The Paphiopedilum Grower’s Manual
© Lance A. Birk - 2004-2006 - All Rights Reserved
Dividing and Repotting
Plants with healthy root systems produce sparkling flowers with heavy substance, fine textures, bright colors, large size and long-lasting qualities. Those plants which have remained undisturbed for several years will always exhibit flowers of better quality and number than those more recently repotted plants, even if they are of the same clone. For this reason you should never be in a hurry to divide and repot a well‑grown, specimen plant.
Unfortunately, one of the problems with Paphiopedilum growing is, that just as these specimen plants are doing their best, it becomes necessary to repot them, either because they have outgrown their container or else the potting medium has broken down. If attempts are made to circumvent this by potting them in larger containers originally, the mix will only decompose that much sooner.
The answer to the repotting question lies in the proper attention during the process of dividing and repotting, and in correctly judging the time to do it. More importantly, if proper cultural techniques are followed and maintained, when the time does come for repotting, the plants will withstand the shock it causes, and can resume their growth with a minimum of stress. Successful methods of dividing and repotting will be explained in this chapter.
The best time to repot a plant is before it needs it, and during its period of active growth. Most Paphiopedilum species grow actively in the spring, therefore you should set aside time during those months to take care of this necessary requirement.
Plants which may seem able to last for one more season in the same pot should be repotted sooner during their ‘up’ cycle of producing new growth and roots, rather than during their ‘down’ cycle when roots are dying from bad soil and leaves are lost for want of roots to support them. Plants kept in forward motion of active growth will be much more healthy than those whose cycles have been interrupted or reversed.
There are easily recognizable signals to watch for to determine the proper time for transplanting. Plants which have become top‑heavy and fall over on the bench are prime candidates for repotting. Those with leaves so numerous they cover the surface of the pot, preventing proper irrigation, should be repotted unless a means of soaking them each time they are irrigated is found to leach out salts which accumulate. If a pot does not drain properly it should have the soil replaced.
Potted plants which have been tried in different locations, but never seem to do well, often find renewed vigor with a renewal of the potting compound. If you see numerous roots at the surface of the mix it probably is past time to repot, and if a finger will easily penetrate to the second knuckle, into the potting soil, that plant needs repotting immediately.
Incidentally, when you obtain plants potted in a mix much different from your own, you should wait a month or two before attempting to change their mix. While it is a good idea to keep your potting compound uniform, this time-lapse will allow the recent acquisition the time to recover from the stress of moving, and to adapt to a new environment. Growers living in milder climates will pay less attention to these concerns, and they will repot their plants practically at any time they show the need.
The best method to determine whether or not your plant needs to be repotted is to knock it out of its pot and examine the root system. The potting soil should not have decayed too much, and the roots should be loosely entwined rather than tightly enmeshed. If there are numerous firm roots, with most of them in active growth, as can be seen by whitish new root tips, this is the best time to repot.
If repotting time coincides with the growing season of the species under examination, and you see few or no healthy root tips, the plant could be losing them as fast as they are being produced. In this case, the plant must be given fresh compost to allow it to continue its growth. Finding a few dead roots along with live roots on a healthy plant is normal and should not be a cause for alarm.
Inspection of the compost is important at this time, since it will give you important information about the ingredients in the mix, your method of watering, and whether or not pests are hiding in it. Regardless of what you used for a potting compound, you will be able to see if it has decomposed faster, or slower than you expected. Mixes containing several different ingredients frequently have one ingredient decompose faster than others. At this time it might be a good idea to reflect upon its necessity, and perhaps omit it during the next potting session.
Possibly an ingredient may have deteriorated faster because it was of inferior quality, such as might be the case with soft fir bark. By using a better grade of bark the next time, you may eliminate this problem. And if all the roots on the outside of the root ball are alive and healthy, while those in the center are dead, it is an indication that the mix either holds too much water, meaning that it also restricts air flow, or that it was watered too frequently.
Root hairs attach themselves to certain ingredients in the compost and not to others. Plants growing in mixes combining fir bark, gravel, volcanic rock and moss, frequently have roots attached only to one or two of those ingredients. Root hairs usually fail to attach to materials like volcanic rock because they hold too much water, or not enough, or possibly because they retain higher concentrations of undissolved solids.
