Dendrobium anosmum and their relatives, warning signs of cultural trouble

Vigorous and healthy root growth, note that the cane producing the roots is twice as thick as the previous growth

New roots are white older ones are grey green, absence of root growth is a clear signal of trouble

Fungal and bacterial infections can strike with astonishing speed and virulence, this is all that remained of a specimen plant of Dendrobium formosum var. giganteum.  If the gravity of the situation had been recognized on time at least some pices would have been saved for propagation

This Dendrobium nobile has been growing for many years in an avocado tree under hot tropical conditions.  It has never bloomed although in all aspects it is mature plant fully capable of blooming.

Dendrobium nobile blooming in a shady and cool location.

A Dendrobium phalaenopsis derived hybrid which lost all its roots due to inappropiate potting, all the old roots are dead but some new roots are showing their tips near the base of the canes.

The buds at the base of this canes are dead so the plant is producing new growths from buds higher up in the cane.

The base of these canes of Den. primulinum was damaged by sunburn and died.     The canes were bent so that the keikis produced by them can attach themselves to the basket.  Notice the many keikis and their abundant root growth.

Den. phalaenopsis hybrid grown with its roots exposed.  Note the abundant flower production and the fully leafed new cane.  It is normal for older canes to lose their leaves after the first year.

Under good care some keikis will bloom even when they are not affixed to anything

When they are growing at their preferred temperature and lighting range, well cared pendent dendrobiums grow vigorously, without any particular trouble and bloom reasonably well. But when they are grown under conditions that are unsuitable for them several things happen that serve as a warning signs that the plant is not doing well. I will detail some that I have learned from the bitterest experience. This is a work in progress and I will try to add information as time permits.

I. When your plant needs a colder rest period to bloom than you can provide.

If a plant needs a colder rest period to bloom but otherwise the conditions are to its liking you will get an endless production of handsome canes, which will be plump and healthy but will never bloom or even get in bud. Because circumstances prevent them from blooming these plants channel their energy into growth and can produce quite large plants. One Den. chrysanthum I have eventually produced a ten feet long cane. This particular plant has never produced even a single bud under the local climatical conditions. Dendrobium nobile will not usually bloom in coastal Puerto Rico but will bloom nicely if moved to locations about a 1,000 feet high in the mountain areas and in certain colder inland areas. There are plants here and there that bloom under conditions that are not in their usual preferred range but usually they do so erratically or poorly.

II. When the temperature is not in the preferred range for growth.

The first signs of trouble in this case is usually a lack of root growth. Unfortunately some pendent dendrobiums can survive for many years growing weakly and with root systems that barely sustain whatever meagre growth they manage. It can happen that the plants perk up and do produce good growth during brief times when conditions are to their liking, but as soon as temperatures drift out of their preferred range the plants weaken again. I brought a Den. falconeri that managed to survive ten years by growing acceptably during the brief weeks that local temperatures dipped and then sulking the rest of the year. Strenuous efforts to sustain this plant only lengthened the agony. Eventually the plant dissolved into a mass of tiny canes and diminutive keikis that were too weak to survive the summers heat. Keiki production on a a same year growth is also a very bad warning sign. It usually means that the plant inability to produce roots has made it transfer its energy to keiki production.

III. When it is not getting enough sunlight

If your plant is not getting enough sunlight to bloom properly you will probably get a few blooms right on the tip of the cane. A plant that might produce dozens of blooms might only produce two or three. The canes themselves might get to be abnormally long and thin. The leaves will have a deep green color.

IV. When roots are not entering the potting mix, or holding the mount.

This probably mean the mix is unsuitable for the plant because it has some characteristic that is inhibiting or killing root growth. A friend of mine accidentally killed many of his orchids by mounting them on the wood of a plant whose wood is permeated by a substance this plant secretes to kill other plants that  might compete with it for food or sunlight.  

V. A growth coming from a cane other than last years cane, if last year cane doesn't grow.

It probably means that the base of its newer cane is dead and the plant is trying to keep alive by producing growths elsewhere. In some plants, (this is an specially insidious occurrence in pendent dendrobiums) a cane that has shed its leaves can continue attached to a dead base without any obvious signs of distress for months before decay reveals that the base is dead.

VI.When a cane suddenly stops growing in the middle of producing a new leaf.

Usually means that something has severed the connection between the growing tip and the base of the plant. I have seen this happens when an insect gnaws the middle of a cane and makes a cavity but leaves it mostly attached to the base on the sides of the cane. This can cause the death of the whole cane, not just the tip.  On some ocassions this can signal a bacterial or fungal infection of a stealthy nature that only becomes obvious when the cane starts to decay rapidly at a time when it should have been growing.

VII. Blackened and sunken areas between the base of the plant and the lower part of the cane.

Can mean sunburn to this area, can result on the death of the plant but the survival of some of the canes.

VIII. Profuse keiki production on plants that normally produce them sparingly.

A sign of root loss, or of loss of the buds at the base of the plant.

IX. A weaker cane than the previous year's cane.

Plant is not getting what it needs to grow well, common in newly repoted plants that have suffered severe root loss and plant adjusting to new environments.

All this information is courtesy of the need to unwind after an unexpedtedly streesful day at work.