Growing Medium for Trilliums
When sowing seeds, sow in either good quality John Innes No 1 compost with equal quantity alpine grit, or sterilized loam, leafmould/pine needle duff, and small alpine grit (equal parts), and cover with alpine grit. Plastic pots 8.5cms square with extra depth I have found most suitable so the seedlings do not require potting on (which they resent) until after the second year of growth. I plunge my pots into a sand plunge but remember they may require two 13 week cold spells at just above freezing point to break their dormancy. I shelter mine with a sheet of glass from the worst of the winter rain but do not allow them to dry out. It is wisest to sow fresh seed as the germination is reduced by 90% if the seed is dried, Pseudotrillium rivale is the exception to this rule. Seed is best kept, for a short period, in the seed capsule, or moist kitchen toweling.
Trillium plants are best transplanted just as their tops are dying back in June or July but never let the roots dry during the transplant or the succeeding summer months. They are woodland plants which root deeply so should be grown in lightly shaded areas and do not like stagnant water or spring drought. They like a deep woodland soil namely one including leafmould and/or pine needles which is free draining. Being mainly woodland plants they cannot support themselves in windy conditions so shelter them from moderate breezes or stronger winds..
Pine needles when collected are best from the lower layers of the forest floor together with a little soil where the microrrhiza proliferate. This should be placed in a black plastic refuse bin liner with a small amount of lime and a small amount of general fertilizer and allowed to compost for a year. Leaves are best shredded, left in an open topped enclosure and will then rot quicker than usually
These composted pine needles/leaf mould should be then mixed with an equal part of sandy grit and an equal part of John Innes No 2 compost or sterilized loam (microwave). This makes a free draining mixture but poor in nutrients and is used when planting outside or for pot culture. Some species require extra loam or clay, others extra sand and others extra lime stone chippings but I will attempt to describe which of these in the following species list, so click at the bottom of the page. All trilliums in the wild appear to have a mulch of dried leaves around them.
When they are in active growth feed with Phostrogen ( N,P,K is 14,10,27 ) or Vitex 111, 2 or 3 times each season.
Plant Pot Culture
Use the above mixture for potting up with additions depending on the species. Trilliums are deep rooted so use extra deep pots often called rose pots or long toms. The pots are best placed into a deep sand plunge bed and not into the garden soil or placed on staging. Do not stand the pots on the soil for any length of time as this will allow worms to enter the base drainage holes. Worms in this mixture convert it into a compacted slimy mix which trilliums can not tolerate.
This method is used for the South Eastern trillium species which require hot dry summers and not much frost. When I first suggested my intention to grow trilliums under glass then the members of Trillium-L forecast doom. They will get too hot and burn off , without a winter chill they will not break their dormancy, they will be diseased etc etc. In 2 years practically all have grown, set seed and multiplied, the only failure is Trillium reliquum.
I constructed a 12 inch high raised bed across the end of the glasshouse (4ft by 10ft ) and filled it with grit, leafmould and soil in equal amounts. Certain areas I enhanced with silver sand, others with clay, others with limestone chippings and in the corner a small rock scree for T.decumbens. I keep this bed on the dry side during the year but once in early spring do flood it. It is fed with liquid Phostrogen every three weeks.
Photograph of this bed at the end of the Trillium photographs page.