Thursday, November 29, 2012

Dendrobium keiki, What causes them to appear?



Dendrobium harveyanum keiki producing a second cane, because it has substantial
roots it can be removed with little fear that it wiil die.

Keikis from unbloomed stem of Dendrobium Yellow Chinsai, probably caused
by too much nitrogen in the fertilized applied late in the growing season

Dendrobium anosmum keikis, these are tiny and have little green tissue to support
independent growth removing keikis this size is not adviced.

Dendrobium anosmum keiki, this plant has a good size for a keiki and a significant growht of roots.   It can be removed with confidence that it has enough reserves to start growing idenpendently

These Dendrobium anosmum keikl have three canes with means they are over due for removal
from the cane, the original cane has decayed completely.

Dendrobium primulinum keiki, although on the small side for a keike the fact that it has two canes
will help this plant adapt to independent living without too much trouble.

Dendrobium fimbriatum oculatum keiki.  This keiki is quite large and can be treated
right away like an adult plant onece it is removed from the cane.

One characteristic of some Dendrobium species is that they have the capacity to produce plantlets from the meristematic tissue that lies in the form of small buds along the sides of the canes of the adult plants.  Most of the year these buds lie dormant, but if they are activated by hormonal changes in the plant they can turn into floral stems or into little plantlets.  In the hobby these little plants are known as keiki, this is the Hawaiian word for baby.  I will use the term keiki to refer to this form of propagation on the rest of this article.  Keikis are plantlets produced vegetatively by the mother plant, it is an asexual type of reproduction which means that the little plants will be exact copies of the mother.
 The frequency of keiki production varies wildly in the Dendrobium genus.  Some species will never, or only very rarely produce them, I have yet to see a keiki in a plant of Dendrobium farmeri or Den. secundum.  In other cases some plants will produce keiki and others of the same species will not.  This is my experience with Den. harveyanum, one plant has produced several keiki while another has never produced them.   Some species will almost always produce one to a few keiki from older canes, an example of these are Den. anosmum, Den. cucullatum and Den. primulinum.  In the extreme of keiki production Den. crumenatum and Den. kingianum produce them frequently and sometimes abundantly. 
There are several circumstances that can stimulate the production of keiki.  A relatively common occurrence is the production of keiki instead of flowers.   Normally canes will not produce keiki in their first year, before they have bloomed.  If a mature cane produces keiki instead of flowers when its blooming season comes around, this means something has disrupted the sequence of metabolic processes that produce the hormonal changes that turn the resting vegetative buds into floral buds.  In Dendrobium descended from Den. nobile and related species, if the plant is given a fertilizer with a high nitrogen content during the latter part of the growing season or the resting plant experiences too high temperatures, this can “short circuit” the blooming response and then it can either not bloom or it can produce keiki where blooms would have been expected.    I have seen plants produce keiki all along the cane where flowers should have been.  In rare cases a plant can both produce keiki and some flowers.   A few days ago a friend showed me one of his Den. nobile hybrids where the plant had produced keikis instead of flowers and then some of these keiki had produced a single flower from the tip of their tiny canes.
In many Dendrobium species the sudden production of keiki by a plant on canes young and old is a signal of significant root loss.  I have frequently observed this on Dendrobium species from the Spathulata section and on hybrids descended from Sphatulata/Phalaenanthe section.  These hybrids are produced by the millions and are commonly sold on Walmart, Home Depot and other stores because they travel well and their flower sprays last for weeks in good condition even in hot weather.  The problem with these Dendrobium is that most the people that buy them often now virtually nothing about their growing needs.   When these orchids are repotted they are frequently put in dense bark mixes that are kept wet.  If the mix is so dense and soggy that it doesn’t allow oxygen to reach the roots, the roots die.   The one common indication that the roots have died is the complete defoliation of the plant.  That is all canes, young and old shed their leaves due to the loss of the capacity for water uptake.   By the way, it is normal for the older canes of many types of Dendrobium to be leafless, it is abnormal for a cane of the year to lose their leaves, particularly in the evergreen types that are common in the retail market.  If the plant is cared for well, it might start growing in its season and if it has a number of healthy canes it can even produce a reasonably large mature growth that will in time produce a new root system.  But if, the loss of roots has been accompanied with the loss of the lower vegetative buds, the plant can produce keiki from the top of the canes.  I have seen plants that have lost the lower vegetative buds because the owner buried the base of the stem under the potting media and the new growths have succumbed to rot.  By the way, sometimes a Dendrobium will produce a new cane from a bud that is located slightly higher in the stem than previous growths, this is not a keiki, as canes produced this way can develop normally to full size.  This sometimes happens when the buds at the base of the stem are lost.
Keiki produced at the top of the canes varies hugely in quantity and quality depending of the ancestry of the plant.  I have an antelope Dendrobium (of the Spathulata section) called Percy’s Passion.  This plant lost its roots and produced a single very large keiki that is for all purposes a small adult plant.  This keiki has even bloomed with a substantial inflorescence while still attached to its mother’s cane.  In these cases these keiki can be cut from their stem, potted and treated as an adult plant, they don’t need any special considerations.
On the other hand some plants will produce tiny keikis at the very tip of the canes.  These keiki are typically one to two inches long and depending on the parent species, can have a substantial quantity of roots or almost none.  Keikis that are smaller than two inches are a special case. They are much more fragile than those that are over two inches and might not survive being detached from the cane.  If they have few roots they will need care that addresses their particular needs and it may be more than the average grower might want to provide, also they will take a long time to reach maturity.  In my experience that hardiness and vigor of these tiny keiki vary depending on the species.  Keiki of anosmum, cucullatum, crumenatum and primulinum larger than two inches long, are quite hardy and survive very well if given appropriate care and an environment with high air humidity.  I have not been so lucky with small keikis of the Phalaenanthe section and of the “antelope” Dendrobium of the Sphatulata section.    In my experience keiki from these groups take more time to grow larger, produce roots more slowly and succumb to rot more readily.  Admittedly this is probably due to the particular environment in which I keep the keiki in my orchid growing area, some people elsewhere might have a different results.
I have observed that older canes sometimes produce keiki even in the absence of any of the issues that I have detailed previously.  My guess as to what causes this is that keiki production in older canes is probably related to the loss of the roots that are connected to that particular cane.  In these cases the plant still has a healthy root system in his younger canes and all the canes receive moisture from those roots, so this keiki production is not related to any distress from the part of the plant.  I don’t cut out these keikis until they have at least two canes and a significant number of roots. 
If a cane losses its vascular connection with the rest of the plant it can start producing keiki.  This may happen if part of the stem rots or is damaged.  If the base of the stem is buried in the media the death of the base of the stem might not be evident to the casual observer.  Also even though the cane connection to the vascular system is severed there still might be a substantial amount of dead but not decayed tissue holding the cane together with the rest of the plant.  When this happens to my pendent Dendrobium I may cut the cane in the part that has decayed and plant the keiki, still with the cane attached, in another container or mount.  This often makes a huge difference in the speed in which the keiki reaches adults size, as the piece of cane can provide, if large enough, with enough support to allow the keiki to produce a substantially larger new cane in its next growth phase.
Many growers propagate their Dendrobium using the capacity of these plants to produce keiki.   They cut the older canes into three to four node sections and lay them in sand that is kept moist.  I have seen this method producing satisfactory results with canes from “soft cane” Dendrobiums such as anosmum, cucullatum and with many of the types of the Dendrobium that are available at department stores and that are lumped in the literature under the denomination “evergreen”.



1 comment:

Blog da Bete said...

bastante keike
que beleza
abra├žos