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Thalictrum polycarpum
Tall Meadow-rue
California, southwestern Oregon, western Nevada
Growing Zones
USDA Hardiness Zones
7 - 9These zones indicate the coldest temperatures this plant can typically survive.
What's my zone? →Frost Tolerancehardy
Overview
Thalictrum polycarpum is a herbaceous perennial reaching 3-7 feet (90-210 cm) tall and 18-30 inches (45-75 cm) wide, forming open upright clumps from a short woody rhizome. Stems are slender and slightly branched in the upper third. Leaves are alternate, twice to thrice ternately compound, with leaflets 0.5-1.5 inches (12-38 mm) long, three-lobed at the tip, blue-green above and paler beneath, on long slender petioles. Plants are dioecious; flowers lack petals and consist of small pale green to purple-tinged sepals that drop early. Male flowers bear pendant clusters of pale yellow stamens 0.2-0.3 inches (5-8 mm) long in branched panicles 8-16 inches (20-40 cm) above the foliage from April through June. Female flowers produce achene clusters that ripen tan and persist into autumn. Bloom period at the colony level lasts 4-6 weeks. Plants spread slowly by short rhizomes and self-seed in moist undisturbed sites. Foliage yellows and dies back in late summer in dry sites, persisting into October on wetter sites. T. polycarpum replaces T. fendleri on the Pacific slope and is sometimes treated as a variety of that species in modern floras.
Native Range
Native to California, southwestern Oregon, and adjacent western Nevada. Grows in moist meadows, riparian woodland, oak-pine transitions, and seasonally wet flats at 1,000-7,500 feet (300-2,300 m) elevation in the Coast Ranges, Sierra Nevada, and Klamath Mountains.Suggested Uses
Used in California native plant gardens, oak woodland understories, rain gardens, and tall mixed borders in zones 7-9. Spaced 18-24 inches (45-60 cm) apart in groupings of 3-5 plants for visible vertical effect. Combines with Iris douglasiana, Heuchera micrantha, and Tellima grandiflora in moist California woodland plantings. Not suited to dry hot interior valleys without long-term irrigation.How to Identify
Appearance
Size & Dimensions
Height3' - 7'
Width/Spread1'6" - 2'6"
Reaches mature size in approximately 3 years
Colors
Bloom Information
April through June across the range; begins early April at lower elevations in the California Coast Ranges and extends into early July in the high Sierra Nevada. Individual male flowers last 5-8 days as the stamens hang from open buds. Total bloom period at the colony level lasts 4-6 weeks. Wind pollination connects male and female plants across 100+ feet (30+ m); isolated females in cultivation rarely produce viable seed.Detailed Descriptions
Flower Description
Pale yellow stamens (male); inconspicuous green sepalsFoliage Description
Blue-green above, paler beneathGrowing Conditions
Sun Requirements
Requires 2-6 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
Establish in moist well-drained loam rich in organic matter at pH 6.0-7.5; plants decline in compacted clay, alkaline desert sites, or extended summer drought. Water deeply during the first 2 growing seasons; mature plants tolerate brief dry spells but go early dormant in extended drought common in California summers, dropping leaves by July in dry years. Partial shade is required below 1,500 feet (450 m) in zones 8-9; full sun in those zones causes leaf scorch and reduced bloom. Few pests trouble the species. Powdery mildew develops on stressed plants in late summer and is cosmetic only. Both male and female plants are needed for seed production; sex is set at germination and is not visible until first bloom. Plants tolerate division poorly; transplants suffer 30-50 percent loss in the first season.Pruning
Cut yellowing stems at the base after foliage has died back in September or October. Earlier cutting interrupts nutrient translocation back to the rhizome. Removal of seed-bearing stems on female plants in late summer limits self-seeding; plants self-seed modestly under cultivated conditions.Pruning Schedule
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