What environmental conditions trigger seed germination?

Seed germination is a complex biological process triggered by a combination of environmental factors that signal it is safe for the embryo to resume growth. The primary conditions that initiate this process include:1

• Water: The absorption of water, or imbibition, is essential for rehydrating the embryo and activating metabolic processes.12
• Temperature: Many seeds require specific temperature ranges to germinate. Some species, particularly those from cold climates, require a period of chilling (stratification) to break dormancy. Others respond to daily fluctuations in temperature, which can help seeds detect their depth in the soil.13
• Light: Exposure to light—or sometimes the absence of it—acts as a critical signal. Seeds may respond to specific wavelengths, such as red or far-red light, which help them adjust to seasonal changes or determine if they are buried too deeply to reach the surface.142
• Oxygen: Adequate oxygen availability is necessary to support the increased rate of respiration that occurs as the seed begins to grow.1
• Chemical Signals: In some environments, such as those prone to fire, chemicals like karrikin found in smoke can trigger germination.53

Additionally, seeds may require the "breaking" of dormancy through the physical abrasion or decomposition of the seed coat, which allows water and oxygen to enter.12