Another Fantastic Bucket Orchid

Our magnificent Coryanthes bruchmülleri has been flowering regularly since it reached maturity last summer. C. bruchmülleri is the Goliath of the genus, with flowers four to five inches in diameter.

Coryanthes bruchmülleri grows in lowland wet forests near the border of Colombia and Venezuela. In the wild, Coryanthes are typically found growing in ants' nests in a mutualistic relationship with the ants. It's not uncommon to read that Coryanthes are difficult to cultivate, perhaps lacking something provided in nature by the ants. In our greenhouses, without ants, they are no more difficult than any other member of the Stanhopeinae, provided you can exclude the slugs and bush snails that consume the roots and new shoots. Our tactics: frequent repotting, applications of diatomaceous earth, and eliminating the source of new introductions -principally orchids from Hawaii. I'm happy to report that we've got a capsule gestating on one of our plants. It will be terrific to get this fantastic species in production.

Now opening: Coryanthes macrantha

We've produced a bumper crop of Coryanthes seedlings that are now reaching flowering size. Coryanthes, with their provocative morphology and intense fragrances are simply the best teaching tool ever for introducing students (or anyone!) to orchid pollination concepts, and Euglossine bee pollination in particular. But, since the flowers only last about three days, a large number of plants are needed for a continuous display.

We are very fortunate to have a mircro prop lab to allow us to produce orchid seedlings. Coryanthes are somewhat weedy in the sense that they reproduce rapidly. They have a very short capsule maturation (60 days), produce copious quantities of seed and robust, fast growing, fast flowering seedlings.

After they outgrow the plug stage, our Coryanthes seedlings grow best on vertical mount, rather than in a pot or basket. Tree fern slabs have worked well for us, but last year, in an attempt to wean ourselves from our tree fern dependency, we tried a new slab material: coarse filter media, borrowed from our aquarium colleagues.

Filter media isn't a good choice for every orchid, but the Coryanthes love it. Within a couple of months, their roots completely fill the interior spaces of the slab.

We are super excited to have more of these fascinating orchids on display for you to see. Look for them this year in the Orchid Display House!

Our War On Slugs

These days, 7 am finds me iphone flashlight in hand, visiting each greenhouse, searching the orchid collection for slugs, who I then crush under foot. This summer has brought an unusual amount of slug activity in all of our greenhouses, an unexpected development in the middle of a bright dry summer. They have made their way into pots and hanging baskets, eating root tips, new shoots, young flower spikes and flowers.

One triumph in our war on slugs has been among the Bucket Orchids (Coryanthes), usually a prime favorite of slugs, bush snails, cockroaches and practically any other pest you can name. Everybody, it seems, loves a Coryanthes. But this year the Coryanthes are producing flush after flush of absolutely pristine new roots and shoots. Our secret weapon: diatomaceous earth applied to bare root plants.

Diatoms are unicellular algae with lots of silica in their cell walls. Silica is the major constituent of sand, but it is also found in living organisms. The fossilized remains of diatoms are mined from deposits in the western US, Canada and Germany. The granulated product has industrial uses in filtration systems. Diatoms can also be milled to create a talcum-like powder, called diatomaceous earth, which is abrasive, porous and hygroscopic (moisture absorbing). Diatomaceous earth kills insects and mollusks by abrasion and dehydration.

We began our campaign against slugs on our Coryanthes two years ago. The battle plan had two phases: Remove their sanctuary and then apply treatment. First, we removed all of our Coryanthes from their pots and washed away the mossy medium and the slug eggs; then we mounted the plants on wooden rafts or tree fern slabs so that their roots were exposed and there were fewer places for mollusks to hide.

We began applying diatomaceous earth to our Coryanthes at the height of the slug and bush snail season. Bush snails are tiny. Dozens can hide in the crevices between pseudobulbs. A good way to monitor slug and snail populations is to check the exterior of the raft an hour after watering. Before treatment, I found at least one slug and 10 to 50 bush snails on each wooden raft. We applied diatomaceous earth weekly throughout the spring and summer to the exposed roots, in between the pseudobulbs and to the leaves.

This summer, after renewed applications, there are 0 to 2 bush snails per plant and no sign of chewing damage to root tips or leaves from slugs or cockroaches. We plant to continue applications through the autumn.

