I recently acquired one of these, and have done some research on care. One reference states, "Dendrobium aggregatums are 'evergreen', which means they do not drop their leaves as some of the tall cane dendrobium orchids." They require seasonal changes in water and fertilizer applications. If you need more information, I can post it; let me know.
Ann

hello, Ann, that would be good. I have googled to get info on its culture and I can't determine what went wrong. it is mounted in a basket. I water it once a week which is less than during active growth period. I thought it was not enough light so I moved it to under 2 - 32W full spectrum florescent tubes and it still happens.
sue

I'm not an expert, but I have two Den. aggregatum for almost a year now, they haven't flower for me yet. I bring them in at end of Oct., and I didn't water them since then, and they're still alive. I hope that I can see some flower when spring comes.

Sue, Here is what I have. Sorry for the length--it's from a few different references. NOTE THE COMMENTS RE: SPIDER MITES. This may be your plant's problem.

Dendrobium Lindleyi I,H from Vietnam. Aka Dend. aggregatum. Miniature, usually best as a mount. Needs a dry winter rest. Bright light. Plants skirt themselves with pendant clusters of bright yellow flowers in mid-spring. The flowers usually take up more space than the plant when in full bloom. Likes lots of food water after blooming until fall, then neglect them - cool temps, little water, no fertilizer. Keep the light bright year round.
Dendrobium aggregatum is one of the Callista species and is native to Burma, northern India and southern China. Other species in the Callista family include: Den. chrysotoxum, Den. densiflorum, Den. farmeri. These are classified as dwarf dendrobiums. They do not grow into tall canes but have short spindle-shaped pseudobulbs bearing thick, leathery leaves. These orchids like to be mounted on bark or cork. Dendrobium aggregatums are 'evergreen', which means they do not drop their leaves as some of the tall cane dendrobium orchids.
Care Tips: Dendrobium aggregatum definitely require a change in the cultural requirements at various times of the year and become dormant in the fall through winter months. They should be suspended and mounted on bark or cork for optimal growth. Grow them with your cattleyas (intermediate to warm conditions) but they require somewhat cooler temperatures during the winter months. In the winter move them to a cooler location and provide them with cooler night temperatures and dry conditions. Good air circulation is necessary.
Light: Dendrobium aggregatum takes high light, so keep them with cattleyas.
Watering: Watering is a crucial element for this orchid. (and may be the most difficult regimen to follow!) During spring and summer, water well when growth is developing. Be generous with your watering and fertilizing. As Autumn approaches, it is important to cut back on your watering and fertilizing schedule. Dendrobium aggregatums require dry conditions in the winter. During the fall and winter, water your plant only enough to keep the pseudobulbs from shriveling and dying. Be aware that the pseudobulbs will become wrinkly during this dormant period. You will need to learn the distinction between what is considered wrinkly and when the orchid will need some water to keep it from dying. Don't fertilize at this time. This severe drying and rest period is difficult to do especially if you are heavy handed with the water or if you are more accustomed to watering. But stick with it!
As Spring arrives and flower buds begin to emerge, increase your watering schedule. Water well while flowering and with the signs of new growth. As late Spring and Summer progress, increase watering and water thoroughly. If the tips of the leaves begin to brown, reassess how much fertilizer you are providing. Perhaps the concentration is too high and the leaves are experiencing some fertilizer burn. Or try changing your watering schedule. Determine how your orchids respond to any regimen you have established and be flexible to change if needed.
Flowers: Flowers usually appear Spring to Summer and is dependent upon adequate light. The Dendrobium aggregatum orchids form hanging clusters (like grapes) of yellow-orange flowers. The flowers are truly delightful. Flowers are approximately 1 inch in diameter, are flat with round lips. Flowers are delicate and cascade gracefully. Flowers last approximately 1-2 weeks.
Miscellaneous: Watch for spider mites. They love to live among the pseudobulbs. Spider mites are difficult to rid and will suck the life and energy out of the plant. If your plant takes a downward turn, begins to yellow, check carefully for any infestation.
Dendrobium aggregatum does necessitate a considerable change in their care in order to produce flowers. They need a solid rest period. Dendrobium aggregatum is a difficult orchid for a novice grower. It is truly difficult not to water! It took me two years to finally get it right! If it is not flowering for you, try something a little different: cooler temperatures, more light, less water. It does take time to master this species. Simply put, remember these tips: Spring to Fall give adequate amounts of water, fertilizer and light. Fall to winter give cooler temperatures (especially at night), water SPARINGLY to prevent them from drying out, keep on dry side.
Overwatering this orchid will only induce growth and will prevent it from flowering. This dormancy period is crucial. Sometimes the best advice one can give is just forget about your plant during these months of dormancy. You may think the plant has died and may be tempted to discard it. Be patient and diligent with their extreme care requirements and you will be rewarded with gorgeous inflorescences.

