In short
- Yellow pea-like flowers appear in May and June, densely covering the green stems along their whole length.
- It does not resprout from old wood — prune only the current year's green growth, right after flowering.
- It tolerates transplanting poorly: a deep taproot forces you to plant young container-grown specimens straight into their final position.
- It needs poor, sandy, free-draining soil; nitrogen fertilizing and permanently wet ground harm it.
- All parts are poisonous — they contain sparteine and cytisine; horses are especially sensitive to them.
Botanical data
- Family
- Fabaceae (Fabaceae)
- Height
- 1–2 m
- Width
- 1–2 m
- Habit
- Upright
- Growth rate
- Fast
- Position
- Full sun
- Soil
- Sandy
- pH reaction
- pH 4.5–7
- Moisture
- Dry, Moderate
- Bloom
- May–June
- Hardiness
- USDA 5b–8b
- Propagation
- From seed, From cuttings
Characteristics
A shrub with erect, densely branched stems forming a loose, broom-like mass usually 1–2 m tall and of similar width. The stems themselves are the most distinctive feature: dark green, stiff, markedly angular and longitudinally grooved, performing photosynthesis all year round — which makes the shrub look evergreen even though it is formally deciduous. The leaves are small and quickly drop: the lower ones trifoliate, the upper ones simple, barely a few millimetres long, so in high summer the plant may be almost leafless. The flowers are typically pea-like, golden-yellow, about 2 cm across, borne singly or in pairs in the leaf axils. Pollination works by an explosive mechanism: under the weight of a sufficiently large insect the keel bursts open, and the tensioned stamens and style shoot upward, dusting the visitor with pollen. The flowers produce no nectar — pollen is the only reward for the insect, so broom can be valuable for bees and bumblebees but is not a honey plant. The fruit is a flattened pod several centimetres long, ripening black in July and August and fringed with hairs along the edges. On hot days the pods burst with an audible crack and twist into a spiral, flinging the seeds several metres; a single mature shrub can produce up to a dozen or more thousand seeds a year, and these remain viable in the soil for as long as twenty years. Below ground the plant builds a deep taproot with nodules of nitrogen-fixing bacteria — hence its ability to grow on completely barren sands, and hence too the difficulty with transplanting. It grows fast and reaches its final size in 2–5 years, but is short-lived: after about ten years it begins to thin out from the base and die back whole stems at a time.
Popular cultivars
- ‘Firefly’
- A cultivar with golden-yellow flowers with reddish-brown wings, densely strewn along the stems. It grows to about 1–1.5 m tall and wide and flowers in late spring and early summer. Like the whole species it requires free-draining soil and a position in full sun.
- ‘Golden Sunlight’
- A single-coloured cultivar, with intensely golden-yellow flowers without a red flush — the closest to the colour typical of the wild-growing species, but of a purer and more even shade.
Growing and care
Watering
Once established it needs virtually no watering — excess water is more dangerous to it than drought. Water only in the first season after planting and during exceptionally long rainless spells. Permanently moist ground leads to root rot.
Fertilizing
Thanks to its symbiosis with root-nodule bacteria, broom fixes atmospheric nitrogen and copes on barren soils without feeding. Nitrogen fertilizers are actually harmful: they give soft, over-vigorous shoots, weaker flowering and poorer overwintering.
Planting
Poor, sandy, free-draining soil with an acidic to neutral reaction, in full sun; do not enrich the hole with compost or fertilizer, and do not apply liming either. Plant only young container-grown plants and straight into their final position — the deep taproot means that older specimens and field-dug material usually fail to take.
Pruning
Shorten only the current year's green, leafy growth, even by half to two thirds of its length. Annual pruning keeps a compact habit and delays the shrub going bare from the base.
Companion plants
Good companions
Naturalny towarzysz żarnowca na wrzosowiskach i piaszczyskach — te same wymagania co do ubogiej, kwaśnej i przepuszczalnej gleby oraz pełnego słońca, a kwitnienie obu gatunków przypada na inne pory sezonu.
W naturze żarnowiec rośnie w widnych borach sosnowych i na ich obrzeżach; sosna daje mu ażurowe, nieprzyciemniające stanowisko na suchym piasku.
Zbieżne wymagania świetlne i wodne: pełne słońce, sucha i przepuszczalna gleba oraz brak nawożenia. Uwaga na odczyn — lawenda woli podłoże obojętne do zasadowego, także wapienne, a żarnowiec kwaśne do obojętnego i źle znosi wapń, więc obu roślinom odpowiada wyłącznie wąski wspólny zakres pH około 6,5–7,0.
Bad companions
Hortensja wymaga stale wilgotnej, próchnicznej gleby i regularnego podlewania — czyli dokładnie warunków, w których korzenie żarnowca gniją.
