By Ron McHatton with Photographs by Greg Allikas

Summer presents challenges in the form of increased pest activity, fungal and bacterial problems in traditionally wet areas and desiccation in those areas with Mediterranean-like climates where summers are typically quite dry. Careful observation of your plants is the best way to identify small problems before they become big problems, and in the summer, the time between these two events is dramatically shorter due to higher temperatures.

Pest Control

For small collections, the best thing to do is to physically wipe insects of and clean the plant. Isopropyl alcohol and a cotton swab are effective against most pests and if you want to increase its effectiveness, a drop of Ivory dishwashing liquid added to the alcohol helps wet the typically waxy surface of orchid leaves. If you haven’t been watching carefully and the infestation gets out of control, you might have to use chemicals. Few pesticides are specifically rated for use on orchids, but you can use any that are labeled for ornamentals. Use care and follow the label directions. This is not a situation where if a little is good, more will be better.

In areas with dry summers, mites can be a serious problem, especially on phalaenopsis. These creatures attack the surface of the leaves producing a sort of rough silvery appearance. Mites are not insects and insecticides offer little or no control. Mites do not like humid conditions so efforts to increase humidity are beneficial. Light infestations can be controlled by thoroughly cleaning plants but in hot, dry climates light infestations rapidly become serious and control is best accomplished by the use of a miticide.

In areas with wet summers, wet foliage and high humidity encourage the spread of fungal and bacterial diseases. Bacterial diseases do not respond to fungicides and vice versa so it’s important to know which disease you are dealing with. Perhaps the easiest way to distinguish between the two is by smell. The most common bacterial disease in orchids produces a foul smell often likened to dead fish. If you’ve ever had cut flowers stand too long in water, you know the sort of smell we’re talking about.

Diseases can spread quickly. Bacterial diseases kill plants especially rapidly and time is of the essence. Both bacterial and fungal diseases are spread by splashing water, and this includes rainfall. Use a clean cutting tool such as a single-edge razor blade, cut off the infected tissue as well as at least an inch (2.5 cm) of clean, green area and then treat the cut surface with a fungicide. Even if the problem is bacterial, you don’t want a fungal infection to start in the wound. Cinnamon — the common spice — is effective against fungal diseases and can be used to coat the cut surface. It’s perhaps not as effective as a chemical fungicide but it’s readily available and does work.

Where it’s wet, keep your plants as dry as possible. Alternatively, provide a lot of air movement. When you water, try to do so as early in the day as possible. This will allow adequate time for the foliage to dry before nightfall.

In dry-summer areas, the bane of orchid growers is extremely low humidity, and this leads to two issues. The first of these is an increase in the rate at which plants dry out and the other is the ever-presence of mites.

Summer Sun

How does sun affect orchids? Solar radiation is much more intense in the summer and plants that have been thriving in full sun all winter may need a little extra protection (shade) when the sun is at its strongest or, often during the late afternoon, when the temperatures are highest. Orchids are easily sunburned and you should take care when moving plants around, especially if you are moving plants grown inside during the winter to a spot outside for the summer. Sunburn, while not in itself a serious problem is irreversible and will make your plants look ugly. In serious cases the plant can be killed outright and any leaf damage is an invitation to a secondary infection in the damaged area.

Capitalizing on the High-Growth Season

Because of increased light and temperatures, your plants will benefit from more fertilizer (increased frequency, not concentration). This is especially true for those varieties that put out new growth during this time. Avoid fertilizers that contain significant amounts of urea (formulations with more than 20 percent nitrogen). Urea nitrogen is much less readily available to orchids in soilless mixes than ammoniacal and nitrate forms.

By Thomas Mirenda

Family Gatherings and Grilling Bring Together the Holiday Spirit

Summer fun reaches its peak in July, with the hot weather finally arriving and sunscreen flying off the shelves. For kids, it just doesn’t get any better than July — barbeques, cooling off in the sprinkler or pool by day and backyard fireworks displays by night. Occasionally, there will be the unusual child who gravitates away from all the hullaballoo in the backyard and finds that shady spot where orchids are growing. With bursts of Epidendrum and brassia flowers and huge cornet like scapes of glowing encyclia and myrmecophila blossoms reaching skyward, many a budding interest in orchids has been ignited by the fascinating array of plants in bloom this month. Keep an eye out for those young ones who see the miracles of nature as more than rivals for the glitzy fireworks, but as the true marvels they are. Take the time to nurture and perhaps share a plant or two with a youthful relative or neighborhood nature child.

Heat

With temperatures often rising into the 90s, many orchid plants are stressed. Large and tender new growths generated this past spring are maturing and hardening off but are still susceptible to sunburn, heat stress and fungal infections. Therefore, the bulk of our activities this month are related to minimizing the effects of heat on our plants.