"I thought it was not enough light so I moved it to under 2 - 32W full spectrum florescent tubes and it still happens."

Two tubes are still not enough light for a species Dend. its not even close. Four tubes minimum, even then I might stick a 23W CFL at one end of the bank and put the aggregatum at that end of the fixture. Your dend. has been light starved for quite awhile and recovery will not be quick but if the light is improved likely it would recover in due time.

H

Good point Howard. Do you think lack of light is the only cause of this orchid's yellow leaf problem?
Ann

thanks, Ann, Howard, yuewen. at one end of the tubes I have a 40w cfl and at the other end a 27w cfl. I will put it closer to the 40w cfl and see what happens. i have checked for spider mites but did not see any. Maybe I'll spray with neem oil just in case.
sue

You don't really 'see' spider mites, you see the evidence of their existence. The yellowing of the foliage will not be the even, sickly yellow of overwatering it will be more mottled. The surface of the foliage will be matte (dull) rather than smooth. You should look carefully 'under' the leaves where you may see webs. Still, mites or not, light will help. It will give the dend the energy it needs to repair whatever ails it. Just took a look at the o.p.'s zone information. Zone 5. Hmmm. I can't see Zone 5 this time of year, even indoors, generating the kind of temps that would allow an infestation of anything to overcome the defenses of a reasonably healthy orchid. The activity of insect pests is directly proportional to the ambient temp. At higher ambients they can really increase their numbers exponentially and take down even strong plants. At household ambients that shouldn't happen unless the plant is already weakened for some other reason, like a lack of good light.

H

hello, Howard, thanks for your thoughts and advice. I have put it under the 2 32W tubes at the end where I also have 40w cfl. how long do you think I will be able to discern any difference?
sue

Unlike the deciduous dendrobiums, aggregatum doesn't need a long, bone-dry rest. I think it is Yamamoto (Hawaii) who recommends about 2-3 weeks fully dry, and minimal water during the other winter months. I personally don't fertilize anything during our short winters. He says to adjust the drying period to flood with water about 6-8 weeks before you want your flowers. Thought I'd try that this year, so I flooded last week. Theoretically, my plant will flower early March. We will see.
Regards - Nancy

Hi Sue - the 'flooding' is done after the several weeks of dry rest! But yes, it means essentially running water over the plant until it is well and truly hydrated.
I don't know anything about artificial light (we use the real thing here) - do they generate heat? That could be problematic.
I also grow this species on a slab, so over-wetting is not an issue, but it could be with one that's basket-grown.
Regards - Nancy

Sue, as far as the watering goes, I run mine dry( meaning no watering at all) from late Nov to March till I see the spikes. No fertilizer too. Even though I call it Dend aggravatum it has bloomed reliably every single year for the last few years. Occasional rain/drizzle does wet the pot, as I grow mine outside.
If you plant is suffering for any reason, you may want to sacrifice the blooms this year and let it eat and grow well- just a thought.

hello, Nancy, the cfl does not generate any heat and it is in the basement where the temp. is about 58F.
sambac, because you leave it dry for those months, do you lose any leaves during that period?
thanks for your help.
sue