Plant propagation is the process of creating new plants from a parent source, and for Corylus species (hazelnuts), two distinct approaches are used. The choice between sexual and asexual methods determines whether the resulting plant will be a unique individual or a perfect clone of the mother tree. These techniques range from planting a nut to highly technical methods used in commercial nurseries. They produce trees with fundamentally different genetic outcomes.
Sexual Propagation: Growing from Seed
Growing a hazelnut from seed is primarily used in breeding programs or for those seeking genetic novelty, as it introduces variability. Hazelnuts exhibit physiological dormancy, meaning the embryo must undergo a chilling period before it can germinate. This process, known as stratification, mimics the natural winter cycle by requiring the nut to be held at cold, moist temperatures, typically between 0°C and 7°C (32°F and 45°F), for at least four weeks to several months to break dormancy. The nut is often pre-soaked in water for 12 to 24 hours to rehydrate the seed coat before being placed in a moist medium like peat moss for cold storage. Once stratification is complete, the seeds can be planted and will germinate when temperatures rise above 10°C (50°F). The major limitation is that the resulting tree will not be genetically identical to its parent, making seed-grown trees unsuitable for commercial orchards focused on consistent quality and yield.
Asexual Methods for Home Growers
Asexual propagation creates plants that are genetically identical clones of the parent, ensuring the desired traits of a cultivar are maintained.
Suckering and Layering
The simplest and most accessible asexual technique for home growers utilizes the hazelnut’s natural tendency to produce suckers. These shoots emerge from the base or root crown and can be carefully dug up and transplanted during the dormant season, as they are already rooted stems.
Another reliable method is simple layering, which uses the plant’s ability to produce roots when a stem is buried while still attached to the parent. Simple layering involves bending a low-growing, one-year-old shoot down and burying a section of the stem, leaving the tip exposed. Roots form along the buried portion over the growing season, and the new plant can be severed from the mother plant the following dormant season. Mound layering, or stool layering, is a commercial variation where the parent plant is cut back (coppiced). The new shoots that emerge are then treated with rooting hormone and covered with medium to encourage rooting.
Advanced Asexual Techniques
For commercial production, specialized asexual techniques are employed to overcome specific challenges, such as the problem of excessive suckering.
Grafting
Grafting involves joining a desired hazelnut scion onto a non-suckering rootstock, such as Turkish hazel (Corylus colurna). This technique controls the tree’s growth habit and prevents the recurring need to remove suckers from the base of the plant. Hazelnut grafting is technically challenging due to the slow formation of callus tissue at the graft union, though recent research has shown improved success rates with specialized methods.
Cuttings
Propagation via cuttings, where sections of stem are rooted, is common for many woody plants but has historically been difficult for hazelnuts. Hardwood cuttings have poor success rates. Even softwood cuttings typically require specialized conditions, such as misting systems, bottom heat, and specific hormone treatments, making them impractical for the average home grower.
Preparing the Environment for Success
Hazelnuts require specific environmental conditions to thrive and become productive. They perform best in well-drained, loamy soils, as they are highly susceptible to root rot in waterlogged conditions. A soil pH ranging from slightly acidic to neutral (6.0 to 7.5) is optimal for nutrient uptake and growth. The climate must provide an adequate chilling period during winter for successful bud break and nut production. Hazelnuts require a specific number of chilling hours, defined as time spent between 0°C and 7°C (32°F and 45°F), with most cultivars needing 800 to 1,200 hours to break dormancy. Finally, because hazelnuts are wind-pollinated and generally self-incompatible, successful establishment requires cross-pollination. This means planting compatible pollinizer varieties nearby to ensure effective pollen transfer and subsequent nut set.