Scorching Hot Horticulture: A Guide for Summer Planting
Caring for Plants During Heat Waves: A Guide Based on the American Horticultural Society's Heat Zone Map
As temperatures rise, it's crucial to understand how to care for plants during heat waves to ensure their survival. The American Horticultural Society (AHS) has developed a Heat Zone Map to help gardeners select plants adapted to their local heat conditions.
According to the AHS Heat Zone Map, regions are categorized based on the number of days each year when temperatures exceed 86°F (30°C), which is a temperature at which plants begin to suffer from heat stress. To care for plants during a heat wave:
- Water deeply and frequently, especially for newly planted trees and shallow-rooted plants. Watering ensures the root zone stays moist enough for effective transpiration (plant cooling), as plants lose water faster in high heat.
- Provide shade for sensitive plants during peak hot hours to reduce heat stress and leaf dehydration. Shade cloths, garden umbrellas, or natural shade can help. If lacking a shaded area, consider providing shade with a shade cloth or similar.
- Choose heat-tolerant plants suitable for your AHS Heat Zone to increase survival chances during prolonged hot periods. The American Horticultural Society's Heat Zone Map contains 12 zones across the United States.
- Mulch around plants to conserve soil moisture and keep roots cooler. This is particularly important for container plants, which dry out more quickly and require extra attention to watering.
- Monitor plants closely for signs of heat stress such as wilting, leaf scorch, and leaf drop, and adjust care accordingly.
While the Heat Zone Map focuses on heat tolerance, combining this with your USDA Hardiness Zone knowledge can improve overall plant care by balancing winter cold hardiness and summer heat resilience.
Healthy plants are more able to tolerate heat than those stressed by lack of irrigation and nutrients or weakened by disease and pests. Plant in soil that is well-draining, rich in organic nutrients, and easy to keep irrigated. Additionally, plant at the correct depth; roots that are too close to the surface will fry during a heat wave.
In some cases, it may be necessary to replant with heat-tolerant vegetables such as beans, chard, or carrots. Water plants early in the morning to minimise water loss due to evaporation.
Amy Grant, a gardening expert with 30 years of experience and 15 years of writing, emphasises the importance of these practices. With careful planning, a garden specific to your climate, and consistent care, you can successfully navigate heat waves and enjoy a thriving garden.
- To maintain a thriving garden during heat waves, it's advisable to select heat-tolerant plants suitable for your AHS Heat Zone, which can be found on the American Horticultural Society's Heat Zone Map.
- For plants that struggle with the heat, providing shade during peak hot hours and watering deeply and frequently, especially for newly planted trees and shallow-rooted plants, can help reduce heat stress and optimize plant cooling.
