Bonsai seeds are highly specialized tree seeds that have evolved complex mechanisms to ensure they only germinate when conditions are perfect. In nature, this can mean delays of months or even years before sprouting. Proper preparation is necessary to bypass these natural delays and encourage successful germination in a controlled environment. Initial steps, such as water soaking and intensive treatments, enable the embryonic plant to begin its growth cycle.
Understanding Seed Dormancy
Preparing tree seeds is necessary due to seed dormancy, an adaptive trait that prevents sprouting during unfavorable periods like winter or drought. Tree seeds often exhibit two primary forms of dormancy: physical and physiological.
Physical dormancy occurs when a hard, impermeable seed coat prevents water from reaching the embryo, which is required for germination. Physiological dormancy is an internal chemical block within the embryo, often regulated by plant hormones. This block prevents growth even if water is available. Seed preparation addresses both mechanisms by softening the physical barrier or neutralizing the chemical inhibitors.
The Simple Water Soaking Procedure
Soaking is the first step in preparing many tree seeds, addressing physical dormancy by softening the hard seed coat. This process allows the seed to rehydrate, bringing its moisture content up to the level required for metabolic activity to resume. Place the seeds in a container and cover them with room temperature or warm water, avoiding boiling water to prevent embryo damage.
The typical soaking duration ranges from 12 to 48 hours, but the water must be changed every 12 hours to prevent mold or bacteria growth. Viable seeds usually swell noticeably after absorbing water. Seeds that float are often non-viable and should be discarded. Swollen seeds are ready for the next stage of preparation or planting.
Scarification and Stratification Techniques
Simple water immersion is not sufficient for all species, often requiring specialized treatments: scarification and stratification.
Scarification
Scarification physically weakens the seed coat to allow water entry. This is done manually by gently rubbing the seed against sandpaper or using a sharp tool to nick the outer shell. When performing mechanical scarification, work slowly and avoid damaging the embryo, which is often located near the seed’s attachment point.
Stratification
Stratification breaks physiological dormancy by simulating natural seasonal temperature cycles. Cold stratification involves placing prepared seeds in a moist medium, such as damp peat moss or sand. Store them in a refrigerator at 34 to 40 degrees Fahrenheit (1 to 5 degrees Celsius). This cold, moist period mimics winter conditions, lasting one to six months depending on the species, and breaks down internal chemical inhibitors. Some tropical species may require a period of warm stratification before the cold phase.
Moving from Soaking to Germination
Once the pre-treatments are complete, the seeds are ready to be planted in a suitable growing medium. The planting medium should be well-draining and sterile, such as a mix of peat moss and sand or a specialized seedling mix, to prevent fungal diseases from attacking the delicate sprouts. Seeds should be planted relatively shallowly, typically at a depth of about one to two times their diameter. For most small seeds, this translates to a depth of approximately 1/8 to 1/4 inch.
After planting, the container should be placed in a warm area that receives indirect sunlight, which encourages the final stage of germination. Maintaining consistent moisture is important, but the medium should never be waterlogged. A fine mist or gentle watering is recommended. Covering the container with clear plastic helps to maintain the humidity required for the newly planted seeds to sprout.