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Rocky Juniper is similar to Virgin Juniper, they are often confused, there are many similar varieties. Species interbreed readily at population boundaries in the Missouri basin, forming natural hybrids. Rock juniper grows in the mountains of western North America. Usually the culture lives at an altitude of 500-2700 m above sea level, but along the shores of the Puget Sound bay complex and on Vancouver Island (British Columbia) it is found at elevation zero.
Description of rock juniper
The species Rock Juniper (Juniperus Scopulorum) is a coniferous dioecious tree, often multi-stemmed, from the genus Juniper of the Cypress family.In culture since 1839, often under incorrect names. The first description of rock juniper was given in 1897 by Charles Sprague Sargent.
The crown at a young age is pyramidal; in older plants it becomes unevenly rounded. The shoots are clearly tetrahedral, thanks to which Juniper Rock can be easily distinguished from Virgin. In addition, in the first type they are thicker.
The branches rise at a slight angle, begin to grow from the ground itself, the trunk is not exposed. The bark on young shoots is smooth, red-brown. With age, it begins to peel and flake off.
The needles are most often grayish, but can be dark green; varieties with a gray-blue or silver crown are especially valued in cultivation. The needles on young specimens are hard and sharp; they can remain so at the beginning of the season on the top of the main shoot of adult plants. Then the needles become scaly, with a blunt tip, located opposite, pressed against the shoot. At the same time, it is quite tough.
The length of prickly needles and scaly needles is different. The sharp one is longer - up to 12 mm with a width of 2 mm, the scaly one - 1-3 and 0.5-1 mm, respectively.
Needles of an adult rock juniper in the photo
How fast does rock juniper grow?
Rock juniper is classified as a species with medium growth vigor; its shoots increase by 15-30 cm per season. In culture, the pace slows down somewhat. By the age of 10, the height reaches an average of 2.2 m. An adult tree does not grow so quickly, at the age of 30 it stretches by 4.5, sometimes 6 m. The diameter of the crown of rock juniper can reach 2 m.
Species plants live a very long time in nature. A dead tree was found in New Mexico with 1,888 rings on its trunk.Botanists believe that in that area, individual specimens reached an age of 2 thousand years or more.
All this time, rock juniper continues to grow. Its maximum recorded height is considered to be 13 m, the crown can spread to 6 m. The diameter of the trunk until 30 years of age almost never exceeds 30 cm, in older specimens it ranges from 80 cm to 1 m, and according to some sources, 2 m.
The disadvantages of the species include low resistance to urban conditions and severe rust damage. This makes it impossible to plant rock juniper near fruit trees.
When purchasing a crop, you should pay attention to the following fact. Not only junipers, but also all North American conifers grow much slower in Russia, which is due to different climates. In the USA and Canada, there are no such temperature fluctuations as in the countries of the former Soviet Union; soils and annual precipitation rates differ.
Frost resistance of rock juniper
The species plant overwinters without shelter in zone 3. For the Moscow region, rock juniper is considered a quite suitable crop, as it can withstand temperatures down to -40° C.
Flowering juniper rock
It is a dioecious plant, meaning male and female flowers are produced on separate specimens. The males are 2-4 mm in diameter and open and release pollen in May. The female ones produce fleshy cones that ripen in about 18 months.
Unripe juniper fruits are green and may be tan. Ripe ones are dark blue, covered with a bluish waxy coating, about 6 mm in diameter (up to 9 mm), round in shape. They contain 2 seeds, rarely 1 or 3.
Seeds germinate after prolonged stratification.
Varieties of rock juniper
Interestingly, most varieties are based on populations growing in the Rocky Mountains, stretching from British Columbia in Canada to New Mexico (USA). Of particular interest are cultivars with bluish and steel-gray needles.
Rock juniper Blue Haven
The Blue Heaven variety was created before 1963 by Plumfield Nursery (Fremont, Nebraska), its name translates as Blue Sky. In landscape design, Blue Haven juniper has gained immense popularity due to its bright blue needles that do not change color all year round. Its color is more intense than other varieties.
Forms a uniform, squat pin-shaped crown. It grows quickly, adding more than 20 cm annually. By the age of 10, it stretches 2-2.5 m with a width of about 80 cm. The maximum size is 4-5 m, crown diameter is 1.5 m.
To the characteristics of Blue Haven rock juniper, it should be added that a mature tree bears fruit annually.
