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Growing Zones
USDA Hardiness Zones
5 - 7These zones indicate the coldest temperatures this plant can typically survive.
What's my zone? →Frost Tolerancehardy
Overview
Ulmus 'Frontier' is a deciduous hybrid elm reaching 40-50 feet (12-15 m) tall and 25-30 feet (7.5-9 m) wide at maturity, with an upright vase-shaped crown. A controlled cross of U. carpinifolia and U. parvifolia developed at the U.S. National Arboretum and released in 1991 for resistance to Dutch elm disease and elm yellows phytoplasma. Bark gray-brown, smooth on young trees, developing shallow vertical fissures and minor exfoliation on mature trees. Leaves alternate, 2-4 inches (5-10 cm) long, ovate-elliptic with single to shallow doubly serrate margins; emerge medium green and remain dark green through summer, turning burgundy-red to red-purple in fall. Reddish-brown bisexual flowers in tight clusters open before leaf emergence in March or early April. Flat samaras 0.3-0.4 inch (8-10 mm) across mature in May. Growth rate 1-2 feet (30-60 cm) per year on suitable urban sites. Resistant to Dutch elm disease and elm yellows in inoculation trials and to elm leaf beetle defoliation. Tolerates compacted urban soils, road salt, and seasonal drought once established.
Native Range
Ulmus 'Frontier' is a hybrid of cultivated origin and is not found in wild populations. The parent species U. carpinifolia is native to Europe, North Africa, and southwest Asia, while U. parvifolia is native to East Asia. The cultivar was developed at the U.S. National Arboretum in Washington, D.C., and released to the nursery trade in 1991.Suggested Uses
Commonly planted as a street tree in zones 5-7 with 25-30 foot (7.5-9 m) spacing for canopy coverage. Used in residential lawns and small commercial landscapes; red-purple foliage holds on the tree from late October through mid-November in zones 5-7. Tolerates compacted soils, road salt, and seasonal drought; performance is reduced on continuously wet sites.How to Identify
Appearance
Size & Dimensions
Height40' - 50'
Width/Spread25' - 30'
Reaches mature size in approximately 25 years
Bloom Information
Reddish-brown clusters of bisexual flowers open before leaves in March or early April depending on latitude, with peak bloom lasting 5-7 days. Flat green samaras 0.3-0.4 inch (8-10 mm) across develop within 4-5 weeks of pollination and mature to papery tan in late April to May. Wind disperses samaras up to 300 feet (90 m) from the parent tree. Bloom timing shifts 2-3 weeks later in zones 5-6 compared to zones 7-9.Detailed Descriptions
Foliage Description
medium to dark green in summer; turns burgundy-red to red-purple in fallGrowing Conditions
Sun Requirements
Requires 6-12 hours of direct sunlight daily
• Full Sun: 6+ hours of direct sunlight
• Partial Shade: 3-6 hours of direct sunlight
• Full Shade: Less than 3 hours of direct sunlight
Care & Maintenance
Care Guide
Newly planted trees require 10-15 gallons (38-57 L) of water per week during the first growing season, decreasing to bi-weekly watering during the second season. Mature trees tolerate 6-8 weeks of summer drought without significant leaf drop. A 2-3 inch (5-8 cm) layer of organic mulch in a 4-foot (1.2 m) radius around the trunk reduces lawn competition and conserves moisture. Annual fertilization is unnecessary on most soils; chlorosis is uncommon and develops only on highly alkaline sites with low organic matter. Resistant to Dutch elm disease and elm yellows in inoculation trials and to elm leaf beetle defoliation. Twig dieback rarely occurs after late spring frost in zones 5-6 and is followed by complete recovery within one growing season.Pruning
Structural pruning is performed in winter from December through February while the tree is dormant. Removal of co-dominant leaders before the tree reaches 6 inches (15 cm) of trunk diameter prevents future bark inclusions. Cuts up to 3 inches (8 cm) callus over within 2-3 growing seasons. Spring and early summer pruning increases risk of bark beetle attraction in zones 5-7.Pruning Schedule
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