Read About Plants

Many orchids, particularly those from seasonally dry forests, such as encyclias, myrmecophilas and brassavolas, seem to do well in the summer heat. Even the many deciduous Dendrobium species and hybrids that require cool winter temperatures are growing rampantly now. Their adaptations of extreme succulence and large pseudobulbs give them the ability to withstand heat and dryness better than orchids from more seasonally uniform habitats like montane tropical rainforests, such as miltonias, many paphiopedilums, pleurothallids and even phalaenopsis. These orchids tend to have smaller pseudobulbs, or none, and have less succulent foliage. For these plants, shade and hydration during the summer heat is a real necessity.

Cooling Plants

Basically, there are three strategies for cooling off your plants: shading, misting and air flow. All of these strategies either separately or combined can ease the stresses of summer heat on orchids significantly. But taken to excess, these heat defenses can do more harm than good.

Shading

Most of our orchids benefit from some shading during the hottest months, but many also need bright light to grow strongly and store enough nutrients to bloom once their new growths have matured. Cattleyas, cymbidiums, standard dendrobiums and vandas will languish with weak and spindly new growths if kept constantly in deep shade. For such plants, misting and air flow are better strategies for cooling. For phalaenopsis and most pleurothallids, deeper shade gives better results.

Misting

Many high-light orchids, notably vandas and cymbidiums, benefit from a fine cooling mist at the height of the day’s temperatures. Feel your orchid’s leaves on a hot day. If they are hot to the touch, they have shut down and are in danger of burning. Just a quick wetting down with a light mist is often enough to cool the leaves down. Cymbidiums in particular seem to grow better when cooled in this way. Automatic misting systems are available for both outdoor and greenhouse growers. Still, beware of wetting down leaves in full sun, as the water can overheat or act like a lens. This usually happens only under glass or on window sills where the air flow is poor. The other danger with misting is waterlogging your plants. Don’t mist so much that your plants never dry between waterings. Also, remember that water sitting in the new growths of your phalaenopsis plants at night is a sure recipe for the dreaded crown rot.

Air Flow

Perhaps the most important and overlooked aspect of cooling is air movement. A beam of light hitting a thermometer will make it register much higher than the actual ambient temperature. The same is true of leaves. If light hits the same portion of a leaf on a hot day with no breeze to cool it, it will overheat and burn quickly. But if a light moist breeze is caressing your plants, it will dissipate this heat. This can also be done to excess, for example, if the air movement is too strong, it can prevent plants from taking in carbon dioxide, or cause desiccation.

Microclimates

Put maximum/minimum thermometers and monitor the light and air flow in various spots of your growing areas. You’ll be surprised at how much they can vary. You might find, for example, that the sunny south side of your greenhouse near the exhaust fan is a prime spot for dendrobiums. Or the cool, breezy spot under the beech tree is ideal for the miltoniopsis. There is a copper beech tree near our facility here in Washington, DC., where legend has it that Abraham Lincoln used to like to sit and write because it was 10 degrees cooler under that tree than anywhere else in the infamously torrid DC summer. There may be spots like that in your own back yard. Seek them out. Those are great spots to summer your orchids.

Fertilizing

Even though your plants have been growing so well these last few months, beware of fertilizing on hot days. When plants overheat, they shut down metabolism and basically stop growing. If their medium and roots are imbued with plentiful, but unused, fertilizer, it can sour your mix and burn your roots. Take the time to leach your plants of excess fertilizer salts, and use plant foods sparingly (if at all) during excessively hot weather.

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Originally published in Orchids Magazine – July 2006

Thomas Mirenda is the orchid collection specialist at the Smithsonian Institution and an AOS judge. 3000 Cedar Lane, Fairfax, Virginia 22031

Growing orchids outside isn’t much different than indoor orchid care.

Your plants need the right temperatures, lighting, humidity, and water, as usual. You may find that you need to water more frequently outdoors, perhaps even daily. This depends a lot on wind conditions and humidity. If your climate’s temperatures don’t agree with what an orchid needs, keep it indoor!

Very few orchids like direct sunlight; and a shade cloth or a shade tree is usually required that provide alternating light and shade as the sun moves across the sky, provided the light doesn’t stay in one place long enough to cause sunburn!

Pay extra attention to your plants outside as it’s much easier for bugs to get at them, and you’re more likely to have to deal with things like caterpillars! One recommendation is to spray outdoors orchids with a mix of water, horticulture oil or neem oil and several drops of liquid dish detergent every 3 weeks to keep insects away. Also keeping orchids raised off the ground helps to control pests.

By Susan Jones

Like people, orchids, especially those that prefer cooler, shadier environments, can suffer from heat stress during the hot summer months. The midday sun is intense, especially during the summer, and the high temperatures that bright sunshine brings can burn your orchids quickly, especially the more sensitive types such as phalaenopsis, pleurothallids, paphiopedilums and miltonias.

Heat stress is a condition that occurs in orchids and other plants when excessive heat causes an imbalance in transpiration, the process by which moisture evaporates from the plant’s tissues. When that rate of evaporation exceeds the pace at which moisture is being replaced through water taken up by the orchid’s roots, the plant becomes dehydrated — leaves soft and wilted, pseudobulbs wrinkled and ridged. The instinctive response in this situation is to overwater the orchid to correct the dehydration. This can instead make matters worse by rotting the plant’s root system, further hampering its ability to take in much-needed hydration. The roots can only absorb so much water at one time. In addition to watering, control of heat and humidity play a significant role in the prevention and management of heat stress.

