This orchid can be a difficult plant to grow although many growers find it to be their easiest bloomer. If you can make this plant happy, it will grow and bloom in what may be seemingly undesirable conditions.
Natural Growing Conditions
The Dendrobium aggregatum is an epiphyte, that means a plant that grows on another plant but isn't parasitic, hailing from North-East India through Indochina and Thailand. Plants have been found at altitudes of above 500 metres, but can also be grown in warmer to intermediate conditions. The plant is open to a variety of different situations as long as it gets plenty of light, water, and a winter rest.
This plant has short, thick pseudobulbs, thick bulb-like stems that store water. Bulbs are clumped together by the bases and taper slightly to a point near the leaf-bearing end. Pseudobulbs are usually covered with a thin, papery covering called 'sarong' that protects new growth. It is not necessary to remove this covering unless you are worried about an insect, mite, or fungal infection. The pseudobulbs turn reddish with exposure to sun, so you know that they're getting the right amount of sun. Some people say that old, leafless pseudobulbs look like candied dates due to this tinting. If hacking up your plant sounds like a good idea, for whatever reason, make sure that there are five to nine pseudobulbs in each division.
The leaves on a Den. aggregatum are short and thick. The leaves are placed singularly at the end of each pseudobulb and have a slight crease down the centre. They tend to be elliptical in shape and slightly flexible, although it isn't recommended that they be flexed unnecessarily. Leaves tend to be a darker green but lighten with exposure to the sun. Yellow leaves aren't a good sign.
Roots are usually thin and white with a slightly rough texture. Growing tips are translucent and green and are easily damaged, so be careful if you are handling the plant.
Den. aggregatum has very delicate flowers of orange or yellow that hang from a thin inflorescence. The inflorescence grows from near the base of the pseudobulbs and usually takes several weeks to develop enough to bloom, which can be agonising for even the most patient of growers. Flowers, if well cared for and kept in high humidity, can last anywhere from a week to a month. The flowers are flat without a pronounced labellum1 and smell faintly of honey. You really have to stick your nose in the flower in order to smell it, but it is most fragrant in the early morning and early evening when there is dim light. In general, ten to twenty flowers will develop on an inflorescence2, although younger plants may have fewer. Inflorescences in this plant do not rebloom and should be cut off after they have dried up and turned brown.
This plant grows best mounted due to its epiphytic nature. Usually, a medium such as cork, fern bark, or teak is used. Mounting allows plants to completely dry out between waterings and allows air circulation. Orchids, like people, do not like having 'wet feet.' If you are mounting your orchid yourself, make sure to place a pad of sphagnum moss around the roots to prevent it from drying out too fast. Most people use fishing line to attach the plant, but quilting thread and wire are always handy. These ligatures can be removed once the plant establishes itself by hugging the mount with its roots.
If potted, a medium that drains quickly and thoroughly should be used. Dendrobiums do not like to have their roots disturbed, so it is best to anchor the plant in a substrate such as lava rock.
The Den. aggregatum needs a lot of diffused sunlight3. When pseudobulbs turn a reddish colour, the plant is receiving the most light it can handle and should be left in place unless it starts to sunburn. During the plant's winter rest, the amount of sunlight should be maintained. Some people like to 'blast' their plant with sun during this rest, but the plant is less capable of healing itself if it is cooked. It seems that constant 'blasting' works quite well for making this plant happy.
For mounted plants, a lot of water is necessary. This, of course, is dependent on the atmospheric humidity and the temperature. The plant should not dry out. Potted plants should be allowed to completely dry out after watering. In a well-drained medium, this should take no more than a day or two. Orchids are very sensitive to excessive salinity; so, if water is being processed through a softener or has large quantities of minerals, distilled rainwater (also dependent on area conditions), or reverse osmosified (R/O) water should be used.
Fertilisation, while not necessary, should be done regularly. Plants should not be fertilised more than once a week in any circumstances. Fertiliser should not be given to ailing plants or plants with dry roots. Fertilising a plant with dry roots can lead to burnt roots, which is never very nice. Some growers use bloom boosters, though they have not been proven to aid in flower production.
Den. aggregatum requires a winter rest period. For several months, the plant should be exposed to 10-15°C temperatures at night with slightly warmer days. The plants can take a light frost, but it is not recommended. Watering should be gradually withdrawn and fertilising completely stopped. Plants should be watered very sparingly throughout the rest period if the pseudobulbs show extensive shrivelling. Some shrinkage should not be alarming and plants may be partially deciduous. Sun exposure should remain the same from the growth period through the rest period in order to ensure spring blooms and growth.