When does scotch broom bloom?

Scotch Broom Pruning: When And How To Trim A Scotch Broom Plant

Scotch broom (Cystisus scoparius) is an attractive shrub that rises to about 10 feet (3 m.) high with an open, airy growth pattern. Despite the beauty of its bright yellow spring flowers, it can easily look disheveled if not pruned correctly. Pruning a scotch broom shrub must be done conservatively and at the correct season. Read on for information about scotch broom maintenance.

Scotch Broom Pruning

Scotch broom plants may require pruning because of broken or diseased branches, like any other shrubs. More often, however, gardeners decide to prune a scotch broom plant because it has outgrown its allotted space or grown scraggly as it matures.

However, once the plant is fully grown, it may be too late to reshape it by trimming and it can even get out of hand, requiring control. Scotch broom maintenance must begin while the shrub is young.

How to Trim a Scotch Broom

The first rule for pruning a scotch broom shrub involves timing. Although broken or diseased branches can be pruned off at any time of the year, size or shape pruning should only be undertaken in late spring, immediately after flowering.

This rule about pruning a scotch brook shrub in springtime is critical if you want an attractive bush. The scotch broom sets its buds for the following year just after spring flowering. If you snip in autumn or winter, you will dramatically reduce the number of flowers your plant produces the next summer.

What Age to Prune a Scotch Broom Plant?

It is also important to begin trimming when the tree is young. Begin your scotch broom pruning before the tree is mature, and prune back its stems annually. This stimulates growth to prevent that scraggly look.

But when you prune a scotch broom plant, be conservative about how much to trim. Only trim back a little to shape the tree. Never cut off more than one-quarter of the foliage in any one year. If you need to do more scotch broom pruning than this, spread the clipping over a number of years.

Once the tree has grown large, it is too late to repair its scraggly look. According to experts, the mature branches do not retain many green buds. If you cut these branches back severely, you are not likely to get a fuller plant; in fact, if you prune a scotch broom shrub in this manner, you may kill it.

Scotch broom is beautiful, but noxious

“Its invasive habit and economic costs have landed Scotch broom on the State Weed Board’s list of noxious weeds, along with its relatives French, Portuguese and Spanish brooms and gorse,” Hulting said. Scotch broom costs Oregonians an estimated $40 million per year in lost timber revenue and control efforts.

What can you do to control this noxious weed? Prevention is the best method, especially in areas where the ground and other plants have been disturbed by overgrazing or development, Hulting said. Care should be taken not to transport soil that is contaminated with Scotch broom seeds.

“Quickly re-vegetate disturbed sites with fast-growing, competitive native plants to limit Scotch broom spread,” he said. “Native trees (such as Douglas-fir or red alder), shrubs (such as woods rose, currants and snowberry) and native grass mixes can help prevent and slow Scotch broom infestations.”

OSU Extension recommends that you learn to identify Scotch broom and the other non-native broom species in the Pacific Northwest that have the potential to become weedy. The publication, Scotch Broom (PNW 103), which has color photos, identification information and control measures, is available online.

If you find Scotch broom on your property, Hulting recommends:

  • Dig it up, including the crown.
  • Cut it back to the ground each year before it sets seed.
  • Keep an eye out for seedlings each spring and pull them up, roots and all, while they are small.

Since Scotch broom seed lasts for years in the soil, vigilance is necessary to prevent reinvasion by new seedlings.

Several broad-spectrum herbicides, including glyphosate and imazapyr, can be effective in controlling Scotch broom infestations. Avoid spraying when plants are blooming; the flowers can prevent thorough coverage to plant tissues.

“Be careful when using herbicides to minimize drift and injury to non-targeted plants,” Hulting warned. If you are unsure about the use of herbicides, contact your county Extension educator.

Remember to wear protective clothing, read the label and follow instructions, and be cautious. You can be liable for injury or damage from herbicide use.

Scientists continue to investigate biological control possibilities for Scotch broom and other noxious weeds. The Oregon Department of Agriculture has released a species of seed weevil whose larvae feed on the developing Scotch broom seedpods. They can destroy up to about 80 percent of the broom seed inside the pods.

You can pop open a mature, brown Scotch broom seedpod to see if seed weevils are working. Look for tiny white larvae. Do not spray plants with seed weevils.

