Identifying a somewhat rare tree in North Dakota
"Fielding Questions" columnist Don Kinzler also answers questions about cutting back ornamental grasses and how to keep a new hydrangea shrub alive through the winter.
Q: I have attached two pictures of a tree. One taken in September and one when it bloomed in June. Do you know what kind of tree this is? I have never seen one like it before. The tree is located between Fairmount and Hankinson in southeastern North Dakota. — Moni C.
A: The tree is Northern catalpa. It’s somewhat rare in North Dakota, compared to other more common trees like ash, elm, oak, maple and linden. There is a very large specimen in Wahpeton, N.D., which holds the state record at 54 feet in height.
Northern catalpa is an attention-getter, both when flowering and when the long seed pods develop. Blooming in June, the showy bell-shaped white flowers are highlighted with purple and yellow and frilled at the edges.
The seed pods are quite dramatic as they hang from the tree, each reaching a length of 8 to 20 inches and filled with papery seeds. The huge leaves average 6 to 12 inches long.
Northern catalpa, whose botanical name is Catalpa speciosa, is generally considered winter hardy to zone 4. It’s better adapted to sites south of Interstate 94 than regions to the north.
Catalpa makes a beautiful specimen-type tree where you’d like to feature something unique. They’re best planted in protected microclimates within established neighborhoods. Open, windswept sites often result in dieback and freeze-out.
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Q: Do ornamental grasses need to be cut back every year, or can they be left alone? — Duane N.
A: For optimum health, ornamental grasses are best cut back to just above ground level once a year. New growth arises from the ground each spring, and if the old dried tops aren’t removed annually, a tangled mess would soon accumulate, and over time the grass’s health would deteriorate. Prairie fires often accomplished this cleanup in nature.
There are two options for the yearly cutback of ornamental grasses. Because the above-ground stems and seedheads are often quite ornamental, they add beauty to the winter landscape if left intact during winter. Cut down to near ground level in spring before new growth emerges.
Alternatively, ornamental grasses can be cut down in fall after several hard freezes. If your springs are hectic, and you’re afraid you won’t get the task done before new growth starts, then cutting back in fall is preferred.
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Q: I planted a new hydrangea shrub in our landscape this year and it has been producing beautiful dark pink blooms! How do I keep it alive through the winter? — Kayla C.
A: Do you know what the name of the hydrangea is? Hydrangea types vary greatly in their adaptability. Several types are well-adapted to most parts of the Upper Midwest, while others struggle. Several of the dark pink flowered cultivars are more closely related to the florist hydrangea, and are not as winter-hardy as the adapted cultivars. The first step is checking the plant tag for the exact hydrangea species and cultivar name.
For types that are borderline in adaptability, such as the Endless Summer series, a winter mulch applied in early-to-mid-November is a good safeguard. Covering the plant with about 12 to 24 inches of leaves, straw or shredded wood helps protect the plant, with the mulch removed next spring before growth begins.
If you choose shredded wood, after serving its purpose as a mound of winter protection, the mulch can be pulled away and left in a layer around the hydrangea during summer. Hydrangeas love moisture, and mulch keeps soil moist and cool.
If you have a gardening or lawn care question, email Don Kinzler, NDSU Extension-Cass County, at firstname.lastname@example.org. Questions with broad appeal may be published, so please include your name, city and state for appropriate advice.