Rocky Mountain Bristlecone Pine (Pinus aristata) is one of three closely related species known collectively as bristlecone pines. In 1992 a rocky Mountain Bristlecone Pine estimated to be 2,480 years old was discovered on Black Mountain in Colorado. “Aristata” in the Latin name means “prickliness.”
I. Appearance and Characteristics
Pinus aristata, the Rocky Mountain bristlecone pine (or the Colorado bristlecone pine), is a long-living species of bristlecone pine tree native to the United States. It appears in the Rocky Mountains in Colorado and northern New Mexico, with isolated populations in the San Francisco Peaks in Arizona and the Kaibab National Forest north of the Grand Canyon. It is usually found at very high altitudes, from 7,000–13,000 feet (2,100–4,000 m), in cold, dry subalpine climate conditions, often at the tree line, although it also forms extensive closed-canopy stands at somewhat lower elevations.
Pinus aristata is a medium-size tree, reaching 2–6 m (8–20 ft) high and 3–4.5 m (10–15 ft) wide. Mature trunk diameter is highly variable. The bark is grey-brown, thin and scaly at the base of the trunk. The leaves (‘needles’) are in fascicles of five, stout, 2.5–4 cm (1–1+1⁄2 in) long, deep green to blue-green on the outer face, with stomata confined to a bright white band on the inner surfaces. The cones are ovoid-cylindrical, 5–10 cm (2–4 in) long and 3–4 cm (1–1+1⁄2 in) broad when closed, purple at first, ripening yellow-buff when 16 months old, with numerous thin, fragile scales, each scale with a bristle-like spine 4–8 mm (3⁄16–5⁄16 in) long.
The cones open to 4–6 cm (1+1⁄2–2+1⁄2 in) broad when mature, releasing the seeds immediately after opening. The seeds are 5 mm (3⁄16 in) long, with a 10–20 mm (1⁄2–3⁄4 in) wing; they are mostly dispersed by the wind, but some are also dispersed by Clark’s Nutcrackers, which pluck the seeds out of the opening cones. The nutcrackers use the seeds as a food resource, storing many for later use, and some of these stored seeds are not used and are able to grow into new plants.
It differs most conspicuously from the two other bristlecone pine species in that the needles usually have only one resin canal (or rarely two), and these are commonly interrupted and broken, leading to highly characteristic small white resin flecks appearing on the needles. This character, which looks a bit like ‘dandruff’ on the needles, is diagnostic of Pinus aristata; no other pine shows it (though sometimes, scale insect infestations can look superficially similar).
It is a long-lived tree, though not attaining the longevity of Pinus longaeva. The oldest known tree, which grows high on Black Mountain in Colorado, was found to have a 2,435-year tree ring record (and overall estimated age of 2,480 years, per Craig Brunstein) in 1992. However, trees rarely live over 1,500 years.
This species was previously described as a subspecies of Pinus balfouriana (Pinus balfouriana aristata). Pinus aristata is currently regarded as one of three closely related species known as bristlecone pines and is sometimes named Rocky Mountains bristlecone pine or Colorado bristlecone pine. In addition to its informal and regional names, the trees are referred to as the foxtail pine or hickory pine.
Pinus aristata is by far the most common of the bristlecone pines in cultivation, where it is a very attractive slow-growing small tree suitable for small gardens in cold climates. Even so, it is never as long-lived as in the wild, typically living less than 100 years before it succumbs to root decay in the warmer, moister conditions prevalent in most inhabited places.
II. How to Grow and Care
Sunlight
Rocky Mountain Bristlecone Pine thrives best under full sun conditions, which means it requires at least 6 hours of direct sunlight daily for optimal growth. Although rocky Mountain Bristlecone Pine tolerates partial sun, prolonged periods of reduced light may lead to suboptimal growth and health, as intense light is crucial for its photosynthetic process and overall vigor.
Adapted to its native high-elevation habitats, Rocky Mountain Bristlecone Pine is resilient and capable of enduring intense solar exposure, which contributes to its longevity. In landscaping, Rocky Mountain Bristlecone Pine should be planted in locations where it can receive unobstructed sunlight to mimic its natural environment and ensure its healthy development.
Temperature
The Rocky Mountain Bristlecone Pine is mostly native to the northern hemisphere and can withstand many challenging environmental conditions. Tolerant of temperatures ranging between -60 to 50 ℃, making it suitable for hardiness zones 11 and below, this is a plant that grows best in well-drained, deep and moist soil.
