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by Ken Slump

Posted by Sys Admin over 3 years ago.

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Providing for the Requirements of Plant Root Systems

IF YOU THINK ABOUT IT, THERE IS little that is more foreign to an epiphyte than life in a flowerpot. Epiphytic orchids, in particular, are plants that typically send roots sprawling across limbs, branches and twigs, not only to secure their attachment but also to ensure opportunities to procure adequate moisture and nutrients for their survival.

This became vividly apparent to me when I made my first attempt at growing an orchid outdoors on a small tree in South Florida. The orchid was a somewhat diminutive Brassavola nodosa hybrid that I carefully tied to an ornamental tree near my home’s entrance. I placed the plant in the tree shortly before heading north in the spring, with the hope that the rainy season ahead would sustain it until my return in the autumn.

When I next saw the plant just four or five months later, I was astounded at the roots it had produced. A number of them had extended well beyond the clustered pseudobulbs, both above and below the plant’s location on the angled branch on which it was perched. It was gratifying to see that the orchid had found itself a home.

My biggest surprise, however, was how far the plant’s new roots extended. Several of them had meandered along the small limb to extend almost 3 feet (1 m) from the little plant’s base of operation.

Like all experienced orchid growers, I had often observed the intriguing growth of orchid roots over, under, around and through their growing medium and containers. It appeared as though this little orchid had produced a length and volume of roots that was considerably greater than I would have expected if I had extricated the same plant from a satisfactory container habitat after the same amount of time.

It seemed to me that the roots had developed in response to the need for water in a setting where moisture was not retained for longer periods by virtue of a growing medium in their proximity. Apparently this was necessary and achievable for the orchid in this more naturalistic setting. While my simple observation could not have been further removed from a valid scientific study, it led me to further contemplate and reconsider the relationships involved in the practice of container orchid culture.

The main purposes of container culture are to provide for the re-quirements of the plant’s root system so as to sustain the life of the plant, while at the same time offering finite containment and thus a certain amount of control, if not portability, of the plant. But, as noted, epiphytic orchids do not fit into the same mold as those plants of terrestrial origin that have been traditionally grown in containers.

MATERIALS  These days, most pots and containers for growing plants are made of either of two materials:  plastic or clay. Both types have advantages and disadvantages and the majority of growers seem to prefer or be more successful with one type over the other.

Clay or terra-cotta pots have enjoyed longer usage and were the nursery standard for many years. These pots have a number of points to recommend them. They are readily available in many sizes and shapes. Perhaps their main advantage is their porosity — they have the ability to “breathe” by allowing moisture to pass through them, thus helping to alleviate the potential problem of a soggy, moisture-retentive growing medium.

Clay pots can be expensive and, the larger ones, are heavy. The weight issue may actually be an advantage in the case of orchid plants, which so often have thickened leaves or pseudobulbs that tend to make the plants top heavy, such as the canes on upright-growing dendrobiums.

Clay pots are fragile, but can be sterilized with heat or chemicals for reuse. Due to their porosity, chemical salts can tend to accumulate on their surfaces. The color range available is rather narrow, but most plants somehow seem to look good in them. Orchid growers can usually find terra-cotta pots specifically produced for orchid culture. Such pots have additional holes or slits in their sides to assist in allowing the growing medium to dry out quickly.

In many cases, it is the converse of the characteristic of the terra-cotta pot that is true for their plastic counterpart. Yet many growers would use nothing else.

Plastic pots are also readily available in many sizes and shapes. Containers made of plastic do not breathe, and are, in fact, moisture retentive, even though they typically have more drainage holes in them than a clay pot of similar size. They are inexpensive, lightweight and come in a variety of colors.

Chemical salt buildup from fertilizer applications is not a problem with plastic pots. There are plastic pots manufactured with extra holes or slits designed specifically with orchid culture in mind. But if you want to make your own, it would certainly be easy to cut or melt such features into standard plastic pots. 

There are plastic pots available now that are made of translucent or somewhat clear plastics that are quite popular with some orchid growers because moisture levels and root growth can be observed. Such pots also have the advantage of offering the chlorophyll present in many orchid roots an opportunity to help nourish the plant through photosynthesis. Many phalaenopsis growers, in particular, seem to favor this type of pot.