Frost resistance - zone 4. Tolerates urban conditions satisfactorily.
Juniper rock Moffat Blue
The Moffat Blue variety has a second name - Moffettii, which is more often used in special sources and on English-language sites. It is highly decorative and has satisfactory resistance to air pollution.
Some domestic nurseries are trying to present the variety as a new product, but it has been grown in America for a long time. The cultivar appeared in 1937 thanks to breeding work carried out by the Plumfield nursery. The seedling from which the variety “began” was found in the Rocky Mountains by L. A. Moffett.
The crown of Moffat Blue is wide, pin-shaped, and in an adult plant it gradually acquires a rounded shape.The branches are dense and numerous. The variety grows at an average speed, adding 20-30 cm per season. By the age of 10, in conditions approximately resembling natural ones, the tree can reach 2.5-3 m.
In Russia, the size of the Moffat Blue rock juniper is more modest - 1.5-2 m, with a crown width of 80 cm. And it will never give an increase of 30 cm, and it is unlikely that it will grow by 20. A mature Moffat Blue tree is believed to be the same size as the species. But observations of culture have not been conducted long enough to say this with complete confidence.
The cones of the Moffat Blue rock juniper are dark blue with a bluish bloom, 4-6 mm in diameter.
The main charm of the variety is given by the color of the needles - green, with a silver or blue tint. Young growth (which can reach 30 cm) is intensely colored.
Frost resistance – zone 4.
Rock juniper Wichita Blue
The variety was created in 1979. Wichita Blue rock juniper is a male clone and reproduces only vegetatively. Forms a tree reaching a maximum height of 6.5 m with a diameter of no more than 2.7 m, with a wide, loose crown of thin tetrahedral shoots raised upward. The bluish-green needles do not change color throughout the year.
Wintering without shelter - up to zone 4 inclusive.
Juniper rock Springbank
An interesting, rather rare variety, Springbank, was created in the second half of the 20th century. He annually adds 15-20 cm, which is considered a low growth rate. By the age of 10, it stretches up to 2 m; a mature plant reaches 4 m with a width of 80 cm.
The crown is cone-shaped, narrow, but due to the hanging tips of the shoots it seems much wider and somewhat unkempt.The upper branches are spaced from the trunk, young shoots are very thin, almost thread-like. Rock juniper Sproingbank looks good in free-style gardens, but is not suitable for formal ones.
The needles are scaly, silver-blue. Requires a sunny position, as in partial shade the color intensity decreases. Frost resistance is the fourth zone. Propagated without loss of varietal characteristics by cuttings.
Juniperus rocky Moonglow
The variety was created from a seedling selected in the 70s of the last century at the Hillside nursery, and is currently one of the most popular. Its name translates as Moonlight.
Juniperus scopulorum Moonglow forms a tree with a pyramidal crown. It belongs to the fast-growing varieties, the annual growth is more than 30 cm. By 10 years it reaches a height of more than 3 m and a crown diameter of about 1 m, at 30 it stretches 6 m with a width of 2.5 m.
The characteristics of Moonglow rock juniper include silver-blue needles and the beautiful outlines of a dense crown. To maintain it, a light shaping haircut may be required.
Frost resistance - zones from 4 to 9.
Juniperus rocky Skyrocket
The name of the rock juniper variety is correctly written as Sky Rocket, in contrast to the Virginian Skyrocket. But this is of little importance. The variety originated in 1949 in the Shuel nursery (Indiana, USA). It quickly became one of the most popular, which it remains so to this day, despite being severely damaged by rust.
Forms a crown in the form of a narrow cone, with a sharp top and tightly pressed branches. This makes the tree seem to be reaching into the sky. In addition to its exceptionally beautiful crown, this rock juniper attracts attention with its blue needles.The needles are sharp when young and become scaly over time. But at the top of the tree and the ends of mature branches, the needles may remain prickly.
Skyrocket is a variety that reaches a height of 3 m by the age of 10 years with a crown diameter of only 60 cm. Perhaps this does not make it the narrowest of all junipers, but among rocky ones it certainly is.
At a young age, the tree holds its shape well and does not need pruning. Over time, especially with irregular care, that is, if years of careful care are replaced by seasons when the plant is “forgotten”, the crown may become less symmetrical. The situation can be easily corrected with a haircut, which the culture tolerates very well.
Without shelter, Skyrocket rock juniper can overwinter in zone 4.
