Hawthorn (genus Crataegus) is a resilient tree or shrub prized for its fragrant spring flowers and the small, apple-like fruits known as haws. Propagating hawthorn from seed is a process that demands significant commitment and patience, primarily due to the seed’s inherent “double dormancy.” This complex mechanism prevents immediate sprouting. Successfully growing these trees requires deliberately manipulating the seeds’ environment to mimic the natural conditions necessary for germination. This process involves precise preparation and a lengthy cold treatment to overcome the seed’s biological barriers.
Preparing Hawthorn Seeds for Germination
The first major hurdle is the physical dormancy imposed by the hawthorn seed’s hard outer casing, the pericarp or seed coat. This dense shell acts as a protective barrier, preventing both water absorption and gas exchange required for the embryo to begin growth. This barrier must be compromised through scarification before the seed can hydrate and respond to temperature cues.
Physical scarification involves manually weakening the seed coat by lightly sanding the seed with fine-grit sandpaper or carefully nicking the shell with a small file. The goal is to create a tiny opening without damaging the delicate embryo inside. Alternatively, chemical scarification uses a controlled acid bath, but the manual method is safer and more accessible for homeowners.
Scarification is performed immediately after extracting the seeds from the fruit pulp. Removing the pulp is important because it can contain germination-inhibiting chemicals that must be washed away. Once the seed coat is compromised, the seed is ready to absorb moisture and proceed to the next phase of dormancy breaking.
The Cold Treatment Requirement
After addressing the physical barrier, the seeds must overcome the second challenge: physiological dormancy of the embryo. This condition is broken by a two-stage temperature process called stratification, which simulates the passage of a full year in nature. The specific sequence and duration of temperatures are required for successful germination.
The initial stage is warm stratification, which allows the immature embryo to fully develop or breaks down chemical inhibitors within the seed. This phase typically lasts between 90 and 120 days, during which the seeds are held at room temperature, ideally between 68°F and 77°F (20°C and 25°C). The seeds are mixed with a moist, sterile medium, such as sand, peat moss, or vermiculite, and placed inside a breathable plastic bag or container.
Following the warm period, the seeds require a prolonged cold stratification phase to mimic winter and prepare the embryo for sprouting. This treatment involves moving the seeds and their moist medium to a cold environment, such as a refrigerator, where the temperature is consistently maintained between 35°F and 40°F (2°C and 4°C). The cold phase must last significantly longer, usually between 120 and 180 days.
Throughout both stratification periods, the moisture level of the medium must be checked regularly. Ensure it remains damp but not waterlogged to prevent mold or rot. This entire warm-then-cold sequence often takes up to eight months to complete.
Planting, Sprouting, and Initial Seedling Care
Once the extended stratification period is complete, the seeds are ready for planting, typically in late winter or early spring when the outdoor soil is still cool. Successful stratification is sometimes indicated by the first few seeds beginning to show signs of radicle (root) emergence within the stratification bag. These seeds should be sown immediately to prevent excessive root growth in the confined bag, which can lead to damage during planting.
The seeds should be planted in a well-drained medium, such as a mix of compost and sand, at a shallow depth of about half an inch to one inch. Using individual pots or a dedicated seedbed allows for easier management of the small seedlings. Hawthorn seedlings prefer a location that receives full sun to partial shade, and while they tolerate various soil types, a soil with average fertility is sufficient for initial growth.
Germination may take several weeks after planting, even following proper stratification, and the initial growth rate of hawthorn seedlings is notoriously slow. Young sprouts require consistent moisture, particularly during dry periods in their first year, but they should never be left in saturated soil. Protecting the emerging seedlings from common pests and fungal issues like mildew is important, which can be managed by ensuring good air circulation and avoiding overhead watering late in the day. The seedlings are usually not hardy enough for permanent transplanting into the landscape until they have completed at least one full growing season, often when they are one to two years old.