Scotch Broom (Cytisus scoparius)
KINGDOM Plantae
PHYLUM Anthophyta
CLASS Eudicotyledonae
ORDER Fabales
FAMILY Fabaceae
Scotch Broom can be considered a beautiful addition to the landscape or it can be considered an invasive weed that should never have been brought from the British Isles to the Pacific Northwest. In either case, it is here to stay. This plant grows to about 3 m tall. The densely packed leaves on upright branches are trifoliate (three leaflets) and clover-like. The leaves are lost in winter, and the plant becomes a cluster of dense, hard branches, not nearly so attractive as in spring, when each plant may become covered with yellow pea-like flowers, about 2 cm in length.
The flowers are pollinated mostly by bees, both honeybees and bumblebees. When the bee enters the flower, it opens explosively and dusts the insect with much of the pollen contained. Then the bee is forced to go elsewhere to continue foraging and will eventually visit another plant, thus mixing the genes.
The pollinated flowers are followed by flattened black seed pods about 2-3 cm long. As the pods dry, they burst open with an audible snap and expel their seeds to some distance, a mechanism for avoiding the immediate shade and nutrient and water capture of the parent plant.
Like other legumes (members of the pea family), Scotch Broom fixes atmospheric nitrogen through symbiotic cyanobacteria in nodules along its roots. The nitrogen is converted to nitrates, which are important nutrients for plant growth. Thus the broom is actually improving the soil for itself and other plants. But because it grows so densely, not much else can grow in its presence.
Scotch Broom is a popular ornamental plant and has been planted in freeway medians for years for this reason. It spreads rapidly to disturbed and deforested lands and competes with the seedlings of native or plantation trees. The Puget Sound prairie ecosystem is threatened by the rampant growth of Scotch Broom. Biological control of it has had some success. It is also poisonous to livestock, and its pollen is allergenic to some people.

Scotch Broom

Cytisus scoparius

CONTROL

Family: Fabaceae

Other Common Names: Scot’s Broom, Broom

Origin: British Isles and Central and Southern Europe. Was brought to BC from Scotland in the 1850’s as a garden ornamental by Captain Walter Grant who first planted it in Sooke.

Description: This woody perennial shrub grows to 3 meters in height and can be identified by its yellow pea-like flowers with subsequent flat green seed pods which turn brown at maturity. The bright yellow flowers may have a red marking in middle and stems are leathery green.

Reproduction: Spreads primarily by seed, which can persist in soil for up to 60 years. Over 10,000 seeds can be produced per plant. Seed capsules explode and distribute seeds up to 7 m away from the source plant. Plants typically start producing seeds after three years and
usually live about 17 years, but can survive as many as 25 years.

Legal Status: Invasive Plants Regulation, Forest and Range Practices Act. Listed under Bylaw 2347 in the Comox Valley Regional Districts’ Weed Control Regulation Bylaw.

Impacts
Economic – Invades rangeland reducing crop values. Invades forest land, preventing forest succession. Increased risk of high intensity wildfire as the plant contains high amounts of oils. Obstructs sight lines on roads, resulting in increased maintenance costs for removal.
Ecological – Can produce dense, impenetrable thickets that impact Garry Oak woodlands and other Sensitive Ecosystems. Limits the movement of large wildlife. Possesses photosynthetic stems which enable year-round growth, leading to displacement of native plant species.
Human – Its fragrance can produce an allergic reaction in some people.

Habitat: It is typically found in in dry, disturbed sites including fields, meadows, dry riverbeds and roadsides. Broom can remove nitrogen from the air, “fixing it” in the soil. Nitrogen is a nutrient necessary for plant growth. This adaptation allows broom to establish readily on poor soils. As broom is moderately shade tolerant, it can remain as part of the forest understorey as well as thrive in full sunlight.

Distribution: Typically concentrated on Southern BC islands and southern coastal mainland, it can now be found from mid-coast BC (Queen Charlotte Islands) to the interior, with sightings reported in the Kootenays and Castlegar.

Management Strategy:

Small seedlings (less than a pencil width) can be pulled when the soil is moist, taking care to not disturb the soil.