Or, it may be because certain particular ingredients do not offer the necessary surfaces to which the root hairs can attach. Root hairs do attach to fir bark because they are able to assimilate moisture and nutrients from it; it makes little sense to use an ingredient in a potting compound which prevents this.
During the process of dividing and repotting you will see if centipedes, snails, slugs, mealy bugs or any other pests have taken up residence inside the pot. Examine the mix from several pots, carefully, to determine if you have a problem. If you see any of these pests, then you can take necessary steps to eliminate them, or to at least keep them under control.
Do not confuse decomposed potting mix caused by the activity of centipedes, worms or other pests, with unsatisfactory potting ingredients or watering techniques. The former can be identified mainly by the fact that the soil mix will be reduced to an almost paste-like, rather than a granular and irregular texture.
There are times when certain robust and healthy‑looking plants can present an unexpected problem during repotting time. While these plants exhibit their best health, both in flowering and in vigor, the massive condition of the tightly bound root system can prevent them from being readily divided.
The problem arises when you separate the roots, which can become severely damaged during the cleaning process, and again during their division. Such a plant is sure to be the cause of grief, for by the time the job is done, you will have several large healthy growths, but without enough roots left to support them.
Divisions of plants in this condition quickly lose their vigor. Lower leaves fall off and older growths die. Soon you may be left with a "snitch," which is a plant so small and so sickly, that no matter what treatment you give it, nothing seems to work. The snitch usually remains about the same size; it may grow a new leaf, but then it will lose an older leaf. Finally, after years of attention and concern, it will suddenly die. Snitches should be culled as soon as they are recognized.
One never thinks of a healthy plant becoming a snitch, but if the condition is unavoidable and you are forced to damage or destroy most of its roots, then repot a severely root-bound Paphiopedilum, but keep those divisions to four or five growths each. This will ensure that they will have enough energy within each division to produce the new roots required to maintain their health.
Growers living in Southern California and the southern parts of the United States, the Caribbean, Hawaii, the Mediterranean and similar areas, seldom worry about the time of year for repotting their plants, because the climate is mild enough to repot at any time. But for many growers it is an important consideration and they should watch their plants carefully to distinguish between plants that have a rest period, and those which grow continuously.
The former should be repotted as they commence their new growth, and the latter should be done during the spring months. Certain species begin their period of active growth in mid‑winter, and if they are not been maintained in good health, they will suffer considerably if transplanted during that time.
Since many Paphiopedilum growers cultivate their plants inside greenhouses, you should be aware that the heaters used to heat those enclosures cause a marked drop in humidity. Even un-vented, natural gas heaters, whose products of combustion are water and carbon dioxide, will cause plants to dry out rapidly. Plants with damaged root systems will only able to assimilate moisture through their leaves, and if the humidity is too low for them to do so, they will slowly expire. Frequent, light misting during the daytime will help prevent this for those freshly repotted plants.
Normally, each individual growth or fan of a Paphiopedilum will make one or more new leads, which become the new growths. Each growth will produce its own set of roots, which primarily support that one growth, but both older growths and new growths will receive nourishment from the same roots. Unlike other orchids, single growth divisions of mature paphiopedilums frequently produce flowering growths within a 12‑month span. In the same thought, do not remove forward divisions of an un-bloomed plant.
There are some species of paphiopedilums which exhibit different growth patterns that you will need to be aware of, and as you maintain your collection, they should be noted.
One group includes the species which take three years from the breaking of an ‘eye,’ or new growth, until they reach flowering maturity. Others are those particular plants which have made two or three years of growths without producing corresponding root systems. P. druryii and P. praestans are two species which seem to do this regularly, however any species can do it on occasion. Do not make single growth divisions of species with these peculiarities.
You should start with a clean workbench, and then gather your clean pots, your potting mix, clippers, name tags, pencil and work tray. Assemble the plants to be repotted and make space for those that have been completed. Plan to do your repotting several days after watering, because if the root-ball is wet, the compost will cling to your tools and fingers. Working with a small group of a dozen plants in your work space is easier than trying to do too many at once.
Examination of the root system will tell you many things about your culture, so begin by knocking the plant out of the pot. Gently remove the old compost from the roots and separate them as you do. Be particularly careful of new root tips. Rough handling at this time will lengthen the time for recovery from the trauma of transplanting.
