Oncidium, Dendrobium, and Cymbidium Orchids: Key Differences

There are more than 800 genera of plants in the Orchidaceae family and some 28,000 species among them. It is the second largest of all plant species, behind Asteraceae, which contains sunflowers, daisies, and chrysanthemums, to name a few. It stands to reason that identifying a particular plant in this group could prove tricky. 

Although there are many genera, only a couple of dozen (give or take) show up commonly in nurseries and other retailers. Among these, nearly all are tropical. They prefer temperate climates with high humidity. These plants tend to be picky about sunlight and water, and the same rules don’t apply to every orchid. 

There are three popular genera with names that, while they differ somewhat, have a similar sound. They are oncidium, dendrobium, and cymbidium. It’s easy to get one confused for the other, and they have some variations in optimal care. Let’s take a look at the factors that make it possible to differentiate between these three types of orchids. 

How to Tell the Difference

There are four obvious facets of an orchid’s appearance that help us identify it and place it in a particular species. The first and often the deciding factor is the growth habit. The remaining aspects to look at are cosmetic and include the leaves, the flowers, and the overall shape and size of the plant.

Growth Habits

There are two aspects of growth that help identify most types of orchids. The first is where they grow, and the second is how. These tropical plants can be epiphytic, lithophytic, or terrestrial. 

Oncidium orchids are nearly always epiphytes, growing high up in trees, closer to the canopy overhead. Dendrobiums are a large genus and include species that fall into all three categories. Some are also deciduous and lose their leaves in winter. Cymbidiums are semi-terrestrial, growing in the ground but sending up thin aerial roots.

In terms of how these plants grow, there are two growth habits of orchids: monopodial and sympodial. All three of the plants we are examining are sympodial. 

The factors these two habits influence most are potting, and propagation. Where they naturally grow determines what type of container and potting mix is best. Propagating a sympodial orchid tends to be easier, as you simply cut groups of pseudobulbs apart. They already each have their own roots. For monopodial orchids, it’s necessary to cut through the middle of the plant and root the top portion.

Leaves

Since all three of these are sympodial, they grow these individual pseudobulbs. Each one is a tiny plant of its own, with its own personal root system. Each pseudobulb produces leaves with their own distinct appearance. 

Oncidiums have strap-like leaves that vary in size according to species. Each pseudobulb will grow between two and five leaves. Dendrobiums grow tall canes with leaves growing at intervals on opposing sides. The number of leaves depends on the size and age of the orchid. 

Cymbidiums are different because they are terrestrial. Their strap-like leaves appear to grow in a clump. In reality, they grow the same way as other sympodial orchids, overlapping as new leaves grow from the center. 

Blooms

Sympodial orchid pseudobulbs each produce leaves and flower stems. The number of flower stems depends on the species. Most of the three plants we are discussing grow one to two stems per pseudobulb. The number, size, and appearance of the blooms differ between generas but will typically be similar across species in a single genus. 

Of the three, oncidiums have the smallest flowers with the greatest number per stem. Many species are fragrant, with at least one that smells like chocolate.  Cymbidiums have the largest, and some hybrids are fragrant but less frequently. Dendrobiums have mid-sized flowers, and they lie in the center in nearly every facet. 

Overall Shape and Size

Orchids cover a wide range of sizes. They include the minuscule Platystele jungermannioides at two to three centimeters tall, to the giant Grammatophyllum speciosum, which can be up to 25 feet tall. Most, however, fall into a similar range of about one to four feet tall. 

Oncidiums are the smallest of these three with a typical range of one to two feet. Dendrobiums skew larger, from six inches to four feet tall. Cymbidiums are similar, maturing to between one and four feet tall. 

Oncidium

Oncidiums are native to Central and South America, as well as Florida and the West Indies. They grow at a wide range of elevations from sea level to over 8,000 feet above. As a result, they are adaptable and have a wider range of care possibilities than most orchids. 

Care

These plants need containers with excellent drainage and a coarse, bark-based potting mix. They have exposed roots in nature, so they need plenty of air circulation to avoid root rot. Your container should not hold water, and your potting mix should only stay slightly moist. 

