This month, Sally Petitt turns her attention to the orchid family – bewitching in both breadth and beauty
Images by Howard Rice
Did you know the orchid family is actually the largest plant family in the world? There are estimated to be 410 flowering plant families worldwide, containing more than 350,000 species, but the orchid family – with more than 760 genera and 28,000 species – is one of the most species-rich (rivalled only by the daisy family).
Orchids are cosmopolitan in their distribution, with species growing in cloud, tropical and temperate forests, grasslands, bogs, semi-arid and arid regions.
They are either epiphytic or terrestrial in habit. Epiphytic species grow on a host plant, and their aerial roots will absorb nutrients and moisture from the air anddebris around it. Some epiphytic orchids have swellings at the base of the stems (pseudobulbs) which store water. On the other hand, terrestrial orchids grow on the ground and their roots absorb nutrients and moisture from the soil.
The flowers of orchids are all similar in being twisted 180° – so most orchid flowers are blooming upside down! Many have two lateral petals and one modified petal, or lip, that attracts pollinators and acts as a landing pad for them.
The diversity of flower shape, colour and size is vast and, given the range of habitats in which they occur, there’s bound to be an orchid to suit most conditions, as well as horticultural experience.
Noteworthy natives
The UK has 56 native orchid species, all of which are terrestrial and summer flowering. Some of these are widespread, such as the common spotted orchid (Dactylorhiza fuchsii), which grows in woodland, verges, marshes and dunes and can occur in great drifts of pink and white in moist, well-drained, alkaline and acidic soils.
Other species are rarer, including the ghost orchid (Epipogium aphyllum), which occurs in dense pine and deciduous woodland on alkaline and slightly acidic soils. It lacks chlorophyll (the green pigment that provides leaf colour in plants and captures light energy from the sun for photosynthesis) and instead derives its nutrients from soil mycorrhizal fungi.
The ghost orchid is known in only a few locations in the UK, and it’s also shy to bloom, producing flowers sporadically. In 2024 it was recorded as having flowered in the UK for the first time since 2009.
Such is the scarcity of many orchid species globally that their habitats are protected to make sure that populations are not lost to habitat destruction, over-collection by enthusiastic growers or to climate change.
Care and cultivation
The Cambridge University Botanic Garden has few native terrestrial orchids, although bee orchids do appear spontaneously and we have an established population of the common spotted orchid (Dactylorhiza fuchsii). Our glasshouses, however, provide a range of environments in which we grow several hundred species and cultivars from a diversity of habitats and climates across the globe.
In cultivation, tender orchids resent standing in water and need free-draining, composted bark. They should only be watered as the compost dries, so weekly is usually sufficient in summer. Epiphytic species will also grow well when mounted onto bark and frequently sprayed with water to maintain a humid atmosphere.
Some genera are familiar, such as the Phalaenopsis (moth orchids) and Cymbidium cultivars, which are readily available and easily grown at home, even by those who consider themselves horticulturally challenged. Both of these species require little input, provided they are given the correct conditions. Moth orchids thrive in bright light, ie a south-facing windowsill, at temperatures above 16°C; while Cymbidiums prefer slightly cooler temperatures (but at least 10°C) and good light (but not direct sunlight), ie a west- or north-facing window.
Other genera are more demanding and challenging in cultivation, and some species that we grow here in the Garden are rare in cultivation and in the wild.
Prize specimens
Several species are of particular note in our collection. Vanilla planifolia (vanilla) is a trailing orchid growing up to 15m in length and bearing fleshy aerial roots that help it cling to host trees. A native of Mexico and north and central South America, it grows in lowland tropical forests, but is now rare in its native range due to habitat destruction and over-exploitation. Today, vanilla is grown more extensively in South America, Java, New Guinea, Malaysia, the Seychelles and Madagascar, although the absence of its natural pollinator (the Melipona bee) means that this species must be pollinated by hand in order to produce vanilla pods.
Angraecum sesquipedale (Darwin’s orchid) is a tropical epiphytic species from Madagascar. A winter-flowering species, it
has a waxy-looking white flower with a nectar spur (an elongated part of the flower containing the sugary liquid) of up to 45cm. Darwin predicted that this flower could only be pollinated by one specific insect with a proboscis (tongue) long enough to reach the nectar at the base of the spur. He was correct in his prediction, but it was only after his death that one species of hawk moth, with a suitably long proboscis, was identified as the pollinator of this plant.
Both of these orchids have a fragrance that is attractive to humans. Bulbophyllum fletcherianum, on the other hand, has a malodorous scent that helps it attract pollinating blow flies and carrion beetles in its native New Guinea. This species has a flower cluster up to 30cm across, consisting of 30 individual hooded, deep purple flowers, and is one of the largest orchids, with leaves reaching up to 1.8m in length. In contrast, the Bulbophyllum subpatulum from New Guinea is tiny, with yellow or yellow-brown flowers up to 5mm in diameter and leaves of only 5cm in length. You need to keep your eyes peeled to spot this one in our tropical houses.
Feeling inspired?
This is only a taster of the orchid family, but with such an array of flower shapes, forms and colours, it’s easy to understand why so many are inspired to specialise in cultivating this fascinating family.
Some are easy to grow, while others may present greater challenges, but if you are inspired to extend your horticultural boundaries, a visit to the glasshouses at the Botanic Garden will provide plenty of orchid inspiration. Meanwhile, organisations such as the Cambridge Orchid Society can offer advice to both novices and experts alike.
Gardening jobs for February
- Divide and replant snowdrops after flowering, ie in the green.
- Finish mulching flower and vegetable beds to deter weeds and retain moisture.
- Cut back late-flowering Clematis, eg viticella group.
- Sow tender tomatoes and chillies (which will require a long growing season) in a heated propagator or on a windowsill.
- Prune Buddleja and ornamental elders (Sambucus) to the base to encourage a compact habit.
- Cut back ornamental grasses.
Sally Petitt is head of horticulture at Cambridge University Botanic Garden. From gardens for the senses to beds of roses, explore more of Sally’s gardening tips.