Larger plants must be cut down at the base or just below ground height, preferably between March to June, when the flowers are out but have not yet gone to seed. It is also important to remove cut plant material from desirable areas as these old plant parts will release toxins into the soil that prevent re-establishment of desirable plants.

Promptly establish competitive shrubbery, including snowberry, salmonberry, thimbleberry, and Oregon grape, as well as red alder trees for shading and
competition for nitrogen, to reduce broom growth.

Additional Information:

Invasive Species Council of BC – TIPS Factsheet

Field Guide to Noxious and Other Selected Weeds of British Columbia

Broombusters.org

King County Weed Alert

King County Best Management Practices

Best Practices for Scotch Broom in Garry Oak and Associated Ecosystems

Invasive.org – Controlling Scotch Broom in the Pacific Northwest

Return to Priority Invasive Plants

Species Cytisus scoparius

Scotch broom (Cytisus scoparius) is an escaped garden ornamental, common west of the Coast-Cascade Mountains in southwest BC, and is concentrated at the southern end of Vancouver Island. It has also been reported on the Queen Charlotte Islands as well as in parts of the Kootenays and North Okanagan–Shuswap areas.
Scotch broom is an evergreen shrub, with bright yellow, pea-like flowers that may have red markings in the middle. Stems are woody and 5-angled, with lower, stalky leaves composed of 3 leaflets and upper, un-stalked leaves. Flat, hairy seedpods are initially green, turning brown or black with maturity. Scotch broom grows to 1-3 metres in height at maturity.
Scotch broom spreads by seed and lateral bud growth, and mature plants can produce up to 3500 pods, each containing 5-12 seeds. As seedpods dry they split and spiral, expelling the contained seeds up to 5 metres. The plant can also spread to new disturbed areas through seed transport by vehicles and machinery. Photosynthetic stems also enable year-round growth.
Due to its affinity for light-dominated, disturbed areas, any disturbance activity, such as road or home construction near infested areas, can enhance spread. Scotch broom invades rangelands, replacing forage plants, and is a serious competitor to conifer seedlings; Douglas fir plantation failures in Oregon and Washington have been credited to infestations of this plant.

Dense thickets can:

  • increase wildfire fuel loads, thereby escalating wildfire intensity;
  • obstruct site lines on roads, resulting in increased maintenance costs for removal;
  • limit movement of large animals; and
  • displace native plant species.

A few native and ornamental alternatives to plant instead of Scotch broom include: Prickly Rose; Shrubby Cinquefoil; Forsythia; Deciduous Yellow Azalea; and Japanese Kerria. Read more about these alternatives in the Grow Me Instead booklet for BC.

Scotch broom identification and control

Scotch broom, a non-regulated Class B noxious weed, is an evergreen shrub that grows 6-10 feet tall and forms dense stands throughout King County, including in pastures, empty lots, and on roadsides. Leaves are small, short-lived, and simple or 3-parted. Branches are erect and angled, with prominent ridges. In March-June, produces bright yellow, pea-like flowers all along stems, followed by black, hard seedpods with hairy edges. Reproduces via seeds that can persist in soil up to 60 years. Prefers full sun, but tolerates shade.

History and impact

This familiar plant, also known as Scot’s Broom, is an invasive flowering shrub that grows commonly throughout the Puget Sound region. Originally introduced from Europe as an ornamental and for erosion control, it is highly aggressive and forms dense, monotypic stands which reduce wildlife habitat and hinder re-vegetation of upland sites and wetland buffers.

Legal status in King County, Washington

Public and private landowners are not generally required to control infestations of Scotch broom that occur on their property in King County, Washington. The one exception is on the WSDOT right-of-way of I-90 east of mile post 34 and on the WSDOT right-of-way of Highway 2 where it dips down into King County before crossing Stevens Pass, in order to reduce Scotch broom’s spread to neighboring Kittitas and Chelan Counties.

Scotch broom is a Class B Noxious Weed in Washington, first listed in 1988. Because control is not generally required in King County, it is on the list of Non-Regulated Noxious Weeds in King County.

This species is also on the Washington quarantine list (known as the prohibited plants list) and it is prohibited to transport, buy, sell, offer for sale, or to distribute plants or plant parts, seeds in packets, blends or “wildflower mixes” of this species, into or within the state of Washington.

