<em>Trillium</em>: planting, cultivation, care and use

Description and botany

Genus Trillium is native to North America and Asia and comprises 45 species. In gardens, species native to North America, being hardier, are most often encountered. As with many genera of bulbous plants, species within genus Trillium are very diverse but all share same striking three-petalled flowers.

In wild state, Trillium develop in woods, forests and other moist, shaded sites.

Formerly placed in Liliaceae, Trillium are now recognised as Melanthiaceae. This little-known family comprises nearly two hundred species across 16 genera. Except for Trilliums, these oddly named plants, such as “false hellebore” (Chamerion luteum) or “four-leaved herb-paris” (Paris quadrifolia), have not made a notable entry into gardens.

Trilliums are geophyte plants that possess a rootstock. This underground storage organ allows them to store nutrients and energy necessary to complete a new cycle. Rootstock needs first to grow before allowing plant to flower. Most Trillium species are beauties that take time and several years may be necessary before first flowers appear.

Trillium grandiflorum – botanical illustration

Name Trillium derives from ternary rhythm of their morphology: flowers with 3 petals and 3 sepals, 3 leaves, 6 stamens and 3 carpels.

Foliage is most often dark green, sometimes with blue or bronze tints, sometimes maculate, spotted or striate. Leaves are composed of 3 ovate leaflets. Foliage is deciduous and disappears by summer. On average, expect to enjoy plant vegetation for around three months per year. If worried about losing Trillium during summer, mark location with a label or small stake.

In April–May, Trillium flowers appear. Each Trillium flower is composed of three petals and three sepals and emerges above foliage. Flowers are most often sessile (attached directly to stem) but sometimes pedicellate. Flower colour varies greatly between species and sometimes within a single species: white in many cases (notably T. grandiflorum) but also red (T. erectum), reddish-brown (T. cuneatum, T. sessile), yellow (T. luteum) or pink (T. rivale, T. undulatum). Trillium cernuum even bears white flowers with brown at centre. Flower size ranges from 2 to 8 cm.

Many species’ flowers emit a scent. Sometimes pleasant but sometimes very unpleasant: in that case scent serves to attract flies that pollinate those species. Plants in genus Trillium are however self-fertile and fruit formation can therefore be observed even if garden hosts only one Trillium.

Trilliums are beauties that take time and one sometimes needs to wait a year before seeing first flowering. Conversely, once established, Trilliums are very regular and flower every year. Flower longevity is very long, from 2 to 3 weeks.

Fruiting appears in summer as berries, reddening in autumn.

A few Trilliums: Trillium sessile / Trillium grandiflorum / Trillium luteum

Different varieties of trilliums

Trillium grandiflorum

One of the best-known and easiest trilliums to grow. Flowers of pure white that blush pink as they age.

• Flowering time May, June
• Height at maturity 25 cm

See the product sheet

Trillium grandiflorum Flore Pleno

Double form of previous variety, this superb variety bears double pure-white flowers.

• Flowering time April, May
• Height at maturity 25 cm

See the product sheet

Trillium erectum

Magnificent trillium bearing splendid mahogany-red flowers. Plant with a striking, unusual effect.

• Flowering time May, June
• Height at maturity 40 cm

See the product sheet

Planting

Where and when to plant Trilliums?

Trilliums are woodland understorey plants that will thrive in a rich, fertile, slightly acidic, well-drained and cool soil. Beware of calcareous soils (pH above 7), which Trilliums particularly dislike. If soil is not acidic enough, you can add heather soil at planting.

To encourage development of your plants, place them preferably in a partially shaded position. Sun will be necessary at flowering time in spring, so it is ideal to plant your bulbs beneath the shade of relatively late-leafing deciduous trees. These will not hinder flowering but will allow Trilliums to benefit from necessary coolness during summer.

Planting in a pot is also possible; choose a relatively large container and remember to keep it in partial shade.

Trilliums need some space to develop; allow about 30 cm² for each bulb.

Trilliums are preferably planted in spring, ideally from February to March. If you haven’t had time, you can still plant bulbs from January to April; planting outside this period would be detrimental to bulb development. Trilliums are particularly hardy, so do not fear exposing them to early spring cold.

