As a new orchid grower, one of the first pieces of cultural information we are given is that we should make sure to let the potting medium dry out between waterings, as the plants will otherwise get root rot. Some will even include the explanation that the constant moisture favors the growth of fungus, and that is what attacks and rots the roots. Unfortunately, that is simply untrue.
If the mere presence of water was the cause of root rot, then there would be no possibility of growing orchids in hydroponic, semi-hydroponic, or water culture, all of which are quite viable techniques. Wild plants would also not be able to survive during the many months some experience in monsoon seasons, which is often when they thrive. If we take a different approach and blame it on fungi, then how would we expect orchids to grow in the wild, in natural environments that are no doubt overrun with all sorts of fungi, bacteria, and the like?
Instead, we should blame it on suffocation and poisoning, and consider what happens when we water a potted plant.
When we water, some (most) of the liquid simply runs through the pot, some of it is absorbed by the potting medium components, while more of it is held by surface tension in between the medium particles. The smaller the space between the particles, the more easily that so-called “bridging water” is maintained, allowing it to more completely cut off the air flow pathways.
If the air flow to the root system is stifled long enough, the gas exchange is compromised, and the roots die due to a combination of suffocation from the lack of oxygen, and poisoning by its own waste gases.
Once the root tissue dies, the natural resistance to pathogens is eliminated, and the roots will rot.
If you think about it, that mechanism is likely the misinterpreted basis for the “let the medium dry out” myth: as the plant absorbs moisture, and more of the liquid evaporates, those bridging water droplets go away, opening up the air flow pathways and allowing the root system to “breathe” again.
Rather than suffocating the plants at each watering, the better approach is to prevent the extensive occurrence of bridging water in the potting media, and keeping the spaces larger is the key:
Root rot normally happens when an orchid grower waits to long to repot, letting a plant suffocate its roots in a dense, mucky mess. Of course, it’s often our most valuable or favorite plant, so how do we get the plant to recover?
First, keep in mind that as a “natural creature”, the plant has a survival mechanism, so it wants to recover. Then, with that in mind, consider that our job is to give it the highest likelihood of doing so. The keys to recovery are high humidity, warm temperature, and subdued light.
Consider the following scenario:
It may be difficult to maintain those conditions, so one thing to consider is the “Sphag-n-Bag” treatment to create a good, controlled environment (see below).
Another option – one that adds to the probability of survival, but is not a substitute for providing the conditions above – is the application of a rooting hormone. Brand is not critical, but freshness is (the hormones degrade with time, temperature and light exposure). The most effective treatment method for a root-free plant is a soak:
It is not necessary to repeat that, but you may begin adding the hormone to your irrigating solution once root growth has begun. Do not fertilize until the plant is established in its new pot and fresh medium.
OK, you’ve managed to rot the roots off of your plant, but you don’t want to lose it. What can you do? Many orchid growers resort to the old “sphag-n-bag” technique. By the way, this is good for getting new imports established, too.
First, let’s consider the needs of the plant: It needs water to survive – water is the life’s blood of the plant. It provides turgidity to the tissues and cells, it is a chemical component used in the production of the sugars during photosynthesis, and it is used by the plant to control the osmotic pressure of ions inside- and outside of the cells. So if you have no roots, how does the plant get water?
Misting is of little value, as the plant cannot take up a substantial amount of liquid water through its leaves, and the brief period that the humidity is raised by periodic misting is likely insufficient to be of much benefit. The key is maintaining high humidity, not so much because of the easier absorption of water vapor (which is the case), but because a saturated environment prevents further loss of water from the plant tissues while it attempts to grow new roots. Basically, the sphag-n-bag concept uses a small bit of damp sphagnum as a moisture supply, and a plastic bag as a “micro-greenhouse” in which the elevated humidity can be easily maintained.
That’s simple enough, but a big mistake that many folks make is placing the plant in direct contact with moss that’s too wet. The technique I use involves preparing the plant, then setting up the “rescue” environment:
Placing the plant in that warm, shady location (not dark) is important: The warmth will induce some growth activity, but the shade serves to moderate the vegetative growth while the plant develops new roots. Furthermore, warmth results in a higher moisture content of the air in the bag, and the shade prevents the bag from becoming a broiler, as it would become if direct sun hits it.
In a few weeks, the plant is likely to have developed a new root system, at which point it can be repotted. Another idea for those of you who grow your plants in Semi-Hydroponic™ culture: Pot up your suffering plant and then place the plant – pot and all – in the bag. It will get all of the benefits of the sphag-n-bag environment, but has the bonus of growing its roots into the medium without the need for repotting afterward.
Ray Barkalow has been growing orchids for over 45 years, and owns First Rays, which offers horticultural products to the hobby grower. He may be contacted at firstname.lastname@example.org and you can visit his website at FirstRays.com.