Growing Epiphytes in a Dry Climate

By Kris Kopicki

Adelaide has the reputation of being Australia’s driest city, and with good reason. Despite our record setting weather, it’s not uncommon to see subtropical plants surviving our vicious summers if watering can be maintained. This got me thinking about how much extreme weather our subtropical orchids could survive, provided they were kept reasonably hydrated. That was back in 2008, and at that point, I had no experience growing epiphytes, with my collection comprising solely terrestrial species. Having just moved into a new house, I also had no orchid housing, so my epiphytic experiment was going to need to take place under our easterly facing veranda and surrounding trees. The veranda has a few clear sheets that provide some light throughout the day.

To explore lighting, I used a large piece of weld mesh curved to form a cylinder. A makeshift tree if you will. The idea being that plants favouring higher light can be placed on the north east, and plants favouring shade on the south west. Being quite portable, I could move it around as the seasons change. Species were placed according to my research on their favoured lighting conditions. This seemed like a reasonable starting point.

I chose to grow the majority of my plants on mounts, even though many local growers use pots culture for better water retention. The plan was to eventually construct a shade house for my terrestrial collection, and so any epiphytes were going to need to occupy the only remaining space, the roof and walls. Terrestrial orchids are the top dogs in my collection, so rather than adapting my conditions to suit epiphytes, I was investigating if they could fit in with my plans.

Water was always going to be the big problem with this setup, particularly in summer when the temperatures can be relentless. One of the things that kept coming up in literature was to avoid frequent watering in winter, and particularly to keep plants away from winter rain. I was most puzzled by the last statement, as research on the climate of central and northern NSW revealed that winter rains far exceed an Adelaide winter. Also notable were the temperature averages, which showed that while coastal areas were slightly warmer than Adelaide, temperatures in the hills were often much less. This was great news, as it meant many plants would easily withstand Adelaide winter minimums. I decided the best strategy was to water as frequently as possible, so long as the media was dry between watering. The drying was very important to avoid fungal problems and to avoid saturation of the roots. My watering strategy was going to need to make up for the total absence of humidity during summer, so watering 2-3 times a day would likely be a minimum.

Realising that summer would be the breaking point for my plants, fertilising became a key strategy. The idea being that plants with large healthy root systems could make better use of any available water to get them through our hot days. My search for the best way to fertilise lead me to the decision of feeding a little and often. The reasons cited seemed logical enough. Plants are only able to absorb a small amount of nutrients at a time, so infrequent applications of large amounts of fertiliser would lead to waste, so plants would essentially be starved. I chose to alternate between fertilisers which avoids any nutrient deficiencies that one brand may have over another. Applications were made daily, except one day a week where plain water was used. I used 10% of the recommended dose. The first mix was Manutec Orchid Food, replaced with Manutec Orchid Bloom Booster during spike development. The second mix was a combination of Seasol and Powerfeed. Rainwater was always used to avoid build up of salts, which could potentially be a problem with such a high watering frequency.

The majority of species selected were from central and northern NSW, though species from as far north as Cape York were also trialled. It seemed logical to trial plants that eastern states growers considered easy and progressively move to more difficult species. Some of the species purchased in 2008 include: Sarcochilus x Fitzhart, Sarcochilus falcatus, Sarcochilus olivaceous, Sarcochilus aequalis, Sarcochilus spathulatus and Sarcochilus hirticalcar. These species are quite diverse, some thick and fleshy, others very thin and delicate.

Plants were purchased through winter and spring. Initial results were promising, with good root growth and rapid leaf development once the weather warmed up. A few Sarcochilus falcatus and hirticalcar received sun burn during early spring. While they do like bright conditions, it seems even a mild spring sun can damage them. The plants were then moved to a more sheltered location where only very early morning sun was received. Most of the plants flowered well, with the exception of x fitzhart and hirticalcar, which were too small.

As expected, summer proved to be a challenge. Given that the plants had almost no protection from the record heat of the 2008/2009 summer, they seemed remarkably resilient. Growth came to a standstill, and some root tips burned. During an extended period of temperatures over 40°c, a couple plants of Sarcochilus olivaceous and spathulatus were found desiccated, and some leaf tips burned on Sarcochilus falcatus. I decided that this was probably the limit of what they would handle and brought the plants inside the house during severely hot days.

