Why An Early Spring Means Trouble

Laelia purpurata 'Adam's' x "alba"  flowering this week in the FOC*

We had an exceptionally mild winter this year followed by a very early spring. Atlanta's dogwoods flowered a month before the Dogwood Festival.

Greenhouse plants are not exempt from the effects of an early spring. I was only slightly surprised and a little dismayed this week to see the first flush of flowers on our bench of Laelia purpurata orchids. They typically flower for us in late May and June.

Why dismayed? In a normal year Atlanta's plants have to endure almost four months of daily daytime temperatures above 90º. Ninety degrees outside translates into 85º in the greenhouse when the humidity is high.  Laelia purpurata certainly doesn't mind the heat, but our soft-leaved intermediate growing orchids begin to show signs of heat stress after four months. Since the daytime temperatures are already above 90º, they have a long slog ahead. A few years of this and some of these orchids will simply disappear from our collection.

Just as worrying is the effect of the mild winter and prolonged summer on pest populations. Aphids and some thrip species originate outdoors, so a population boom outdoors spells trouble indoors or in a greenhouse where there are no natural predators.

Resident populations of scale and mealybugs can also explode. As temperatures rise the generation time (the length of time an insect needs to become reproductive) shortens. A long hot summer means many more generations of pests at work on a population of plants already weakened by heat stress.

Stanhopea tigrina flowering on May 1

Moreover, hot conditions limit our use of our favorite low toxicity pesticide, Neem oil, which can harm a plant that is heat and drought stressed. I would hate to have to resort to conventional pesticides because of the heat. This year we started our spray cycle with Neem oil a month early.

One weapon that I have at my disposal is the ability to manipulate the greenhouse environment. By programming the exhaust fans and evaporative cooler to run not just during the day, but also during the coolest part of the night (3 am to 6 am) I can drive down the night temperature to a reasonable level.

Even so, we're in for a long battle.

*Synonyms:
Sophronitis purpurata Van den Berg & Chase (2000)
Cattleya purpurata Van den Berg (2008)

Embreea rodigasiana

Embreea rodigasiana flowering this week in the Fuqua Orchid Center

In the back up greenhouses at the Atlanta Botanical Garden is a bumper crop of seedling Embreea orchids that have just reached flowering size. They are making their debut this month in the Orchid Display House. Embreeas are considered to be rare and difficult in cultivation, so we are delighted to be able to show them to you.

Embreea is a striking orchid that resembles the closely related genus Stanhopea. It shares with Stanhopea the pollination syndrome associated with male Euglossine bees,--large tropical bees that collect fragrance. The waxy flowers are huge (about four inches) and their eucalyptus-like fragrance is highly attractive to Euglossines. The flower points downward and the column and lip together form a chute to guide the bee past the pollen masses located at the tip of the column.

Embreea produces a single-flowered spike, rather than the massive multiple flowered spike of Stanhopea. The horns on the lip have a very distinctive hatchet shape.

Since Embreea rodigasiana comes from an especially wet area of western Colombia--the Choco region--we water our plants more frequently than we do our stanhopeas. Embreeas absolutely need a humid greenhouse in order to flourish outside of the warm tropics. Our plants do well in a mixture of New Zealand sphagnum and chopped tree fern fiber. A wire or net basket is needed in order to accommodate the pendant spike which often grows downward through the medium.

Don't miss these! You can find them in the Orchid Display House this month in baskets hanging below the beams of the cedar pergola.

Horizontal Twist II

Horizontal Twist, 2008, Beverly Pepper (American b. 1922)

I hate rust. All greenhouse managers hate rust. Rust is the enemy, the relentless destroyer of greenhouses.

Why, then, is the surface texture of Horizontal Twist so appealing? The richly colored scurfy surface of COR-TEN steel, is, after all, rust. (Okay, okay, call it an oxidated surface.)

It was Sarah Carter of our staff who drew my attention to the magnificent staghorn ferns directly above the sculpture.

Platycerium wandae

The thick carpet of rusty spore patches on the underside of the fronds matches the sculpture perfectly in color and texture.

