Probably all amateur orchid breeders of the Phalaenopsis genus have faced the "nightmare" of terminal stems. And, as in any environment with opinions issued online, the approved opinions are often outnumbered by those of people who argue only through their own experience limited to a few encountered cases, or personal opinions, the community of Internet users who breed orchids is no exception to this phenomenon.

Although in very rare cases it may mean the end of the life cycle, most specimens of Phalaenopsis with a terminal stem end up deteriorating due to the growing conditions. Some enthusiasts consider them from the start, erroneously, as lost plants, completely ignoring their potential.

In order to have a justified opinion, it is necessary to issue and gradually approach some hypotheses.

1. What are terminal rods?
2. What triggers their appearance?
3. What effects do they have on plants?
4. What actions or measures should be taken?

What are terminal rods?

A terminal floral stem is represented by the emergence from the central zone of vegetative growth of a bud with subsequent floral development. More precisely, in the area of ​​the leaf crown, for example, in the species of the Phalaenopsis genus, instead of a new leaf, a floral stem appears. This aspect is known in orchid species with monopodial growth, generally belonging to the tribe Vandeae, from the subfamily Epidendroideae, which includes the subtribes Aerangidinae, Angraecinae, Aeridinae, Agrostophyllinae, Bromheadiinae, Polystachyinae. It is important to remember in this context an important aspect related to the biology of the Vendeaelor, namely the type of monopodial growth, which implies a single direction of growth, located in the apical part (at the top of the plant), and opposite the root zone, from which the roots emerge, through opposition to species with sympodial growth, where there are multiple directions of growth. In the case of monopodial species, we can assume that there is an apical dominance probably hormonally controlled, which suppresses the development of lateral buds in growths or implicitly separate plants. If instead of the usual leaves that will indicate that the plant is in full growth process, elongating its stem unidirectionally, a floral stem appears, it is decent to assume that the plant in question will stop leaf growth in that direction. This aspect, however, does not mean that the plant will die, or will enter a stagnant period, since the cancellation of apical dominance, in most cases, activates the development of lateral buds, by means of plant hormones or growth regulators from the cytokinin group. Basically, this phenomenon, of the development of lateral buds, is also observed in the case of cytokinin treatments, either in the form of keiki paste, foliar treatments, or even unintentional destruction of the terminal bud. Moreover, it can be observed that the appearance of terminal rods is more frequent in species with a higher capacity to produce keiki, and the ability to form new lateral growths is frequently used in some Aeridines, for example, Vanda, Mokara, Trichoglottis, by applying the technique known as topping or decapitation, where the removal of the terminal bud stimulates the emergence of adventitious plants that grow on the basal area left after decapitation. It is interesting to note that the dormant buds of the Phalaenopsis species possess a polyvalence of development, being able to form vegetative buds, which will give rise to some plants, namely keiki, or to the same extent they can form floral buds, which will lead to the emergence of floral stems. This aspect is exploited by the administration of hormonal treatments with cytokines, more precisely the keiki pastes, which convert the buds of the floral stems into vegetative buds. We can, in this sense, agree that said conversion is possible and takes place spontaneously, induced or naturally in the case of vegetative, growing buds, which become floral if certain conditions are met. And from here, terminal rods.

What triggers the appearance of terminal rods?

The appearance of terminal rods is generated by the conversion of the vegetative bud of monopodial orchids into a floral bud, and can have multiple causes, of a physical nature (mechanical beheading of specimens, intentional, for reproductive purposes, or accidental), chemical (there is information that some antifungal treatments, antibacterials, insecticides or miticides, applied abundantly, can cause this event) or biochemical - physiological (hormonally induced naturally - at the age of plant maturity or artificially, by administering cytokinins). Finally, all these causes induce the production or metabolism of cytokinins, their accumulation in the tissues, and the triggering of the activation of lateral buds, which will eventually lead to the production of keiki, new plants that emerge on the stem of the mother plant. Some species and varieties are more likely to form terminal stems, and it is interesting to note that the same varieties will also be the ones where the appearance of basal plants (keiki) is more frequent. Some breeders link the reason for the appearance of terminal rods either to the excessive abundance of light radiation, or to the use of systemic insecticides, but there is still no definite information on this phenomenon.

What effects do terminal stems have on plant health and development?

Although the flower stalks naturally appear in the case of the Phalaenopsis genus in basal or lateral positions, it is possible that they also emerge in apical positions. As a rule, this phenomenon triggers the emergence of basal seedlings, i.e. keiki, since the respective plant will no longer grow, but will continue to function perfectly normal from a biological point of view, producing flowers and investing much more energy in vegetative reproduction.

In many cases, as the AOS ( Questions About Phalaenopsis ) experts inform us, the appearance of terminal rods is an indicator of the fact that the respective plant has reached maturity and will stop its upward growth, but there are many cases where the plants continued to grow after drying of the flower stem. A certain aspect in the treatment of plants with terminal stems is represented by the fact that the respective plant will with certainty produce at least one basal keiki, depending on the species, variety, hybrid, as it is known that some varieties are more prolific than others.