All things considered, the majority of plants made it through one of our hottest summers with little or no damage. With the onset of cooler weather, leaf growth resumed, albeit a bit slower than during spring. Roots recovered very quickly from the heat damage. With all four seasons now under my belt, my collection of epiphytes rapidly expanded, including species of Bulbophyllum, Dendrobium, Dockrillia, Sarcochilus, Plectorrhiza and Schistotylus.

In August 2009, I purchased a weldmesh shade house from Queensland. It offered a lot of bench space for my terrestrial species, while providing hanging space virtually everywhere. I covered the walls in 50% shade cloth, and 70% shade cloth for the roof. I chose to use white marble chip for the floor. Now at this point you’re probably thinking this sounds quite different to the typical structures used for subtropical orchids in a temperate climate. Typically they are designed with a solid roof or walls, keeping humidity high. The downside to that design is air movement is severely restricted, possibly leading to the well documented fungal problems. In my design, humidity is still quite low during summer, but the shade cloth does restrict airflow, offering some protection from hot drying winds.

The shade house offers better light than the veranda, while providing protection from sunburn. It also has the potential to function as a giant evaporative air conditioner by wetting the walls and floor. Summer soon arrived to test out my new growing conditions. Very minimal damage was incurred. Some placement changes were needed to provide more light for some species, and less for others. Most species incurred some root damage, but they quickly recovered after summer. I used a layer of 50% black shade cloth over the top for protection during summer. Terrestrial pots were no warmer than the ambient air, a good indication that the cover was doing its job.

It turns out there may be good reason why such delicate plants with no obvious water storage mechanism can survive such harsh conditions. It has the unfortunate name of Crassulacean acid metabolism (CAM). Plants produce sugars through photosynthesis. To do this, they need energy in the form of light and carbon dioxide from the air. The leaves are covered in tiny pores called stomata that open during the day to acquire carbon dioxide. While the stomata are open, the plant is vulnerable to water loss through the leaves in hot and dry conditions. CAM plants have solved this problem by effectively delaying photosynthesis until night time, when temperatures are more manageable. A number of studies have been done on Australian orchids to show that many species employ CAM photosynthesis. Despite their resilience to day time conditions, CAM plants are still vulnerable to our extreme summer nights, like January 2009’s record minimum of 33.9°c. I’ve found that hosing down the plants and shade house at night helps to prevent or minimise damage.

The vast majority of species I’ve trialled are still alive and well today. Some are species that experienced growers have told me they find difficult to maintain year after year. Here are some of my observations on a range of species I grow.

Sarcochilus spathulatus

Climate Tolerance: Can be vulnerable to extreme heat, but once a good strong root system is established they seem to be quite hardy. They will show heat stress by dropping older leaves. Some root tip damage can occur in extreme heat, but is harmless.

Lighting: A northerly aspect suits them well. Keep them a good metre or more from the shade cloth to avoid sun damage to the leaves.

Watering & Feeding: They relish my feeding and watering scheme, producing roots twice the width of existing roots prior to purchase.

Growing Medium: Cork produces good results. I have also used Melaleuca species for their slightly better water holding properties and rough bark. Some sparse moss around the roots is helpful to protect them while they establish on the mount.

Growth Habit: Slow root and leaf growth over the coldest part of winter. Leaf growth is quite vigorous once temperatures start moving into the 20’s. Growth slows during very hot weather, usually sometime in January. Growth resumes again in autumn, with a burst of new root growth. Spikes appear around April and flowering occurs during September.

Comments: A fantastic miniature species with small sprays of beautifully fragrant flowers. Once established they are easy to care for if watering is kept up over summer.

Sarcochilus hirticalcar

Climate Tolerance: This species does not seem to adapt to our dry climate. I have achieved good results using a cheap mini hot house inside my shade house. I kept the door closed, but not zipped up to allow minimal ventilation. The temperatures get very hot during summer, but they seem fine with it as long as the humidity is maintained. They will show heat stress by dropping older leaves, and will die very quickly. Root damage can occur if the humidity is too low, even in cool weather.

Lighting: A northerly aspect suits them well. Keep them a good metre or more from the shade cloth to avoid sun damage to the leaves.

Watering & Feeding: They relish my feeding and watering scheme, producing good strong roots.

Growing Medium: Cork produces good results. I have also used Melaleuca species for their slightly better water holding properties and rough bark.

Growth Habit: Growth occurs over the whole year due to the warm conditions of the mini hot house. It is slower over winter, but still quite active compared to other species. My plants were too small to flower last year.