A few tips for using diatomaceous earth for slug, snail and cockroach control:

• Look for "Food Grade Diatomaceous Earth" in order to get freshwater diatoms. Avoid "Pool Grade," which is saltwater-derived.
• Keep the package sealed and out of the greenhouse or any other humid environment. The powder is highly porous and once it absorbs water from the atmosphere, it loses its ability to dehydrate pests.
• Wear a dust mask. Silica dust is harmful to lung tissue.
• Apply diatomaceous earth once a week to the entire plant and its mount when the surfaces are dry: the new shoots, leaves, flower spikes, the slab and in between pseudobulbs. Let it sit at least overnight before you water again, since water will wash it away.
• Any soft brush will work as an applicator, but I like the idea of battling an enemy with a cosmetic brush. Drugstores carry them.

Bucket Orchid Season

Our Bucket Orchids (Coryanthes) are producing a lovely autumnal flush of growth. Some pretty incredible flowers will follow in a couple of months. Here's one of the earliest, Coryanthes mastersiana.

Coryanthes mastersiana produces two to three flowers on each inflorescence. It somewhat resembles the Brazilian species Coryanthes speciosa, but the fragrance is very different. According to Günter Gerlach's website, Coryanthes mastersiana grows together with Coryanthes flava and Coryanthes elegantium in western Colombia and Ecuador.

Above is a diagram to help you make sense of the peculiar anatomy of Coryanthes flowers. The lip, often the most elaborate of an orchid's three petals, is modified in Coryanthes to facilitate pollination. The bucket, or epichile, fills with liquid from two glands protruding from sides of the column. At the rear of the bucket, and just visible in the photo, is an opening where the bucket meets the anther cap at the apex of the column.

When a male Euglossine bee scratches the surface of the hypochile in order to obtain liquid fragrance, he slips into the bucket. With his wings drenched, his only escape is to paddle to the rear opening and force his way through the small opening. In doing so, he rubs up against the sticky end of the pollinarium, which ends up attached to his body. At a subsequent Coryanthes the process is repeated, but this time he leaves the pollinia behind on the stigmatic surface of the column.

Coryanthes produce some of the most incredible flowers in the entire orchid family and this year I plan to set more capsules on our plants.

Openings: Coryanthes macrantha seedlings

Of course it's loads of fun to receive an orchid in flower. But even more fun is the exquisite anticipation that builds as you await the very first flowering of a newly matured plant. Will it resemble its parents? Will it be a surprising new color or shape? Or something intermediate? Do you ever envy plant breeders who experience this excitement for a living? Think about it. Many of them wait years to see their photosynthetic offspring's first flowers.

Flowering for the first time this month in our warm greenhouse are some seedlings of a fairly rare light colored form of Coryanthes macrantha, one of the Bucket Orchids.

Usually only a small percentage of the seedling offspring of an atypical form will resemble their parents. So I was expecting flowers with the typical bold red splashes. Surprise! Our first seedling has bred true. The petals and sepals are nearly white.

Of all the species of Coryanthes, Coryanthes macrantha is the most widely distributed. And throughout its range it exhibits some very striking color variation. Dr. Günter Gerlach's Coryanthes page on the Munich Botanical Garden's website has an outstanding catalog of Coryanthes descriptions and photos if you want to go crazy looking at the diversity in this remarkable genus. Dr. Gerlach notes that while the color and morphology of Coryanthes macrantha seedlings may vary throughout their range, the fragrances of all the clones that he examined are very similar. Coryanthes macrantha is pollinated by fragrance collecting Euglossine bees of the genus Eulaema.

Openings: Coryanthes alborosea

Coryanthes alborosea red form flowering at the Atlanta Botanical Garden

This vibrantly spotted and spattered orchid is one of the siblings of the Coryanthes alborosea that I photographed last week. The seedlings, which are now flowering for the first time, are the result of a selfing of the red splashed color variant. A small percentage of the seedlings look like their parent.

This is a plant that leaves me awestruck. If you tried to describe it to a friend what would you say? Do you think anyone would believe you?

A Bucket Orchid Opens

Coryanthes alborosea opening at the Atlanta Botanical Garden.