With the clippers, cut away the dead roots, (those hollow and collapsed ones), then cut those which are partially decayed, back to fresh tissue. Trim off dead or yellowed leaves and any old flower spikes.
If the plant is large and has many growths, examine it for natural lines of division. Twist and pull at these points. The plant should break at the rhizome between growths, but if it does not, it can be severed with a sharp knife. Certain plants have no discernable rhizome and they must be studied carefully for their possible line of division. If a knife is used, the cut must be made carefully in order to cut through the rhizome itself, and not the growth of the plant.
Large‑growing species such as P. philippinense have very tough and thick rhizomes which require the use of a sharp, serrated knife, or a pair of sharp and sturdy clippers. Small and succulent species, such as those in the Brachypedilum section, must be severed with a thin, sharp knife, since they have the nasty habit of breaking off at the base of the plant rather than at the rhizome. The result can be a plant broken in two, with its leaves in your one hand and roots in the other; neither of which will survive.
After each division has been cleaned, trimmed and set aside, you should immediately write a new nametag for it. Do not wait to do this, for it is easy to mix up plants during repotting. Discard the old compost and rinse, or wipe the tray clean. Remove the debris, used pots, etc., from your workspace and allow yourself sufficient space in which to repot.
Next, stack up your fresh clean pots, fill the work tray with new compost and prepare your work area so you may work in a smooth and uninterrupted motion. Place the plants to be potted on one side, the tray of compost in front of you, and an empty tray for repotted plants to your other side. You will find that if you work from one side to the other during the repotting process, it becomes a much simpler chore.
Begin repotting by taking a clean pot in one hand and a division of the plant in the other. Place the roots inside the pot and position the rhizome about one inch below the rim of the pot. Then, hold the plant with your thumb and forefinger, and the pot with your remaining fingers of the same hand. With the other hand, fill in the potting compound. Frequent vigorous tapping of the sides of the pot, and thumping it on the workbench will settle the mix evenly about the roots. Once the plant is held in place by the compound, both hands may be used to fill additional mix into the pot.
The finished plant should have its rhizome just below the surface of the mix, slightly higher if you use a dense mix. The plant should be firmly positioned. If it is loose, pot it again. Do not use a potting stick, but instead use finger pressure to keep the plant from moving after you have finished.
Trimming off a lower leaf if necessary, will allow you to lower the plant in the pot and it sometimes helps those individual plants that just do not seem to want to be potted firmly. Make certain each repotted plant has its own nametag, and then place it on the growing bench. Water each pot thoroughly.
‘Potting on’ is the practice of taking a plant out of one pot and repotting it into a larger pot, then adding fresh compost around the outer edge of the root-ball, without cleaning off the older potting mix. Ideally it will provide a means whereby a plant can continue its growth uninterrupted, without the trauma from being transplanted. When Osmunda was the predominant planting compost used for orchid growing, it usually produced good results. With the advent of the newer mixes, the practice has remained, but unfortunately the results have changed.
Unlike Osmunda, which lasted for several years, attempting this with the modern potting compounds, which break down after a few years, can result in the loss of roots and possibly even the plant as well. Inexperienced growers can fall readily into this trap, since the advice is still found in so many publications. Unless a more permanent potting mix is found, (rather unlikely), Paphiopedilum growers should remove all of the old, loose compost from the roots of their plants during repotting.
‘Crocks’ are another problem. They are the broken pieces of clay pots, placed in a layer at the bottom of pots "to help drainage." Recently, the types of crocks used have consisted of plastic ‘peanuts’, volcanic rocks, gravel or several other kinds of large inert materials. Unfortunately, both older and some newer literature often promotes this.
In practice however, crocks actually prevent proper drainage of most mixes, by interrupting the capillary action which draws the water to the bottom of the pot. Additionally, those empty spaces at the bottom of the pot are perfect hiding places for slugs, snails and other nasty pests. Since there does not seem to be any convincing evidence for their benefit, I recommend that crocks should never be used.
Dividing and repotting is a simple, but time‑consuming chore. There are no mysteries about it and anyone can do it properly. Its importance cannot be underestimated, as the timing is most important for successful Paphiopedilum culture. What will separate a good grower from a not-so-good grower is the one's response to the plant’s need for repotting, and to accomplish the job before the plant becomes stressed.
If in doubt about when to repot, knock the plant out of its pot to check the root system. Its condition will answer your question.