Expanding On-Farm Propagation of Hazelnuts in the Upper Midwest Through Seed-Graft Layering

Seed-Grafting Methods

Seeds from hybrid hazelnut plants were harvested in early September 2023, stored in cool moist conditions until de-husked in early October. Immediately after de-husking, the seeds were soaked in water for 12 hours, and then stored in a ventilated plastic storage tub at 39 F until late February 2024. Seeds were soaked in water for 12 hours approximately once per month during the stratification period.

To produce etiolated shoots with adequate thickness for grafting, seeds were placed in black plastic trays to exclude light and retain high humidity, placed in a 75 F mist house, and watered daily. Once radicles appeared, four to six germinated seeds were planted at a depth of 12 cm (4.7 in) into AB36 Anderson Bands with Sun-Gro 852 Professional potting mix and watered thoroughly. The planted seeds were then grown in a 75 F greenhouse. Once the shoots emerged from the soil (2-4 weeks), the seedlings were rinsed of potting soil, stored in plastic trays and grafted within 6 hours of harvest.

Scion wood from hybrid hazelnut genotypes were harvested in early November 2023 from the apical 20 cm of 7-month old coppice shoots produced by coppicing the source plant in April. The stems were then stored in unventilated contractor trash bags at 39 F for 14 days. The bags were then transferred to a freezer and stored at 28 F until used for grafting in the spring. Five days prior to each grafting date, the scions were transferred to a 39 F cooler.  On the day of grafting, individual scionwood stems were cut into 1-2 node sections with the basal end cut into a wedge.

To graft, scion pieces were removed from black plastic trays and allowed to air dry until free surface water had evaporated. Rootstocks were selected in an attempt to match the diameter of the scion wedges, but often the scions were moderately thicker than the rootstock shoots they were grafted to. The rootstock shoots were cut at the thickest, straightest portion of the stem of adequate length for grafting, remaining stem length averaged 1-2 in. The shoot was split in half with a scalpel to a depth equal to the length of the wedge of the scion, a 2.5mm silicone vegetable grafting clip was attached to the base of the shoot to prevent the shoot from splitting further when inserting the scion, the scion was inserted into the cleft, and the clip moved upwards along the stem to secure the graft union. The grafted plant was then inverted and dipped quickly (less than 1 second) into an approximately 50/50 (v/v) mix of paraffin and cheese wax and immediately placed into a bin of cool water for 15-60 minutes to cool and harden the wax and avoid heat injury to graft union.

Grafted plants were potted into Proptek 28 pots (28 Cell 10×20″ Pot-In-Frame Tree Propagation System, Blackmore Co.) with a 50/50 (v/v) mixture of Pro Mix BRK and Sun Gro 852 Professional potting mixes with 4.7g/L of Osmocote Plus (15-9-12) slow-release fertilizer incorporated into the medium prior to planting. Grafted plants were then grown a greenhouse set at 77 F / 72 F daytime/nighttime temperature under halogen lamps set to 16 hr days for subsequent graft healing and growth. Grafts were watered and rootstock sucker shoots were removed as needed. Successful grafts broke bud 10-21d after grafting, and were fertigated weekly with Jack's Professional 20-3-19 Petunia FeED Plus Mg at 400 ppm N. Graft success was assessed 7 weeks after grafting; grafts with >12.7 cm (5 in) shoot growth, a healthy terminal growing tip, and healthy leaves were deemed successful. The mean grafting success for each treatment rep was calculated by dividing the total number of successful grafts by the total number of grafts. To calculate a treatment mean, the grafting success was averaged across the replications for each treatment.

High Tunnel Layering

The successfully grafted plants were stored in a cooler over the winter of 2024/2025 and planted into a high tunnel greenhouse at Hauser's Superior View Farm on May 1, 2025. Each bed consists of two rows with 18" between plants and 18" between rows. For comparison, we also established beds of plants of the same genotypes produced from softwood stem cuttings. This will allow us to compare the number of layered stems we can produce from grafted plants to the number we can produce from stem cuttings growing on their own roots. Though the original intent was to layer the plants during the summer of 2025 we felt the plant vigor and growth rates were not sufficient to support layering in the establishment year. So, we let the plants grow all year and will layer them in the summer of 2026.

To prepare for the layering in 2026 we partnered with Wild Hollow Farm near Sanborn, WI to conduct a layering trial with 2 and 3 year old mother plants in a high tunnel greenhouse. The plants were cut back to the ground in March of 2025, allowed to regrow until the last week of June and were then thinned and layered. To layer, the leaves from the basal 12" were removed from each stem and the bare stems treated with K-IBA dissolved in water at a concentration of 2000 ppm. A 12" high, 18" wide tube was wrapped around each plant and filled with sawdust. Water was applied all summer long and the plants will be dug in November of 2025 to determine # of rooted stems per mother plant. This will provide valuable data for the trial layering in 2026 at Hausers.

We had excess grafted plants from some genotypes so we let them grow in the greenhouse during the summer of 2025 and transplanted them into the field at the Bayfield Go-First Farm near Ashland, WI the first week of October 2025. Our plan is to grow them as single stem trees by pruning any and all suckers that emerge from the ground. We also sent some extra grafted plants back to the University of Minnesota to layer them with a pot-in-pot system in 2026.