The St. Mary’s Broom Blue Spruce (Picea pungens ‘St. Mary’s Broom’) is a distinctive dwarf conifer prized for its compact size and striking blue coloration. This slow-growing evergreen offers a unique aesthetic, making it a desirable choice for gardeners with limited space or those seeking a vibrant accent in their landscape.
Understanding St. Mary’s Broom Blue Spruce
The St. Mary’s Broom Blue Spruce exhibits a compact, mounding, or bun-shaped growth habit. This dwarf conifer grows very slowly, generally adding only 1 to 6 inches in height per year. At maturity, it usually reaches a height of 1 to 4 feet with a spread of 2 to 5 feet. It does not develop a central leader, naturally maintaining its dense, rounded form.
The needles of St. Mary’s Broom Blue Spruce display a steel blue to silvery blue hue, with new growth in spring emerging brighter. These needles are relatively long and widely angled. This cultivar originated as a “witches’ broom,” a dense, abnormal growth found on a larger blue spruce at the Saint Mary’s Convent in New Jersey. It is also hardy, tolerating cold temperatures down to USDA Zone 2, and shows good tolerance to urban pollution and environmental salt.
Planting Your St. Mary’s Broom Blue Spruce
Proper site selection is important for St. Mary’s Broom Blue Spruce. It thrives in full sun, which helps intensify its blue color. While it can tolerate partial shade, its color may be less pronounced. Well-drained soil is essential, as this plant does not tolerate standing water.
The St. Mary’s Broom Blue Spruce adapts to a range of soil types, including loamy, sandy, or clay, and tolerates acidic, neutral, and mildly alkaline pH. For heavy clay soils, amend the planting area with a soil conditioner to improve drainage. When planting, dig a hole wider than the root ball, ensuring the top of the root ball is at or slightly above ground level. Loosen any feeder roots before placing the plant, then backfill with the amended soil and water deeply to settle the soil.
Ongoing Care and Maintenance
Consistent watering is important for the establishment of your St. Mary’s Broom Blue Spruce, especially during its first year. Newly planted specimens should be watered deeply about once a week until the ground freezes in the fall. While established plants are drought-tolerant, they still benefit from deep watering during prolonged dry periods. Avoid overwatering, as standing water can be detrimental to the plant’s health.
Fertilization for St. Mary’s Broom Blue Spruce is minimal due to its slow growth rate. If fertilizing, a conifer-specific formula, such as a 4-8-8 blend, applied sparingly in the spring, is effective. Alternatively, a 12-12-12 fertilizer can be applied in early spring and again in late fall. This plant naturally maintains its mounding shape, requiring little to no pruning. Any necessary pruning involves trimming back new growth or removing dead or damaged branches, best done in spring after new growth emerges or in late winter.
This conifer is resistant to most pests and diseases. However, like other blue spruces, it can occasionally encounter issues such as Cooley spruce gall (cone-like growths) or white pine weevil (affecting leader growth). Pine needle scale may appear as small white dots on interior needles, leading to needle drop if untreated. Maintaining proper watering and soil conditions helps prevent stress, which can make plants more susceptible to problems. Deer tend to avoid this plant, making it a good choice in areas where deer browse.
Landscape Design Ideas
The compact size and blue foliage of St. Mary’s Broom Blue Spruce make it a versatile plant. Its mounding, ground-hugging habit is well-suited for rock gardens and alpine garden settings. It also serves as an excellent groundcover, creating a dense, steel-blue carpet.
This dwarf conifer is also suitable for small garden spaces, foundation plantings, or as a focal point in mixed borders. Its slow growth means it will not quickly outgrow its space. St. Mary’s Broom Blue Spruce can also be successfully grown in containers, offering year-round color and texture for patios, balconies, or entryways.