Rock juniper Blue Arrow
The name of the variety Blue Arrow is translated as Blue Arrow. It originated in 1949 in the nursery of Pin Grove (Pennsylvania). Some consider him an improved copy of Skyrocket. Indeed, both varieties are mega-popular, similar to each other, and owners often think for a long time about which one to plant on their plot.
At 10 years old, Blue Erru reaches a height of 2 m with a width of 60 cm. The crown is cone-shaped, the branches are directed upward and spaced from the trunk at an acute angle.
The needles are hard, needle-shaped on young plants, and change to scaly with age. If the rock juniper Skyrocket has a bluish color, then the Blue Arrow shade is more blue.
Great for formal (regular) plantings. Overwinters unprotected in zone 4. Keeps its shape in adulthood better than Skyrocket.
Rocky juniper in landscape design
Rock junipers willingly use landscape designs when decorating the territory.They would recommend planting the crop much more often, but it does not tolerate urban conditions well and is often affected by rust, which can destroy the harvest of fruit trees.
Interesting! Many varieties of rock juniper have analogues among the cultivars Juniperus virginiana, which are much more resistant to disease, but they are not so beautiful.
Use in landscape design depends on the shape of the tree crown. Rock juniper cultivars with their branches close to the trunk, such as Skyrocket or Blue Arrow, are planted in avenues and are often placed in formal gardens. In landscape groups, rock gardens, rock gardens and flower beds they can serve as a vertical accent. With proper garden planning, they are never used as a tapeworm.
But rock junipers with a wide-pinned crown, for example, Moonglow and Wichita Blue, will look good as single focal plants. They are more often planted in romantic and natural gardens. You can form a hedge from them.
When planting, do not forget that the crop does not tolerate gas pollution. Therefore, even in a country house, rock juniper is recommended to be placed inside the territory, and not above the road.
Planting and caring for rock juniper
The culture is drought-resistant and quite healthy, this is clear from the description of rock juniper, and it requires minimal care. The tree can be planted in rarely visited areas or where it is not possible to provide abundant watering. The main thing is that the place is open to the sun and the soil is not too fertile.
Rock juniper should be planted in autumn in regions with warm and temperate climates.It can last all winter if the hole is dug in advance. Planting rock juniper in the spring makes sense only in the north, where the crop must have time to take root before the onset of real cold weather. Summer there is rarely so hot that significant damage is caused to the young plant.
Preparing seedlings and planting area
Rock juniper will respond favorably to rocky inclusions in the soil, but will not tolerate compaction, close groundwater or excessive watering. It must be placed on the terrace, a thick drainage layer must be made, or an embankment must be built. In heavily saturated areas, it will be necessary to carry out measures to drain water or plant another crop.
A sunny place is suitable for rock juniper; in the shade, the needles will become faded, and their beauty will not be able to fully reveal itself. The tree must be protected from wind for the first two years after planting. When the powerful root grows, it will prevent the juniper from being damaged even during a storm.
The soil for planting a tree is made more loose and permeable with the help of turf soil and sand; if necessary, it can be deoxidized with lime. Fertile soils will not benefit rock juniper; a large amount of sand is added to them, and if possible, small stones, gravel or screenings are mixed into the substrate.
The planting hole is dug to such a depth that the root and drainage layer can be placed there. The width should be 1.5-2 times the diameter of the earthen ball.
At least 20 cm of drainage is poured into the hole for planting rock juniper, 2/3 is filled with soil, and water is added until it stops being absorbed. Let it sit for at least 2 weeks.
It is better to buy seedlings from local nurseries. They must be grown in a container or dug up together with a ball of earth, the diameter of which is no less than the projection of the crown, and lined with burlap.
The substrate in the container or earthen ball should be moist, the branches should bend well, and the needles should emit a characteristic odor when rubbed. If planting is not done immediately after purchase, you will have to make sure that the roots and needles do not dry out yourself.
How to plant rock juniper
Planting rock juniper is not difficult. It is carried out in the following sequence:
- Part of the soil is removed from the planting hole.
- A seedling is placed in the center.
- The root collar should be flush with the edge of the hole.
- When planting juniper, the soil must be compacted so that voids do not form.
- The tree is watered and the tree trunk is mulched.
Watering and fertilizing
Rock juniper requires frequent watering only during the first time after planting. When it takes root, the soil is moistened several times a season, and then during a long absence of rain, and in a dry autumn.
