Black Locust - 'Purple Robe'
Robinia pseudoacacia
Black Locust - 'Purple Robe' (Robinia pseudoacacia) is a tree suited to the Colorado Front Range, rated "Not Recommended" on the 2024 Front Range Tree Recommendation List. It matures to about 30–50 ft tall and 20–35 ft wide, fast-growing, needs medium water, and prefers full sun. Black locust suckers prolifically and is on Colorado's watch list as invasive in riparian corridors, better to choose a native alternative.
medium water30–50 ft tall and 20–35 ft wideDeer-resistantToxic to dogs
Photos
- Photo 1: (c) Tom Scavo, some rights reserved (CC BY)
- Photo 2: (c) Tom Scavo, some rights reserved (CC BY)
- Photo 3: (c) Douglas Goldman, some rights reserved (CC BY-SA), uploaded by Douglas Goldman
- Photo 4: (c) Douglas Goldman, some rights reserved (CC BY-SA), uploaded by Douglas Goldman
- Photo 5: (c) Sandy Wolkenberg, some rights reserved (CC BY)
At a glance
Will it survive here?
- Hardiness zones
- USDA 3–8
- Water needs
- medium water
- Sun
- Best in full sun.
- Soil
- clay, loam, sandy
- Soil pH
- 6.0–8.2
- Hail tolerance
- high
- Wind tolerance
- moderate
- Salt tolerance
- high
- Tolerates
- Slopes & erosion control, Hot south- or west-facing walls
How big, what shape?
- Mature size
- 30–50 ft tall and 20–35 ft wide
- Mature form
- Irregular / open
- Spacing / clearance
- ~35 ft of clearance
- Growth rate
- Fast
- Lifespan
- Short-lived
What it looks like, and when
- Bloom time
- late spring
- Bloom color
- white
- Foliage
- Deciduous
Who else benefits
- Pollinator value
- high
- Deer
- Generally deer-resistant
- Colorado native
- No
Site factors to consider
- Critical: Insects & DiseasesPest and disease pressure is the main knock here, so keep it vigorous with steady water and a well-chosen site.
- Watch: SuckersIt throws up shoots from the roots and base, so plan on cutting suckers to keep it from turning into a thicket.
- Watch: Re-seedsIt sets seed freely and plants itself around the yard, so pull the volunteer seedlings unless you want more of them.
Frequently asked questions
- Is Black Locust - 'Purple Robe' good for the Colorado Front Range?
- Yes, Black Locust - 'Purple Robe' is a well-suited tree for Colorado's Front Range, rated "Not Recommended" on the 2024 Front Range Tree Recommendation List.
- Why is Black Locust - 'Purple Robe' not recommended on the Front Range?
- The main catches here: Pest and disease pressure is the main knock here, so keep it vigorous with steady water and a well-chosen site.
- How big does Black Locust - 'Purple Robe' get?
- It matures to about 30–50 ft tall and 20–35 ft wide.
- How much room does Black Locust - 'Purple Robe' need?
- Give Black Locust - 'Purple Robe' about 35 ft of clearance from buildings, fences, and other trees so the mature canopy isn't crowded.
- What shape does Black Locust - 'Purple Robe' grow into?
- Black Locust - 'Purple Robe' typically grows into an irregular, picturesque outline that varies from plant to plant. This is the species' usual mature form, named cultivars (columnar, weeping, or compact selections) can differ, so check the specific cultivar.
- Is Black Locust - 'Purple Robe' hardy on the Front Range?
- Black Locust - 'Purple Robe' is hardy in USDA 3–8. The Colorado Front Range spans roughly USDA 4b–6a, so it is well within range.
- How much water does Black Locust - 'Purple Robe' need?
- It needs medium water once established.
- How fast does Black Locust - 'Purple Robe' grow?
- Black Locust - 'Purple Robe' is a fast-growing tree. Growth rate depends on water and site conditions on the Front Range.
- How long does Black Locust - 'Purple Robe' live?
- Black Locust - 'Purple Robe' is relatively short-lived for a tree, so plan to replace it sooner than a long-lived shade tree. Actual lifespan varies with site, water, and care.
- Is Black Locust - 'Purple Robe' safe for dogs?
- No. Black Locust - 'Purple Robe' is considered toxic to dogs. Keep pets away and check with your vet.
- Is Black Locust - 'Purple Robe' deer-resistant?
- Black Locust - 'Purple Robe' is generally considered deer-resistant, though no plant is deer-proof when browse pressure is high.