Zasilanie i podlewanie sąsiadów odbija się na żarnowcu: wypuszcza miękkie, wybujałe pędy, słabiej kwitnie i gorzej zimuje, a na mokrym podłożu jest podatny na zgniliznę korzeni.
The evidence level indicates whether the relationship is backed by research, observation, or gardening tradition.
Diseases and pests
The disease develops in overly wet, poorly aerated substrate and attacks the roots and the base of the stem. The roots turn brown, rot and lose their bark, which slips off easily, and a dark, watery rot appears at the stem base. The above-ground part wilts, yellows and dies back despite moist soil – a characteristic symptom, because the damaged roots no longer take up water. Especially at risk are houseplants, succulents and cacti (from overwatering), and in the ground conifers, rhododendrons, ericaceous plants and strawberries on waterlogged sites. The process begins inconspicuously at the root hairs and root tips, which darken and disappear, after which the rot advances towards the framework roots and the root collar. Healthy, pale, active roots waste away — what remains is a dark, rusty-brown or blackish, watery mass, and the outer layer of the root bark slips off like a glove, exposing the discoloured central cylinder. In trees and shrubs, infection of the collar and the base of the trunk (stem-base rot) shows as a dark, often streaking patch, sometimes with oozing, and the bark there is moist and sunken; in conifers and rhododendrons, browning and dieback are seen from the bottom or from the centre of the crown while the soil is still moist. Characteristic is the nested (patchy) occurrence of symptoms in the bed — where water and the pathogen accumulate locally. It is worth distinguishing the two causal oomycete genera: Pythium mainly attacks seedlings and fine roots, causing damping-off and root rot in cool, wet substrate, whereas Phytophthora also attacks older, woody plants, framework roots and the collar, more strongly in warmer, water-saturated soil. Key for diagnosis is the contradiction of the symptoms: the plant wilts and looks 'dry', although the substrate is wet — this results from the destruction of the roots, not from a shortage of water.
AphidsSmall (1–3 mm) soft-bodied insects, green, black or pink, feeding in clusters on young shoots and the underside of leaves. They excrete sticky honeydew. The diagnostic feature that distinguishes aphids from other small sucking insects is the pair of siphunculi (tubular projections) at the rear of the abdomen together with a tail-like cauda; a single colony usually holds wingless forms (parthenogenetic females) alongside winged migrants that fly onto new plants in summer. In summer aphids reproduce parthenogenetically and viviparously over many generations, so the population builds up explosively; in autumn many species produce a sexual generation that lays overwintering eggs on the host, and host-alternating species move between a winter host (often a tree or shrub) and a summer host (a herbaceous plant). Feeding symptoms include curling, crinkling and distortion of young leaves, stunted growth, yellowing, and the shedding of buds and fruitlets. Abundant honeydew coats the leaves, and the sooty mould fungus that develops on it forms a black film which limits photosynthesis; the honeydew is fed on by ants, which in return defend the colony against predators. Aphids are also important vectors of plant viruses (mosaics among them), transmitting them from plant to plant even during a brief probing puncture.
Toxicity
| For whom | Level | Notes |
|---|---|---|
| Humans | Moderate | All parts contain quinolizidine alkaloids (sparteine, cytisine, lupanine), most of them in the seeds. Within a few hours of ingestion nausea, vomiting and diarrhoea appear, and at larger doses weakness, coordination problems and convulsions. |
| Horses | High | Horses are among the animals most sensitive to broom's alkaloids. Do not plant near paddocks, pastures or along fences through which animals reach for the branches. |
| Dogs | Moderate | Eating the shoots or seeds causes drooling, vomiting, diarrhoea and weakness; at a larger dose muscle tremors, coordination problems and an irregular heartbeat may follow. Do not plant in dog runs where they chew branches; if ingestion is suspected, contact a vet. |
History and origin
Broom is a species native to western and central Europe, occurring naturally in Poland mainly in the west of the country — on heaths, in open pine woods and on sandy slopes. The specific epithet points straight to its oldest use: the Latin scoparius means broom-like (from scopa — a broom), and the Polish miotlasty, German Besenginster and English broom all say exactly the same thing. Bundles of the straight, springy stems served for centuries to make brooms and to weave fascines. The plant also has its own episode in European history: a sprig of broom, in Latin planta genista, was the emblem of Geoffrey of Anjou, father of Henry II. From this nickname comes the name of the Plantagenet dynasty, though it was adopted as a family surname only around 1450, when Richard, Duke of York, took it up. In old medicine the herb of broom was used as a diuretic and cardiac remedy. Sparteine, isolated from it, entered twentieth-century pharmacology as an antiarrhythmic drug and a stimulant of uterine contractions, but because of its narrow safety margin it was withdrawn; today broom is not a herbal raw material and should not be used on one's own. A separate chapter is the species' career outside Europe. Introduced to North America, Australia and New Zealand as an ornamental shrub and for stabilizing slopes, it escaped control and is today one of the more dangerous invasive weeds there, officially fought against in California and on the northwestern coast of the USA, among other places. Responsible for this is the same combination of traits that makes it useful on barren sands: nitrogen fixation, explosive seed dispersal and a long-lived seed bank in the soil.
