They say the best things come in threes and Trillium is no exception. These highly-sought-after rhizomatous plants that command high prices are made up of parts in sets of three.
The flowers have three petals that bloom above three sepals and three large leaflets. They are spring-flowering perennials that multiply into fine clumps and are perfect for shady woodland.
Most hail from North America, but some are found in Japan and China. They can be divided into two groups - the sessile type, meaning petals sit directly on the leaves without a flower stalk, and the pedunculate group, which do have flowers stems and often have reflexed petals.
They are a beautifully-formed plant, producing large leaves that are attractively mottled. The flowers can be white, greenish-yellow, pink or maroon, with their petals long and narrow or broad and showy. They grow from a rhizome, emerging in March or April, then flower, set seed and die down from July to October.
Most Trillium are fully hardy, although growers in colder regions of the UK find the sessile types from the southern areas of the USA need the protection of a greenhouse.
The easiest species to grow in the garden include T. grandiflorum Award of Garden Merit (AGM), the best-known Trillium with its large white flowers; T. sulcatum, bearing lovely dark red flowers; T. cuneatum which has green and purple sessile flowers and T. chloropetalum, with its large dark-red flowers.
Trillium should be planted in dappled shade, in a moist, humus-rich soil that does not dry out when they are in growth but which never gets waterlogged. Generally they prefer a neutral to acid soil, but there are exceptions. T. undulatum needs a very acid soil, T. rivale an alkaline one, and T. chloropetalum, T. cuneatum, T. erectum AGM, T. grandiflorum AGM and T. luteum AGM all occur in soils on the alkaline side of neutral.
They are best planted in late summer with the rhizomes placed just below the surface. Plants should be kept well-watered during dry weather in spring and early summer and given an annual mulch in early spring, preferably with leaf mould.
Trillium are slow to establish but, once they do, form fine clumps and are long lived. If they need to be divided it is best to do it a few weeks after they have flowered. They are slow to raise from seed, making them expensive.
A good spot for Trillium is in the woodland garden, but they can also suit a rock garden or an alpine house. If put into a border they prefer to be among shrubs that provide shelter from the wind. They associate well with other woodland plants, including hellebores, Cyclamen, Hepatica and Tricyrtis.
Slugs are keen on Trillium and the plants can also be attacked by aphids. Some sessile types can be susceptible to Botrytis after a wet winter or spring.
What the Specialists say
- Stella Rankin, owner, Kevock Garden Plants & Designs, Midlothian
"Trillium are wonderful - they add a lot to a woodland garden and look effective at the edge of a shrub border. They have interesting shaped leaves with attractive markings and very pretty flowers, which can be either upright or hanging.
"T. grandiflorum AGM is the most common. The flower is a very clean white. I also like T. rivale AGM, the tiny one, which is charming.
"They should be grown in humus-rich soil, in damp but not too wet conditions, with plenty of leaf mould and good compost. Their ideal aspect is part shade. Slugs are keen on them, so watch out for that."
- Hugh Nunn, owner, Hugh Nunn Nurseryman, Worcestershire
"Trillium are popular because they offer simplicity. They are superbly formed and have great scarcity value.
"The species that really stands out for me is T. albidum, a very fragrant Trillium, and others that look really good are T. grandiflorum AGM, T. grandiflorum f. roseum, T. flexipes and T. sulcatum.
"My growing tips are to plant them in dappled shade if possible, using plenty of organic matter at the root and as a mulch. Keep them moist during the year of planting and watch out for Botrytis."
- Carl Denton, Trillium specialist, Yorkshire
My favourite is T. chloropetalum 'Val Mulvihill'. T. chloropetalum usually has reddy-purple or white petals but when I visited New Zealand's South Island I met a lady who had diversified into growing and hybridizing Trillium in her farmstead woodland. She showed me round her garden and as we turned a corner an intense yellow colouration struck me. It was this chloropetalum.
"I had never seen such a beautiful Trillium before. I have since brought this clone back to England and it has been awarded by the Joint Rock a Preliminary Commendation. I am slowly bulking up this clone but it is not on the market yet.
"The best place to see Trillium is in the woodlands of Canada, where they carpet the floor as bluebells do here. In my garden I have them in association with Fritillaria melaeagris in an orchard. This has an added advantage that when the rabbits come in they prefer to eat the fruits and leaves the Trillium alone.
"Trillium need dappled shade in May and June and shelter from high winds. Slugs and snails are fond of them but fine chippings or dry grit or sand will deter them. Any in pots should be plunged into sand which proves very effective."
SPECIES AND VARIETIES
T. albidum is an early-flowering species with fragrant, upright white flowers and large faintly-marbled green leaves. Height: 20-50cm.
T. chloropetalum is an easy species to grow. It is a sessile type, with large dark-red flowers that sit directly on top of the leaves. Height: 45cm.
- T. chloropetalum var. giganteum AGM (H4) has large upright cherry-red flowers from March onwards above lightly-marbled leaves.
- T. cuneatum is an easy, sessile species. It has red-brown upright flowers above mottled green leaves. Appears above ground in March, and flowers between March and April. Height: up to 30cm.
- T. erectum AGM (H4) has plain green leaves and dark-red flowers on short stems arising from the centre of the leaves. This is one of the quickest species to form a good clump. Height: 30 cm.
- T. flexipes has large, nodding flowers that are usually white, but occasionally maroon, with a white ovary. Height: 50cm.
- T. flexipes 'Harvington Selection' is a robust strain bred by Hugh Nunn. It bears white flowers with light-pink ovaries in April. It has outward-facing flowers. Height: 40cm.
- T. grandiflorum AGM (H4) is one of the easiest Trillium to grow and also one of the best species. It bears large white flowers in April and May above plain green leaves. Height: up to 30cm.
- T. grandiflorum 'Flore Pleno' is a double form that looks like a Gardenia. It is rarely found because it is considered difficult to propagate. Height: 30-40cm
- T. grandiflorum f. roseum is an attractive pale-pink form of grandiflorum with light-green foliage.
- T. kurabayashii is often confused with T. sessile because it has similar broad petalled, upright flowers of deep purple-red and slightly mottled leaves. But it is a taller, more robust species and grows well in the UK. Height: 50cm.
- T. luteum AGM (H4) is a sessile type with bright yellow, upright flowers that smell lightly of lemon and leaves heavily mottled with silver. Can look good from April through to June. Height: 15-30cm.
- T. rivale AGM (H3) is a tiny plant that has silvery-veined, embossed blue-green leaves and an upright-facing flower of white or pale pink, dotted inside with speckles of deeper pink and violet, with bright yellow anthers. A popular form is 'Purple Heart'.
- T. sessile is a small species that bears deep-red long-petalled flowers at the centre of three mottled leaves. Height: 20cm.
- T. sulcatum bears maroon flowers with broad petals between April and May. Similar to T. erectum but has more recurved petals and pointed keel shaped sepals. Forms good clumps. Height: up to 40cm.
- T. vaseyi flowers in May and has the largest flowers. They are maroon, with long, recurved petals, and fragrant. Slow to grow to full size. Eventual height: 40cm.