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Deciduous Shrubs
Cytisus scoparius
Scotch broom
Fabaceae
Western and central Europe; invasive throughout Pacific Northwest
At a Glance
TypeShrub
HabitUpright
FoliageDeciduous
Height5-10 feet (1.5-3 m)
Width3-6 feet (0.9-1.8 m)
Maturity4 years
Growing Zones
USDA Hardiness Zones
5 - 9Zone 5
Zone 6
Zone 7
Zone 8
Zone 9
These zones indicate the coldest temperatures this plant can typically survive.
Frost Tolerancehardy
Key Features
Attracts Pollinators
Deer Resistant
Drought Tolerant
Maintenancevery low
Overview
Cytisus scoparius (Scotch broom) is a large, densely branched deciduous shrub native to Europe, reaching 5–10 feet (1.5–3 m) tall and 3–6 feet (0.9–1.8 m) wide. It is included in HORT 108 as a plant identification subject because of its prominent presence in Pacific Northwest landscapes — but its planting status must be stated clearly: Scotch broom is a Category A noxious weed in Washington state and a Class B noxious weed in Oregon, where it is one of the most aggressively invasive plants in the region. It has colonized tens of thousands of acres of roadsides, meadows, prairies, grasslands, and open forests throughout western Washington and Oregon, displacing native vegetation and altering soil chemistry through nitrogen fixation. Sale and intentional planting of Scotch broom is prohibited in Washington. Its identification is important for removal and management. The plant is architecturally distinctive: green, 5-angled, ridged stems are photosynthetic year-round, giving a rush-like appearance. Leaves are small, trifoliate, often sparse. In April through May, vivid golden-yellow pea-shaped flowers 0.75 inch (19 mm) smother the green stems in a spectacular display that can be impressive even while acknowledging the plant's ecological harm. Seed pods are hairy, flattened, 1–2 inches (2.5–5 cm) long, audibly popping in summer heat to eject seeds up to 15 feet (4.5 m) — a prolific and persistent seed bank. Highly toxic to horses and livestock. DB note: category is listed as 'Broadleaf Deciduous Trees' — correct category is 'Deciduous Shrubs'.
Native Range
Native to western and central Europe from the British Isles south through Portugal and east to Ukraine. Introduced to the Pacific Northwest in the 19th century and now extensively naturalized as a serious invasive weed throughout the region.Suggested Uses
Included here for plant identification purposes — Scotch broom is one of the most recognizable and ecologically significant invasive plants in the Pacific Northwest and is a required identification subject in HORT 108. Its presence is widespread on roadsides, disturbed open land, prairies, grasslands, and forest edges throughout western WA and OR. Do not plant. For similar garden aesthetics (yellow pea-flowers, upright green stems), consider native alternatives: Genista pilosa (prostrate), Cytisus praecox 'Allgold' (less invasive, though monitor), or Acacia cognata in protected locations. Report new infestations to county noxious weed control boards.How to Identify
Appearance
Size & Dimensions
Height5' - 10'
Width/Spread3' - 6'
Reaches mature size in approximately 4 years
Colors
Flower Colors
yellow
Foliage Colors
green
Fall Foliage Colors
no change
Bloom Information
Bloom Period
~4 weeksJ
F
M
A
M
J
J
A
S
O
N
D
Spring
Detailed Descriptions
Flower Description
vivid golden yellow (pea-shaped)Foliage Description
small, trifoliate, often sparse; green stems photosynthetic year-roundGrowing Conditions
Sun Requirements
Full Sun
Requires 6-12 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
Soil Requirements
pH Range5.5 - 7.0(Neutral)
357912
Soil Types
sandloamrocky
Drainage
well drained
Water & Climate
Water Needs
Very Low
Frost Tolerance
hardy
Time to Maturity
3-5 years
Drought Tolerance
Drought tolerant when established
Care & Maintenance
Care Guide
This entry is provided for identification and management purposes. Scotch broom is a Category A noxious weed in Washington (prohibited from sale and intentional planting) and a Class B noxious weed in Oregon. It is not recommended for planting in Pacific Northwest gardens. For removal: young plants can be pulled by hand or with a weed wrench tool before the taproot establishes; cut established plants at the base (they do not resprout reliably when cut below the first branch junction); systemic herbicides (triclopyr or glyphosate) applied to cut stumps or foliage are effective. The persistent seed bank means multiple years of follow-up are required after initial removal. Do not compost seed pods — seeds remain viable for decades in soil.Pruning
Pruning is not recommended for garden cultivation as this plant should not be grown in PNW landscapes. For management of existing invasive stands: cut stems at the base before seed pods mature (before July) to prevent seed dispersal. Cutting alone stimulates regrowth and must be repeated. Removing seed pods before they pop (June through early July) reduces the seed bank. Professional removal programs typically combine mechanical removal with targeted herbicide application over multiple seasons.Pruning Schedule
J
F
M
A
M
J
J
A
S
O
N
D
late spring