Pines in the Arboretum

UNIVERSITY OF MINNESOTA MtJ ARBORETUM REVIEW No. 32-198 PETER C. MOE Pines in the Arboretum Pines are probably the best known of the conifers native to The genus Pinus is divided into hard and soft pines based on the northern hemisphere. They occur naturally from the up the hardness of wood, fundamental leaf anatomy, and other lands in the tropics to the limits of tree growth near the Arctic characteristics. The soft or white pines usually have needles in Circle and are widely grown throughout the world for timber clusters of five with one vascular bundle visible in cross sec and as ornamentals. In Minnesota we are limited by our cli tions. Most hard pines have needles in clusters of two or three mate to the more cold hardy species. This review will be with two vascular bundles visible in cross sections. For the limited to these hardy species, their cultivars, and a few hy discussion here, however, this natural division will be ignored brids that are being evaluated at the Arboretum. and an alphabetical listing of species will be used. Where neces Pines are readily distinguished from other common conifers sary for clarity, reference will be made to the proper groups by their needle-like leaves borne in clusters of two to five, of particular species. spirally arranged on the stem. Spruce (Picea) and fir (Abies), Of the more than 90 species of pine, the following 31 are or for example, bear single leaves spirally arranged. Larch (Larix) have been grown at the Arboretum. It should be noted that and true cedar (Cedrus) bear their leaves in a dense cluster of many of the following comments and recommendations are indefinite number, whereas juniper (Juniperus) and arborvitae based primarily on observations made at the University of (Thuja) and their related genera usually bear scalelikie or nee Minnesota Landscape Arboretum, and plant performance dlelike leaves that are opposite or borne in groups of three. could differ at other locations. Unlike other conifers that mature their seeds in one !growing Pinus cembra (Swiss Stone Pine) is well suited for small season, pine seeds require two seasons, and even a ra1re third, yards because it grows slowly and will not grow out of to reach maturity. The 31 or more species of pines that are scale with the house and other plantings. hardy in Minnesota offer a wealth of horticultural diversity. They range in size from prostrate shrubs to trees of truly im- A pressive height and diameter; specimens of eastern white pine W over 200 feet tall and 6 feet in diameter at the base are on record. Most pines are readily cultivated, adapting themselves to a wide variety of cultural conditions as long as climatic toler ances of the species are observed. Pines are drought tolerant and some species are known for their ability to grow well on poor soil that will not support other trees. Unfortunately, pines are subject to a number of disease and insect problems. White pine blister rust is perhaps the most serious disease problem, especially in northeastern Minnesota where it is quite common. This fungus disease, which has cur rants and gooseberries as the alternate host, attacks most of the soft or five-needle pines. It can be controlled partially in ornamental plantings by pruning out and destroying infected branches. Insect pests include the white pine weevil, various pine shoot moths, sawflies, and scale insects. The weevil and pine shoot moth can be controlled by pruning out and de1stroying wilted shoots that contain the larvae. For control of sawflies and scale insects, see Controlling Insect Pests of Shade and Ornamental Trees, Entomology Fact Sheet No. 28. The yellowing of pine needles in the fall generat es many calls to the Arboretum. This is not normally a disease symp tom, but merely indicates that the tree is shedding its oldest needles. Pines vary in length of time needles are retained on the branches. Some lose their needles the fall of the third year, ebut others such as the foxtail pines retain their needles for 10 years or more. Pinus albicaulis (Whitebark Pine). This pine grows nly at ele· vations of more than 5,000 feet in the Rocky Mou~ntains from Alberta and British Columbia south to Colorado and Nevada. The tree grows slowly and is only a shrub at the timberline. At the present we have no mature plants of this specie'S (as ours were found to be Pinus flexilis or limber pine). Ma1ture trees can be distinguished by the creamy white, scaly bark and the cones that, unlike the limber pine, do not open when mature. New plants of this species have been propagated and hopefully will prove hardy, since the whitebark pine is native to areas having similar climate to ours. Pinus aristata (Bristlecone Pine). This plant is a shrub or small tree found at elevations