These prefer a lot of light compared to most orchids. The thicker their leaves, the more tolerant they are of direct exposure. Some even tolerate full sun. Those with more delicate foliage will need between 20 and 60% shade. Too much sun will cause the leaves to take on a purple hue. Too little, and it’s unlikely to bloom. 

Oncidium roots tend to be finer and more delicate. This means they are more delicate and easier to damage. A good watering routine is vital for their health. Water about once a week. Fertilize every two to four weeks at the same time as watering. 

All orchids like extra humidity. Without it, your leaves may begin to crinkle and turn brown at the tips. These are happy in the range of 40-70% humidity, though 40% is on the low end.

Blooms

Oncidium orchids produce a lot of flowers, a minimum of 25 per stem. A single mature plant can produce many stems, so it’s not uncommon for one of these to produce hundreds of flowers in one season. The flowers are small and dainty. They typically consist of at least two colors and have a large, ruffled labellum. 

The shape and size of the labellum compared to the rest of the petals is noteworthy in this group. Oncidiums have the nickname “Dancing Lady,” as these frilly labellums resemble twirling skirts. The blooms are usually warm colors, red, yellow, orange, white, and pink, but some also have shades of purple. 

Dendrobium

Dendrobiums are fast growers, and the genus consists of at least 1,800 species. They are native to Southern Asia, where they live in cloud forests, tropical islands, and monsoon environments. They are more cold-tolerant than most orchids and tolerate a wider range of temperatures. 

This is the only genus that contains some deciduous plants. All other orchids are evergreen. Some dendrobiums shed all of their leaves in the winter after blooming. Don’t throw it out when this happens, they will all grow back in a few months. During this time, expose them to cooler temperatures to encourage bud setting. 

Care

Their environmental flexibility makes these great beginner orchids. Aside from Phalaenopsis, these are probably the easiest to keep alive. All except a few terrestrial species need bark mix in place of potting soil. They all need containers with excellent drainage. 

In terms of light, bright, indirect sun is best for these, though they do like some direct sun in the morning. Protect them in the afternoon. They also prefer humidity in the range of 40-70%.

Because they have a small root system compared to the overall size of the plant, these need more water than most. During the growing season, you may want to water these twice per week rather than once. Just make sure your container has good drainage, or you’ll end up with root rot. 

Blooms

Dendrobiums have larger blooms than oncidiums but are typically smaller than cymbidiums. These grow on long stems with about four to eight per stalk. They are popular in floristry for their beauty and because they are sturdy. 

You’ll often see dendrobium flowers used as garnish. All orchids are edible. Many resemble phalaenopsis flowers and are referred to as phalaenopsis dendrobiums. They are well-balanced with a rounded labellum, typically in a contrasting color. Pink, purple, yellow, and white are the most common colors for this genus. 

Cymbidium

Cymbidium orchids are native to Asia and Australia, where they commonly grow at high elevations. They are tolerant of a wide range of temperatures but require a period of cooler nights in the spring to induce blooming. 

Care

Because they are semi-terrestrial, they have markedly different care needs. They still need good drainage, but because they grow in the ground, they tend to be less sensitive to moisture and hardier overall. You can pot these in a fine bark mix with peat moss, perlite, coco coir, or sand mixed in. Potting mix customized for this plant will have smaller particles and hold more moisture than standard orchid bark. 

You can use a standard clay pot with at least one drainage hole for these, and they don’t mind crowding. They like a significant amount of light, but any direct exposure should take place in the morning. Shelter from direct afternoon rays is important, as it can burn the leaves. 

Water this plant about once a week, but pay attention to the potting medium. You want it to be lightly moist and dry slightly between waterings. These prefer mild temperatures and are most tolerant of 40-80°F weather. They are happy with humidity right around 50%. 

Blooms

I find cymbidium flowers to be among the most beautiful of all orchids. They are often called boat orchids, after the Greek word kymbe which means boat. It refers to the shape of their labellum, which is significant and deeply curved. 

These are the largest of the three groups, and one stem may hold up to 20 blooms. They are sturdy and waxy and come in a wide range of colors. Some of the more common shades are green, pink, yellow, and orange.