Understanding plant dormancy: What it is and why it matters

Winter in eastern Idaho brings freezing temperatures, snow, and a seemingly lifeless landscape, but your plants are not dead. They are simply waiting. Whether it’s an apple tree, a lilac bush, or a tiny seed buried in the soil, plants enter dormancy as a survival strategy against the cold. Dormancy is not just “sleeping” — it’s a survival mechanism that ensures plants will be ready when conditions improve. Understanding dormancy helps you choose the right varieties, protect your garden from winter damage, and ensure a strong start to the growing season.

True dormancy vs. environmental dormancy

There are two types of dormancy: true dormancy (endo-dormancy) and environmental dormancy (eco-dormancy). True dormancy happens when a plant’s internal processes prevent growth, even when external conditions are favorable. This is regulated by plant hormones like abscisic acid. Many fruit trees, such as apples and cherries, rely on true dormancy to prevent bud break during the winter.

Environmental dormancy occurs when a plant is ready to grow, but external factors like temperature or moisture are still unsuitable. For instance, a peach tree may be physiologically ready to grow after winter but stays dormant because temperatures are still too cold for safe growth. Understanding these differences helps gardeners predict when plants will emerge from dormancy and how to protect them from late frosts.

Seed dormancy and the role of stratification and scarification

Seed dormancy ensures that seeds don’t sprout prematurely. Some seeds remain dormant until certain environmental triggers — like cold, moisture, or light — signal that it’s time to germinate. Cold stratification is used to break dormancy in seeds that require a chilling period before they can sprout. For example, milkweed and certain perennials need to experience cold temperatures to germinate. Gardeners can simulate this by refrigerating seeds in a moist medium for several weeks.

Scarification is another method used for seeds with tough outer shells, such as lupines or morning glories. By nicking, scratching, or soaking the seed coat, water can enter, allowing the seed to germinate. These techniques help gardeners start plants that require dormancy-breaking conditions.

Chilling hours and their role in breaking dormancy

Chilling hours are essential for breaking dormancy in many fruit trees and perennials, ensuring that plants don’t grow too early and risk frost damage. A chilling hour is defined as one hour when temperatures are between 32°F and 45°F, the ideal range for dormancy-breaking processes. Plants that need chilling hours, like apples, cherries, and peaches, require a specific number of hours to accumulate before their buds can break dormancy.

For instance, apples require 1,000 to 1,500 chilling hours, cherries need about 800 to 1,200 hours, and peaches typically need 600 to 1,000 hours. If a plant doesn’t receive enough chilling hours, it may experience irregular bud break, delayed flowering, or reduced fruit production. If a plant accumulates too many chilling hours and warm temperatures arrive too soon, the plant may break dormancy prematurely, leaving it vulnerable to late frosts.

Managing dormancy in gardens and orchards

Managing dormancy is crucial for ensuring healthy growth and successful fruit production. One key factor is selecting plant varieties suited to your climate and chilling hour requirements. In areas like eastern Idaho, where winters are cold, it’s essential to choose fruit trees, such as apples, cherries, and peaches, that meet the chilling hour requirements to ensure healthy bud break in spring.

Gardeners should also consider the USDA plant hardiness zone, which indicates the minimum winter temperatures a plant can withstand. Eastern Idaho is primarily in zones 3b to 5a, influencing the types of plants that will thrive. Monitoring weather conditions is also critical to protect plants from premature bud break, which can occur if a warm spell arrives too early. Row covers, frost blankets, and irrigation systems can help protect plants from late frosts. Pruning techniques also encourage healthy growth and prevent early sprouting.

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