I have been growing lady slipper orchids, genus Cypripedium (here after called Cyps), in a warm temperate climate for 7 years in southern Japan (latitude 34 N). In the spring, when the plants are emerging and flowering, I get a jolt of shear joy – mission accomplished. Then, in June, the monsoon rains kick in and the rotting begins. Bugs get more active and slugs are a constant threat.
By late July (as I write this), I am positively sure that all is lost for the season since just about everything is worn, torn, ripped, rotted or eaten. The oven heat of August and September seems to only emphasize the point – growing Cyps in a hot summer climate is madness. Come November, with its cool rains and falling maple leaves, I dare to check the plants and am often surprised with what not only endured, but even grew well that year. The following article is the method I’ve worked out over the years to grow these lovely terrestrial orchids.
First of all, let me explain the climate I’m working with. Kyushu, the southernmost main island of Japan, is a warm temperate climate sitting on the eves of the subtropics. A typical day in January has a high around 7 C (44.5 F) and a low of 2 C (35.6 F), with an daily average around 5 C (41 F). Why spend so much time worrying average temperatures? The reason is simple – to vernalize adequately (have a proper dormancy period), most Cyps require at least 3 months of an average temperature at or below 5 C. My town, situated just on the edge of a mountain range, barely fulfills that requirement. In fact, the average temperature is a bit warm in the winter months.
If winter weren’t trouble enough, June and July create more problems. This is due to the inordinate rainfall of the summer monsoon. A meter or more of it can fall in just 6 weeks, something most Cyps don’t enjoy. In mid July the rains stop and the oven turns on. Average highs are in the low 30s C (90-92 F) with lows only down to the upper 20s C (80-82 F). Fall comes late, with October drying off and slowly cooling off, but the true colder nights don’t come until late November or early December.
There is no equivalent climate in the USA that I know of, but the seasonal temperature range is similar to Atlanta, Georgia or Charleston, South Carolina. Due to the moderating seas, extreme highs and lows are much less severe by comparison. The coldest recorded temperature for the Fukuoka City area was almost -7 C (20 F) and the highest was around 38 C (100 F), but typical extremes are more like -3 C (26.5 F) and 36 C (97 F). Overall, it rarely goes below freezing or above 35 C (95 F). The consistency of the heat in summer coupled with a warm fall and too warm winter are what challenge the Cyp grower here.
From my observations and experiments I can tell you the following about growing Cyps in a hot summer climate:
1. They will diminish in pots even if they succeed for a few seasons. The main reason is soil temperature. Pots simply get too hot. I have tried many methods of cooling the pot down, but none have worked to their satisfaction. The only species I can maintain long term in pots so far is C. formosanum, but by far it prefers growing in the ground.
2. Seedlings will be a real challenge to get to adult size, if indeed you can even keep them alive. To date I have managed to grow only a handful to subadult size. For example, I grew C. parviflorum v. parviflorum from deflasked seedlings to almost blooming size and then they diminished this year. Ditto with C. formosanum – they grow slowly bigger each season, but it is like watching paint dry. I have C. macranthos that grow year after year but so far have failed to put on any size. And so it goes.
3. Organic material in the soil needs to be kept to a minimum, optimally less than 10%. I use seedling grade orchid bark, fine grained pumice, and a material called kanuma that is something like perlite, but holds water a bit better. The ratio used is roughly 5 parts pumice, 1 part kanuma, and 1/2 part bark. C. japonicum and C. formosanum both like more organic matter, so I up it to around 30% with these only. Since the bark and kanuma are acidic in reaction, a bit of lime can be added in the fall.
4. Sunshine is a no-no since the root run will get too hot. Bright shade, say that suited to Cattleyas is enough for most species. Plants that require more light to thrive likely will be problematic, such as C. reginae or C. candidum.
5. Plants will grow or diminish regardless of your efforts. The following species and their hybrids are good choices: C. formosanum, C. japonicum, C. kentuckiense, and C. parviflorum v. pubescens. Others that might be OK include C. fasciolatum and C. henryi. Also tolerant of heat if grown correctly is C. debile, but it is a tough plant to maintain long term, as is C. acaule. Cool growers like C. parviflorum v. parviflorum (as well as v. makasin), C. macranthos, C. flavum, etc. are not likely to make it for very long.
6. Plants grow best in elevated beds of the above mentioned compost that must remain well watered, especially during hot, dry spells in summer. The native soil here is a sticky clay-loam that would kill a Cyp outright. The area I grow in is wet much of the time in summer, so I first make a mound about 30 cm (1 foot) tall of the pure native soil. One top of this goes another 30 cm of the Cyp compost. Bricks or rocks are placed at the sides to hold the bed together. In summer the root run stays cooler than the air due to evaporation off the top of the bed. The wetter earth at the base wicks upward, thus keeping the evaporative cooling going. The only rub is you have to keep the bed moist at all times.
7. Fertilizer should be applied every few weeks from April through June. Fertilize often from the beginning of growth, through flowering, and until the real heat hits – say when the average daily temperature goes above 25 C (77 F). At that point stop fertilizing. If your fall tends to be warm through October you can give one last shot of fertilizer the last month of growth. After that point stop fertilizing. DO NOT fertilize plants that have gone dormant. Any good liquid based fertilizer around an NPK ratio of 6-6-6 is fine, but use one that contains micronutrients as well. I use a very dilute solution, perhaps 1/3 the rate on the bottle.
To summarize, if you are in a hot climate I recommend starting with healthy adult or near adult plants. They should be heat tolerant species or hybrids. They should be grown in elevated beds of nearly pure inorganic, free draining compost in bright shade. Fertilize often from the beginning of growth, through flowering, and stop when it gets consistently hot. Also very important: never let the bed dry out because that will not only stress the plants, it will allow the soil temperature to increase dangerously, and will cause the plants to go into early dormancy or even die.
So, good luck with this endeavor, if you dare. It can be thrilling and fun, but is also fraught with disappointment.
Here is a list of plants I have attempted using this method (species followed by the hybrids):
-debile (does OK, but isn’t reliable long term)
-formosanum (grows, flowers, and increases)
-japonicum (grows, flowers, and increases)
-kentuckiense (grows and flowers, but has good and bad years)
-parviflorum v. pubescens (grows and flowers, doesn’t increase)
-parviflorum v. parviflorum (grows slowly, but isn’t viable)
-macranthos (same as parviflorum v. parviflorum)
-Gisela (parviflorum x macranthos) (grows well, increases slowly, but doesn’t flower)
-Philipp (kentuckiense x macranthos) (grows and flowers, doesn’t increase)
New this year (fingers crossed):
-Aki Pastel (pubescens x macranthos)
-Lothar Pinkepank (pubescens x kentuckiense)
-Michael Alba (henryi x macranthos)
-Sabine Alba (kentuckiense x fasciolatum)
-Victoria (pubescens x fasciolatum)