A closer look at the beautiful rust colored spore patches 

Staghorn ferns, like our Platycerium wandae, produce two different types of leaves: clasping shield fronds that surround the root ball and attach the young sporling to a vertical surface; and the staghorn-like fertile fronds which develop spore patches when mature. Our staghorns produce a tremendous quantity of rust colored spores that germinate readily on the cedar pergola.

Schefflera macrophylla stem

Ferrugineous (ferrum = iron) is the Latin adjective for rust colored. Staghorn ferns aren't the only example of ferrugineous surfaces in nature. Schefflera macrophylla from south China & Vietnam wears a velvet mantle of rusty hairs on its stem and petioles.

Rhododendron konori

Rhododendron konori, one of the Vireya Rhododendrons in the Tropical High Elevation House, produces leaves and buds covered with an attractive dusting of rusty scales (which are multicellular epidermal hairs).

Horizontal Twist, with its lovely patina of rust, looks entirely at home among these plants. Who would have imagined that rust could be so beautiful?

Openings: Week of April 30

Cyrtochilum serratum in the Tropical High Elevation House

Whenever one of our ravishing cyrtochilums flowers I want to call the newspaper. They are just so exceptional in every way--exceptionally beautiful, exceptionally rare in cultivation, and unfortunately, exceptionally difficult to grow outside of the cloud forest. I feel flattered when one of ours flowers.

All of the Cyrtochilum species are native to the misty upland forests of the Andes where their extraordinarily long rhizomes scramble up trees and shrubs. But it's the flower spike, or inflorescence, that will make you stop for a second look. It's a graceful twining strand that winds its way up, around and among surrounding trees like rainforest tinsel, with as many as 100 flowers per strand.  Cyrtochilum serratum is  native to Ecuador and Colombia. If you guessed that Cyrtochilum is closely related to Oncidium, the Dancing Lady Orchid, you are correct.

Medinilla magnifica

Magnifica indeed. Without a doubt, the most commented upon plant in the Orchid Center right now is Medinilla magnifica, one of the all time great plants for conservatories. Not an orchid. It is a large shrub in the mostly tropical and frequently ornamental Melastomataceae. I have noticed M. magnifica for sale in Atlanta garden centers this month. It is not hardy in Atlanta. Melastomes, even large ones like Medinilla magnifica, are easily rooted by cuttings.
We have quite a nice collection of melastomes at ABG, and if you like M. magnifica you will love our recently installed Medinilla miniata, similar in size and aspect, but with fiery red flowers. Melastomes come in all sizes, but they are easy to recognize. The leaves are opposite with veins that lie parallel to one another. The flowers have a peculiar feature: the stamens are elbow-shaped.

Pleurothallis cyanea on a tree in the High Elevation House

If you visit the Tropical High Elevation House this week you will see a burst of flowers on some of my favorite clamshell orchids, Pleurothallis cyanea, P. gigantea and P. teaguei,  P. marthae and ever-blooming P. titan. I love the thick coriaceous leaves on Pleurothallis cyanea.

Cavendishia grandifolia

Cavendishia grandifolia is one of the most impressive plants in the Tropical High Elevation House and certainly our largest shrub. It's astonishing to realize that this plant, with its fifteen foot pendant branches is an epiphyte. It's a mighty plant that can support one of these sprawling monsters. Each of the thick platter-like leaves is ten to twelve inches long. You can get a closer look at those gorgeous tubular flowers here. We have two grandifolias: the one pictured above cascades over the waterfall; the other is draped over the arch of the tepui.

Lots of orchids in flower this week! Please stop by for a visit.

Horizontal Twist

Installation of Horizontal Twist, one of Beverly Pepper's marvellous contemporary sculptures, took place in the Fuqua Orchid Center last Wednesday. Horizontal Twist is with us as a part of the Garden's new sculpture exhibition Independent Visions, which opens this week. I must admit I was alarmed when our Exhibitions Manager, Cathleen Hunt, proposed to place the sculpture in the Formal Bed. What kind of crane could fit in a four foot wide space and hoist a 2200 pound work of art over a two foot high water feature and into the center of a bed 25 feet long? It would take hours.

