Growing a plum tree from a seed indoors offers a rewarding experience for the patient gardener. The process requires understanding the seed’s need for a simulated cold period to break its natural dormancy, a mechanism that prevents it from sprouting during the wrong season. This cold treatment, known as stratification, is a necessary step that mimics the seed’s natural journey through a winter cycle before germination can begin.
Preparing the Plum Seed for Planting
The initial step involves thoroughly cleaning the pit to ensure success during the subsequent cold treatment. Any remaining fruit flesh or sugar residue must be completely removed, as this organic matter can quickly promote mold and fungal growth in a humid environment. Scrubbing the pit under running water with a small brush or cloth is sufficient to achieve a clean surface.
Once the hard outer pit is clean and dry, the true seed, or kernel, must be carefully extracted. This almond-shaped kernel is the reproductive part that requires planting. Although the hard shell protects the kernel in nature, it can hinder germination indoors, so it should be gently cracked open using a nutcracker or a light tap from a hammer. Use caution to avoid damaging the soft kernel inside. Selecting several healthy seeds is recommended, as not all kernels will be viable or survive the procedure.
Simulating Winter: The Stratification Process
Plum seeds possess internal growth inhibitors that prevent sprouting until they have undergone a prolonged period of cold. Stratification involves artificially providing the required cold and moisture within a controlled environment, typically a refrigerator.
The plum kernel should be placed in a slightly damp medium, such as peat moss, vermiculite, or a folded paper towel. The goal is a consistently moist, not soaking wet, environment to prevent the seed from rotting. This prepared medium and seed are then sealed inside a breathable plastic bag or a closed container to maintain humidity.
The container is then placed in a refrigerator, where the temperature should be maintained between 33 and 41 degrees Fahrenheit (1–5 degrees Celsius). This range effectively mimics the conditions of winter soil. The required duration for this cold exposure is usually between 8 and 12 weeks, although some varieties may require up to 90 to 120 days.
During this time, the seed must be checked every two weeks to monitor moisture levels and look for signs of mold growth. If the medium appears dry, a small amount of water can be added, and if mold is present, the seed should be rinsed and placed in a fresh, slightly drier medium. Successfully stratified seeds will often begin to sprout a small white root, indicating the cold period has successfully broken dormancy.
Placing the Sprout into Soil
Once the plum seed has sprouted a root during the cold treatment, it is ready to be moved into a pot. Selecting the correct container is important, and it must have adequate drainage holes to prevent waterlogging, which can cause root rot. A standard, well-draining potting mix provides the necessary aeration and moisture retention for the developing roots.
The sprouted seed should be planted about half an inch to one inch deep in the soil. The delicate root, which is the start of the taproot, should be pointed downward into the potting mix. Planting the seed too deeply can deplete its energy reserves before the sprout reaches the soil surface.
Immediately after planting, the soil should be thoroughly watered until the excess drains from the bottom of the container. This initial watering settles the soil around the developing roots and provides the moisture needed to transition from the stratification medium. Placing the pot on a drainage saucer will prevent water damage to surfaces while allowing the excess moisture to escape.
Early Care for the Plum Seedling
The newly potted plum seedling requires a stable environment to continue its growth after the cold period. It should be kept in a location that provides bright, indirect light for at least six hours daily. A sunny windowsill that avoids harsh, direct afternoon sun is often a good location, or a supplemental grow light can be used to ensure consistent light exposure.
Maintaining a consistent room temperature, generally between 65 and 75 degrees Fahrenheit (18–24 degrees Celsius), is conducive to healthy early growth. Plum seedlings are sensitive to overwatering, so a regular watering schedule should only be established once the top inch of the potting mix feels dry to the touch. This practice helps to balance moisture without saturating the roots.
As the seedling grows, it will eventually require a larger container to accommodate its expanding root system and prevent it from becoming root-bound. Before transplanting the young tree outdoors, a process called hardening off is necessary. This involves gradually acclimating the seedling to natural sunlight, wind, and temperature fluctuations by placing it outside for increasing periods over one to two weeks. Note that a plum grown from seed may take several years to mature and produce fruit.