By C. Rae Hozer
When grouping like-items, using an odd rather than an even number is a good design technique. This applies whether arranging cut flowers in a vase or adding landscape plants to your yard. The human mind seeks order and uniformity. When we see an even number, items are envisioned as pairs.
Subconsciously, we expect an even number of items to match and to be balanced side-to-side and top-to-bottom. A single line of plants in a landscape inspires similar thoughts. In our minds, plants of the same variety (whether an even or odd number) installed in a row should be the same height and equally full or the image seems off-kilter. Precise symmetry is rare in nature. Plant two clematis vines on either side of a driveway by a garage (both the same cultivar, purchased the same day at the same place, transplanted under optimum conditions and maintained similarly). In my experience, after a few years one will flourish while the other either languishes or perishes.
Homeowners who choose evergreens for an informal hedge or screen often plant them in a row close enough to grow together as they mature. A gap created when one plant dies makes the wall of plants less functional as a screen. And the lineup will look all askew until a younger, smaller replacement plant catches up to the size of the others. Two rows of plants installed at staggered intervals are better than a single file arrangement. Using a double row containing more than one species can be an even better option.
Bad aesthetics isn’t the only problem when many specimens of just one species are planted together. A monoculture can be a disaster waiting to happen. If one develops an insect infestation or disease infection, their close proximity and genetically similar vulnerability puts all plants of that type at high risk. Leyland Cypress (x Cupressocyparis leylandii) for example, is a species susceptible to the fungal diseases Seiridium canker, Botryosphaeria canker and Cercospora needle blight. Spores which spread the maladies can be carried by winds, splashed by rain or irrigation water or transmitted on blades of pruning equipment to other parts of the tree and to other Leyland Cypress growing nearby.
What was that mystery evergreen pictured in the prior article? A local nurseryman identified the conifer from those emailed photos as some type of cryptomeria. Japanese cedar and (in Japan) ‘Sugi’ are common names for Cryptomeria japonica. The typical species shape is pyramidal. The foliage is smooth to the touch. Leaf color can vary depending upon variety. It could be pale bright green, blue green, dark green or green with gold tones. The needles of some cultivars turn bronze in winter. The variety in the photos was probably a ‘Yoshino.’ In sun or very light shade where the soil is rich, and well-drained but moist; this cultivar grows 2 to 3 feet per year to over 30 feet tall. The tree takes more than ten years to reach maturity.
The nurseryman recommended against adding more full-sized cryptomeria. ‘Black Dragon’ which has dark green foliage and the typical pyramid shape but gets only 8-12 feet tall with a four- or five-foot spread and Cryptomeria japonica ‘Globosa Nana’ a globe-shaped cultivar with bright green leaves that grows 3 to 6 feet tall and as wide are two slow-growing dwarf cryptomeria that could be used with the existing full sized cryptomeria and other medium sized evergreens to create an attractive privacy screen. YouTube has videos which suggest other small screening plants that can be effective. See "In the Garden with Mark Viette: Privacy Plants" at https://www.youtube.com/watch?v=-bj52N9oLyk and "Garden Time: Privacy Plants" at https://www.youtube.com/watch?v=DlNcH36YAT4.
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Plateau Gardening is written by Master Gardeners for gardeners in Tennessee’s Upper Cumberland Region. Contact UT Extension Cumberland County at P.O. Box 483, Crossville, TN 38557 (484-6743) for answers to horticulture questions, free publications and how to become a Master Gardener. Send email comments or yard and garden inquiries to Master Gardener Rae, MGardenerRae@frontiernet.net.