Comments: A challenging species to maintain in Adelaide. Once conditions are favourable, growth is vigorous.

Sarcochilus falcatus

Climate Tolerance: One of the most heat tolerant of the small Sarcs. They will show heat stress by dropping older leaves. Some root tip damage can occur in extreme heat, but is harmless.Lighting: I have grown them successfully in a range of lighting conditions, even with a southerly aspect. Even lighting over the course of the day will keep them from moving towards the strongest light. Keep them a good metre or more from the shade cloth to avoid sun damage to the leaves.

Watering & Feeding: They relish my feeding and watering scheme, producing roots twice the width of existing roots prior to purchase.

Growing Medium: Cork and Callistemon produce good results, but Melaleuca species seem to encourage an extensive root system. Some sparse moss around the roots is helpful to protect them while they establish on the mount.

Growth Habit: Slow root and leaf growth over the coldest part of winter. Leaf growth is quite vigorous once temperatures start moving into the 20’s. Growth slows during very hot weather, usually sometime in January. Growth resumes again in autumn, with a burst of new root growth. Spikes appear around February-March and flowering occurs during September.

Comments: My favourite Sarc. species, I can’t seem to stop collecting different forms. One of the hardiest species, they can be grown outdoors if watering is regular over summer. Regular feeding produces a vigorous root system and masses of sweet smelling flowers.

Sarcochilus olivaceous

Climate Tolerance: Can be vulnerable to extreme heat, but once a good strong root system is established and provided with a shady location, they are surprisingly resilient for a rainforest species. They will show heat stress by dropping older leaves. They can be nursed back to health from quite extensive heat damage, even from loss of the growth tip. Some root tip damage usually occurs in hot weather, but is harmless.

Lighting: A southerly aspect suits them well during summer, however brighter conditions may be needed in winter. Keep them a good metre or more from the shade cloth to avoid sun damage to the leaves.

Watering & Feeding: They relish my feeding and watering scheme.

Growing Medium: Cork produces good results. Moss around the roots is helpful to protect them.Growth Habit: Slow root and leaf growth over the coldest part of winter. Leaf growth is quite vigorous once temperatures start moving into the 20’s. Growth slows during very hot weather, usually sometime in January. Growth resumes again in autumn, with a burst of new root growth. Spikes appear around April and flowering occurs during September.

Comments: An interesting little rainforest species that adapts well to our climate with minimal protection. Plants are commonly sold and cheap, definitely worth a go.

Sarcochilus aequalis

Climate Tolerance: Very tolerant of extreme heat, showing almost no damage.

Lighting: A northerly aspect suits them well. Keep them a good metre or more from the shade cloth to avoid sun damage to the leaves.

Watering & Feeding: They relish my feeding and watering scheme, producing healthy roots.

Growing Medium: Cyathea (Tree Fern) mounts give good results. Some moss around the roots is helpful to protect them while they establish on the mount.

Growth Habit: Quite a slow growing species with virtually no leaf growth over the coldest part of winter, and minimal root growth. Leaf growth resumes once temperatures start moving into the 20’s. Growth slows during very hot weather, usually sometime in January. Growth resumes again in autumn, with new root growth. Spikes appear around May and flowering occurs during September- October.

Comments: A slow but hardy species. Not the most spectacular of flowers, but the foliage looks great against a black Cyathea mount.

Rhinerrhiza divitiflora

Climate Tolerance: Very tolerant of extreme heat. Some root tip damage can occur in extreme heat, but is harmless.

Lighting: I have grown them successfully in a range of lighting conditions, even with a southerly aspect.

Watering & Feeding: They relish my feeding and watering scheme, producing healthy roots.Growing Medium: Cyathea (Tree Fern) mounts give good results. Some moss around the roots is helpful to protect them while they establish on the mount.

Growth Habit: Quite a slow growing species with virtually no leaf growth over the coldest part of winter, however the roots remain active. Leaf growth resumes once temperatures start moving into the 20’s. Growth slows during very hot weather, usually sometime in January. Growth resumes again in autumn, with new root growth. Spikes appear around June and flowering occurs during October.

Comments: Not commonly sold or seen in collections, but quite a tough species. It’s a reliable flowerer, producing masses of spidery flowers. The only downside is the flowers only last for a few days. They have very unique raspy roots and tough leathery foliage.

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