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Clean sweep

26 January 2023
11. scotch broom

Brush away any preconceptions to see our underrated native brooms in a new light. Words & Photos Gillian Vine

Perhaps it’s psychological but the word ‘broom’ tends to make gardeners shudder, especially those who live in Canterbury, Otago or the central North Island, where Scotch broom (Cytisus scoparius) – introduced in the 1830s as hedging – is a pest. Add the fact that white Spanish broom (Cytisus multiflorus) is a weed in some regions and you’ll appreciate why broom gets the thumbs down, even the attractive pink, white, red and bicoloured cultivars of Scotch broom.

Our distantly related Carmichaelia are charming members of the same family (Fabaceae) as the despised thugs. Kōwhai and kākābeak are related, too – just look at the pea-like flowers to spot the family resemblance. Maybe it’s the fear that they’ll prove as thuggish as their imported relatives, but few of the 24 indigenous Carmichaelia species are seen in gardens.

In their favour

Native brooms have plenty to recommend them for gardens, large or small. They range in size from tiny Carmichaelia corrugata (8cm tall), C. monroi (15cm) and C. astonii (20cm) to larger weeping tree broom (C. stevensonii) at 8–10m, coastal tree broom (C. muritai) at 5–6m and scented broom (C. odorata) at 3–8m. The smallest species are ideal for dry rockeries or pot culture. In containers, plant in gravelly soil and don’t overwater.

The pea-like flowers are mauve, purple or pink, often two-toned, except for William’s broom (C. williamsii), which has larger, lemon-yellow blooms with maroon markings. Unlike the others, which flower in spring and summer, William’s broom blooms from July to October, adding useful colour to the garden from midwinter. It also throws out occasional blooms outside its main flowering season.

Carmichaelia leaves are tiny, sometimes even non-existent, as in pink broom (C. carmichaeliae), desert broom (C. petriei), Cromwell broom (C. compacta) and dwarf C. astonii. Where leaves are absent, green stems turn sunshine into energy (through photosynthesis).

Our brooms are hardy and prefer dry soils, although weeping tree broom copes with more moisture, while climbing broom (C. kirkii) and swamp broom (C. arborea) like damp ground.

Some negatives

Nothing is perfect and so it is with Carmichaelia. Because most are found naturally in dry parts of Marlborough, Canterbury and Otago, they may struggle in humid, warmer northern areas. Worth trying in these regions are C. australis and C. williamsii.

A few species sucker, particularly William’s broom and Holloway’s broom (C. hollowayi), but this negative could be a positive if the suckers can be lifted with roots and grown on as, like the majority of Carmichaelia species, they are critically endangered in the wild.

Growing broom

Only about a quarter of the species are readily available from nurseries, and these tend to be the taller shrubs. For the ‘tinies’, the best source is probably a specialist alpine group where members share or sell plants.

NZ brooms are generally easy to grow from fresh seed, although patience is needed as germination can take up to a year. Some can be propagated from semihardwood cuttings but it is not always easy – my three attempts to grow scented broom in this way all failed miserably.

Treat them mean by growing in poor, gravelly soil and hold back on water. Lime can be beneficial, as the natural home of most Carmichaelia is limestone country.

If you like growing from seed and have a friend with a Carmichaelia plant, beg some ripe seed in late summer or autumn and try your luck.

But whether you hit the specialist nurseries or grow your own, try to ignore broom’s bad reputation and help save at least one of our most underrated natives.

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