This, and the next few posts, will be a bit random because I am going to feature a few insectivorous plants. The only reason is that at Dublin Botanics at the weekend there were several that looked good. I will start with the cobra lily: Darlingtonia californica. I usually like to post only about things I am growing or have grown and I have not tried this one but I have seen it in the wild many years ago when I made a trip to the Darlingtonia State Natural Site in Oregon.
Darlingtonia is a monotypic genus (meaning there is only one species in the genus) and is found only in Oregon and northern California, in damp, nutrient-poor soils. It is closely related to Sarracenia, the pitcher plants, and these too are American (in the continental meaning) but these are found in the east, south and north of the USA, and Canada. Darlingtonia differs in its flower shape and also in the shape of the leaves or ‘traps’ which are much more elaborate with their two ‘fangs’ and covered hood that give them the ‘cobra’ look.
Like the sarracenias and most insectivorous plants they are able to grow in nutrient-poor soils because they are able to supplement their diet by catching small insects that then fall into the hollow leaves and are digested. Unlike sarracenias, that have incomplete ‘lids’ on their traps and fill with rain water, darlingtonias regulate the water level in their traps by secreting fluid. Insects are lured into the traps by scent and the light that shines through the ‘windows’ in the hood. They then slip into the digestive fluid below, drown and are digested and the plant absorbs the nitrate that is lacking in the soils where they grow. Although a rare plant it is locally abundant and in the state park where I saw it there were hundreds if not thousands of plants. Unfortunately I don’t have access to the images here. It always seems a bit much for a plant that eats insects to then expect other insects to pollinate the flowers but the drooping flowers with liver-coloured petals are insect-pollinated although, as far as I know, the pollinator is unknown. It is speculated that beetles are responsible because of the colour of the blooms and the fact that the blooms produce no nectar and are pretty robust. Beetles are clumsy insects and damage smaller blooms and as they feed on the stamens they inadvertently pollinate the flowers.
In recent years insectivorous plants have become relatively common in garden centres but you won’t find darlingtonias because they are very tricky to grow. This is because they only grow where water temperatures, in their boggy habitats, are low. Most insectivorous plants need a low-nutrient, moisture-retaining but coarse compost and a mix of peat and grit, sphagnum moss, fine potting bark or perlite is needed. Sarracenias are easy to keep happy if the pot is stood in water but temperatures above 25 cause the roots of darlingtonias to die – fast. So constant watering with water as cold as you can supply is best and these are not good for the windowsill. However, they can take warmer air temperatures in summer providing the roots are kept cool and that nights are cool too. In winter they can take a few degrees of frost without any damage but, like any potted plant, the roots are more vulnerable to freezing when in a pot than when in the soil, so do not let the pot freeze through.
They need growing outside or in a very well-ventilated alpine house, in full sun or very partial shade. It is best to water with rainwater although, in the wild, the plants may grow in bogs above alkaline rocks. It is natural to think that a plant as odd and exotic as this requires cossetting but although it does have very specific needs it must not be smothered with warmth.
Curiously, this plant has an AGM (Award of Garden Merit) from the Royal Horticultural Society which, I am afraid, makes a bit of a mockery of the scheme which is supposed to acknowledge plants that are exceptional as garden plants – something you could hardly say of this plant, despite its curious beauty.
If you are just starting out with insectivorous plants you should try something else first by all accounts but in the UK or EU if you fancy a challenge you can get this, and many other excellent plants from the equally excellent Mathew Soper at Hampshire Carnivorous Plants – http://www.hantsflytrap.com