Dendrobium Leaves

[Alan Sailer]

I am am pretty new to orchids but have been happy with my successes. A half dozen phalaenopsis have been doing well for me over the past three years.

I have a single dendrobium which has bloomed twice since I bought it. After the last bloom another stem started growing. It reached about six inches with about six leaves, all a healthy green.

Two weeks ago the plant started blooming again. From an older stem. What I don't understand is that all the leaves on the new stem have yellowed and fallen off. What's that all about?

The plant is indoors, LED lighting and is soaked once a week, the same as my phalaeniopsis plants.

Thanks for any reply's.

Cheers.

[estación seca]

Welcome to the Orchid Board!

Dendrobiums naturally occur over a huge part of the Earth, from Japan throughout eastern and southern Asia into Australia. There are many different kinds from different climates, with different growth requirements. Does your have a label with a name, or can you provide a photo?

In general once a week during the growing season might not be enough for most Dendrobiums. They are heavy water users while making new growths. But there are other things that might cause the leaf drop. Photos would help.

Some people can't post photos until they've made 5 posts. If you reply to this one that will be two for you. You can go to other threads and make replies there as well to get yourself to 5 posts.

[Roberta]

Many Dendrobiums bloom on bare canes. Some ONLY bloom on bare canes that have lost their leaves. So no worries there.

[Alan Sailer]

Thanks for the reply's.

I will try and get a picture up. After I meet the six post limit. As far as the water, maybe the "stress" of blooming highlighted the under-watering? The plant was growing well until the bloom.

Interesting about the bare canes. The bloom is from the oldest cane which has four leaves. The newest cane is the one turning yellow.

I may have been able to attach a photo. The newest cane is at the front of the image. The other cane has always been yellow but seems to be getting worse. And the third cane is great green and blooming.

Cheers.

[Roberta]

It is very likely that you could post pictures now... I have see quite a few instances of very new members who were able to post pictures using the "Manage Attachments" function in the Go Advanced screen for posting replies.

---------- Post added at 11:57 AM ---------- Previous post was at 11:29 AM ----------

Thanks for the photo! The plant looks good. Questions come to mind, though, looking at the photo. Does the decorative pot have a hole at the bottom? If not, you need to get the plant out of it. If it does have drainage, not as urgent, but the medium appears to be on the old side. If you haven't repotted it since you bought it, it's a candidate... The ideal time to repot is when you see new roots - even if it is blooming. If the mix is badly broken down, you're better off repotting, in the hopes that a better environment will inspire new root growth. But a healthy orchid is all about roots - if those go bad due to bad medium, the plant will decline. If you repot, just remove and rinse off the medium that comes off easily. Don't worry about getting every last bit, which will likely damage roots. A bit of old medium left behind won't harm.

[Alan Sailer]

Roberta,

It is about three years old (from time pf purchase). And I have not re-potted. The drainage is excellent, lots of holes. One white root is peeking over the edge.

If you strongly suggest re-potting during blooming I'll do that. Standard mix, orchid mix and bark?

Thanks for the help.

Cheers.

[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.

[Roberta]

If there is evidence of new roots starting (just little green tips peeking out) then go ahead and repot. It won't hurt if you wait a bit to let it finish blooming. But it definitely wants repot fairly soon. I don't know what is in the "standard mix" or "orchid mix" ... you need a well-draining mix, personally I would use medium bark with some fairly large perlite (Not the powdery stuff that is used for soil) or pumice or lava rock. (If you don't have access to any of those additives that just help keep the mix open , plain old bark works fine) Dendrobiums typically need to get almost dry before watering again, and need air around the roots.

[Shadeflower]

This is like my dendrobium although yours is white.

They are warm growing phals, they do not like temps under 20 degrees C, can handle 18C lowest.

But this looks like the roots have gone bad and more serious than wrong temps. you need to see what is going on in the pot. It looks too soggy. So either the mix retains too much water or you have possibly been overwatering but you better check the roots.

[Alan Sailer]

Great. I've gotten exactly what I want. Hopefully I can get this thing thriving. It's always just looked hanging in there.

The phal... are all thriving so I am not hopeless as an orchid person.

Cheers.