The genus Dendrobium includes species native to all of East Asia, from the Pacific to the Himalayas, Australia, and New Zealand.

It is certainly one of the most numerous genera in the orchid family, comprising more than 900 species that live in very different habitats: at sea level and up to 3500 m altitude, some in regions with a temperate climate, others where temperature and humidity are constant throughout the year, others in tropical climates. This means that Dendrobium species have very different cultivation needs, shapes, and sizes: we have very small Dendrobium 3-4 cm in size and very large Dendrobium several meters long with various shapes and colors that make this species unique and irreplaceable for orchid lovers.

All this is complicated by the fact that there are numerous hybrids on the market and consequently many types of Dendrobium.

The morphology among Dendrobium is very diverse; we find species with evergreen leaves and others with deciduous leaves, some with single leaves, others grouped.

One characteristic that the different groups have in common is forming keikis (photo on the side) both at the height of the nodes and at the base of the stem, which are nothing more than a new orchid plant that, once sufficiently large, can be detached from the mother plant and repotted independently.

In general, to understand how to cultivate Dendrobiums, we must remember that they are plants that have a very rapid vegetative period, meaning they develop green parts and roots very quickly, but take much longer to flower and produce seeds. This situation is dictated by the fact that the vegetative rest in nature corresponds to the seasons less favorable for their development, i.e., cold and dry conditions, in which the plant could not survive except by entering dormancy and using the reserves stored in the pseudobulbs during the phase of full development. In nature, this unfavorable period is longer than the favorable periods, which is why they have this particular cycle.

Considering that they are plants from very diverse habitats, it is impossible to generalize about their cultivation techniques. For this reason, some divide Dendrobiums into six groups, and typical cultivation environments are described for each.

FIRST GROUP

This group includes deciduous and cold-greenhouse Dendrobiums that require a period of vegetative rest.

The following species are found:

1. Dendrobium nobile;
2. Dendrobium chrysanthum;
3. Dendrobium wardianum;
4. Dendrobium victoriae reginae.

Here we find Dendrobium nobile, certainly the most famous among the species in this group.

All these plants are native to Southeast Asia, including Nepal, Bhutan, northeastern India, Burma, Vietnam, Laos, and part of southeastern China, at altitudes between 200 – 1500 m.

This group, like the second, has the peculiarity of losing its leaves during the dry and low-temperature period that naturally coincides with winter. During this period, in fact, lacking sufficient water and temperatures to grow, the plant enters vegetative rest, loses its leaves, thus saving its nutrient reserves and living on the reserves accumulated in the pseudobulbs. With the arrival of warmth and rain, it quickly restores its reserves and prepares for reproduction, i.e., flowering and seed production (let's never forget that plants flower for species propagation).

In addition to these species, there are also numerous hybrids, mainly obtained by crossing Dendrobium nobile x phalaenopsis or Dendrobium nobile x Dendrobium bigibbum.

For these orchids, the cultivation cycle is particular and also applies to derived hybrids.

From mid-autumn (November) until mid-winter (February), they should be kept as cold-greenhouse plants with temperatures around 10°C, in a very bright place (in their natural environments, light is much more intense in winter than in summer) and given very little water, just enough to prevent wilting, no fertilization, and excellent ventilation. For the amount of water to give, one can regulate by observing the stems: if they start to wrinkle, a little water is needed, but very little. The lower the temperature, the less water should be given.

As soon as flower buds form, which generally coincides with spring, some watering can be done until the end of flowering. When even the last flower has fallen, suspend watering again until new roots begin to sprout from new shoots. At that point, the plant should be moved to an area with higher temperatures, and regular watering and fertilization should resume. During this period, they can also be moved outdoors. During this period, the light should not be too intense.

Throughout spring and until mid-summer (August), fertilization should have a high nitrogen content at a dose of 1/2 g/l once a week.

After that, from mid-summer (August) until autumn, fertilizers with very low nitrogen content and high phosphorus and potassium content are used at a dose of 1/2 g/l once a week.

This alternation of dry and cold periods with normal and warm periods is fundamental for flowering. In fact, the primary cause of non-flowering in this group of orchids is precisely the lack of this alternation. Instead, the plant will produce keikis, which are nothing more than new plantlets that, once sufficiently large, can be detached from the mother plant and repotted independently.

To summarize, to successfully cultivate Dendrobiums of this group and their hybrids, two fundamental requirements are needed: in spring

– very warm summer, much fertilization, constant humidity, and not too intense light, followed immediately by a cold, dry period, no fertilization, and much light until flowering, which will occur at the end of winter – beginning of spring.

The Dendrobium can safely stay outdoors during the warm season but must be accustomed gradually; in fact, it tolerates direct sun once grown outdoors if acclimatized early in spring and if ventilation is excellent.

Regarding humidity, during summer it should be high, around 80%, which should be gradually reduced as winter approaches to 60% until it is completely suspended in winter.

