Interest in alternative tree syrup is growing

In southern Ontario, walnut syrup is currently produced in small hobby batches from sap harvested from maturing trees that are found growing in small groups or are growing randomly along fencerows of farm fields.  In many cases, squirrels likely planted the walnut trees.  Sap is collected from walnut trees using buckets, since operations are not practically large enough at this time to install modern vacuum tubing.

Walnut syrup is made using the same harvest practices and processing equipment as maple syrup.  Walnut sap is boiled down to reach a sugar concentration of 66 – 67 ⁰Brix, similar to maple syrup.  This finished density may or may not be ideal for walnut syrup, but it seems to work for now.  Researchers may refine walnut syrup density and other processing practices in the future.

Unlike maple trees that can be found growing naturally in large dense populations typical of a sugar bush, wild walnut trees are far less abundant.  Wild walnuts are naturally most abundant in southern areas of the province and grow best in Carolinian climates or climates moderated by large bodies of water, like the Great Lakes.

Uses for walnut trees

Walnut trees are utilized in both the horticulture and forest industries, for food and for wood production.  Syrup from walnut trees could be produced in larger quantities if landowners establish managed plantations, intensively managed commercial orchards having multiple products of food and wood or, integrated into farm windbreaks or wide shelterbelts, with precautions considered for juglone-sensitive crops.

Juglone leached from fallen leaves and green husks in high concentrations into adjacent streams or ponds is toxic to some species of fish and other marine organisms.  Therefore, avoid planting walnut trees in stream buffers.

Tapping a walnut tree for syrup will create holes and staining in the wood of the lower trunk.   This evidence of sap harvest in saw log boards was once viewed as a defect by mill operators.  However, the tapped wood is now frequently utilized in unique furniture and panels as a value-added character of historic importance.

Walnut trees grow best on deep, moist, fertile loam or sandy loam soils and do not tolerate dry or flooded soil.  In fertile southern locations, commercial orchards are tile drained and irrigated to create or establish ideal growing conditions for annual food production, while minimizing weather-related risks to orchard health and annual profit. Juglone is not present in the edible walnut kernel.

Walnut trees can be planted further north in colder areas for wood and syrup production, however annual nut production may not be reliable where blossoms and nut crops can be damaged or ruined by spring frost or deep cold winters.  Similar to fruit trees, walnut trees tend to grow faster without an annual load of nuts.

The orchard shown above is actually a specialized nursery operation having a mixed planting of improved walnut cultivars, shellbark and shagbark hickory and named selections of northern pecan trees.   Budwood is collected in late winter and is grafted onto germinated rootstock seedlings.  Then after one season of growth, the grafted trees are sold as bare-root trees or in pots, as improved propagated cultivars to be planted as orchard trees for nut production.  See the website for Grimo Nut Nursery.

Budwood can be grafted higher up on an older seedling stem, for example 10 to 12 feet high, where a higher valued sawlog of wild black walnut may be grown and eventually harvested when the orchard is renewed or renovated after many years of nut production.   The landowner would learn and apply grafting techniques themselves, which can be fun to try.

Collections of old walnut cultivars are maintained at the University of Lincoln Nebraska.  The Northern Nut Growers Association (NNGA) is an active group of dedicated researchers and devoted growers who hold an annual summer conference, hosted by various U.S. states and Canadian provinces, to observe northern temperate examples of nut production.

The Ontario chapters of the NNGA are the Society of Ontario Nut Growers (SONG) and the Eastern Society of Ontario Nut Growers (ESONG).  Search their websites for detailed information.  New members are always welcome.

International conferences on walnut production are hosted by the International Society for Horticultural Science (ISHS) Division of Temperate Tree Nuts (Temperate = cold climate regions).  ISHS Link: https://www.ishs.org/walnuts-and-pecan .   Countries, research scientists, growers and value chain partners who are involved in commercial tree nut production attend the ISHS conferences to learn leading edge technology and advanced production practices.

Pest management in commercial orchards is an important practice for farmers.  Walnut orchards consisting of improved propagated cultivars frequently share the same insect pests and diseases that affect wild forest trees.   Food safety in nut kernel production is directly linked to the effective management of insect pests and diseases in orchards.

Fresh, locally grown nuts typically have superior flavour when compared to imported nuts.  Vacuum packaging of kernels plus cold storage will improve the storage life of nuts and maintain quality.   Oxidation of nut oils following long open storage is a leading cause of off-flavour in kernels.  A small percentage of people are sensitive to allergenic proteins found in tree nuts.