Dividing and repotting plants is a regular occurrence, but one which worries
many growers, especially those who have recently caught the orchid growing affliction.
Repotting is required when -
- the plant has outgrown its existing container - or
- the growing media has broken down
With adult plants, repotting will be required after two or three years. Smaller plants may be repotted
every 3 to 6 months to ensure the mix is always in optimum condition to facilitate maximum growth and quicker flowering.
You can either -
- repot the plants into a larger container, but there can be limits to this, or you can
- divide the plants into a number of pieces, each of which is separately potted.
In considering the necessity to divide a plant, obviously the size is a prime consideration. With many
plants, larger specimens flower more readily, with multiple spikes, and which can produce a magnificent display.
However, larger plants are often difficult to maintain in good condition, and there can be physical limitations
to both the moving and displaying such specimens.
The basic details of dividing and repotting are the same with all orchids. In this article cymbidiums
are illustrated, but the same principles can be applied to virtually all the sympodial orchids under cultivation.
On each side of a pseudobulb in the axis of the leaves are a series of buds. The new growths develop from
these buts, usually just from one of the sides, although a second one on the opposite side of the pseudobulb may
also break into growth with vigorous plants, producing a multiple lead plant.
The first years growth is illustrated at the top illustrations of the following table.
After that new growth matures over the following season, this process repeats itself over the ensuing years.
In the following illustration each years new growth is depicted by a black dot. In the second year,
the single mature pseudobulb has produced two leads. At the end of three years the original single pseudobulb
has developed into a three lead plant, the most recently matured pseudobulbs producing a two lead growth
and single lead growths., The right had illustration is only for the first 2 years.
Identifying the growth pattern is important as it can assist in the correct dividing of the plant. With
cymbidiums the joining rhizome is short, and it can be more difficult to see h ow the plant has developed.
With, for example, cattleyas, the growth direction can be generally easily ascertained.
GROWTH OVER 3 YEARS
The older pseudobulbs will retain their leaves for 2 to 3 years or even longer in some cases, but will eventually
loose them. When all leaves are lost, the remaining bare pseudobulb is called a "back bulb".
They are not dead, however, at this stage. Removed, they can be often coaxed back into growth, and will eventually
produce new flowering plants. The old defoliated pseudobulb is buried to one third to half its depth in potting
mix in a small pot, and over several months most will develop a new growth. They can also be often started
into growth by placing in a plastic bag with some damp sphagnum moss and kept in a warm shaded area. When
the new roots reach some 25 mm long, the plant can them be potted up into your normal potting mix. Over some
3 to 5 years, a new flowering plant will be produced. Those pseudobulbs not removed will eventually rot over
several years. In the growth of specimen plants, the development of back bulbs and their final demise will
often limit how far one can go in this direction. Some plants will retain leafy green bulbs for a number
of years; other plants will readily produce many back bulbs.
The growth pattern is important when one is dividing a plant, as it influences where one actually makes the
break. With smaller plants, the connecting rhizome can be easily seen, but with larger specimens it can be
difficult to follow the growing sequence. Often by working back from the most recent growth, and moving the
pseudobulbs, you can ascertain where the connecting rhizome runs. In making a decision to divide a plant,
remember that a flowering division should contain at least three green pseudobulbs - those still with their leaves.
Generally the old leafless back bulbs will be removed. Although they will not harm the plant, they will not
do much to benefit it. Take time to ascertain where the rhizome runs. If you do not you may end up with a
number of single pseudobulbs, which can take 3 to 5 years to reach flowering size again.
PLANT REMOVED FROM
CONTAINER SHOWING ROOTS
To repot or divide, first remove the plant from its existing container. Often the plant will come
away when the plant is inverted. Sometimes a quick crack on a shelf or bench will do the job. With
plastic pots, the alternative pressing of the sides can also release the roots. When the plant is removed,
work the old mix away with the fingers, or a jet of water. You may have to unwind the larger roots. Ensure
all the old mix is removed. Old dead roots should be trimmed away. With the removal of the media, often
the rhizome can be more easily seen. Separate the plants into pieces as required. you may break the rhizome
by hand, which is the preferable method as it prevents the spread of virus disease in particular. You can
cut with a knife, but flame the cutting instrument between plants.
PLANT REMOVED FROM CONTAINER,
THE ROOTS TEASED OUT
SO THEY ARE ALL FREE
THE RIGHT POT
WOULD HOLD THE WHOLE PLANT
THE CONTAINER ON THE RIGHT
WOULD HOLD A SMALL DIVISION
After the pieces are separated the cut rhizome should be treated to prevent the entry of any pathogens. A fungicide
or pruning past can be utilised; an inexpensive treatment is to use flowers of sulphur in a puffer pack.
The cuts can also be allowed to callus over by exposure to the atmosphere for an hour or so. The largest
roots may have to be removed. Some growers cut the bottom third of the roots off, on the theory that their
removal eliminates any potential problems at this stage as damaged roots often die, and cutting such material away
allows the roots to more quickly regrow and re-establish.
SMALL DIVISION READY FOR REPOTTING
PSEUDOBULBS TO EACH SIDE
LEFT HAS NEW GROWTH DEVELOPING
RIGHT CAN BE SEPARATELY POTTED UP
Now you have broken the plant into a number of pieces ready to insert into a new pot, you have to decide
on the size of the pot. You should ensure that the roots just fill the container chosen, although tend to
underepot slightly. At this stage you will have prepared the potting mix as noted in the seasonal notes.
THE POTTING MIX BEING POURED AROUND
Place the plant in the container, and pour the mix into the pot. Work the mix around the roots with your
fingers. You can also bump the pot onto the bench, or tap the sides of teh container to ensure an even distribution
of the growing media. Ensure the plant is placed to allow maximum forward growth - the older parts placed
to one side, the growing leads placed to ensure they have room to grow for the next few years.
The rhizome should be placed 25 mm below the edge of the container, with the mix just covering the rhizome.
Make sure the plant is firm in the container, but not too tight. A good guide for firmness is that you
should just be able to pick a freshly potted plant up by its leaves, and it will not come out of the pot.
If one or two plants out of ten do come out, then you know you have the density of the mix about right.
After repotting has been completed, place the plant in a warm shaded location, and keep just damp.
Once new root growth commences in 2 to 3 weeks, the plant can be returned to the normal growing regime.
Remember that all plants, divisions and back bulbs should be labelled. A plant without a label looses
much of its value.
The repotting and dividing procedure is more easily understood if actually seen done. Many orchid societies
at their shows and displays have potting demonstrations, and if this process worries you attendance at one of these
demonstrations is highly recommended. If you ask an experienced grower, most will also be prepared to assist.
GOOD LUCK AND GOOD REPOTTING