Australia is home to a bewildering variety of terrestrial orchids, however perhaps no other group is more commonly recognized than the greenhood orchids, genus Pterostylis. This article focuses on three members – P. curta, P. nutans, and their artificial hybrid, P. Nodding Grace. All can be grown easily on a cold windowsill provided some basic cultural requirements are met.
At one time all greenhoods were placed in the genus Pterostylis. Recently though, a split was made – those that generally flower in the fall without a basal rosette of leaves are now in the genus Diplodium, while the winter/spring flowering species that retain their leaves when in bloom remain in Pterostylis. The plants discussed in this article are from the latter group.
Pterostylis curta (the blunt greenhood) and Pterostylis nutans (the nodding greenhood) have overlapping ranges in Australia being found in woodlands from coastal southeast Queensland, New South Wales, Victoria, southeast South Australia, Tasmania, and Lord Howe Island. They prefer moist habitats in the wild, but the range of forest types they’re found in is broad, from grassy woodlands to riparian forests to subtropical rainforest, and even in exotic pine plantations. In habitat these are colony forming plants, increasing rapidly by tuber offsets. Remarkably, I’ve seen no record of the two ever hybridizing with each other in the wild.
Pterostylis Nodding Grace is an artificially produced hybrid that was registered by R.C. Nash in 1984. The exact cross is P. curta (seed parent) and P. nutans (pollen parent). I find it hard to believe that these two species haven’t crossed naturally somewhere in their vast distribution. Perhaps I just haven’t found a record of its occurrence, or maybe one has yet to be discovered and recorded. It is possible they have different pollinators and so are sexually isolated in the wild (a strong possibility given the differences in their flower morphology).
The common name, greenhood, speaks to the flower’s shape – something like a horned animal with a hood over its head. The general morphology of a Pterostylis flower is a hood-like structure composed of the dorsal sepal fused to the lateral petals, two lower sepals pointing outward from the flower (often upward, but not always), a tongue-like lip within the hood, and just behind the lip a winged column (the sex organ containing both male and female parts). For orientation, see the photo on the left of P. curta.
The long and short of it is that a pollinator (always a type of fly for this genus) lands on the lip having been attracted to the color of the flower or in some cases the odor (both color and odor resemble carrion, but they don’t smell bad to humans). The lip, being hinged at its base, springs backward toward the column, thus pinning the poor fly down. The trap then slowly releases and the fly escapes with no prize (Pterostylis produce no nectar), but with luck the pollen of the flower attaches to its back. The fly visits another flower and the process is repeated, this time depositing the attached pollen onto the next flower. Clever, huh?
While P. curta has an upright facing flower with the opening of the hood in an outward position and the horn-like sepals pointing upward, in P. nutans the hood is almost fully closed and the sepals point laterally or even downward. P. Nodding Grace, not surprisingly has an intermediate shape. All are green in color, but both P. curta and P. Nodding Grace have a red-orange pigmentation in the the hood, sepals, and lip areas. Only the very tip of the hood in P. nutans has red-orange color. In all three the hood is translucent, with P. nutans being the most (presumably to tell the fly which way is out when it is released).
Plants grow from small bulbs, not more than a large bean in size. These are produced at the ends of unbranched stolons that grow from the previous year’s bulb. Typically, these dive downward, but I’ve also seen them running along the surface of the growing medium. Regardless, bulbs are always produced underground since the stolon eventually finds its way into the substrate. To avoid this I suggest planting new bulbs at least 5 centimeters deep, and even deeper is fine too. Plants are fully dormant from late spring through early autumn.
Sometime in September or October the plants commence growth. Before Christmas time they will be nearly fully grown, bearing relatively small rosettes of bright green leaves. These can be up to 10 centimeters across in vigorous plants, and little as half that size to flower well. Since these plants increase rapidly via offsets it is important to make sure they don’t crowd the pot too much. I’ve seen that overcrowded pots produce much smaller growths, and these in turn will make smaller bulbs for the coming season.
