AOS Monthly Checklist for July and August

By Ned Nash and James Rose

Cattleya

Cattleyas this month require careful attention to their watering and fertilizing needs owing to characteristically high temperatures. Evaporative cooling is a must in areas of the country where it is effective. Where it is not (the more humid regions), care needs to be paid to proper venting to keep temperatures within reason. Bottom vents in conjunction with top vents provide enough rising airflow to help keep plants cool. Increased air flow lessens humidity and dries plants out more quickly, necessitating more frequent damping down and watering, in areas where high humidity is not a problem. Higher light and heat indicate more fertilizer. The growths your plants are making now are the source of this autumn, winter and spring’s blooms, so applying adequate fertilizer this month is the best way to ensure future blooms. Higher temperatures and humidity may also lead to fungal or bacterial rot problems, so it is important to closely observe your plants for any early indication of problems. Pests are also at a high point this month for the same reason.

Paphiopedilum

Cooling and air circulation are especially critical in these two months to prevent stress and avoid disease problems. Watering needs to be closely monitored to ensure that plants do not dry out. Warmer-growing hybrids will be at the peak of their blooming, with attention needing to be paid to staking of spikes. Look for water lodging in growths, which can rot emerging spikes and lead to the loss of the entire growth.

Phalaenopsis

Most, if not all, potting should be complete by now. This month and next are when these plants achieve their maximum growth. This growth will be that from which they set their spikes for the coming season. The more leaves the plants grow, the better potential for spiking will be realized. Growers in cooler areas such as the Pacific coast have the advantage this month, should they choose, of cooling for early season spikes. Lots of heat and light call for liberal applications of water and fertilizer.

Cymbidium

Summer can be the most rewarding season for cymbidiums. Growths should be coming strong now. The leaves of the new growths are best when they are broad and fairly stiff. The color should be a light green to nearly yellow. Early flowering varieties should be showing flower spikes, so move the plants into a cooler area with lower light. For mid-season varieties, lower the dosage of nitrogen to assist in spike initiation.

High-elevation Plants

For cooler-growing plants, such as masdevallias, other pleurothallids and the like, the next few months will be a challenge. During the hottest times, keep your plants more shaded and be sure to keep the humidity level much higher. Do not let plants dry out. Delay any potting until the weather cools.

Laelia purpurata

The flowering season of this majestic plant will be coming to an end, presenting a good time to report. As soon as the new roots start to appear, clean off old bark and repot into a clean medium- grade fir bark. Place the plant in a little less light and higher humidity to relieve stress until it is more established, which is about one month after potting.

Odontocidium

Many of the intergeneric crosses between odontoglossums and oncidiums, such as Odontocidium, Wilsonara and Colmanara, will be blooming now. Take special care to train the spikes for best floral display. Keep plants under fairly shady conditions. Watch for snails and slugs.

Vandaceous

Genera Plants will be growing quickly now and really enjoying the hot humid days so similar to their native habitat. Watch for pests though, as many of these also enjoy the same conditions as the plants. Check flower spikes so that they can extend unimpeded for the best flower presentation later.

This article was published in the August 2010 issue of VAOS News.

This summer has been not only hot, but hot with low humidity. If you provide the proper air movement required to keep your orchids from overheating in this weather, you are also accelerating the loss of water from your orchids.  If the orchid’s loss of water exceeds its ability to acquire water your orchid experiences water stress, usually indicated by shriveled leaves or bud drop. Some of my orchids that typically love high light that are near the glass even have burned leaves because they do not have enough water in their leaves to keep the leaf cool. Most plants, including orchids, have stomata or microscopic openings on the bottoms of leaves. Stomata open, allowing water to evaporate and cool the leaf.  If the orchid does not have enough water, it cannot keep its leaves cool.

Over the years there are many experienced growers, many commercial growers of orchids, that told me they routinely violated one of the cardinal rules found in most books on growing orchids. Most books suggest watering orchids early in the morning so that they will be dry by nightfall. Failure to do so, according to the books, will cause rots. During the middle of summer, however, I routinely violate this paradigm.

Whenever nights are warm, I heavily water my orchids near or just after sunset. The object is for them to be soaked all night. The next morning, I water heavily again and often fertilize at this time. When I go out to water in the morning, vanda roots are swollen and green, as are the visible roots of my cattleyas and phals. Rots are very rare and almost always on newly purchased orchids or plants that have already had problems.

My orchids had been looking water stressed, but a week after staring this regimen, bulbs have become plump and new leaves abound. There are even newly branching roots.

If you decide to try this approach, keep the days between watering the same as you did before. Apply only water in the evening and fertilize only in the morning.  If you live in an area where night temperatures get lower than 60F be sure you never fertilize at night. In the morning, plants are well hydrated and there is no risk of fertilizer toxicity, even at high levels. Roots are also ready to take up fertilizer as their surface condition has changed from hard and stiff to soft and pliable. If you live in an area with hard water, salts that accumulate on the medium, pots and roots will become soluble overnight, allowing them to be flushed out the next morning.

If you ever visit the tropics where many cultivated orchids originated, it is

surprising to read the prohibition to never water at night. In their natural habitat, orchids are soaked at night by rain or dew. Rarely will you ever find an orchid with rot in nature. In the wild, orchids grow very slowly and are very limited by nutrients. Their leaves are thick and hard; even immature plants.

Bacteria require nutrients to grow and the presence of water laden with nutrients in and on leaves is an invitation for bacterial and fungal invasions that cause rots.  Orchids can grow quickly if pushed with lots of fertilizer. However, cell walls are thin and soft on these orchids making it easy for fungi and bacterial invasion.  Cells also are loaded with excess nutrients providing fuel to any invader.

Growing under lower nutrient conditions does cause slightly slower growth and causes orchids to put more energy into root growth. This produces a better rooted orchid, less susceptible to disease, even if you water at night.

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Courtney T. Hackney writes a monthly column and is a contributing writer for several FL orchid societies.

Email: Hackneau@comcast.net

VAOS News, August 2010 issue.

Orchid Pests and Diseases by Sue Bottom

Here is an excellent summary with photos of orchid pests and diseases.