Iris × thompsonii
Thompson's Pacific coast iris
Attracts PollinatorsAttracts HummingbirdsDeer ResistantDrought TolerantContainer Friendly
Native to North America
Overview
Iris x thompsonii is an evergreen, rhizomatous perennial iris of natural hybrid origin between I. douglasiana and I. innominata, one of the Pacific Coast irises of western North America. It forms clumps of narrow, grass-like evergreen leaves 8–18 inches (20–45 cm) long, dark green and often tinged red-purple at the base. Branched stems carry flowers in mid to late spring, each 2.5–3.5 inches (6–9 cm) across, in a range that spans cream, yellow, lavender, and purple, often with darker veining on the falls. The flowers combine the slender form of I. innominata with the sturdier stems of I. douglasiana. Plants form slowly spreading clumps from shallow rhizomes and stay evergreen in mild climates. They grow in full sun to part shade on lean, well-drained, acidic soil and tolerate summer drought once established. They establish poorly after root disturbance and are slow to recover from division, which is done in autumn as new roots form. Wet, heavy, or limey soil and summer irrigation in clay cause rhizome rot.
Native Range
The hybrid occurs in the wild in California and Oregon where the ranges of I. douglasiana and I. innominata overlap. It grows in open woodland, on grassy slopes, and in clearings on well-drained acidic soil.Suggested Uses
Planted in borders, rock gardens, and dry, woodland-edge plantings of mild-winter and Mediterranean climates, spaced 12–18 inches (30–45 cm) apart. Used as an evergreen clumping perennial for water-wise gardens.How to Identify
Appearance
Size & Dimensions
Height8" - 1'6"
Width/Spread1' - 1'6"
Bloom Information
Flowers open in mid to late spring, mainly April and May, on branched stems above the foliage. Each stem carries several buds that open in succession over a few weeks. Colours range from cream and yellow to lavender and purple, often veined on the falls.
Detailed Descriptions
Flower Description
Cream, yellow, lavender, to purpleFoliage Description
Dark green, red-purple at baseGrowing Conditions
Sun Requirements
Requires 4-8 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
Grows in full sun to part shade on lean, sharply drained, acidic soil with a pH from 5.5 to 6.8. Tolerates summer drought once established and needs no water through the dry season. Wet, heavy, or alkaline soil and summer irrigation in clay cause rhizome rot. Plants establish poorly after disturbance, so division is done in autumn when new roots form, not in spring or summer. Evergreen foliage holds through mild winters and may brown in hard cold. Hardy through about USDA zones 7–9.Pruning
Old or browned leaves are trimmed away in late winter before new growth starts. Spent flower stems are cut to the base after bloom. No other pruning is needed.Pruning Schedule
J
F
M
A
M
J
J
A
S
O
N
D
winter
Container Growing
✓ Suitable for container growing
Minimum container size: 2 gallons