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

Description and botany

Genus Trillium originates from North America and Asia and comprises 45 species. In gardens, it is mainly the North American natives, which are hardier, that are encountered. As with many bulbous genera, species in genus Trillium are diverse but all share the same strange three-petalled flowers.

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

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

Geophyte plants belonging to Trillium possess a rootstock. This underground storage organ allows them to store nutrients and the energy needed to complete a new growth cycle. The rootstock must grow for a time before the plant can flower. Most Trillium species are beauties that take their time, and several years may be required before first flowers appear.

Trillium grandiflorum – botanical illustration

Name Trillium comes 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 tinged with blue or bronze, sometimes maculate, spotted or striate. Leaves are composed of 3 ovate leaflets. This foliage is deciduous and disappears by summer. On average, foliage is visible for about three months a year. If you fear losing sight of your Trillium over summer, mark the location with a label or small stake.

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

Flowers of many species emit a scent. This can be pleasant but may also be very unpleasant: in that case it serves to attract flies that pollinate those species. Plants in genus Trillium are, however, self-fertile and you can therefore witness fruit formation even if only a single Trillium is present in your garden.

Trillium are beauties that take their time and it may be necessary to wait a year before first flowering is seen. Conversely, once established, Trillium are very regular and flower every year. Flower life is long, lasting 2 to 3 weeks.

Fruiting appears in summer as berries, turning red in autumn.

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

Different varieties of Trilliums

Trillium grandiflorum

One of the most well-known and easiest-to-grow Trilles. Pure white flowers turn pink with 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 pure white double flowers.

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

See the product sheet

Trillium erectum

A magnificent Trille showcasing splendid mahogany-red flowers. A plant with a unique and spectacular 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 thrive in rich, fertile, slightly acidic, well-drained and cool soil. Beware of alkaline soils (pH above 7), which Trilliums particularly dislike. If soil is not acidic enough, it is possible to add heather soil at planting.

To encourage development of your plants, place them preferably in a partially shaded position. Sunlight is required during flowering in spring, so it is ideal to plant bulbs under the shade of relatively late-leafing deciduous trees. They will not hinder proper flowering but will provide Trilliums with the cool conditions needed during summer.

Planting in pots 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 have not had time, it is still possible to 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 cold temperatures of early spring.

Tapetum of trilliums in woodland understorey

How to plant Trilliums?

Further reading: Plant rare bulbs

Like many bulbous plants, Trilliums are planted directly into the ground, at the spot where you want them to flower.

• Plant Trilliums at about 10 centimetres deep. Make a large planting hole, wider than bulb diameter, of about 25 centimetres across. Work soil to loosen it

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

• Bury bulbs 10 centimetres deep then firm down.
• Water, even in winter.

Propagating trilliums

Dividing Trillium

Main method to propagate your Trillium is division of stumps. In autumn, when plants are dormant, rootstocks can be divided. After lifting the stump, use a cutting knife (disinfected to avoid spreading diseases) to cut the rootstock into several fragments. Each must have a dormant eye. Then plant each fragment and water to help plants re-establish. Before dividing your Trillium, however, it is important to note that these plants have a very low rate of multiplication and you will therefore need to wait several years, generally five or six, before rootstocks are sufficiently developed to be divided. If you want a massed display, you will need to plant a large number of bulbs from the start.

Sowing Trillium

As with all flowering plants, Trillium can in theory be propagated by sowing. But this method is so complex that we can only advise against 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 hydrophilic, which means they must be kept in a medium with high humidity. 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) then low temperature (for 5 to 8 weeks). With T. grandiflorum, you must even wait one year after germination before the first leaf emerges.

Fruiting of a Trillium / Sowing

Care

Delicate plants, Trilliums need a few simple cares to flower again. Their growing season lasts only four months and biggest risk is forgetting them in a corner of your garden. Flowering the following spring would then be seriously compromised.

The Trillium are above all woodland-floor plants that prefer damp conditions and therefore need 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, daily if bulbs are planted in a pot. In summer, Trillium are not visible but it is still essential to water the spot where they are planted, otherwise the bulb would dry out.

To preserve soil freshness and enrich it at the same time, add forest compost and leaf mulch in autumn and spring.

After flowering, it is best to cut back spent stems to encourage formation of new flowering stems. Cut stems at their tip using 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 natural ways to fight slugs.

Companion planting for trilliums

Trillium present in garden only three to four months a year, so best pair them with plants that will cover their absence for remainder of year. Choose plants attractive for much of year, otherwise bed will quickly turn into collection of weeds.

Trillium are woodland plants and will therefore naturally thrive when paired with plants with similar preferences for light and water.

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

To create a woodland-edge scene, pair Trillium with Hostas, ferns or Heucheras, or with barrenworts (Epimedium).

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

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 Trillium with Magnolias or white dogwoods, or late red-flowering Camellias with white-flowered Trillium?