Going Nuts: The Oak and Nut Tree Collection at the Arboretum

By Alan Branhagen

Director of Operations

In what tree collection was the first tree planted at the Minnesota Landscape Arboretum?  If you answered Oak and Nut Tree Collection you would be correct. Dr. Leon Snyder planted a shellbark hickory (Carya laciniosa) as the very first tree planted at the Arboretum (and actually before the property had been officially acquired).

Nut trees were once a popular tree selection for their value of lumber and edible nuts. They have fallen out of favor and are now rarely, if ever planted. We have this pre-conceived notion “they’re messy” and yes, a good one drops a lot of nuts.  We also know walnuts make it impossible to grow a prized tomato nearby, and most fruit trees languish under them too (most native woodland plants thrive beneath walnuts). When it comes to lumber and a delicious treat or addition to classic baking – then they are beloved!  Considering the environmental movement, the trees are known for their high value to wildlife, an important cornerstone of the food chain.  Edible landscapes and food forests are gardening trends on the upswing, and nut trees a key component of these landscapes.

So what are nut trees? We’ll exclude the oaks for their own future story, but they include the walnuts and their relatives including the butternut, hickories which includes the pecan, beech, and non-edible wingnuts. Other nut trees found elsewhere in the Arboretum includes the hazelnuts and chestnut.  Nutting is an almost forgotten word but was used to describe going afield in the fall looking for nuts to collect and take home to utilize for eating and baking. It’s almost gone by the wayside with some of us older folks still recalling fond memories of grandparents partaking in this: grandpa storing and cracking nuts in the winter and grandma baking with the treats (or both or vice versa!). Walnuts and hickories were an important food source during the Great Depression but now called “white linen” food gracing meals prepared by celebrity chefs or on specialty locavore plates.

Nut trees are readily planted by squirrels but are otherwise available almost solely from specialty mail order nurseries in small sizes. Walnuts and hickories grow deep tap roots that don’t conform to modern practices of efficiently producing trees for prices homeowners are willing to pay.  Hickories are especially slow, seemingly spending energy below ground rather than above, but once established grow surprisingly fast. These characteristics make the trees very drought tolerant but in our age of instant gratification, they do not conform. They are worth the wait!

The Arboretum’s nut tree collection includes fine examples of some really unique trees and their best cultivars for nut characteristics. Our Director Pete Moe planted some of the “newer” post-1970’s trees with guidance from the Northern Nut Growers Association – Pete also lent me the classic book “Growing Nuts in the North” by Carl Weschke who lived in St. Paul with a farm in River Falls, WI.  We have Mr. Weschke’s namesake black walnut and shagbark hickory – the latter with a great story on how it was discovered: it originated from Iowa near my hometown. (you can access this book on-line: gutenberg.org/files/18189/18189-h/18189-h.htm)

Page 5 - Walnut - Photo by Alan BranhagenWalnut

The Arboretum’s walnuts include the Minnesota native black walnut (Juglans nigra) and some select cultivars, one of which is ornamental (YES, ornamental!). The fernleaf black walnut ‘Laciniata’ really is a beauty with two delightful trees in our collection. Other varieties were selected for their larger or easier to crack nuts and hardiness to zone 4 conditions.  Black walnuts have a unique flavor some savor while others find too strong and you can also tap the trees like sugar maples to make syrup.  The Arboretum makes a small batch each year for tasting along with our maple syrup.  The butternut (Juglans cinerea) is Minnesota’s other native walnut. Unfortunately, butternuts are mired by an imported plague: butternut canker, which has severely marred and killed the best trees. A few trees still thrive for whatever reason. Butternuts are large and football-shaped with a sticky coating but the nutmeats have a rich buttery taste, more mild than black walnut (I hadn’t eaten one for over 35 years until now – wow was it delicious!).

Page 5 - Butternuts Ripening on Tree - Photo by Alan BranhagenButternut

The “English” or Persian walnut (Juglans regia) is the walnut found in most grocery stores for its ease of cracking and mild flavor – we have one small selection from the tree’s hardiest outpost in the Carpathian Mountains of Eastern Europe but it still struggles here. Of greater interest are our six mature English x black walnut trees (Juglans x intermedia). They produced a light crop of nuts this year but plenty to taste and they were delicious – without the aftertaste of black walnut but richer flavored than a typical English walnut. The nuts are also easier to crack than black walnuts and even look intermediate between a dark black walnut and light brown, smoother-shelled English walnut.

