Documents: Regional Gardens (Canada) - Prairie:

Rock Garden Musings
by Alexej (Sasha) Borkovec
November 10, 1999

*C. pisifera* Snow'. - A rounded , gray-green bush that really looks as if it were covered with snowflakes, especially in the spring and summer. It is a strong grower and its pruning presents the familiar dilemma of smallness versus good appearance. The only solution I found was to shave it rather substantially every second summer. The first year, much of the snow' effect is destroyed but it appears, in full glory, the second year. Size after 13 years: 46 x 52 cm.

*C. pisifera* Squarrosa Minima'.- Also known as Squarrosa Pygmaea' is a spherical bush, silvery with just a hint of green but becoming dark green when wet. If the lower branches are removed, only the top part retains its foliage and the plant resembles a giant mushroom. Frequent shaving and manual nipping off the slender shoots that appear throughout the growing season is essential to maintain dense appearance and to keep the size down. Even so, older specimen tend to become quite large. Size after 30 years : 66 x 61 cm (sphere), 65 x 40 (mushroom-like).

*C. thyoides* Andelyensis',- A columnar, very slow-growing tree that may become too tall in time and must be carefully pruned. It has a single leader that, after some 10 years, will need periodic but very gentle shortening. The sprays are small and dark green giving the plant an airy look. It tolerates some shade. Size after 12 years: 28 x 11 cm.

*CRYPTOMERIA*

A monotypic genus that offers a large number of dwarf cultivars some of which, especially the white-variegated ones, are not hardy in my garden (USDA zone 7a). Most of these plants were developed and named in Japan and their nomenclature is complex and confusing. However, the two popular varieties described here are fairly well defined and their names are generally accepted. Both are fully hardy in my garden. Propagation by fall cuttings is easy but a full year is required for the cuttings to develop an adequate root system.

*C. japonica* Elegans Nana'.- An extremely dense bush or tree with stiff, spiny, very dark green needles that can be shaped by hard pruning to any desirable shape. It is a vigorous grower that needs frequent removal or shortening of branches. New growth starts from young or old wood and if the plant is shaped as a tree the new growth from the trunk must be periodically removed. In the fall, clusters of male flowers develop at the ends of leading shoots. However, in my opinion, these brownish, congested, almost woody flowers are not very attractive and I consider their removal during pruning more beneficial than harmful. By hard pruning and shaping the plant as a tree, the appearance of great age can be created in just few years. In full sun, this cultivar will turn rich, deep bronze in winter, more distinct than any other conifer I know. It does well also in partial shade but the color change is not as intense. Size of a 29-years old tree-shaped specimen: 57 x 70 cm with a 9 cm wide trunk.

*C. japonica* Vilmoriniana'.- Although this very popular and common dwarf is easy to maintain small for the first 5-8 years, its pruning becomes more difficult afterwards and unless done very frequently and with great care, it may disfigure the plant. The reason for it may be the almost perfect spherical or ovoid growth this plant exhibits without any pruning. The bright green, short needles form round brushes that project out of the plant's surface in all directions and slowly increase its overall size. Only a careful shaving performed twice or three times a year will slow down the growth and maintain good appearance. Fortunately, this conifer is very easy to propagate or transplant and either of these two steps may be preferable to pruning old specimen. The winter coloring is bronze but less intense than that of the previous cultivar. Size of a 10 years old plant: 39 x 32 cm.

*JUNIPERUS*

This genus of over 40 species provides several hundred cultivars of low stature in a broadest variety of color and texture. For a rock garden, some are simply indispensable, but all too many seem to resent pruning and are so slow to recover that their suitability for limited spaces is questionable. Many junipers, especially those derived from *J. procumbens* and *J. horizontalis* are dwarf' only in the sense that they are low-growing, but they are vigorous growers that may lengthen their branches 30 cm or more in one year. If there is a need to cover a bare wall or some other unsightly feature, then these plants can do the job better and faster than any other conifer, however, if they are placed in some more valuable site in a small rock garden, severe pruning will have to be done quite often and only varieties that will tolerate it can serve the purpose. I have several of these plants in my rock garden but because I am unsure of their proper cultivar names I have not listed them here.

*J. chinensis* Echiniformis'.- The ideal, truly dwarf conifer for a small rock garden. The very sharp, spiny foliage is deep green and the growth is dense and so slow that no pruning whatever is required for many years. Because propagation by cuttings is very difficult, most commercial plants, including mine, are grafts. The only problem I encountered with this plant were spider mites whose attack is usually discovered only after the infestation is quite heavy and the foliage color changes from shiny to dull green. Repeated application of an appropriate insecticides (read the label!) may be required. Size after 23 years: 24 x 45 cm.