of more than 7,500 feet in Colorado, Arizona, and New Mexico. Unlike most other pine:; the needles remain on the branches 10-12 years, producing an interesting foxtail effect. Another distinguishing feature is that the leaves exude small drops of white resin that dry on the leaves and look much like pine needle scale. The bristlecone pine is hardy here but does not grow as well as it does in its native habitat, probably because of our hot, humid summers. lrhis pine should be planted only on dry sites with good drainage. Pinus armandii (Armand Pine). Native to China, Taiwan, and Korea, this pine has not done well in the Arboretum. We have been unable to locate a seed source that produces hardy plants. The trees that have survived here usually winter burn badly and have poor color throughout the year. The Armand pine is not recommended for planting. Pinus ayacahuite (Mexican White Pine). The Mexican white pine is similar to the eastern white pine when young. Older plants produce spectacularly large cones when the plant grows successfully. Two trees planted in the Arboretum in 1962 are now more than 15 feet tall; however, this pine is not com· Pinus cembra 'Sibirica' (Siberian Stone Pine) is a nicely pletely hardy and usually has some winter injury. shaped, pyramidal tree that is well adapted for planting Pinus balfouriana (Foxtail Pine). Native to the moiUntains of in Minnesota as far north as the Twin Cities. California, this pine has been acquired recently and needs to be evaluated further. Pinus banksiana (Jack Pine). The jack pine occurs from the tree line near the Arctic Circle south to Minnesota and east to New York. Its irregular form, short needles, and snnall twisted cones that point toward the branch tips help distinguish this tree from other two-needle pines. Its picturesque habit makes Pinus cembra 'Sibirica,' the Siberian stone pine, is a botani· it suitable for use in Japanese gardens. Jack pine is native to cal variety of the species native to the Taiga regions of Siberia. areas with sandy soil, but it also grows well on heavier soils. In Trees of this variety have formed nicely shaped, pyramidal addition, seedlings of jack pine witches brooms have produced trees in the Arboretum. Both plants are well adapted for plant· many dwarf types that are being evaluated at the J~rboretum. ing at least as far north as the Twin Cities. The Uncle Fogey jack pine (Pinus banksiana 'Uncle Fogey' ) Pinus cembroides edulis (Colorado Pinyon Pine). This two or is an interesting sprawling or weeping form of this species that three-needle pine, native from southern Wyoming to Mexico, has been propagated from a tree found in Richfield, Minnesota, produces large edible seeds called pinyon nuts. Although the by the late Albert G. Johnson, formerly on th~ sta'ff of the Ar· pinyon pine is native to areas having a harsh winter climate boretum. similar to ours, all of our plants have died due to winter injury. Pinus bungeana (Lacebark Pine). Plants of this Chinese pine This may be due to the fact that our warm, humid weather in survived for up to nine years in the Arboretum before dying of late summer and early fall interferes with hardening of the winter injury. Where the lacebark pine grows well it usually plant. We plan to try more plants of this species using seed forms a small, multistemmed tree with attractive, white exfoli· from high elevations in the northern extremes of its natural ating bark. range. Pinus cembra (Swiss Stone Pine). This choice five-needle pine Pinus contorta latifolia (Lodgepole Pine). The lodgepole pine is native to the mountains of central Europe at elevations of occurs from the Black Hills north nearly to the Arctic Circle 4,000 feet · 8,000 feet. It has beautiful dark green color and a and west to the Pacific Ocean. This species is usually a narrow, dense pyramidal form when young. The tree grows; slowly and tall tree and although hardy here, it has no particular horti· is well suited for small yards because it will not grow out of cultural merit. We are also evaluating hybrid pines resulting A scale with the house and other landscape plantings. from crossing the lodgepole pine with the jack pine. W Pinus densiflora (Japanese Red Pine). This interesting pine Pinus halepensis stankewiczii (Stankewis Jerusalem Pine). A from Japan develops a characteristic flat topped form as it single plant of this native of the Crimean peninsula was ob ages, which, when combined with the reddish brown, peeling tained from the U.S. National Arboretum in 1969. This tree bark, gives the tree a desirable ornamental effect. Our trees is now seven feet tall and has a dense, flattened, oval shape at the Arboretum were grown from seeds of trees growing at and good color.

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