Placing a mounted plant in an empty clay pot can help retain moisture around roots. The microclimate of higher humidity helps prevent heat stress and aids stressed plants in recovering.

Signs of Heat Stress

These symptoms may appear singly, even in otherwise fairly healthy orchids. When they appear in combination, however, it is usually an indication of heat stress or an underlying problem (such as root loss) that has lead to heat stress.

• Yellowing of Plants and Leaves: Too much light causes a plant’s chlorophyll to deteriorate, which can turn your orchid an anemic yellow-green, and eventually cause premature loss of leaves. Most healthy orchids receiving appropriate light levels will be a robust light green.
• Withered Leaves: The culprit, especially in summer weather, can be overheating. If your plant’s leaves feel warm to the touch, they could be getting too much light, and need increased air circulation and shading, or a move to a more protected area.
• Sunburn: Initial signs of sunburn, as in humans, appear as a reddish-purple tint or freckles on leaves and pseudobulbs. In advanced stages, leaf tips and roots may brown, flowers drop, buds blast or flower spikes fail altogether.
• Shriveled Pseudobulbs: Your orchid’s pseudobulbs serve as its water-storage organs, so shriveled pseudobulbs indicate a dehydrated orchid – it is in a stressed state, having used up its moisture reserves.
• Leathery Leaves: This goes beyond mere wilting, and occurs in the advanced stages of heat stress, indicating severe desiccation and possible damage on the cellular level. Depending on how long the condition has persisted, the type of orchid and its overall health aside from the leaf damage, it may or may not recover once its leaves are parched.

Mounted orchids are particularly sensitive to higher temperatures and require additional water and humidity during hot weather. This Cattleya hybrid exhibits the yellowing leaves and wrinkled pseudobulbs typical of heat-stressed plants.

Prevention

Your orchids need lots of attention during the summer months, especially on hot days. With higher temperatures, orchids require more frequent watering to prevent dehydration. High temperatures quickly dry out mounted orchids, those in baskets and even potted plants.

Maintaining the balance between keeping orchids sufficiently hydrated and over-watering can be a challenge. A simple rule of thumb is that an orchid’s need for water increases and decreases with the ambient temperature, so water thoroughly and more frequently during higher temperatures. Most mounted plants and those in baskets, especially vandaceous orchids and other genera grown with little or no media, will benefit from daily watering in warmer weather.

In addition, keep humidity high and air movement continuous, as both of these factors help plants keep their cool on hot days. Adding a fan to the growing area, or locating your orchids where they receive the caress of summer’s breezes, as well as spacing your plants to allow for sufficient air circulation between orchids, can make a big difference in their environment and overall health. This will also help to keep rots from fungi and bacteria at bay.

The benefits from misting orchids during hot weather do not have much sustained effect, so unless one has a misting system in place to maintain that added humidity throughout the day, it is probably not useful to your plants. When watering or misting, always be certain that plants have ample time to dry before night falls, so as to discourage bacterial and fungal growth.

When moving orchids outside for the season, start them out in a shaded spot and gradually increase their exposure to sunlight to acclimate them to the higher outdoor light levels. Make sure to protect them from the strongest sunlight as midday summer sun has more intense UV rays that can burn tender plants. Check the amount of exposure your plants receive at different times during the day as the sun moves, and throughout the year as the earth’s orbit around the sun makes its gradual seasonal changes, which in turn changes the angle of the exposure your plants receive.

For greenhouse growers, consider using shade cloth for added protection during the summer months. Windowsill growers may want to add a sheer curtain during the summertime to keep sunlight reflected by the window glass from causing sunburn.

Finally, always have someone care for your orchids while you are away on summer vacation.

Treatment

Once an orchid has suffered the effects of heat stress, it may take a long time to rebound. Apply fertilizers sparingly, using a weak solution, and flush the growing medium with clean water between applications of fertilizer, as the salts in fertilizers are difficult for dehydrated plants to assimilate, and a regular dose may further burn the plant. Be especially alert for pests on distressed orchids – insects and viruses are more likely to attack weakened plants.

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References

• Dodge, Vivian M. 2003. “Sun Protection.” Vivi’s Orchid Corner. 8(6).
• __. 2000. “Tips for August.” Vivi’s Orchid Corner. 5(7).
• Withner, Carl L. 1997. “Good Orchid Growing or the Concept of Stress on Plants.” Orchid Society of Nova Scotia newsletter, May.

Susan Jones was the editor of Awards Quarterly and assistant editor of Orchids. American Orchid Society, 16700 AOS Lane, Delray Beach, Florida 33446

All reuse must contain the following:
Reprinted from the JULY 2004 issue of Orchids — The Bulletin of the American Orchid Society. Copyright American Orchid Society — aos.org