*J. communis* Compressa'.- This is another true dwarf but of columnar habit. Its needles are shorter and thinner than those of the preceding cultivar and its color is silver-green. Welch considers it highly susceptible to spider mites, wind and frost damage. I cannot confirm the mite problem; I never observed an infestation on any of my five specimen. However, frost and wind damage is an almost yearly occurrence, but only on those plants that are fully exposed to sun and wind. The damaged branches, usually on the northern side, turn brown and must be removed in their entirety. A shortened branch will not break new growth. If the operation is done early in the spring, the neighboring healthy branches will close up the left-over empty space quite rapidly, and the beautiful columnar shape will not be affected.. Otherwise, no pruning is necessary for many years. Size of a 23 years old plant: 44 x 14 cm.

*J. communis* Suecica Nana'. - This cultivar is very similar to Compressa' except for its much larger size and a somewhat less silvery color. Contrary to Welch, my plant seems to suffer even more from winter burn than does its smaller relative, and the healing of the pruned areas takes a good part of the growing season. A very careful placing in a protected site may alleviate the problem. Size after 20 years: 92 x 23 cm.

*J. communis* Depressa Aurea'.- An egg-shaped, dense, rather fast- growing bush with prickly, silver-green needles. The spring new growth is bright yellow-green, but the color changes to green rather quickly. It needs shaving and nipping twice a year, in early summer, after the yellow color fades, and in fall. Size after 10 years: 24 x 19 cm.

*MICROBIOTA*

This genus is represented in rock gardens by only one species and a few of its cultivars.

*M. decussata*.- This unusual, flat-topped bush is apparently not a cultivar and thrives even in shade. It is slow-growing and needs only yearly pruning, which is well tolerated. Its intricate, ferny branches can be shortened and shaped to a low bun and the plant remains small for many years. The tiny leaves are dark green and turn brown in winter. It is a curiosity rather than a beauty. Size after 11 years: 17 x 34 cm.

*PICEA*

The spruces are large trees with many dwarf forms that are hardy and can be grown in a rock garden. Nevertheless, if space is a problem, the selection diminishes substantially, because some of the well-known and easily obtainable cultivars grow in all directions and are difficult to shape as true dwarfs. Frequent transplanting, i.e., root pruning, may be a better solution than shaving and shaping, but all plants mentioned here were kept within limits by shaving and shaping. They tolerate partial shade, but in full sun the growth is somewhat slower.

*P. abies* Little Gem'.- This extremely dense and slow-growing cultivar is rather an exception to the earlier mentioned generalizations. When shaped as a tree by removing all branches from the lower half of the central trunk, a perfect dwarf will be obtained in about 10 years. From then on, only occasional shaving and cutting off stray branches will be required. Its appearance will resemble a very ancient tree with a broad crown, very unspruce-like but quite lovely. The needles are small and dark green, almost black in winter. Size after 22 years: 36 x 64 cm with a 7- cm wide trunk.

*P. abies* Pumila".- Because of its primarily lateral growth, this plant cannot be shaped as a tree. Shaping by removing entire branches is possible and even an old specimen can be kept quite small but I was never able to achieve a truly pleasing shape. Still, the upright growing young shoots are light gray-green and very pretty year round and the plant is well worth growing. Size after 22 years: 28 x 33 cm.

*P. abies* Pygmaea'.- A dark green, upright-growing bush that needs severe shaping to remain small. Size after 28 years: 46 x 49 cm.

*P. pungens* Montgomery'.- A strikingly beautiful silver spruce (Colorado spruce) with silvery blue, prickly needles. The new, spring growth is pure silver with a slight hint of green. It can be shaped as a tree with a flat crown by removing all lower branches during the first 5-7 years of growth. After that only yearly summer shaving is needed. However, this plant is a vigorous grower and the only way I managed to keep it small was to have it confined to a heavy, plastic pot that is submerged in the ground. Once a year, the pot is lifted and all protruding roots are cut off. Size after 10 years: 36 x 39 cm.

*PINUS*

The pine offers a large number of dwarf cultivars and even two dwarf species; some are so slow-growing that no pruning of any kind is required for the first ten or more years. The majority, however, grow more or less vigorously in all directions and even with frequent shaving and shaping the plants are difficult to keep from overgrowing their allotted space. Shaving is best done in the spring, after the new growth forms club-like shoots that can be easily shortened without any damage to the plant. For shaping, entire branches have to be removed because new growth doesn't start on partially cut wood.

*P. aristata*.- The bristle-cone pine is an extremely slow-growing tree if planted in sun and in meager, well-drained soil. Reportedly, some even slower-growing cultivars exist, but the species itself, when planted in a rock garden will require no pruning for the first ten years. It will form a creeping bushlet that can be later shaped as required. Size after 13 years: 10 x 22 cm.

*P. mugo*.- The European dwarf mountain pine is a common feature of high elevations in the Pyrenees, Alps, Carpathians, and the Balkan mountains where it occurs in an endless variety of sizes and shapes. The smaller forms are usually considered selections of *P. mugo pumilio* and at least a dozen cultivars have been named. I was unable to trace the origin of my two representatives of this group, but both are rather strong growers and require not only yearly shaving but also an occasional severe shaping to keep them under control. Size after 20-22 years: 52 x 54 cm and 42 x 48 cm.

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