May 2010 - Tips on Re-Potting

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If emails and casual conversations are any indication, repotting is traumatic for many orchid hobbyists. It is not surprising to most of us that have been doing this awhile, because it was traumatic to us in the beginning too. Given how different orchid roots look, the cost compared to a petunia, and the number of pages in orchid books devoted to the “dos and don’ts” of potting, fear is not surprising. So here is what everyone should remember.

Getting two or more orchids from repotting one should never be the reason to repot, although that is a frequent consequence. Repot when your orchid is at risk because the potting media is breaking down or there is some other problem, e.g. heavy scale infestation that cannot be solved without removing the plant from its pot. Remember that the bigger your orchid is, the more and larger flowers it will have. Always sterilize any instrument that cuts an orchid. The best method is to hold your snips in the flame for a few seconds making sure you have exposed both sides of the entire cutting surface to the flame. A hot cutting tool effectively sterilizes the cut surface of the plant.

Do not worry about damaging roots, since most will ultimately die from the repotting anyway. Some expert growers remove almost all roots when they repot to avoid them rotting later and infecting the rest of the plant. If repotted at the correct time of the year, your orchid will quickly re-grow roots, but it may take a few years to acquire the root mass it had before repotting, hence the suggestion to avoid repotting unless absolutely necessary.

Many times I sit a cattleya with all of its roots removed in the bottom of a clay pot in a shaded portion of the greenhouse until I see tiny new roots starting. Only then do I add the medium and complete repotting. On occasion, I forget a plant and find it fully rooted to the pot the next spring. Again, the key point is that one should only repot during the growing season; i.e. now.
Most books recommend wetting the medium before using it, a recommendation that I do not endorse. This is an open invitation for bacteria and fungi to invade any open wounds on the plant. It is best to use dry medium and wait at least several days before watering your newly repotted orchid. Some growers lay their divisions on newspaper in an unused bedroom until new roots appear. Why waist a pot and medium if the division is not going to grow well.

The key to all repotting is to remember that your orchid has been shocked and lost most of its ability to obtain water. Cattleyas, dendrobiums and other orchids with thickened leaves will be fine if the plant is shaded heavily after repotting until they get new roots. Then, gradually give them more light. Other orchids that are terrestrial-like and/or have fine roots or thin leaves, need more care and may require some misting until new roots appear.

The one exception to the need to keep roots dry is when a medium is used that is toxic to bacteria and fungi, e.g. sphagnum or osmunda. The pH is so low that almost no bacteria harmful to plants will grow. This seems to be the medium of choice for many phal growers.