Flower spikes will begin to form around Christmas and into mid-February. At first growth is slow, particularly in the coldest weather (here that is in January), but as the temperatures rise to 10 C or more daily they will progress much faster. Flowering usually commences from late February to mid-March, but can extend into early April. P. nutans typically never has more than one flower per stem and flower stalks are fairly short, not more than 15-25 centimeters tall. P. curta and P. Nodding Grace can both produce up to at least two flowers per stalk, though one is more common. They also are a bit taller, perhaps up to 30 centimeters in vigorous plants.
Check out this video of these plants growing in my house in southern Japan:
Of the three, P. curta has the largest flowers, followed by P. Nodding Grace, and finally P. nutans. Regardless, the size difference is not that much with P. curta having flowers up to 3.5 centimeters long and P. nutans around 2.0 centimeters. I’m glad to say that individual flowers can last up to a full month in perfect condition. Usually they flower nearly synchronously, so a large potful can be quite a spectacle. If you decide to bring them into a warmer area during flowering, realize that temperatures above 15 C or so will shorten the flower’s life. The flowers first darken to an orange-red as they are fading and then slowly shrivel.
A few cultural tips. First, I recommend you grow these in a very loose mix that has at least some organic matter. I’ve experimented with a number of composts and have settled on one that seems to work nicely: 2 parts fine perlite, one part potting soil, and one part silica sand. Be sure that the pot is completely free draining or you may rot the plants out. Fertilizer should be applied every few weeks during the growth cycle. I’ve used organic and inorganic types with similar results.
Though these are vigorous plants, be careful when fertilizing. I recommend a low N-P-K ratio and at a very dilute rate, somewhere between 1/8 to 1/4 that recommended on the bottle. Natural liquid fertilizers like sea weed extracts and fish emulsion should work well too. Given the small size of the plants, avoid any pelletized products (even slow release) since you will likely burn them.
Second, never allow the plants to dry out during their growth cycle. While these are tolerant plants, they cannot take any drying while in growth. Even a couple days of drying will likely kill them outright. Humidity need not be that high, somewhere around 40-50% should be adequate. In late spring they will begin to go dormant. At this time stop watering them completely. If you continue to water, they will remain green into the summer and the newly formed bulbs will even begin to grow. I’ve seen this with P. nutans in particular. This is not desirable.
If plants remain green into June, simply withdraw watering and that will force them into dormancy. In the fall when they begin growth, carefully keep them slightly moist, but don’t overwater since they are growing new roots and you don’t want to disturb them. Once in full growth you can water as needed to keep them evenly moist. While rainwater is best, you can use tap as long as it is free of chlorine.
Third, repot, repot, repot!!! I recommend removing the plants from their pots every summer and inspecting the new bulbs. If your plants are happy, they should be increasing in number from season to season. You can store them in a sealed plastic bag in a warm place provided the bulbs are completely dry to the touch and replant in early September, or you can repot them immediately into new containers and keep these dry. Word of warning – while they can take dry conditions during dormancy, do not allow them to be baked dry. I recommend putting them in a shady place outside that gets no rainfall. To ensure they aren’t desiccated during this time, very occasionally, sprinkle a little water on the pots. Refrain from actually watering the pots however. If you store them in bags over summer, you’ll see them initiate growth even in the soil less state. You must pot them soon after, before the roots begin to grow. Temperatures during dormancy should be high, between 20-30 C. Don’t put them in the refrigerator. Plant them deep, between 5-10 centimeters down, with the pointier side up.
Fourth, grow them in a bright, shady place. In nature they can live in partial sun, but this is not necessary to grow them. If you live in a climate where there is essentially no frost, say USDA cold hardiness zone 9b or warmer, you can growth them outside. I tried them outside a couple seasons here in my 9a climate and conditions were just a tad too cold for them to grow and flower well. An unheated, frost-free greenhouse is perfect for growing these, but any cool windowsill that is not too dry will do just fine.
Finally, enjoy these neat little plants! Once you get the hang of growing them, you’ll find they are very easy compared to most terrestrial orchids. Unfortunately, the hard part will be finding any for sale or even trade. Currently, the selection available in the US is very limited and only a bit better in Europe.