Repotting can be done either when new roots begin to develop or immediately after flowering.

SECOND GROUP

This group includes deciduous and intermediate-greenhouse Dendrobiums that require a period of vegetative rest.

1. Dendrobium anosmum;
2. Dendrobium findlayanum;
3. Dendrobium pierardii;
4. Dendrobium parishii;
5. Dendrobium heterocarpum;
6. Dendrobium aggregatum.

This group, like the first, has the peculiarity of losing its leaves during the dry and low-temperature period that naturally coincides with winter. During this period, in fact, lacking sufficient water and temperatures to grow, the plant enters vegetative rest, loses its leaves, thus saving its nutrient reserves and living on the reserves accumulated in the pseudobulbs. With the arrival of warmth and rain, it quickly restores its reserves and prepares for reproduction, i.e., flowering and seed production (let's never forget that plants flower for species propagation).

The species belonging to this group are grown like those in the first group, with the only difference that temperatures are constant throughout the year. At night around 12-14°C.

Vegetative rest must be ensured from autumn and throughout winter, when watering will be gradually reduced and eventually watered just enough to prevent wilting, and fertilization will be completely suspended. When flower buds begin to appear and are well developed, which coincides with spring, watering is gradually resumed until the plant is seen to have fully awakened by producing new roots, at which point regular watering and fertilization can be resumed. During this period, spring and summer, they need a lot of light and good air circulation.

Vegetative rest is essential for flower induction.

THIRD GROUP

This group includes evergreen and intermediate-greenhouse Dendrobiums that do not require a period of vegetative rest but must experience the change of season.

The following species are found:

1. Dendrobium chrysotoxum;
2. Dendrobium densiflorum;
3. Dendrobium fimbriatum;
4. Dendrobium moschatum;
5. Dendrobium thyrsiflorum;
6. Dendrobium farmeri.

These Dendrobiums, unlike those belonging to the other two groups, should not be left dry at any time of the year.

During autumn and winter, watering should be reduced but not suspended, and they should be placed in a cool place with night temperatures around 10-12°C.

In spring, watering is gradually increased, and they are generously fertilized, and the plants are moved to warmer and brighter environments and can be safely cultivated like Cattleya.

FOURTH GROUP

This group includes evergreen and intermediate-greenhouse Dendrobiums that require a short period of vegetative rest.

The following species are found:

1. Dendrobium daerei;
2. Dendrobium loddigesii;
3. Dendrobium infundibulum;
4. Dendrobium sanderae;
5. Dendrobium formosum;
6. Dendrobium lyonii;
7. Dendrobium macrophyllum;
8. Dendrobium schuetzei

For these Dendrobiums, winter night temperatures are around 12°C, while in summer, night temperatures should be around 15-16°C. They do not tolerate temperatures that are too high or too low.

Also for this group of Dendrobiums, a rest period of about three weeks with very little watering and no fertilization should be provided. As new shoots begin to form, watering and fertilization are gradually resumed, remembering to always let the substrate dry between waterings.

FIFTH GROUP

This group includes evergreen and intermediate-greenhouse Dendrobiums without a vegetative rest period.

The following species are found:

1. Dendrobium stratiotes;
2. Dendroblum taurinum;
3. Dendrobium undulatum;
4. Dendrobium veratrifolium;
5. Dendrobium gouldii.

Orchids belonging to this group do not like extreme conditions; in fact, they prefer temperatures and humidity that are not too high. They need a lot of light and good ventilation. Watering and fertilization should be regular throughout the year, at most slightly reduced during the winter period.

If, in this circumstance, the buds do not flower or fall prematurely, the night temperature should be adjusted better by increasing it slightly.

SIXTH GROUP

This group includes evergreen and warm-greenhouse Dendrobiums without vegetative rest.

The following species are found:

1. Dendrobium phalaenopsis (also known as Cooktown orchid as it was found near Cooktown in Queensland – Australia);
2. Dendrobium superbiens;
3. Dendrobium biggibum.

This group includes very popular orchids; in fact, numerous hybrids are commercially available, especially of Dendrobium phalaenopsis and Dendrobium bigibbum.

These plants are native to the tropical areas of southeastern Australia, therefore, they come from areas where summers are hot, very humid, and wet, while winters are rather dry. This framework is important to understand how to grow them. In fact, they are warm-greenhouse plants.

First, it must be borne in mind that they do not go into vegetative rest, therefore, they must be watered throughout the year.

In spring – summer, which coincides with the active growth phase, they should be watered generously and fertilized regularly using 1/2 g/l once a week with a high nitrogen content. Summer night temperatures should be around 22-25°C and daytime 28-30°C. During this period, they should be misted regularly to try to maintain a humidity level of around 60-70%. During the warm season, they can be exposed to direct sunlight only in the early morning hours but shaded for the rest of the day.

After flowering, watering should be reduced until new flower stems form.