Watering
Adapted to the harsh conditions of its high-altitude habitat, Rocky Mountain Bristlecone Pine is remarkably drought-tolerant, thriving with minimal moisture. Its native environment endures with low humidity and infrequent precipitation, necessitating a hardy resilience in water retention. For domestic care, Rocky Mountain Bristlecone Pine requires watering once every two weeks, aligning with its natural dry climate adaptation. As an evergreen plant commonly grown outdoors, Rocky Mountain Bristlecone Pine’s needle-like leaves play a crucial role in reducing water loss through transpiration, contributing to its impressive drought endurance.
Soil
Rocky Mountain Bristlecone Pine can grow in a variety of different soil types, including bare mineral soil, sandy soil, volcanic ash, calcareous soil, limestone soil, and everything from dusty soil to red soil. Since it is resistant to drought, it will even grow in barren landscapes. However, it grows best in loose, fertile, well-drained, and slightly acidic soil. In the case of too much alkalinity, needles of potted plants will turn yellow and fall, so it is best to use natural mountain soil in pots and containers.
Fertilizing
Fertilization nourishes rocky Mountain Bristlecone Pine by replenishing essential nutrients, aiding robust growth. Utilize balanced nutrition fertilizers annually in late winter to early spring, as rocky Mountain Bristlecone Pine is adapted to low-fertility soils. Moderate quantities are preferable; over-fertilization can cause harm. Adjust frequency and application based on Rocky Mountain Bristlecone Pine’s life stage and season. Younger trees benefit from more frequent feeding. Always water soil post-application for even nutrient distribution. Follow product guidelines closely for effective care of rocky Mountain Bristlecone Pine.
Planting Instructions
Rocky Mountain Bristlecone Pine is best planted in early spring. Ideally, use healthy and vigorous seedlings with soil balls, as this can greatly improve the survival rate. In the case of many lateral roots, the deep main root can be cut. Otherwise, the root system should be protected to avoid damage.
Plant in a high, dry, well-drained, and well-ventilated place, with loose soil. In low-lying places with accumulated water, or places with sticky soil, try building a platform or changing the soil before planting. The planting pit should be treated with a basal fertilizer before planting. Newly planted large seedlings should be supported to prevent them being blown down by the wind. Before planting, excess branches should be pruned off. Protect the plant’s shape from damage as much as possible, as this will help to restore growth at a later stage.
Ideally, plant indoor potted plants in the spring, and repot every two or three years in the late fall or early spring. Repotting too frequently will lead to the death of the plant. If the plant is growing weakly, find out the cause of this and change the flowerpot soil, or replant in a larger pot.
Cut back on water before repotting, so as to keep the soil slightly dry. Remove the soil ball from the pot, keeping it whole, and then prune away any old roots from the bottom and sides. Remove some of the old soil from the middle of the soil ball, replace with new soil, apply a small amount of basal fertilizer, and then cover the plant with new soil. Ensure a suitable pot size – a deep pot will easily accumulate water, leading to root rot.
Pruning
For an indoor potted plant, any dead, diseased or damaged branches should be removed. You can then adjust the tree’s shape by pruning branches, pinching buds, and trimming leaves, giving you a better ornamental effect. Prune the plant before all of its needles fall off, so as to obtain a compact shape, richer lateral and side branches, and a better form overall. Pruning should be done during the dormancy period, so as to prevent excess loss of sap and damage to the plant’s vigor.
For a plant in a garden, dense lateral branches should be pruned so as to improve the survival rate. Remove excess lateral branches during the vigorous growth period based on needs, focusing on encouraging the trunk to grow tall and straight. Cut off any diseased or dead branches right away, so as to prevent the spread of pathogens.
Propagation
Rocky Mountain Bristlecone Pine is a long-lived, slow-growing conifer best propagated through the meticulous sowing of seeds. Success in growing rocky Mountain Bristlecone Pine from seed involves stratification, mimicking natural winter conditions, to break seed dormancy. Once stratified, seeds must be carefully planted in well-draining soil with appropriate moisture. Germination rates tend to vary, requiring patience and attention to ensure seedling establishment. Although the process is gradual, propagating rocky Mountain Bristlecone Pine through seeds can be rewarding, ultimately contributing to the conservation of this resilient species.
Transplanting
For transplanting rocky Mountain Bristlecone Pine, the ideal period spans from late spring to early autumn (S3-S5), when the plant is dormant, reducing shock and supporting recovery. Choose a sunny, well-draining site, and thoroughly water post-transplant. A friendly reminder, good care leads to a stunning rocky Mountain Bristlecone Pine!
III. Uses and Benefits
The wood can be used to collect rosin; bark, needles, roots and so on can be comprehensively made into various chemical products; seeds can be extracted for oil.