Plastic pots, due to their low cost, are seldom reused. Chemical sterilization would obviously be required to clean them for reuse as they could not withstand sufficient heating for that purpose.

MAKING A CHOICE  Whether to choose a plastic or terracotta pot for your orchids will depend on several factors. The type of orchid, the growing medium, the growing conditions and your cultural practices must all be considered.
Epiphytic orchids that have thick-ened leaves and large pseudobulbs, such as many of the Cattleya orchids and their relatives, often have roots that develop rot if moisture is retained around them for too long. Such orchids seem to thrive in clay pots, particularly those with extra slits or holes in them. These are also among the more top heavy of orchid plants so the added weight of a terra-cotta pot is certainly advantageous.

On the other hand, paphiopedilums lack pseudobulbs. They are found in moist habitats on rocks or near the ground; indeed, many are semi-terrestrial. Plastic containers would seem better suited to their needs. Their cousins, plants and hybrids of the genus Phragmipedium, are generally known as water lovers, so should not only be grown in plastic containers, but may also grow better if situated in a shallow saucer of water as well.

The characteristics of the growing medium you choose should help you select the best material for the container. The more moisture retentive the mix, the more important it is to have a container that will allow that moisture to dissipate, unless, of course, it is a moisture-retentive root zone you seek. Organic media components such as bark, coconut husk chips and sphagnum moss will tend to hold moisture longer than ingredients such as charcoal, perlite or lava rock.

The growing conditions or environment in which you grow your orchids greatly affects their need for water and moisture in the root zone, and helps determine how quickly the pots dry out. Consider the differences between the growing conditions in a humid greenhouse and the environment near the windowsills of a house with central heating. The quality, amount and duration of light are also important criteria that help determine each plant’s moisture need. Two other environ-mental factors that come into play are air movement and temperature.

Finally, your cultural practices will help determine which style of pot will work best. More specifically, it is the frequency and amount of water delivered to each plant that matters. If you tend to overwater, clay pots will provide a margin for error, while plastic ones will exacerbate the problem.

SIZE AND SHAPE  In addition to choosing the best material for your orchid containers, it is important to consider the container’s size and shape. Generally, it is advisable to opt for the smallest pot that will comfortably contain your orchid’s root mass. Another rule of thumb is to allow for only a year or two’s new growth in the size of container you choose.

While some orchids thrive in the pots and containers of standard dimensions, many types seem better suited to the shorter pots that are known in the trade as azalea pots or “two thirds” pots. Some even prefer the very short styles called bulb pans. This is because the roots of many orchids tend to grow toward the outside of their containers and seldom make their way down into deep pots.

Keep in mind that pots made of glazed ceramic, as well as terra-cotta pots that have been sealed or painted, will behave more like plastic pots with regard to moisture retention. Clay pots that are kept within glazed ceramic or metal cachepots will also lose moisture from the root zone more slowly than expected.

Perhaps the best approach in an orchid collection with a lot of variety is to pot the majority in either clay or plastic — whichever seems to work better for you. Then try adapting those genera and species with special requirements by incorporating a 
few different containers. If plastic containers seem to suit the needs of most of your plants, but you have a few that seem to exhibit symptoms of overwatering or have a preponderance of rotten roots at repotting time, try putting those into clay pots. On the other hand, a grower with a preference for terra-cotta containers could grow moisture-loving orchids in plastic pots with a moisture-retentive medium so that those plants might be able to go longer between waterings.

It is a worthwhile goal to be able to water every one of your orchids each time you irrigate them and not have to remember to skip over some that tend to stay too wet, or provide extra watering days for a few that dry out too quickly. A thoughtful balance of the right growing medium in the best container for the particular type of orchid can help you achieve that goal.
It is indeed remarkable how satisfactorily many epiphytic orchid species and their hybrids have adapted to life in a pot. There are some, however, that truly cannot make that transition. Often they are orchids that demand perfect drainage. In such cases, culture in baskets may be an option, or they may thrive if they are grown mounted.

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