From late summer until autumn, a fertilizer with a higher phosphorus and potassium content is used, always at a dose of 1/2 g/l once a week.

From autumn and during winter, watering should be gradually reduced, allowing the substrate to almost dry out between waterings. Great care must be taken not to let the pseudobulbs shrivel too much, as subsequent recovery is quite slow. During this period, fertilization should be suspended or at least significantly reduced in conjunction with reduced watering. Misting should be done to maintain relative humidity around 60-70%. In their natural environments, light is much more intense in winter than in summer, therefore, ensure that during the winter season they receive much more light than in summer. Winter temperatures at night are around 12-14°C and during the day 15-18°C.

Excellent ventilation is important throughout the year.

Repotting is done after flowering or when the plant begins vegetative recovery at the end of winter – beginning of spring. Being epiphytic plants, they can safely be grown on cork bark.

Obviously, under these conditions, watering and misting must be daily, especially in summer. If grown in pots, care must be taken to use small pots, as they do not like large pots. What may appear too small for the plant usually works perfectly. Furthermore, it is important that they have an adequate number of drainage holes as they do not like water stagnation in any way. Cork pieces and fir bark are suitable as a substrate. Repotting is usually carried out when the plants have grown too large for the pot. If you decide to divide the plant, remember to leave at least three pseudobulbs per plant.

In almost all Dendrobiums belonging to this genus, flowers appear at the terminal part of the flower stem, numbering from 5 to 20, and last from one to three months.

Once the flowers have dried, it is preferable not to cut the stem but let it dry naturally. In fact, new lateral branches can grow from that stem, or it can re-flower, or a keiki can develop, which is nothing more than a new plant that, once large enough, can be detached from the mother plant and repotted independently.

There are cultural differences within the group between Dendrobium phalaenopsis and Dendrobium bigibbum, which are often considered a single species even though they are not. Dendrobium bigibbum originates from areas much closer to the equator and therefore requires higher temperatures than Dendrobium phalaenopsis, especially in winter. Morphologically, they are also different: Dendrobium bigibbum has smaller flowers with a larger and more rounded labellum than Dendrobium phalaenopsis.

WATERING AND HUMIDITY

Watering should be done in the morning, to allow the leaves to dry before nightfall and thus avoid the onset of dangerous diseases. Care must be taken to ensure that water does not stagnate between the leaf crevices.

Maintaining a humid environment around the plant is essential. Now, in our homes, it is not always easy to simulate a tropical forest corner. To get closer to this, we can place the pot containing the plant on a saucer (or other container) in which you have placed expanded clay or gravel and in which you will always keep some water. In this way, the orchid roots will not come into contact with the water, which by evaporating will ensure a humid environment around it, just as spraying the leaves once a day.

Let's keep in mind that optimal humidity varies depending on the species and also in proportion to the temperature: high temperatures will require higher humidity, but in this case, it is essential to ensure good ventilation for the plant to avoid dangerous water stagnation that could cause the onset of dangerous diseases.

It is good practice, for the health of all our plants, to equip radiators with humidifiers to prevent the room air from becoming too dry.

FERTILIZATION

Like all orchids, since they are mostly on an inert material, nutrients must be supplied through fertilization.

Fertilizers should be dissolved in irrigation water, preferably not tap water.

Thoroughly wet the substrate before fertilizing to avoid excessive salt concentration.

REPOTTING

Before repotting, the orchid should be thoroughly watered to make the roots more elastic and thus prevent breakage. The roots should be cleaned of all adhering material, and dead ones should be removed with blades or shears that you have previously disinfected well with alcohol or bleach, preferably by flame.

Proceed with great caution and try to disturb the roots as little as possible, and be careful to remove only the dead ones. Every cut surface should be treated with broad-spectrum fungicidal powders that you will find at a good nursery.

Before repotting, thoroughly wash the substrate by immersing it in water for a few days to eliminate any dust present, remove impurities that settle at the bottom of the container, and thus ensure perfect hydration.

If the roots adhere too tenaciously to the pot when unpotting, it is advisable to immerse the pot for about 30 minutes in lukewarm water. If this technique does not work, then cut the pot. Do not force the roots, as they could be damaged.

Ensure there is some space between the pot edges and the roots to prevent the same situation from recurring the following year.

Always ensure that the container you have chosen has an adequate number of drainage holes (otherwise, equip yourself with suitable tools to increase them).

After the orchid is repotted, leave it dry and protected from direct light and temperature fluctuations for several days to allow the cut parts to heal and the roots to adapt to the new situation. Once root activity resumes, resume normal cultivation.

Regarding the type of container, choose the one you prefer (there are many different ones, and your imagination is key here), and if you have chosen a certain size, well, buy a smaller one. It is important that the container has been previously disinfected with either alcohol or bleach. It would also be appropriate for your hands to be clean before proceeding if you are not wearing gloves.