The collection’s Asian walnuts include Chinese, Manchurian and Japanese walnuts: Chinese walnut (J. cathayensis) from western China (foothills of the Himalaya Mountains and Tibetan Plateau) is considered an endangered species, the nuts look like shorter butternuts and are very similar to the Manchurian walnut (J. mandshurica) native 1,000 miles away in northern China (Manchuria) and into Korea and Russia. The Japanese walnut (J. ailanthifolia) from Japan and Russia’s Sakhalin Island is very similar to our butternut, but with much shorter, smaller nuts — and readily hybridizes with our butternut to create the buartnut (J. x bixbyi).  These are all beautiful trees in the collection with large compound leaves making them look like something out of the tropics. They also all produce nuts that are quickly squirreled away.

Hickories are mainly an American nut tree (one minor species in Asia) and the Arboretum’s collection showcases the hardiest, most economically important four species. Shellbark hickory (Carya laciniosa – the hickory with the largest, delicious nuts) was first added to the collection grown from trees planted near Lake Minnetonka by Peter Gideon (of ‘Wealthy’ apple fame) – those original trees were grown from nuts Mr. Gideon collected from his old homestead near Clinton, Illinois in 1878 (these trees are still present in Tonka Bay!). A cultivar ‘Missouri Mammoth’ was planted by Pete Moe in 1984 and those trees are now producing abundant, high quality nuts.

Locally native bitternut hickory (Carya cordiformis) is a wild tree in the collection and its thin hulled, easy to crack nuts are 99.9% of the time too bitter to eat (though squirrels still devour them).  Southeastern Minnesota native shagbark hickory (Carya ovata) was planted soon after the Arboretum’s founding with a good grove of mature trees now. Pete Moe planted many of its cultivars selected for nut quality starting in the 1970’s and those trees are beginning to bear quality nuts now. They are renowned for their beautiful shaggy bark which you can make a fine syrup from too. The flavor of these nuts is extraordinary but they are small and the nutmeat harder to extract (but worth the effort!).

Page 5 - Arboretum Pecans - Photo by Alan BranhagenPecans

Surprisingly the Arboretum also has 13 pecan trees which have grown into fine shade trees. Pecans (Carya illinoinensis) are a beloved nutmeat, grown commercially across the warmer part of the United States. The cultivated “papershell” cultivars have large, easy to crack nuts and are not hardy in the north – in the lower Midwest, “northern” pecans are grown and sold for their smaller, richer flavored, higher in oil nuts.  Wild trees grow as far north as southeastern Iowa and readily along the Mississippi in Illinois and Missouri and up the Illinois River to Peoria. These are the trees parent to those growing at the Arboretum. Our cold winters and shorter growing season usually do not allow Arboretum pecans to flower and fruit. In 2017, the long growing season after a mild winter allowed our first pecans to ripen!  Only one tree has nuts in 2018, after a very late spring, but phenomenal growing season: will they ripen before a hard freeze?  Pecans and hickories do hybridize on rare occasion in the wild and these are known as hicans. Our collection has a hican cultivar ‘Henke’ which is a shagbark x pecan. It is loaded with blimp-shaped nuts this season.

The American beech (Fagus grandifolia) is not well known locally for its nuts as the tree is difficult to procure and needs the right site from the right wild source to grow well here. You also need at least a grove of trees to cross-pollinate with the wind for the nuts to fill out. The nuts are small but tasty. The trees are glorious and magnificent, a major component along with sugar maples in forests of the Upper Peninsula of Michigan and eastern Wisconsin and points east. Our couple large trees at the Arboretum were grown from Wisconsin wild trees and do not produce nuts. I think planting more trees to cross-pollinate is in order.

Wingnuts (Pterocarya spp.) round out our collection but are not grown for their edible nuts. The quarter-inch nuts are better described as nutlets that form along a pendant chain about 6-inches long that adorn the tree like icicles.  The tree grows exceedingly fast and only the Chinese wingnut (Pterocarya stenoptera) from a wide range in China, Korea and Japan is hardy in zone 4. It becomes a fine shade tree but we are now concerned with this species becoming a potential invasive species as we are seeing many, many seedlings near plantings so we cannot recommend the tree at this time.

Page 5 - Shellbark Hickory - Photo by Alan BranhagenShellbark Hickory

On your next walk or drive around the Arboretum be sure and stop and take a walk through the oak and nut tree collection.  It’s sure to inspire with the beauty of these trees – and look for the shellbark hickory where the Arboretum’s collections began – it’s not far off 3-mile drive before you get to woodland.  We are thankful for all the talent and foresight that brought together this thorough collection and all the other outstanding plant collections to the Arboretum.  Director Pete Moe says: “Even though I worked at a large metro area garden center for 4 years in high school I never learned any of our great nut trees until I visited the Arboretum with a U of M Horticulture Class and saw all of these amazing trees. No one was planting nut trees in home yards and it was great that the Arboretum had this diverse collection.”



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