The cherry plum (Prunus cerasifera or Myrobalan plum) is a popular small tree prized for its early spring blossoms and small, edible fruits. This species is often utilized as a rootstock for other plums and is widely grown as an ornamental, especially the purple-leaf cultivars. Growing a cherry plum tree from seed requires patience and specific steps to overcome the seed’s natural dormancy. It is important to know that a tree grown from seed, due to high genetic variability, will rarely be an exact replica of its parent tree, leading to unique fruit and growth characteristics.
Harvesting and Preparing the Seed
The process begins with selecting fully ripe fruit from a healthy tree, which typically occurs from early July to mid-September. After consuming the fruit, the seed-containing pit must be thoroughly cleaned of all residual pulp. This step is necessary because the sugary flesh can encourage the growth of mold or fungus during the preparation or stratification process. Once cleaned, the pits should be allowed to air-dry for a few days before storage or stratification. While some gardeners plant the entire pit, success rates are generally higher when the hard outer shell is carefully cracked to reveal the actual, almond-shaped seed (kernel). If cracking the pit, take care not to damage the soft seed inside. Soak the seeds in water for 24 hours, discarding any that float, as they are likely not viable.
The Step of Cold Stratification
Cherry plum seeds, like those of other stone fruits in the Prunus genus, possess an internal dormancy mechanism that must be broken before germination can occur. This process, known as cold stratification, mimics the natural cold, moist conditions the seed would experience over a winter season. The seeds must undergo a chilling period of 90 to 120 days at a consistently cold temperature, typically ranging from 33°F to 41°F (1°C to 5°C).
The most common method uses a refrigerator, where the seeds are placed in a sealed plastic bag or container with a slightly moist medium. Suitable materials include peat moss, sand, or a paper towel, which should be damp but not soaking wet to ensure aeration and prevent rot. The container is then placed in the refrigerator for the required duration, with moisture levels checked periodically. Alternatively, natural outdoor stratification involves planting the pits directly into a container of soil and burying it over the fall and winter, allowing the natural weather cycle to manage the cold period.
Planting and Germination
Following the stratification period, which typically ends in early spring, the seeds are ready for planting in a small container. A small pot, approximately four to six inches across, with drainage holes is an appropriate size for initial growth. The planting medium should be a well-draining mix, such as a standard potting soil amended with sand or perlite to improve aeration and prevent waterlogging.
The stratified seed should be planted at a shallow depth, generally about one-half to one inch below the soil surface. After planting, the container must be kept consistently moist and placed in a location that receives warmth and bright, indirect light, ideally with temperatures around 65°F to 75°F. Germination can be variable and slow, often taking several weeks or even a few months for the first sprout to emerge. Once the seedling breaks the surface, the initial cotyledon leaves will appear, followed shortly by the development of the first true leaves.
Early Seedling Care and Transplanting
Once the cherry plum seedling has developed its first set of true leaves, it requires careful nurturing. The young plant needs bright, direct sunlight for optimal growth, and should receive at least six hours of light daily. Watering should be consistent, keeping the soil moist but allowing the top layer to dry slightly between waterings to prevent root rot.
Before moving the seedling outdoors permanently, a process called “hardening off” is necessary, which gradually introduces the plant to direct sun, wind, and lower outdoor humidity over a period of one to two weeks. The young tree will thrive with a balanced fertilizer, such as a 10-10-10 NPK formula, applied in the early spring of the following year to support vigorous growth. The ideal time to move the young tree to its final location is typically after its first year of growth, or when it has reached a height of one to two feet. When transplanting, dig a hole that is twice as wide as the root ball and ensure the root collar sits just above the soil line to prevent future trunk rot.