A dormant plant is in a survival state, a period of rest triggered by environmental signals like cold temperatures or drought. The question of whether these resting plants need sunlight has a simple answer: generally, no, but the requirements differ depending on the type of plant. During deep dormancy, the biological processes that require light, specifically photosynthesis, either cease entirely or slow down so dramatically that new energy production is negligible. Understanding the plant’s internal energy strategy during this phase is the key to providing proper care.
Understanding Plant Dormancy
Dormancy is an adaptive survival mechanism where a plant halts visible growth and significantly reduces its metabolic activity. This protective state is typically induced by unfavorable environmental cues, such as the shorter daylight hours and cooling temperatures of autumn. By entering dormancy, a plant conserves energy and protects its delicate tissues from damage due to freezing or desiccation.
This process is a controlled biological state. The plant is still alive, but its energy demands are minimal, allowing it to endure months of harsh conditions. True dormancy requires a specific period of cold exposure to be broken, ensuring the plant does not resume growth during a premature warm spell.
Photosynthesis and Stored Energy Reserves
The primary reason deeply dormant plants do not require sunlight is that they are no longer relying on photosynthesis for energy. Photosynthesis, the process of converting light energy into chemical energy (sugars), slows down significantly as temperatures drop and leaves are shed. In deciduous plants, the process stops almost completely once the leaves fall off.
Instead of light, the plant’s minimal metabolic needs are met by stored chemical energy. Throughout the previous growing season, the plant converted excess glucose into complex carbohydrates, primarily starch, and stored these reserves in structures like roots, stems, tubers, and bulbs. This stored starch is broken down into sugars to fuel the low level of cellular respiration necessary to keep the plant tissues alive during the dormant period. The stored reserves are typically sufficient to last until favorable growing conditions return in the spring.
Practical Light Requirements for Dormant Plants
The practical need for light during dormancy depends on the plant’s strategy for survival. Deciduous plants, which lose all their leaves, enter the deepest state of dormancy and can be stored in complete darkness. For these plants, a cool, dark location, such as an unheated basement or shed, is ideal, as the darkness prevents any signaling that could encourage the plant to prematurely break dormancy. Temperatures should remain cold, typically between 35 and 40 degrees Fahrenheit, but above freezing, to ensure the plant remains in its resting state.
Evergreen plants retain their leaves or needles. While their metabolic activity is greatly reduced, they may still perform trace amounts of photosynthesis, especially on warmer, brighter winter days. Therefore, dormant evergreens stored indoors, such as potted trees, require some light, ideally a location with indirect or low light, like a bright window that is not south-facing. Providing some light helps maintain the health of the remaining foliage without stimulating significant new growth, which would be vulnerable to cold.