Plum trees are a popular choice for home gardens due to their delicious fruit. Successful growth and fruit production depend on understanding their temperature requirements throughout the year.
Understanding Plum Tree Temperature Needs
Plum trees need specific temperature conditions for optimal growth and fruit development. Many varieties require a winter dormancy period, with temperatures between 32°F and 45°F (0°C to 7°C). This chilling period is measured in “chill hours,” representing the cumulative hours a tree needs to break dormancy and flower properly in spring.
Chill hour requirements vary significantly among cultivars, from 200 to over 1,000 hours. After dormancy, plum trees need accumulated warmth, measured in “heat units” or growing degree days, for vegetative and reproductive development. These heat units influence bud break, flowering, fruit set, and ripening, ensuring a productive season.
Cold Hardiness: Surviving Winter’s Chill
Plum trees vary in cold hardiness, with many dormant varieties tolerating winter temperatures down to -10°F to -20°F (-23°C to -29°C). However, sudden temperature drops or late spring frosts after buds swell can be damaging. Frost can injure flower buds, reducing or eliminating the fruit harvest.
Cold temperatures can also cause bark splitting, known as frost crack, on the trunk and larger branches. Young and newly planted trees are especially vulnerable to cold damage due to less established root systems. Protection methods include applying thick mulch around the base to insulate roots and wrapping young trunks with burlap or tree guards. Proper site selection, avoiding frost pockets, also helps by ensuring good air drainage.
Heat Tolerance: Managing Summer’s Heat
While plum trees need warmth for fruit development, excessive heat can challenge their health and productivity. Prolonged temperatures exceeding 90°F (32°C) can cause heat stress, especially with insufficient moisture. High temperatures can scorch leaves, making them brown and crispy, as the tree struggles to transpire enough water to cool itself.
Extreme heat can negatively impact fruit development, leading to fruit drop, reduced size, or poor quality. Consistent, adequate watering during hot spells helps trees cope with increased water demand and prevents stress. Applying organic mulch around the tree base retains soil moisture and keeps root temperatures cooler. Temporary shade for young trees during the hottest parts of the day can further reduce heat stress.
Choosing the Right Plum for Your Climate
Selecting a plum variety suited to your local climate is important for successful cultivation. European plums (Prunus domestica) are more cold-hardy, tolerating colder winters and often requiring higher chill hours. Japanese plums (Prunus salicina) and their hybrids are less cold-hardy but tolerate warmer climates, often with lower chill hour requirements.
American plum hybrids (Prunus americana x salicina or other species crosses) offer wider adaptability, with some varieties showing excellent cold hardiness. To choose, consult your USDA plant hardiness zone for average minimum winter temperatures and research specific plum varieties’ chill hour requirements. Local nurseries or agricultural extension offices can also recommend cultivars for your microclimate, considering both winter cold and summer heat.