Coryanthes alborosea one half hour after opening.

The right-hand flower of Coryanthes alborosea. Note the liquid already accumulating in the bucket.

If you arrive at the Fuqua Orchid Center greenhouses early in the morning you can sometimes catch a Bucket Orchid (Coryanthes) bud in the act of opening. The bud looks like an enormous wrinkled chrysalis. It usually takes a couple of hours to fully open. First, the bud splits lengthwise along its seam, then the petals and sepals reflex backward to reveal the amazing lip. Coryanthes flowers only last about three days.

Wednesday morning I photographed a pair of Coryanthes alborosea flowers as they opened. The half-opened sepals framed the lip like angel wings.

Love the furry cap.

Click here to find out how a Coryanthes flower works.

More Coryanthes in Flower

Coryanthes macrantha flowering at the Atlanta Botanical Garden

More of our extraordinary bucket orchids are flowering. Coryanthes macrantha (above) is one of the parents of the hybrid featured in my last post. You can see what the other parent looks like here. Although Coryanthes are, in my experience, among the more difficult orchids to grow, Coryanthes macrantha has always been a consistently strong grower for us.

I'm also looking forward to seeing the first flowers on the seedling offspring of Coryanthes macrantha var. alba this year.

Coryanthes, the Bucket Orchid

Coryanthes macrantha flowering at the Atlanta Botanical Garden. The genus Coryanthes is called the Bucket Orchid.

How it works. The  Coryanthes "bucket" (facing right) is part of the flower's lip, a highly modified petal. The other two petals and three sepals (left) are reflexed backwards like wings. Coryanthes flowers produce fragrance attractive to male Euglossine bees. After brushing the fragrance from the lip, the bee falls into the bucket.

The back door. After immersion in the liquid-filled bucket a bee must force his way out through a small opening at the rear where a pollen bundle is deposited on his back. 

Autumn brings a flush of new root and shoot growth to our (insert your own adjective) Bucket Orchids. A few, like Coryanthes macrantha, are far enough along in their development to produce flowers. The flower pictured above measures about four inches from top to bottom. A Coryanthes flower would make anyone stop for a second look.

Coryanthes, you make me crazy.

The fabulous but frustrating Bucket Orchid (Coryanthes)

Coryanthes are the most difficult plants I have ever grown. Clearly they are worth the effort--a fragrance that is almost edible, a grotesque (and let's face it, slightly pervy) appearance, a clever pollination mechanism, a symbiotic relation with two species of ants. But absolutely maddening in cultivation, at least in our greenhouses. The plants grow robustly for a year or so before I start to notice the subtle signs of decline: no new shoots appear, a few leaves are shed, and finally, the entire plant is leafless. If I remove the plant from its pot the root system is dead. Coryanthes make me want to bang my head against the wall.

Why? Coryanthes must be the orchid world's biggest mollusk magnets. While the adjacent pots of Phalaenopsis remain mollusk-free, it's rare to find a Coryanthes pot in any of our greenhouses that doesn't harbor at least a couple of slugs, and even worse, their minute evil cousins, the bush snails. Forget the metaldehyde, iron phosphate, beer, copper strips. It seems nothing kills these guys except the bottom of my shoe. And I have actually learned to enjoy crushing bush snails between my thumb and forefinger.

So, this summer I have applied a draconian solution--removing all the organic medium surrounding the roots and attaching our Coryanthes, young and old, to slatted cedar slabs as the new roots emerge. This is indeed a radical step since Coryanthes love moisture, plus it flies in the face of conventional wisdom which recommends mimicking an ant garden stuffed with acidic organic matter. But on these slabs the slugs & snails have nowhere to hide. And the mild but regular drying will make the Coryanthes a less appealing refuge for egg laying. That said, it's still a very humid greenhouse.

Look at those gorgeous root tips! Completely unmolested by slugs.

If the slabs look familiar to you it's because they are in fact simply the bottom of the classic cedar hanging basket sold by the major orchid supply houses. I think most people hang these slabs vertically, but I have decided to use them as rafts in order to retain a bit more moisture around the Coryanthes roots.

Time will tell whether or not this is a good cultural approach for Coryanthes.