For more information on noxious weed regulations and definitions, see Noxious weed lists and laws.

Biology and morphology

Scotch broom is loosely branched with green, slender ribbed branches and small, simple leaves up to half an inch long. It grows from 3 to 10 feet in height. The bright yellow flowers are pea-like, about three-quarters of an inch long. Its seed is borne in dark brown to black hairy, flattened pea-like pods, which when ripe, burst and scatter seeds for yards. Scotch broom grows primarily in open, dry meadows and along roadsides. It is often confused with Spanish broom, which looks similar but is easily distinguished by its rounded, bright green stems, fragrant blossoms, and later flowering time.

Additional information on Scotch broom

What to do if you find this plant in King County, Washington

Because Scotch broom is so widespread, property owners in King County are not required to control it and we are not generally tracking infestations. We can provide advice on how to control Scotch broom, but there is generally no legal requirement to do so.

Lena Scotch Broom flowers

Lena Scotch Broom flowers

(Photo courtesy of NetPS Plant Finder)

Lena Scotch Broom flowers

Lena Scotch Broom flowers

(Photo courtesy of NetPS Plant Finder)

Lena Scotch Broom in bloom

Lena Scotch Broom in bloom

(Photo courtesy of NetPS Plant Finder)

Height: 5 feet

Spread: 5 feet

Sunlight:

Hardiness Zone: 4b

Description:

A high quality flowering shrub for difficult places with dry, infertile soil, excellent for use in massing; bright orange-yellow flowers in spring in a densely branched, twiggy mound; best used in specific landscape situations

Ornamental Features

Lena Scotch Broom is blanketed in stunning red pea-like flowers with orange overtones and yellow centers along the branches from mid to late spring. It has emerald green foliage throughout the season. The grassy leaves do not develop any appreciable fall color. The fruit is not ornamentally significant. The smooth bark and lime green branches add an interesting dimension to the landscape.

Landscape Attributes

Lena Scotch Broom is an open multi-stemmed deciduous shrub with a shapely form and gracefully arching branches. Its relatively fine texture sets it apart from other landscape plants with less refined foliage.

This is a high maintenance shrub that will require regular care and upkeep, and is best pruned in late winter once the threat of extreme cold has passed. It has no significant negative characteristics.

Lena Scotch Broom is recommended for the following landscape applications;

  • Mass Planting
  • Hedges/Screening
  • General Garden Use

Planting & Growing

Lena Scotch Broom will grow to be about 5 feet tall at maturity, with a spread of 5 feet. It tends to fill out right to the ground and therefore doesn’t necessarily require facer plants in front, and is suitable for planting under power lines. It grows at a medium rate, and under ideal conditions can be expected to live for approximately 20 years.

This shrub should only be grown in full sunlight. It prefers dry to average moisture levels with very well-drained soil, and will often die in standing water. It is considered to be drought-tolerant, and thus makes an ideal choice for xeriscaping or the moisture-conserving landscape. It is particular about its soil conditions, with a strong preference for clay, alkaline soils, and is able to handle environmental salt. It is highly tolerant of urban pollution and will even thrive in inner city environments. This particular variety is an interspecific hybrid.

How to Prune a Broom Bush

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Brooms are a group of shrubs in the bean family. Common broom species include Spanish broom (Spartium junceum) and Scotch, or common, broom (Cytisus scoparius). The Scotch broom is larger than the Spanish broom and has arching stems. Both species bloom yellow flowers. Brooms are easy to care for, requiring little water and no fertilizer. Some states, such as California, have listed these brooms as invasive plants. In Oregon, it is illegal to propagate or sell the Scotch broom. Prune the broom bush after it finishes flowering.

Go through the bush removing dead and damaged wood, especially that toward the center of the bush. Cut these canes back to their points of origin.

Remove branches or stems that cross over others and any that protrude from the shape you desire for the bush.

Pinch 1/2 inch from the tips of new growth when it reaches 2 inches in length. This prompts the broom to produce a new branch directly beneath the pinch portion, making the shrub bushier.

Rejuvenate Scotch or Spanish broom by cutting or mowing it to the soil while it is dormant. It will rapidly grow back, producing new, strong stems.

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