Carpet of trilliums in woodland understorey

How to plant Trilliums?

 Read also:  Planting rare bulbs

As with many bulbous plants, Trilliums are planted directly into the ground, in the place where you want them to flower.

• Trilliums are planted at about 10 centimetres deep. Make a large planting hole, wider than the bulb, about 25 centimetres in diameter. Work soil to loosen it

to a depth of about ten centimetres. To allow optimal bulb placement, break up soil clods and remove stones if necessary. If soil needs improvement, add amendments as required. For calcareous soil, add heather soil to lower pH. For poorly draining soil, add a drainage layer made of vermiculite, perlite, pumice or gravel.

• Bury bulbs at 10 centimetres depth then firm soil.
• Water, even in winter.

Propagation of Trilliums

Dividing Trillium

Main way to propagate your Trillium is by dividing stumps. In autumn, when plants are dormant, rootstocks can be divided. After lifting the stump, use a cutting knife (disinfected to avoid spread of disease) to cut the rootstock into several fragments. Each must have a dormant eye. Plant each fragment and water to help plants re-establish. Before dividing your Trillium, however, note that these plants have a very low rate of propagation and you will therefore need to wait several years, generally five or six, before rootstocks are sufficiently developed to be divided. If you want to create a massing effect, it is necessary to plant a large number of bulbs from the outset.

Sowing Trillium

Like all flowering plants, Trillium can in theory be propagated from seed. However, this method is so complex that we cannot recommend it. Seeds, harvested in autumn, will take 1 to 3 years to germinate and a further 4 to 7 years to flower, with a very high mortality rate. Seeds are also hydrophilous, which means they must be kept in a medium with a high humidity level. Radicle and epicotyl (two organs necessary for seedling development) are dormant and require stratification at high temperature (about 30°C for 4 to 6 weeks) followed by low temperature (for 5 to 8 weeks). With T. grandiflorum, you may even have to wait one year after germination before the first leaf emerges.

Fruit set of a Trillium / Sowing

Care

Delicate plants, Trilliums need some simple care to flower again. Their growth lasts only four months and the greatest risk is forgetting them in a corner of your garden. Flowering the following spring would then be seriously compromised.

Trillium are primarily plants of damp woodland and therefore require regular watering, in summer of course but also in spring if weather is dry. Without waterlogging the soil (excess water would cause bulb rot), water as soon as soil begins to dry, every day if your bulbs are planted in a pot. In summer, the Trillium are invisible but it is still essential to water the spot where they are planted, otherwise the bulb would dry out.

To keep soil cool and enrich it at the same time, apply in autumn and spring forest compost and dead leaf mulch.

After flowering, it is best to cut faded stems to encourage formation of new flowering stems. Cut stems at their tip with a pruning shear disinfected beforehand.

Trilliums’ greatest enemies are gastropods, slugs and snails. To protect your plants, you can keep slugs at bay by surrounding plants with ash, eggshells or lava rock. Discover our 7 effective and natural ways to combat slugs.

Companion Plants for Trilliums

Trilliums being present in garden only three to four months a year, it is better to accompany them with plants that will make one forget their absence for rest of year. Choose plants attractive for a large part of year, otherwise bed will quickly turn into collection of weeds.

Trilliums are woodland plants and will therefore naturally do well when paired with plants having same preferences in terms of light and water.

One pairing idea: Helleborus foetidus, Epimedium warleyense, Matteuccia struthiopteris and Trillium grandiflorum

To create a woodland-edge scene, pair Trilliums with Hostas, Ferns or Heucheras, or with Barrenwort (Epimedium).

You can also plant Trilliums in a heather soil bed with other plants that prefer acidic soils, such as Rhododendrons and Azaleas, Japanese Andromedas (Pieris) or Hamamelis. These plants often flower later than Trilliums and will therefore ensure an interesting succession, but take care not to plant bulbs directly at base of evergreen bushes.

Another pairing idea: Trillium erectum, Anemone nemorosa, Corylopsis pauciflora, Narcissus ‘Thalia’, Cyclamen coum pink

To create an attractive display, don’t hesitate to play with contrasts by pairing red Trilliums with Magnolias or white dogwoods, or late red-flowering Camellias with Trilliums with white flowers?