Hazelnut propagation involves various techniques to create new trees, either to grow entirely new varieties or to maintain the specific characteristics of an existing parent plant. Hazelnuts (Corylus) are naturally multi-stemmed shrubs that respond well to both sexual reproduction through seeds and asexual methods that produce clones. Understanding these methods allows a grower to select the best process for their specific goal, such as preserving a high-quality cultivar or increasing the number of plants. The choice of method depends on the desired outcome, as growing from a nut results in genetic variation while vegetative methods create an exact genetic copy of the source material.
Propagation from Seed
Growing hazelnuts from seed requires patience and a specific environmental cue called stratification to break dormancy. The hazelnut seed has a hard shell and a mechanism that prevents germination until it has experienced a prolonged period of cold and moist conditions. This cold stratification prevents the seed from sprouting during a warm spell in the fall, which would lead to the seedling freezing over the winter.
To begin, soak nuts in water for 12 to 24 hours to rehydrate the kernels and discard any non-viable nuts that float. Place the nuts in a damp medium like peat moss or sand inside a sealed container and refrigerate. The ideal temperature range for stratification is 34°F to 40°F (1°C to 5°C), and this chilling period must last for 90 to 120 days for reliable germination.
Once stratification is complete, plant the nuts about one inch deep in a well-draining soil mix in pots or directly into the ground. Seed propagation results in a unique genetic makeup, meaning the seedling will not be an exact clone of the parent and its characteristics may be significantly different. While this genetic variability is useful for breeding programs, it is a disadvantage if the goal is to reproduce a specific, high-quality cultivar.
Utilizing Root Suckers
The simplest method for cloning an existing hazelnut plant is by separating and transplanting its root suckers. Hazelnuts naturally produce these shoots from the base or roots, and they are genetically identical to the parent shrub. This tendency offers a ready supply of pre-rooted young plants for propagation.
The best time to separate suckers is during the dormant season, either in late autumn after leaf fall or early spring before bud break. Use a sharp spade to sever the sucker from the main root system, digging deeply enough to ensure the detached sucker retains sufficient root mass for support.
Immediately replant the sucker in its new location at the same depth it was previously growing. This method is highly effective because the new plant already has an established root system, resulting in a high survival rate and rapid establishment. Growers frequently use this technique to quickly expand their orchards or replace older shrubs with clones of a preferred variety.
Simple and Tip Layering
Layering is a reliable asexual technique that encourages a stem to form roots while still attached to the parent plant, guaranteeing a genetic clone. Simple layering involves bending a flexible, one-year-old shoot down and burying a section of it while allowing the tip to remain exposed. To promote rooting, the buried section is often wounded by scraping away a small strip of bark on the underside, which stimulates root formation above the wound.
Tip layering is a variation where the tip of a shoot is inserted into the soil. The buried tip is stimulated to produce roots and turn upward to form a new plant. In both methods, the buried portion is held in place with a staple or heavy object and covered with soil, which must be kept consistently moist throughout the growing season.
Roots typically form over one growing season. The newly rooted layer is ready for separation in late fall or the following spring when the plant is dormant. The stem is severed from the mother plant just below the new root ball, and the young plant is moved to its permanent site. Layering is preferred over cuttings because the stem remains nourished by the parent plant until the new roots are fully developed, leading to a higher success rate.
Rooting Stem Cuttings
Propagating hazelnuts through stem cuttings is more difficult with Corylus species compared to many other woody plants. The process uses either softwood cuttings, taken from tender new growth in late spring or early summer, or hardwood cuttings, taken from mature, dormant wood in the winter. Softwood cuttings generally root more readily than hardwood, but both require specific conditions.
For softwood cuttings, take a six-inch-long piece of current-season growth and dip the base into a rooting hormone containing indole-3-butyric acid (IBA) at 500 to 1,000 parts per million. Place the cutting in a porous growing medium like a peat and perlite mix. Maintaining a highly humid environment, often achieved through misting systems, is necessary to prevent the leaves from drying out before roots form.
Hardwood cuttings, usually taken from dormant suckers, are challenging but can be encouraged to root using rooting hormone and bottom heat. A propagation mat set to 75°F to 80°F (24°C to 27°C) at the base helps stimulate root development while the top remains cooler. Successful rooting takes several weeks to a few months, and the resulting plants require a gradual acclimation period away from the high-humidity environment before transplanting outdoors.