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Juniperus

Junipers
Genus:Juniperus
Family:Cupressaceae
Type:Trees, Shrubs
Pollination:Wind

Junipers are coniferous evergreen trees and shrubs, belonging in the cypress family (Cupressaceae). Depending on taxonomic viewpoint, there are between 50-67 species of juniper, widely distributed throughout the northern hemisphere, from the Arctic, south to tropical Africa in the Old World, and to the mountains of Central America in the New World.

There are many species to choose from in the landscape, most of which are tough, and very drought tolerant. Some species are widely used as ground covers, others for hedging, but primarily they are used as evergreen "anchoring" plants in mixed borders and foundation plantings.

Description

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Cones and leaves of Juniperus communis

Junipers vary in size and shape from tall trees, 20–40 m tall, to columnar or low spreading shrubs with long trailing branches. They are evergreen with either needle-like and/or scale-like leaves. They can be either monoecious or dioecious. The female seed cones are very distinctive, with fleshy, fruit-like coalescing scales which fuse together to form a "berry"-like structure, 4–27 mm long, with 1-12 unwinged, hard-shelled seeds. In some species these "berries" are red-brown or orange but in most they are blue; they are often aromatic (for their use as a spice, see juniper berry). The seed maturation time varies between species from 6–18 months after pollination. The male cones yellow and catkin-like, with 6-20 scales; most shed their pollen in early spring, but some species pollinate in the autumn.

Detail of Juniperus chinensis shoots, with juvenile (needle-like) leaves (left), and adult scale leaves and immature male cones (right)

Many junipers (e.g. J. chinensis, J. virginiana) have two types of leaves: seedlings and some twigs of older trees have needle-like leaves 5–25 mm long; and the leaves on mature plants are (mostly) tiny (2–4 mm long), overlapping and scale-like. When juvenile foliage occurs on mature plants, it is most often found on shaded shoots, with adult foliage in full sunlight. Leaves on fast-growing 'whip' shoots are often intermediate between juvenile and adult.

In some species (e.g. J. communis, J. squamata), all the foliage is of the juvenile needle-like type, with no scale leaves. In some of these (e.g. J. communis), the needles are jointed at the base, in others (e.g. J. squamata), the needles merge smoothly with the stem, not jointed.

The needle-leaves of junipers are hard and sharp, making the juvenile foliage very prickly to handle. This can be a valuable identification feature in seedlings, as the otherwise very similar juvenile foliage of cypresses (Cupressus, Chamaecyparis) and other related genera is soft and not prickly.

Growing conditions

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Most species prefer a well-drained soil (though at least one (J. virginiana) will grow in wet soils as well), and full sun to very light shade.

Species

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The number of juniper species is disputed, with two recent studies giving very different totals, Farjon (2001) accepting 52 species, and Adams (2004) accepting 67 species. The junipers are divided into several sections, though (particularly among the scale-leaved species) which species belong to which sections is still far from clear, with research still on-going. The section Juniperus an obvious monophyletic group though.

Juniper needles, magnified. Left, Juniperus communis (Juniperus sect. Juniperus; note needles 'jointed' at base). Right, Juniperus chinensis (Juniperus sect. Sabina; note needles merging smoothly with the stem, not jointed at base).
Juniperus phoenicea on El Hierro, Canary Islands
An Eastern Juniper in October laden with ripe cones.

Uses

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Many of the earliest prehistoric people lived in or near juniper forests which furnished them food, fuel, and wood for shelter or utensils. Many species, such as J. chinensis (Chinese Juniper) from eastern Asia, are extensively used in landscaping and horticulture, and as one of the most popular species for bonsai. It is also a symbol of longevity.

Juniper berries are used in the distillation of gin and Jenever and the brewing of sahti. Juniper was also occasionally used in gruit, a mix of herbs used for flavouring beer prior to the use of hops.

The berries and needles are slightly poisonous and can cause irritation after ingestion or contact with the skin.

Maintenance

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Persistent deadwood, rusts, and phomopsis blights can be troublesome for some species. Pruning is best done in winter or otherwise cool weather, as the sharp leaves and resin can cause an itchy rash if they brush exposed skin.

Propagation

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Usually propagated by cuttings or grafting.

Harvest

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Berries are harvested fresh.

Pests and diseases

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Blights

Rusts

Root Rots

Diebacks

Cankers

Heart Rots

Wood Rots

Lesion Nematodes

Aphids

Scales

Spittlebugs

Mealybugs

Flies

Beetles

Weevils

Caterpillars

Sawflies

Mites

Winter Damage:

  • Ice coatings may suffocate branchlets.
  • Prone to brakeage under wet, heavy snowloads.
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References

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Wikimedia Commons has media related to: Juniperus

  • Adams, R. P. (2004). Junipers of the World: The genus Juniperus. Trafford. ISBN 1-4120-4250-X
  • Farjon, A. (2001). World Checklist and Bibliography of Conifers. Kew. ISBN 1-84246-025-0
  • Farjon, A. (2005). Monograph of Cupressaceae and Sciadopitys. Royal Botanic Gardens, Kew. ISBN 1-84246-068-4
  • Junipers of the world
  • Gymnosperm Database - Juniperus
  • Arboretum de Villardebelle Photos of cones and foliage of selected species
  • Ann Fowler Rhoads and Timothy A. Block (2000). The Plants of Pennsylvania: An Illustrated Manual. Anna Anisko, illustrator. Morris Arboretum, University of Pennsylvania Press. p. 108. {{cite book}}: Cite has empty unknown parameter: |coauthors= (help)
  • Christopher Brickell and Judith D. Zuk (1997). The American Horticultural Society A-Z Encyclopedia of Garden Plants. DK Publishing. pp. 573–576. {{cite book}}: Cite has empty unknown parameter: |coauthors= (help)
  • Staff of the L. H. Bailey Hortorium (1976). Hortus Third: A Concise Dictionary of Plants Cultivated in the United States and Canada. Cornell University Press. pp. 615–617. {{cite book}}: Cite has empty unknown parameter: |coauthors= (help)
  • Pirone, Pascal P. (1978). Diseases & Pests of Ornamental Plants (Fifth Edition ed.). John Wiley & Sons, New York. pp. 324–327. {{cite book}}: |edition= has extra text (help); Cite has empty unknown parameter: |coauthors= (help)
  • Cranshaw, Whitney (2004). Garden Insects of North America: The Ultimate Guide to Backyard Bugs. Princeton University Press. p. 601. {{cite book}}: Cite has empty unknown parameter: |coauthors= (help)
  • Pippa Greenwood, Andrew Halstead, A.R. Chase, Daniel Gilrein (2000). American Horticultural Society Pests & Diseases: The Complete Guide to Preventing, Identifying, and Treating Plant Problems (First Edition ed.). Dorling Kindersley (DK) Publishing, inc. p. 196. {{cite book}}: |edition= has extra text (help); Cite has empty unknown parameter: |coauthors= (help)CS1 maint: multiple names: authors list (link)
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