Dendrobium Leaves

[estación seca]

It's in the group called Dendrobium phalaenopsis hybrids. You've flowered it so you have been taking good care of it.

These prefer even warmth and watering through the year. Small amounts of fertiliser when in growth improve growth and flowering. They prefer higher light than Phalaenopsis but not as much as some other orchids. The fact yours flowered proves the light you're giving it is adequate. Leaves normally don't drop until the growth is 3 years or older. They can flower from old growths.

If you mean the smallest growth with one leaf is the newest - with best care it would have been at least as tall as previous growths, perhaps taller, and would still have all its leaves. From your comments I'm guessing it could have used more frequent watering while forming. Have you fertilized it? No fertilizer for a long time also leads to smaller growths and fewer flowers.

Dens make lots of small roots, but they don't always occupy a large volume. The pot yours is in is considerably larger than I would have used for that plant 3 years ago. When you repot select a container that just holds the roots and has horizontal space for 2-3 new growths. Repot so the oldest part of the plant is at one edge, with the new growth pointing at the far edge.

The most important factor for epiphytic orchids is air at the roots. The medium used should have air spaces between particles. Bark decays in 2-3 years. It crumbles, and fills the air spaces. Roots in these areas may die. This is why people recommend repotting into fresh bark every 2-3 years.

Bark works well for most orchids if repotted regularly. Other media can be used. Some people use medium sized chunks of cinders, scoria or pumice, or other pebbles. Others use fired clay balls called LECA, sold at hydroponics shops. Some use wine corks. Inorganic potting media don't break down, so repotting intervals may be longer unless the plant outgrows the pot. Long-fiber sphagnum moss works well too, but watering plants in moss is very different from watering plants in other media. It needs to be replaced every 1-2 years or it compresses and roots suffocate.

After repotting orchids must be staked or fastened so they don't wobble and damage new roots before they are extensive and able to support the plant. This is especially important for taller plants.

If you haven't been watering your Den much the medium might have lasted longer than usual. What I see on top doesn't look too bad, but I can't see what's underneath. If the lower layers are still firm, not mushy, and there are plenty of air spaces, I would feel comfortable waiting to repot until the next new growth breaks, and new roots are just showing. This would also give you more time to read about your plants.