Cymbidium HTC: tropical + miniature + fragrant = ideal for growing indoors

Species of the genus Cymbidium perhaps represent the most appreciated flowers in terms of global horticultural trade, mainly due to the high productivity of flower spikes, ease of cultivation, size, persistence, floral coloration, and presence of fragrance. The species considered classic come from the hilly regions of Nepal and Sikkim, rich in sun, where however a rather cool climate predominates, and growers of this group must reproduce these conditions in order to enjoy flowering success.

Known in cultivation and among collectors by the generic acronym HTC (Heat Tolerant Cymbidium), this functional and geographic group includes small-sized taxa (30-50 cm, compared to 80+ cm in classic species), with strongly fragrant, long-lasting flowers (at least 4 weeks), on numerous, erect or pendulous, multifloral spikes (5-60 flowers), which grow and bloom in tropical climates lacking drastic thermal differences between day and night, unlike the species and hybrids of the genus considered classic, where it is necessary for the night temperatures in the winter season to drop to values of 8 – 4 ℃ to trigger flowering. Hybrids of the HTC group are generally obtained by crossing tropical species, heat-loving (ensifolium, aloifolium, canaliculatum, finlaysonianum, sinense, atropurpureum, madidum, dayanum). From a cultivation point of view, HTC is very close to the procedures applied in growing Dendrobium hybrids.

One of the essential elements for flowering HTC hybrids is light radiation, which must cover a minimum duration of 8 hours per day, with shading of up to 40% during the growth period, but on hot summer days it should be increased to 50% to prevent sunburn. A good indication that the plants receive enough light is the bright green color of the leaves; plants grown in low light conditions have dark green leaves. For species with hard leaves (aloifolium, canaliculatum, finlaysonianum), similar in texture to those of the genus Cattleya, exposure to stronger light intensities is allowed and even recommended, as they can tolerate direct light for a few hours a day.

Special attention should be given to watering, as HTC are more demanding in this respect. Water stagnation in the substrate for long periods should be avoided, but care must also be taken to ensure the root ball never completely dries out. Similarly, and as a resemblance to species of the genus Cattleya, hybrids with hard leaves can tolerate longer dry periods and less frequent watering, even appreciating the complete drying of the substrate.

The optimal growth temperature for HTC species and hybrids ranges between 15 – 35 ℃, which ensures repeated flowering, usually at least twice a year. However, a consequence of their tropical origin is low cold tolerance, so exposing members of this group to temperatures below 10 ℃ for extended periods is not recommended.

Atmospheric humidity is not an important factor for Cymbidium HTC varieties, as they are particularly tolerant in this regard.

The ideal growing medium for this group is represented by pine bark, sometimes amended with perlite, and tall pots or at least pots taller than their diameter should be used as growing containers, since the roots of these taxa tend to grow deep into the substrate. Most species forming the basis of this group are epiphytes, except for Cymbidium ensifolium, which prefers terrestrial habitats, a trait also noticeable in its hybrids. Fertilizations should be done every two weeks during the growth period using a nitrogen-rich or balanced fertilizer, and once a month during the flowering period with a fertilizer rich in phosphorus and potassium.

Some authors and prestigious growers, such as Kobsukh Katraena from Pakkret Orchids, Thailand, propose the following classification of some species based on thermal tolerance, serving as a guide in evaluating this for hybrids that will include them:

Taxon Thermal tolerance

Cymbidium ensifolium subsp. haematodes 10.0

Cymbidium canaliculatum 10.0

Cymbidium aloifolium 10.0

Cymbidium finlaysonianum 9.5

Cymbidium ensifolium subsp. ensifolium 8.5

Cymbidium dayanum 8.5

Cymbidium bicolor 8.5

Cymbidium atropurpureum 8.5

Cymbidium madidum 8.0

Cymbidium munronianum 8.0

Cymbidium chloranthum 7.0