Rock juniper reacts favorably to sprinkling of the crown, and this also prevents the appearance of spider mites. In summer, the operation is performed at least once a week, preferably in the early evening.
Root feeding of young plants is carried out twice a season:
- in spring, complex fertilizer with a high nitrogen content;
- at the end of summer, and in the south - in the fall with phosphorus and potassium.
Foliar feeding, which is carried out no more than once every 2 weeks, will be useful. It is recommended to add an ampoule of epin or zircon to the bottle.
Mulching and loosening
Seedlings are loosened in the year of planting to break the crust formed after watering or rain. It blocks access to the roots of moisture and air. Subsequently, the soil is mulched, preferably with pine bark treated against diseases and pests, which can be purchased at garden centers. You can replace it with peat, rotted sawdust or wood chips. Fresh ones, when rotting, emit heat and can damage or even destroy the plant.
How to prune rock juniper correctly
Pruning of rock juniper can be carried out throughout the spring, and in regions with cool and cold climates - until mid-June. First, remove all dry and broken shoots. Particular attention is paid to the middle of the bush.
In the rock juniper, with its dense crown and branches pressed against each other, without access to light, part of the shoots dies every year. If they are not removed, spider mites and other pests will settle there, and spores of fungal diseases will appear and multiply.
Cleaning the crown of the Rocky Juniper is not a vital procedure, as it is for the Canadian one, but it cannot be called simply cosmetic either. Without this operation, the tree will constantly be sick, and it is impossible to remove the pests.
A shaping haircut is not necessary. Most varieties have a beautiful crown, but often some branch “goes out of order” and sticks out. This is what needs to be trimmed so as not to spoil the appearance.
With age, in some pyramidal varieties the crown begins to spread. It is also easy to tidy up with a haircut.You just need to work not with pruning shears, but with special garden shears or an electric hedge trimmer.
Bonsai are often created from rock juniper in the USA. We usually use Virginian for this, but the cultures are so similar that these are rather traditions.
Preparing rock juniper for winter
In winter, rock juniper needs to be covered only in the first year after planting and in frost resistance zones below the fourth. Its crown is wrapped in white spandbond or agrofibre and secured with twine. The soil is mulched with a thick layer of peat.
But even in those warm regions where it may snow in winter, the crown of the rock juniper needs to be tied. Do this carefully and not tightly so that the branches remain intact. If the crown is not secured, the snow can simply break it.
How to propagate rock juniper
Rock juniper is propagated by seeds or cuttings. Particularly rare and valuable varieties can be grafted, but this is a complex operation and beyond the capabilities of amateur gardeners.
Reproduction of rock juniper by seeds does not always lead to success. Some seedlings do not inherit maternal characteristics and are rejected in nurseries. It is difficult for amateurs to figure out at an early stage of plant development whether it corresponds to the variety, especially since small junipers are completely different from adult ones.
In addition, seed propagation requires long-term stratification, and doing it correctly and not spoiling the planting material is not as easy as it might seem.
It is much simpler, more reliable and faster to propagate rock juniper by cuttings. You can take them all season. But for amateurs who do not have special premises, equipment and skills, it is better to carry out the operation in the spring.
The cuttings are taken with a “heel”, the lower part is freed from needles, treated with a stimulant, and planted in sand, perlite or a mixture of peat and sand. Keep in a cool place with high humidity. After 30-45 days, roots appear and the plants are transplanted into a light soil mixture.
Pests and diseases of rock juniper
Overall, rock juniper is a healthy crop. But he may also have problems:
- Rock juniper is more susceptible to rust than other species. It harms the crop itself much less than the fruit trees growing nearby.
- If the air is dry and the crown is not sprinkled, spider mites will definitely appear. It is unlikely to destroy the tree, but it can greatly reduce its decorative value.
- In warm climates with frequent rains, and especially when the crown is sprinkled late in the evening, when the needles do not have time to dry before night, mealybugs may appear. It is very difficult to remove it from juniper.
- Lack of sanitary pruning and crown cleaning can turn the inside of the crown into a breeding ground for pests and diseases.
To prevent troubles, the tree must be regularly inspected and preventative treatments carried out. Insecticides and acaricides against pests, fungicides - to prevent diseases.
Conclusion
Rock juniper is a beautiful, low-maintenance crop. Its main advantage is its attractively shaped crown, silver or blue needles, its disadvantage is its low resistance to air pollution.
