Small Prunus show promise for Northern Plains landscapes

Interest by the public in small ornamental landscape trees has increased markedly over the past 25 years. Small (15- to 28-foot) flowering trees tend to fit well in residential lots with limited space and one-story ranch-style homes. Smaller trees can also be grown satisfactorily under utility lines. In addition, large trees block much of the potential sunlight available to a residential lot, which reduces the success of growing quality turf, gardens and flowers due to excess shade and the probability of increased disease problems.

Flowering crabapples have been a very popular small tree choice for decades. As woody plant evaluations have proceeded at North Dakota State University, we have noted a number of pear and cherry/plum cultivars that have (or may have) excellent potential for expanding the diversity of adaptable small trees for planting in Northern Plains landscapes.

This article will cover promising cherry and plum cultivars, while the June article (Page XX) focused on pear cultivars.

‘Princess Kay’ has double flowers

Prunus nigra ‘Princess Kay’ is a selected cultivar of Canada plum with showy, fragrant, double-white flowers in early May, which last for seven to 10 days. The species has single flowers. It was introduced by the University of Minnesota and is hardy in Zones 2-3. It is essentially sterile, producing very few fruits.

Trees produce very dark-green, somewhat rough or rugose leaves, which turn to reddish shades in autumn. Trunk and branches are dark brown to black with large whitish lenticels. Trees grow oval to round in form, reaching 15 feet tall by 8-10 feet wide. Good soil drainage is required.

Sargent cherry is handsome

Sargent cherry (Prunus sargentii is native to northern Japan and Korea. Authorities rate this species as the most handsome of the larger tree cherries for Northern states and its hardiness as Zones 4-5.

Consequently, this species had not been evaluated in NDSU trials until a named cultivar, Pink Flair, was received for trial in 2000. We are obtaining plants of this species, plus the cultivars ‘Columnaris’ (columnar Sargent cherry) and ‘Rancho’ from Oregon nurseries for trial evaluation this spring. Both ‘Columnaris’ and ‘Rancho’ were selected for narrower, more columnar growth habits than are characteristic of the species. ‘Rancho’ is described as even narrower in form than ‘Columnaris.’

Pink Flair is hardier

Pink Flair sargent cherry (Prunus sargentii ‘JFS-KW58’) merits widespread evaluation in the Northern Plains, based upon seven years of evaluations. It has not suffered any winter injury to date at our Absaraka site in Zone 3. Single pink flower clusters ornament the trees in spring. No fruits have been observed to date but they are described as 1/3 inch long, ovoid, purple-black drupes ripening in July. Leaves are semi-glossy and dark green. Fall color has varied from attractive red-purple to orange-red in NDSU trials.

J. Frank Schmidt & Son Co. in Oregon lists orange-red for autumn color in its catalog description. Expected height is 25 feet and spread is 15 feet with an upright, narrow vaselike form. Bark is polished purplish with tannish-cream lenticels, but color may change somewhat as trees age. Could this be the first flowering tree cherry with pink flowers that proves to be hardy in Zone 3?

A closer look at Emerald Charm

In the mid-1980s, Greg Morgenson, manager of Lincoln-Oakes Nurseries in Bismarck, N.D., collected seed from a planting of Mongolian cherry (Prunus fruticosa) in the Northern Plains. Some authors list the common name as European dwarf cherry or European ground cherry bush. This species is native in central and eastern Europe to Siberia and typically grows as a multi-stemmed, suckering, dense shrub 4-6 feet tall.

Emerald Charm (Prunus x ‘Morgenson’), a seedling selection, grows into an attractive small tree reaching 20-25 feet by 15-18 feet wide. It grows upright, multi-branched and vase-shaped in form with a uniformly spreading crown. It may be grown as a single- or multi-stemmed specimen similar to Japanese tree lilac. A collaborative release by NDSU, Emerald Charm is a putative hybrid between P. fruticosa and an unknown cherry species. It has good vigor under clean cultivation, averaging 1¼ feet of growth annually over a 16-year period. Growth is most rapid in earlier years.

Emerald Charm produces masses of small, white flowers in spring, followed by dark-green, very lustrous leaves, which are smaller than other cherry species. The thick-textured foliage holds up well during summer heat stress, becoming attractive yellow in autumn color. Emerald Charm is apparently sterile, having produced no fruit after 16 years, even though planted close to five other cherry species. It has been very hardy in Zone 3, one to two zones colder than the hardiness of many cherry species and cultivars.

Bark color is a dark reddish brown, and unlike amur chokecherry (P. maackii), no winter bark splitting has been observed. Propagation by mid-August budding on P. maackii and P. cerasus ‘Meteor’ seedling rootstocks was very successful and eliminates suckering. Budding on P. avium (sweet of mazzard cherry), a somewhat less-hardy rootstock, was not as successful.

This small tree will offer an attractive landscape alternative with superior foliage to most crabapple and other smaller tree species. We are encouraging wholesale nurseries to produce this new cultivar so it can be made available to the public.

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- Dale Herman

July 2008