Prostrate juniper (Juniperus horizontalis) is a low-growing, evergreen conifer valued for its spreading, groundcover habit. These hardy plants offer year-round visual interest with their attractive foliage, which can range from green to blue-green and sometimes take on purplish tones in winter. Its adaptable nature and low maintenance needs make it a popular choice for various landscape applications. This plant grows slowly, reaching about 24 inches tall and spreading up to 5 feet wide, and can live for approximately 30 years.
Planting Prostrate Juniper
Planting prostrate juniper begins with careful site selection. These plants thrive in full sun, requiring a minimum of six hours of direct sunlight each day for optimal growth and vibrant color. Well-drained soil is essential for junipers, as they do not tolerate standing water. They adapt to various soil types, including sandy, loamy, or amended clay soils, though dry, sandy soil is often preferred.
Before planting, prepare the soil by loosening it to improve drainage, particularly if it is heavy clay. Dig a planting hole that is two to three times wider than the root ball, but no deeper than the root ball itself. Carefully remove the prostrate juniper from its container, gently teasing out any circling or pot-bound roots to encourage outward growth.
Position the plant in the hole so that the top of the root ball is level with or slightly higher than the surrounding soil surface. Backfill the hole with loose soil, tamping it down to remove air pockets, and then water thoroughly. For groundcover, space multiple junipers according to their mature spread (3 to 10 feet apart) to allow for air circulation and prevent overcrowding.
Care and Maintenance
Soil and Water Needs
Prostrate junipers adapt to various soil conditions, including sandy, loamy, and amended clay, with good drainage. They are notably drought-tolerant once established, making them suitable for low-water landscapes. During the first year, regular watering helps establish a robust root system (two to three times per week for the initial two months, then once a week). Established plants need little supplemental irrigation, but benefit from watering during prolonged dry periods to prevent stress. Avoid overwatering, which can lead to root rot and other moisture-related problems.
Fertilization
Prostrate junipers are low-feeders and often do not require regular fertilization. If growth appears poor or the soil is nutrient-deficient, a balanced, slow-release fertilizer can be applied in early spring. Follow product instructions for application rates and avoid over-fertilization, which can harm the plant. For new plantings, a small amount of balanced fertilizer can be incorporated into the soil around the plant.
Pruning
Prostrate junipers require minimal pruning, naturally maintaining a spreading, ground-hugging form. Pruning is for shaping, controlling size, removing dead or diseased branches, or promoting denser growth. Light shaping or removal of errant growth is best in late winter to early spring, before new growth emerges. Avoid cutting into old wood that lacks foliage, as junipers do not readily produce new growth from leafless stems. Removing dead branches can be done at any time.
Landscape Uses and Benefits
Prostrate juniper is a versatile groundcover plant. Its low-growing, spreading habit makes it an excellent choice for covering large areas, especially on slopes, where it helps with erosion control. Dense foliage stabilizes soil and prevents washouts.
Beyond slopes, prostrate juniper also finds use in rock gardens, providing a textured, evergreen element that complements rocky features. It is suitable for foundation plantings, offering year-round color and a low profile that does not obstruct views. As a low border or edging plant, it defines garden beds or pathways with its consistent evergreen presence. Its low maintenance needs and drought tolerance make it a water-wise landscaping option. Prostrate junipers are resistant to deer and tolerant of salt spray, making them suitable for challenging environments, including coastal regions.
Common Problems and Solutions
Pests and Diseases
While hardy, prostrate junipers can encounter pests and diseases. Common pests include spider mites and juniper scale. Spider mites cause yellowing foliage; confirm their presence by shaking a branch over white paper to see small dots. Horticultural oil or insecticidal soap can manage them.
Juniper scale appears as small, immobile bumps on stems and needles. Good air circulation through proper spacing helps deter these pests. Fungal diseases like Phomopsis blight cause tip dieback, where branch tips turn brown or reddish-brown before graying. Proper spacing promotes air circulation, preventing fungal issues. Removing affected branches by pruning back to healthy growth limits disease spread.
Environmental Stress
Prostrate junipers can brown due to environmental stressors, particularly winter desiccation (winter burn). This occurs when the plant loses more moisture through its foliage than its roots can absorb from frozen or dry soil, especially on windy, sunny winter days. Symptoms appear as browning or reddening of needles, especially on sides facing wind or reflective surfaces like buildings or roads.
Proper fall watering to ensure moist soil before winter helps prevent this. Poor drainage or excessive moisture can lead to root rot, causing plant decline and browning. Selecting a site with well-drained soil and avoiding overwatering are crucial preventive measures for root rot.