, which has evolved in the cool, moist environments of stream banks and woodlands in Asia, heat is a significant stressor. The primary issue is transpiration. To cool itself, a plant opens the stomata (pores) on its leaves, releasing water vapor. In hot, dry conditions, this process can cause a catastrophic loss of moisture, leading to wilting as the plant's water expenditure exceeds its root system's ability to draw water from the soil. Ligularia's very large, broad leaves have a high surface area, which exacerbates this water loss, making them exceptionally vulnerable to desiccation in the heat.
Our survival in the heat is almost entirely dependent on a constant and ample supply of water. The root system requires consistently moist, cool soil to function efficiently. If the soil temperature rises too high or the soil dries out, root function is impaired, and the entire plant suffers. Well-draining yet moisture-retentive soil is not a luxury for us; it is a necessity. Organic matter in the soil acts like a sponge, holding onto water and making it available to our roots between waterings, which is our primary defense against the dehydrating effects of summer sun and heat.
Direct, intense afternoon sun is our greatest adversary during a hot summer. The radiation from the sun not only raises our leaf temperature but also accelerates the rate of evaporation from the soil. We thrive in partial to full shade, particularly shade that protects us during the hottest part of the day. The dappled light beneath trees is ideal, as it provides protection while still allowing for some photosynthetic activity. A location with morning sun and afternoon shade is often the perfect compromise, giving us energy without the scorching punishment that leads to severe wilting and leaf scorch.
When temperatures become too much for us to handle, our distress is visibly apparent. The most immediate and dramatic response is wilting. Our large, soft leaves will become limp and droop dramatically, a clear sign of water stress. While we can often recover from this wilting if watered promptly and thoroughly, repeated episodes cause long-term damage. The leaf edges and tips, which are furthest from the veins, will often turn brown and crispy—a condition known as leaf scorch. This is irreversible damage to the leaf tissue. Furthermore, extreme heat stress can cause us to go dormant prematurely, halting growth and potentially weakening us for the following growing season.
To help us handle hot summers, you can emulate our natural preferred habitat. A thick layer of organic mulch applied around our base is immensely beneficial. It insulates the soil, keeping our roots cooler and significantly reducing moisture evaporation. Consistent, deep watering that saturates the root zone is far superior to frequent, light sprinklings. For those in particularly hot climates, positioning us on the north or east side of a structure or wall, or beneath the canopy of larger trees, provides the protective shade we crave. In essence, a cool root run and protection from intense solar radiation are the keys to our survival and health during the heat of summer.
