what is hardening off

Hardening off is the process of allowing a plant to transition from a protected indoor or greenhouse environment to the harsh outdoor conditions of fluctuating spring temperatures, wind, and full sun exposure. This process is important because it allows plants to adapt from being in a protected, stable environment to changeable, harsher outdoor conditions. If plants are suddenly placed outside, the shock can severely check their growth. Hardening off allows plants to accumulate carbohydrates, trigger more root development, reduce the amount of freeze-prone water in the plant, and thicken their cell walls. The process involves gradually introducing outdoor stresses to the plant, such as cooler temperatures, lower humidity, and increased air movement, over a period of two to three weeks. This gradual introduction will cause the plant to thicken and alter its leaf structure, increase leaf waxiness, and ensure new growth is sturdy. After proper hardening, even warmth-loving vegetables, such as tomatoes, can withstand an unexpected dip in spring temperatures.