The Regal Elm, Ulmus x ‘Regal’, is a hybrid elm cultivar developed to reintroduce the beauty of elm trees into landscapes. This tree emerged from a University of Wisconsin breeding program, created through a cross between the Smooth Leaf Elm and another elm hybrid. Introduced in 1983, it is known for its enhanced resistance to Dutch Elm Disease. The Regal Elm is a robust and attractive option, combining desirable aesthetic qualities with improved resilience.
Key Characteristics and Disease Resistance
The Regal Elm has an upright, strong central leader, developing an upright-oval to pyramidal form that becomes more ovate with maturity. This tree can reach a mature height of 50 to 60 feet with a spread of 25 to 30 feet, providing substantial shade. Its bark is gray, ridged, and furrowed, sometimes revealing an orange underbark. The leaves are large, dark green, and glossy, with a serrated margin, typically measuring 5 to 10 centimeters in length. Its fall color is minimal or unappreciable.
The Regal Elm’s strong resistance to Dutch Elm Disease (DED) was a primary goal of its development. This resistance, rated good (4 out of 5), makes it a reliable choice where DED has devastated native elm populations. It also resists Verticillium Wilt and black spot. The Regal Elm tolerates leaf scorch, roadside salt, and urban pollution. While generally disease-resistant, some reports indicate susceptibility to elm leaf beetle.
Ideal Growing Conditions
The Regal Elm thrives in full sun, requiring at least six hours of direct sunlight daily for optimal growth. Full sun promotes vigorous and healthy tree development. This hybrid elm adapts to various soil conditions, preferring moist, well-drained fertile soil. It tolerates clay, loam, and sandy soils, and can adapt to both wet and dry locations once established.
The tree is not sensitive to soil pH, performing well in average home landscapes and adapting to alkaline soil. Regal Elm is heat and cold-hardy, successfully growing within USDA plant hardiness zones 4 through 7. Its tolerance to urban pollution, drought, flooding, and road salt makes it suitable for challenging environmental settings.
Planting and Initial Establishment
Proper site selection is crucial, allowing for the tree’s mature size. Ensure at least 50 feet of clearance from buildings and other trees to accommodate its expansive canopy and root system. Planting in spring or late fall is recommended to reduce transplant shock. Container-grown trees can be planted year-round, but avoid peak summer heat or late fall when root establishment is limited.
Dig the planting hole at least 6 inches wider than the root ball and to the same depth, ensuring the root flare sits slightly above ground level. Avoid amending the soil unless it is very poor; a small amount of compost can then be added to the backfill. After placing the tree, backfill the hole halfway, then water thoroughly to settle the soil and eliminate air pockets. Complete backfilling and water again, ensuring the entire planting area is saturated.
Initial watering is crucial for establishment, typically taking about six weeks. Water deeply and regularly during this period, allowing the soil to dry somewhat between waterings. A finger test, inserting a finger about 3 inches into the soil, can help determine moisture levels. Apply a 3 to 4-inch layer of organic mulch around the tree’s base immediately after planting to retain soil moisture and suppress weeds. Keep the mulch several inches away from the trunk to prevent moisture buildup and potential rot.
Ongoing Care and Maintenance
After the first growing season, the Regal Elm’s watering needs decrease. During extended dry periods, especially in summer, deep, infrequent watering encourages a robust and deep root system. Monitor soil moisture levels to prevent both overwatering and drought stress.
Fertilization is not needed in the planting hole; wait until the following spring to apply a balanced, slow-release fertilizer. Apply once or twice a year, ideally in the fall, for nutrient absorption before winter. Spread the fertilizer around the tree’s drip line, rather than directly at the trunk, to promote broader root uptake.
Prune in late winter or early spring before new growth emerges. This timing helps avoid attracting elm bark beetles, which can transmit diseases. Remove any dead, diseased, or crossing branches to maintain structural integrity and promote good air circulation. While resistant to Dutch Elm Disease, inspect regularly for other common elm pests like elm leaf beetles, Japanese beetles, or cankerworms. Monitor for general signs of stress, such as wilting or discolored leaves, for the tree’s long-term health.
Landscape Applications and Considerations
The Regal Elm’s attractive form makes it versatile for various landscape applications. It is commonly used as a street tree, providing a stately presence along boulevards and avenues. Its dense canopy offers significant shade, making it suitable as a large specimen tree in parks, expansive yards, or as a focal point in residential settings.
It tolerates urban conditions, including pollution, compacted soils, and road salt, making it suitable for city environments. Adequate space is necessary to prevent interference with buildings, power lines, or sidewalks. Its strong central leader and upright habit make it a fitting choice for areas where a tall, relatively narrow tree is desired.