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Description

The Douglas iris is one of the most appealing flowering perennials for use in the Western Sycamore Palette. It is a small clumping perennial with strap-like leaves, growing 12-18 in. high and spreading by rhizomes to form clumps 1-2 ft. across. Flowers are most commonly blue-purple, can reach 4 in. across and are showy in early spring. However, many cultivars are available from nurseries on a seasonal basis.

Douglas iris is a vigorous plant that naturally occurs in moist and shaded grassland slopes within the coastal ranges from Oregon to Southern California. It has proven to be highly adaptable to gardens in the Inland Empire particularly if planted in well-drained soils, with moderate amounts of supplemental water throughout summer.

Douglas iris and its cultivars are premium understory plants for borders, around rocks and in light sun and shade conditions. Established plants can tolerate some summer dryness, however, moderate moisture maintains good health and foliage character. Popular cultivars include: I. d. 'Canyon Snow' is a robust and popular selection that has white flowers with yellow markings; I. d. Pacific Coast Hybrid include a variety of flower colors ranging from yellow, rose, burgundy and purple.

Water Needs

The Douglas iris grows well throughout the Inland Empire in partial shade and with normal winter rainfall and moderate amounts of summer water. The chart shown below provides a recommended baseline guide to the monthly irrigation schedule and volume of supplemental water needed to maintain healthy growth throughout the average year. It should be noted there are several winter months marked by an asterisk (*) when rains can provide sufficient moisture and irrigation is not needed. The high and low range of moisture indicates Douglas iris can grow with varying amounts of water; higher amounts of water will result in stronger springtime flowering performance and summer foliage character.

Irrigation Schedule and Graph

Moderate Water Use Plants

Irrigation Schedule 3

  Jan* Feb* Mar* Apr May Jun Jul Aug Sep Oct Nov* Dec*
Runs per Month 0x to 3x 0x to 3x 0x to 3x 2x to 3x 1x to 2x 1x to 2x 1x to 2x 1x to 2x 1x to 2x 2x to 3x 0x to 3x 0x to 3x
Inches per Run 1" 1" 1" 1" 1" 1" 1" 1" 1" 1" 1" 1"
 
Inches per Month 0" to 3" 0" to 3" 0" to 3" 2" to 3" 1" to 2" 1" to 2" 1" to 2" 1" to 2" 1" to 2" 2" to 3" 0" to 3" 0" to 3"

Range of supplemental summer water: 9"-16"
Range of supplemental winter water: 0"-15"

 
0"-3"
0"-3"
0"-3"
2"-3"
1"-2"
1"-2"
1"-2"
1"-2"
1"-2"
2"-3"
0"-3"
0"-3"
  Jan* Feb* Mar* Apr May Jun Jul Aug Sep Oct Nov* Dec*
For more information on how to use this Irrigation Schedule and Graph, click here.

Plant Properties

Plant Type: Perennial, Native
Foliage Character: Evergreen
Habit: Spreading, Robust, Clumping
Growth Rate: Fast
Height: 12 in. - 18 in.
Width: 12 in. - 24 in.
Water Needs: Moderate 3
Foliage Color: Dark green
Flower Color: Purple
Flower Season: Spring
Soil Adaptations: Well-draining soil
Exposure Adaptations: Morning sun, Moderate shade
Function: Rock gardens, Residential spaces, Raised planters, Parks and open space, Mass planting, Grouped, Flowering accent plant, Borders, Banks, Small spaces

Maintenance

If desired, to clean up look, prune out spent stalks in the late fall or at least one month after they finish flowering (6). They can be divided to thin and replant elsewhere in the garden (or give away) by digging up and separating in November, after small roots have grown at the leaf bases, indicating the roots are actively growing. Dividing every few years can also help reinvigorate plants. However, dividing could also stress and potentially kill plants if done at the wrong time, so don't divide all your plants in a single season (2). Give newly divided plants extra water as needed until they have re-established (S).

References

Associations

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