Uses
In the garden, broom is a solution for places where other shrubs fail: dry, sunny slopes, sandy embankments, gravel and heather gardens, and the edges of pine plantings. It is planted singly, in loose groups or as a seasonal splash of colour in naturalistic borders; it combines well with heathers, prostrate junipers and ornamental grasses. The condition for success is refraining from the usual gardener's care. The soil is to stay poor and free-draining, the planting hole is not enriched with compost, and nitrogen fertilizers are not used at all — a fed shrub puts out soft, over-vigorous shoots, flowers more weakly and endures winter worse. Its frost hardiness reaches zone 5, but this is the limit of survival, not of comfortable cultivation: it grows reliably only from zone 6, and in the coldest parts of Poland it freezes back in harsher winters and needs protection or treating as a short-lived plant. It also tolerates limy soils poorly, so it is not planted where the ground has been limed. Once established it needs no watering, and permanently wet ground leads to root rot. Only young container-grown plants should be planted, in spring or early autumn, and straight into their final position: the deep taproot means that transplanted or field-dug specimens usually fail to take. Pruning is carried out every year right after flowering, shortening the current year's growth; you must not cut into the leafless, woody parts, because the shrub will not resprout from them. For the same reason broom is not suited to formal hedges. Because it is short-lived, it is worth treating as a replaceable planting and planning its replacement after roughly ten to fifteen years. Beyond the garden the species is used in land reclamation — to bind drifting sands and to plant slopes and spoil heaps, where the symbiosis with root-nodule bacteria gradually enriches the ground with nitrogen. Because of its alkaloid content it should not be planted on pastures or near horse paddocks.
Trivia
- A broom flower acts like a triggered trap: only an insect of the right mass pushes the keel apart, whereupon the stamens and style shoot out, dusting it with pollen. Insects too light do not set off the mechanism, and the largest bumblebees can simply be too big for such a flower.
- The name of the English Plantagenet dynasty comes from a sprig of broom — in Latin planta genista.
- Garden cultivars of broom with two-coloured flowers, with a reddish-brown flush on the wings, descend from the natural form Cytisus scoparius f. andreanus, found in France in the late nineteenth century. The wild-growing species flowers a uniform yellow.
- Sparteine, broom's main alkaloid, made a career in pharmacogenetics: it was on this compound that the polymorphism of the enzyme CYP2D6 was described, dividing people into fast and slow metabolizers of many drugs.
- A single mature shrub produces up to a dozen or more thousand seeds a year, and their hard coat lets them wait out in the soil for as long as two decades — the main reason it is so hard to eradicate outside Europe.
Frequently asked questions
Why did my broom not resprout after pruning?
Most likely the cut reached into old wood. Broom has no dormant buds in its woody, leafless stems capable of resprouting, so a branch pruned that way simply dries out. Prune only the current year's green, leafy growth, and do so right after flowering. A shrub neglected for several years cannot be rejuvenated — it has to be replaced.
Can broom be transplanted to another spot?
In practice, no. The plant builds a deep taproot which is damaged when dug up and regenerates very poorly — transplanted specimens usually die. That is why you buy only container-grown material, preferably young, and plant it straight into its final position.
Is common broom poisonous?
Yes. All parts, and the seeds most of all, contain quinolizidine alkaloids — above all sparteine and cytisine. Ingestion causes nausea, vomiting and diarrhoea, and at larger doses weakness, coordination problems and convulsions. Horses are especially sensitive, which is why the shrub is not planted near pastures and paddocks; in dogs, eating the shoots or seeds causes drooling, vomiting and weakness.
Why does my broom flower poorly and fall apart?
The most common causes are soil that is too fertile or nitrogen fertilizing, too shady a position, and a lack of annual pruning after flowering. Broom flowers abundantly only in full sun and on poor ground; when fed it puts out long, soft shoots that splay apart under their own weight.
How long does broom live and does it need replacing?
It is a short-lived shrub. It reaches its final size in 2–5 years, after about ten years it begins to thin out from the base and rarely lives beyond fifteen years. Annual pruning after flowering clearly delays this process but does not stop it — it is worth planning the specimen's replacement in advance.
Sources
- RHS — Cytisus scoparius (common broom)Institution / botanical garden
- Missouri Botanical Garden Plant Finder — Cytisus scopariusInstitution / botanical garden
- Colorado State University — Guide to Poisonous Plants: Cytisus scopariusInstitution / botanical garden
- Plants of the World Online (POWO), Royal Botanic Gardens KewDatabase (GBIF, POWO…)
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