It took about 45 minutes. The sculpture arrived swaddled in protective wrapping and was attached to a gantry crane by a crew of experts while I stood nervously by, holding a camera to stave off hand-wringing. Once attached to a chain hoist, the piece was lifted above the height of the bed.

The hoist moves horizontally on a trolley fitted to a heavy aluminum beam. As the operator pulled the guide chain the sculpture moved forward and across the reflection pond.

The sculpture was steadied so that it didn't fishtail and strike the cedar pergola.

Once it reached its destination the piece was pivoted above the bed.

The piece was centered over a platform that will distribute its weight across the bed.

And finally the sculpture was lowered into position.

A few final tweaks were requested by Cathleen Hunt, Exhibitions Manager.

And the crew sprang into action one last time.

Well done! Congratulations, guys.

What are you going to plant around the Horizontal Twist, Sarah?

The exhibition, Independent Visions: Sculpture in the Garden features 19 works by nine different artists. It runs from May through October. The Member Opening is tonight!

Eight Ways to Kill Your Orchid

Confession: Like most professional growers I have killed a shocking number of plants during my career. But wait a minute. Should this be shocking? The way I look at it, if you haven't failed --if you haven't killed lots of different plants during your career as a horticulturist-- then you haven't been stretching yourself enough. I'm not happy about the ones I've loved and lost, but my point is that a good grower --one who learns from her mistakes-- can tell you just as much about how to kill a plant as she can about how to grow it. So here's the guide you won't find on Martha Stewart TV.

Eight Ways to Kill Your Orchid

1. Water it every day.

The Most Frequently Asked Question that we receive at the FOC is, "Do you water the orchids every day?" The answer is, "No, but we check them every day." Checking means looking at the potting mix to see if it is dry. A good grower checks the potting mix daily and learns to recognize the change in color that accompanies the drying process. Checking is what separates the green thumbs from the black thumbs.

2. Establish a watering schedule for your orchid. Make it conform to your schedule. Water it on the same day of the week that you go to the gym, or the grocery or the car wash.

This one is really tempting. But let's say it's September. Did you notice that yesterday was one and a half minutes shorter than the day before? Maybe not, but your plant did. Did you notice that the sun is now lower in the sky than it was in July? Your plant did. So, two months from now, when your plant receives one less hour of light and considerably weaker light intensity does it make sense to water with the same frequency?

3. Water your orchid whenever you water your other plants.

Convenient, yes. Good horticulture, no.

4. Water your Phalaenopsis orchid with ice cubes.

Tell me you don't do this. In nature a Moth Orchid seldom experiences temperatures below 60º. And you're thinking about applying ice water to its roots? Seriously? Why not just put it in the freezer for a day? You can revive it later by dropping it into a pot of boiling water.

5. Find out where your orchid is native to and water it when the weatherchannel says it's raining there. This strategy wouldn't work even if you and your houseplant lived in its country of origin. Why not? Microclimate matters more to an orchid than macroclimate. Even if your condo is located in the rainforest, the kitchen window microclimate where your potted orchid resides is different from the microclimate within the tree canopy outside.

6. Force it to live its entire life in a beautiful pot with no drainage holes, in a dense soil mix, and smothered with florist's moss. 

I know you received it from the florist this way. It looks great, I admit. Shouldn't they know better? What do you think? I think the florist's priority is how the plant looks, not how well it grows. 

7. Force it to live its entire life in the same soil mix that the grower put it in.

After two years an orchid mix is history. Orchids in conventional (peatmoss-based) houseplant soil should be sold with CAVEAT EMPTOR (Buyer Beware) stamped on the pot. The structure of peatmoss (and composted pine bark) is too fine and too dense to be a good long term medium for plants that in nature grow in trees. It retains loads of water and breaks down quickly. At our Orchid Care Clinic we do more post-mortums on orchids in this mix than any other.

You may have received it from the grower in this mix. Shouldn't they know better? Look at it from the grower's perspective. Peat-based mixes are cheap, widely available, uniform, sterile and lightweight (meaning inexpensive to ship). Young orchids reach flowering size rapidly in this mix, saving production time and labor, and then can be swiftly passed along to the consumer. What's not to like?

8. Bring your orchid to our Orchid Care Clinic (good so far) on the coldest day in January. One the way home leave it in your unheated car while your visit every store in Lenox Mall. 
Oh no. More blood on my hands.

