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Propagation

Fruit Collection and Storage: Collecting mature fruit at the optimal time reduces the chances of picking immature (first-year) seed and, therefore, ultimately improves seed quality. Mature fruit is dark blue to nearly black in color with a white waxy coating; whereas, immature fruit is green or light blue and covered with bloom. It is helpful to rub off the waxy coating from fruit samples while picking to assure ripeness and determine the true color of the berries. Maturation requires two years, and both first-year and second-year fruit are often found growing simultaneously on the same plant. With a 2-year maturation, ripe fruit will be found on older growth, as opposed to the current season’s growth. Use a cut test to determine percent fill prior to collecting fruit. Open grown, stunted and stressed wildland trees are often prolific seed producers. Rocky Mountain juniper rates as a good to prolific seed producer over most of its natural range, except in parts of Idaho and Montana where it is only fair. Heavy crops usually occur every 2- to 5-years, but some fruit is produced almost annually.

Avoid collecting from trees with a high percentage of fruit having evidence of insect damage. One potentially serious seed pest is the inconspicuous juniper seed chalcid Eurytoma juniperina. (Figure 8) It leaves small (0.04 in.) exit holes at the base of second-year seed and fruit. Little information is available on the biology or control of this insect. It is assumed that the adult female, a 0.08- to 0.11-inch wasp, oviposits in first-year developing seed. The eggs or larvae probably then over-winter in first-year seed and emerge as adults the following spring and summer. Second-year seed has, therefore, already been damaged by early spring of the second year. Emergence begins in early June in Bridger, Montana. It is not known if multiple generations occur each year. The exit holes are already present at the base of mature fruit at collection time. In some cases, nearly 100 percent of the seed from an individual tree may be lost. No established control protocols are currently available, but might include the timely application of contact or ingestion insecticides. An initial application 5 days before emergence, followed by one or more additional applications at 10-d intervals has been suggested. If control proves inadequate, a systemic insecticide in early- to mid-spring may be applied, although translocation of systemic chemicals to seed tissues is limited. Contact your local university extension specialist or county extension agent for chemical recommendations. Treatment this year is needed to provide protection for next years’ crop.

Picture of the seed pest chalcid Eurytoma juniperina.
Figure 8

Fruit collection is a manual labor operation. Aprons with a large front pocket and either sacks or buckets secured with a strap around the collectors’ neck work well. Wear snug fitting, disposable gloves to prevent sap from getting on your hands. Mature fruit is readily stripped from branches with a rolling and light pulling motion of the fingers, with little or no resultant damage to foliage. Ease of collection appears to be both timing (ripeness) and temperature dependent. By reducing the amount of immature fruit that is collected, cleaning time and product quality are significantly improved. Optimum fruit collection at Bridger, Montana, normally occurs from late October through December, but varies year to year. Some fruit will persist until the following spring or early summer. Monitor fruit condition and persistence often to minimize losses to birds and animals. Expect to collect 4 to 9 pounds of fruit for every 1-pound of clean seed. In the Bridger orchard heavily fruited, 20-year old trees measuring 8-feet tall and wide can produce 25 pounds of fruit and 4.2 pounds of bulk seed. Fruit is best processed as soon as possible after collection, but can be stored for several months under proper environmental conditions. Rocky Mountain juniper fruit stores well in paper sacks in a cooler maintained at 34°F with high humidity (80 to 90 percent). Surface dry the fruit prior to storage to prevent molding. Avoid conditions promote heat build-up and molding such as overly full containers or stacked sacks that reduce air circulation among the fruit.

Fruit Processing and Seed Storage: Rocky Mountain juniper fruit is usually processed in a macerator to remove the skin and pulp from the seed. This species has a tough skin and resinous pulp that make cleaning difficult. (See Plant Materials Technical Note Number 34) Rocky Mountain juniper stores well in sealed containers at 10 to 12 percent moisture content maintained at 20 to 40°F.

Germination: Germination is usually delayed due to embryo dormancy and, possibly, seed coat impermeability. Low and slow germination is not uncommon. Comparing results among growers is difficult because germination is reported in various manners.

