WSU Clark County Extension

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Red Robe Black Locust

Scientific name: Robinia pseudoacacia 'Purple Robe'

Type:Deciduous tree
Plant Requirements
Zone:4 to 8
Sun:Full sun
Plant Characteristics
Height:40 ft
Width:25 ft
Bloom:Fragrant flowers
Bloom Time:May
Bloom Color:Lavender
Additional Characteristics



Wildlife value

Description Purple Robe Black Locust is best known for the 10 days of flowering in the spring when it sets fragrant wisteria-like violet purple blossom flowers in pendant racemes (to 8” long).

This is a deciduous tree that grows to 30-40’ and 20’ wide at maturity. It forms an oval-upright canopy. The leaves are odd pinately compound with up to 23 lance-shaped to ovate leaflets. In the spring the leaves emerge bronze-red but turn to green during the summer before turning yellow in the fall.

The flowers, which resemble those of the common sweet pea, are 1” wide. Bees find them especially attractive. Flowers can morph to 2”-4” long seed pods which are reddish black and persist on the tree into the winter.

This tree is tolerant of many different sites, including those in the urban area where air quality is maybe less than desirable. With its narrow shape it can be used in parking lot islands or boulevard plantings.

As the seed pods mature and drop to the ground the seeds within can germinate. This might present a problem in a garden situation, but not in a lawn planting.

This cultivar is reported to be susceptible to locust borer. In the Pacific Northwest this is not a problem.
For assistance, contact Dr. Charles Brun (, (360) 397-6060 5701
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