Do you have a similar list? Don't hide it. It means you've learned something, and that's good. It means you're growing ...even when you're plants aren't.

How to Grow Dendrobium nobile

Dendrobium Red Emperor 'Prince'

Dendrobium nobile hybrids make stunning potted plants. Staked upright they look exactly like a living bouquet, with flowers spaced so closely that it becomes hard to see the plant underneath. Dendrobium Red Emperor 'Prince', which we used in our Orchid Daze display,  is an especially vivid color combination--deep fuchsia and yellow. We are selling them today and tomorrow at our Gently Used Plant Sale.

Dendrobium nobile hybrids are seldom seen at retail outlets, unlike the ubiquitous Dendrobium phalaenopsis hybrids which you are probably familiar with. Dendrobium is a huge genus, widespread throughout Asia and diverse in morphology. Thus, there are many types (the group is divided into sections) of dendrobiums with different cultural requirements.

The Yamamoto Dendrobium website gives an illuminating description of the habitat: The nobile type Dendrobiums are  native to SE Asia and grow on branches of tall trees (read: needs very bright light) in cool areas up to 3,000 ft. elevation where night temperatures may drop near freezing in winter (read: cold temps are required in winter for bud initiation). There are two seasons: rainy summer and a dry winter in which there is very little rain for four months.'

In a nutshell: warm moist slightly shaded summer followed by cool dry full sun winter. We grow our plants in a 50% shade humid greenhouse and move them to a cold greenhouse (53 to 55 º nights) from November to New Year's.

The folks at Yamamoto have produced some terrific pages with detailed cultural information. If you are buying Dendrobium  nobiles at our Gently Used Plant Sale I would recommend that you keep them at 55º to 75º in order to maximize the longevity of the flowers.

How to Grow the Oncidium Intergenerics

Beallara Big Shot 'Kitty Kat'

Among the Dancing Lady orchids, subtribe Oncidiinae, the Oncidium intergenerics are the ballet corps: beautiful, even fragile looking, but in fact, quite strong.

Beallara Marfitch 'Howard's Dream'

Subtribe is one rung above genus on the taxonomic ladder. Genera within the (formerly) large genus Oncidium are closely enough related that hybridization is possible among them.

Beallara Tahoma Glacier 'Sugar Sweet'

Beautiful but tough--that's the goal of all of the breeding involved in making one of these complicated hybrids.  Want to buy one of those gorgeous high elevation Odontoglossum for your place in Atlanta? Why not just set your money on fire? Try a Beallara instead. Beallara combines four genera. Odontoglossum and Cochlioda for frills plus Miltonia and Brassia for warmth tolerance. There are lots of different Oncidium intergenerics bred for beauty and ease of growing.

Odontioda  Hot Pants 'Hot Stuff'

Oncidium intergenerics

Light

A few hours of mild but direct morning sun on an east facing window sill will provide enough light intensity for flowering. Make sure there are no trees or buildings blocking the light. A west-facing exposure will work if you make sure the leaves don't feel hot to the touch. In a greenhouse, 50% shade.

Temperature

All orchids like a daily 15º difference between day and night temperatures. The annual temperature range should be between 58º low (at night in winter) and 83º high (daytime in summer).

Water

Take a good look at the potting mix every day for the next week and learn to recognize the change in color & moisture that accompanies the drying-out process. The top 1/2 inch of potting mix will be lighter in color and drier on day six than on day one. Drench thoroughly from above when that top 1/2" looks dry. Saucers that allow standing water to accumulate and flow back into drainage holes are a bad idea.

Pots and Potting Media

You did pick a pot with drainage holes, right? Putting that pot inside another pot without drainage holes is cheating. Your plant will know. Your plant will know that you value waterstain-free furniture above its own life and it will die.
Oncidium intergenerics like to grow in relatively small pots in either a fir bark-based orchid mix (which you can buy from most garden centers) or a New Zealand sphagnum moss mixture (purchased online).

Fertilizer

1/2 strength all purpose soluble fertilizer every two weeks.

Odontocidium St. Anthony of Egypt 'Huina Road'