One recommendation is warm moist stratification (68 to 86°F) for 45 to 90 d followed by an unspecified period of cold moist chilling (34 to 37°F). At Bridger, we consistently have germination that is 40 to 50 percent of the TZ viability with a similar treatment. We sow fresh seed (<1 year) in a peat-lite mix directly into containers and then warm moist stratify for 120 d at 75 to 80°F days and 60 to 65°F nights, keeping the seeds moist the entire time. Containers are then moved to a cooler for 150 d at 34 to 37°F. When space is limited, we warm moist stratify and cold moist chill the seeds in sand in cloth sacks or hardware cloth (screen) in the greenhouse or cooler.

Other nurseries report success with various cold:warm:cold sequences. Generally, imbibed seeds are sown in moist sand and chilled at 34 to 38°F in a cooler from January or mid-March until early July (150 to 200 d). Then seeds are either sown directly into seedbeds or buried outdoors in wooden screen boxes or

burlap sacks. Seedbeds are covered with aspen fiber mulch, whereas, buried seeds are covered with 1 to 2 in of topsoil. Seeds are irrigated regularly until the ground freezes, usually mid-November. Seeds in beds receive their cold moist chilling naturally through the winter. However, buried seeds are uncovered and maintained in a cooler at 25 to 28°F. The seeds are periodically inspected for early germination until they are sown either in seedbeds (April) or containers (January through March). Optimal germination occurs at 50 to 60°F and is delayed above 60°F. One nursery reports that 80 percent of seed lots handled this way in recent years had a germination of approximately 50 percent of the TZ viability.

Other juniper seeds have been treated with sulfuric acid for 35 to 120 min plus cold moist chilling for 120 d at 40°F, and this may apply to Rocky Mountain juniper. In recent trials with a single seed lot and multiple treatments, we achieved the highest germination (72 percent of the TZ viability) with a 45-min sulfuric acid soak prior to a 116-d warm moist stratification then 150-d cold moist chilling.

Periodic inspection for signs of active germination is needed. High viability seed may be sown directly, given adequate field or greenhouse space. Geographically separated seed sources respond differently to treatment. The use of fresh seed reduces the warm stratification requirements and the interaction between seed source and warm stratification.

Nursery Establishment: Nursery propagation primarily by seed. Spring planting can be substituted for the acid treatment and warm stratification, whereas fall planting can substitute for the pre-chilling period. In nurseries, seedlings are best established on mulched beds under partial shade. Under proper cultivation, seedlings can reach 6 inches in 3 years. Container production, potting, and root balling can increase survival over bareroot planting, especially during dry years. In nurseries, undercutting of third-year seedlings stimulates strong lateral root development. With age, it becomes increasingly difficult to transplant balled and burlapped, and is best moved before 10 years of age.

Bareroot and Container Handling, Storage, Planting, and Maintenance: Bareroot and container nursery stock can be handled, stored, planted and maintained as other coniferous species. Use accepted horticultural and forestry techniques as described in PM Tech Note No. MT-31, Restoration of Woody Plants within Native Range Communities.

Field Establishment: Under natural conditions, Rocky Mountain juniper prefers to germinate on moist sites under partial shade and is unable to establish itself from seed on exposed, drier sites. Moist sites are, however, conducive to frost-heaving, which can take a heavy toll on seedlings. As a result of the lengthy dormancy period and undependable germination, the use of bareroot or container stock for field plantings is recommended. (See Plant Materials Technical Note Number MT-31) Use standard establishment techniques such as removal of sod-forming grasses, weed control, mechanical cultivation, and watering at planting time to increase success. Field establishment by seed is usually poor except under nursery conditions and is, therefore, not recommended. Rocky Mountain juniper is relatively shade-tolerant during the seedling and sapling stages, but becomes increasingly intolerant with age requiring top light for height growth and crown development and is considered a very shade-intolerant species. Locate on the south or outside rows of windbreak and shelterbelt plantings. Protection of recently planted seedlings from sun and wind during periods of hot, dry weather is advised.

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Last Modified: 11/30/2007