Dendrobium with yellow leaves a few follow up questions

[Stefan Petersen]

Dear Orchid Board

I am new to this forum and have been reading up on the threads about my specific problem, but I have a few follow up questions:

I have a Dendribium, which is a very dear heirloom. Unfortunately the leaves started to turn yellow and it has been happening really fast.

I am really worried. I have read that it might be due to overwatering, and that it would help to take it out of the pot and dry it out. But I am wondering where to put it, when drying it, what should I put it in?

It might also be that the problem is something else. Here are som facts about how I have treated it:

- It has always been planted in bark
- It was replanted it 6 months ago, but I just replanted it again yesterday, because it seemd like the bark was to compact.
- I have always watered it from the top, but 6 months ago I was told that it was better to put the pot in water and let it soak for an hour. And pour the water it didnøt soak out.
- I recently moved it from a warm south faced window during winter and early spring to a north faced (The sun is up for around 17 hours here in Denmark atm). Could it be that it has been in to much direct sunlight?
- I have never used any fertiliser.

Please any advice is dear since this plant is from someone who was very dear to me.

[estación seca]

Welcome.

This looks like a Dendrobium kingianum or a hybrid involving it. It is very dessicated. It has been underwatered for a long time, which is why it is losing leaves.

Fortunately this kind of Den. is very hard to kill, as can be seen by the newer roots.

Repeated unpotting is not a good idea. Put it into a pot with bark. It doesn't matter whether you water from the top or the bottom so long as the entire pot contents become wet.

Being so dry, I would soak it in a bowl of water overnight. The wrinkled leaves may not recover. New growth should be normal.

They tend to make new growth Spring to Summer. They should not dry completely during this time, but neither should they stay soggy wet. Water whenever the bark is almost dry. I would perform the long soak the first few waterings, until the old leaves and pseudobulbs stop improving.

This plant should tolerate your sun through a window if adequately hydrated. It is a high light plant, though leaves might burn in sun without air movement. It would also like your summers outside in dappled shade if animals are not a problem.

Use fertilizer. Use any balanced house plant formulation with micronutrients. Mix 2-3 grams per 4 liters of water, and apply at least weekly from Spring to early Fall. If your water has calcium in it that should be enough. If not use a calcium-magnesium supplement at a different watering than the fertilizer due to solubility issues.

For best flowering they should have a very bright winter with nights 5-10C. This is difficult in a cold-winter climate.

[Roberta]

Also, don't be tempted to cut canes that have lost leaves - they are the reserves for the plant. I have seen "mostly leafless" Den. kingianums come back to life with new growth. Eventually those leafless old growths will shrivel and turn light brown... they can be removed once they are truly dead, but not necessary. But if they are still firm, they are very much alive. My general advice - with growths and roots - don't cut anything, it is too hard to tell what is alive. And with Dendrobiums especially, they can look dead and still be quite alive.

[Stefan Petersen]

Thank you so much for your detailed reply. I am very happy to get qualified help here in this forum, since most plant stores here in DK don't have an in depth knowledge of orchids.

While I was looking at older posts it seemed like, that most people suggested that problems with the leaves turning yellow was due to overwatering. How can I tell if it is dessicated and not the other way around? Sorry for such a beginner question. It is almost like a little bush, so it is difficult to get a finger in and feel the bark. And when I repotted it it seemed like the bark in the bottom was a bit humid while it was dry on top

It has been watered from the top, and I have been a little concerned, that some water might have collected in it, and there for the roots have started to rot.

Once again thank you so much for your help. I am very thankful for your advice. How have you got all your knowledge on orchids? I have just started reading online but was thinking if there might be books or anything like that.

I have attached a picture of the flowers if that makes it easier to determine if it is a kingianum or hybrid.

[Roberta]

Ah, the photo helps a lot. Not in the Den kingianum group, looks like it is a compact form in the "Phalaenopsis-type" Dendrobium group (which has no relationship to Phalaenopsis). A hybrid (probably) of Den. bigibbum variety compactum. So it is a warm-grower, likes house temperatures like a Phalaenopsis, but needs much more light. It also does not want a winter "rest".

When you see new growth starting, you can repot it (I would recommend small to medium bark) and that will give you a chance to look at the roots. (Dehydration can happen either from under-watering or from rotten roots due to overwatering in broken-down medium) As far as watering frequency goes... If you water it well (water flowing through the pot) and let it drain, suggest that you weigh it on a kitchen scale (or postal scale). Weigh it again the next day, etc. When the rate of weight loss becomes slow (not much more water to evaporate) then time to water again.

As for where the knowledge comes from? I think for most it us, the majority is from experience and talking to other orchid growers either in societies or online. (And the sad experience of what doesn't work...) There is a lifetime of learning possible... welcome to the "orchid addiction"

[estación seca]

I was wrong; this is a Den. phalaenopsis hybrid. That is the former name for Den. bigibbum, and it is not a Dendrobium-Phalaenopsis intergeneric cross. It got the name because flowers resemble those of genus Phalaenopsis, an unrelated orchid.

This kind of Den. prefers even warmth, light, watering and fertilizer all year. Many people let them get just dry between waterings in winter but I keep them moist, since I have mostly warm winters. I was fooled because your plant is much shorter than most Den. phal hybrids.

Your plant's leaves look dessicated. They have linear wrinkles and are curling. Some have turned light brown the way they do with inadequate watering. This group should retain all leaves on the pseudobulb for multiple years. (Other Dens are not like this. It is a huge genus.) When leaves drop it is usually because the plant isn't watered enough or it got too cold.

The pseudobulbs have deep vertical creases. This is a sign of dessication.

You can tell how moist is the bark by lifting the pot. Pay attention after the long soak, and lift it each day. In bark, while pushing new growth, you might need to water this plant every 1-3 days. When not pushing new growth, perhaps every 3-5 days. It depends on ambient temperature, light and relative humidity.

Overwatering isn't usually the real problem - it is insufficient air at the roots. Medium with substantial air spaces can and should stay moist for this kind of Den. All Dens making new growth should be watered heavily. Some need much less water in winter. Don't worry about wetting the entire plant with a water spray. They like that.

Most of us read everything we can. But long-time growers, experience and mistakes are the best teachers. OB in my opinion is the best Web site for orchid information, which is why I read it. The American Orchid Society has a lot of information.

There are not many generalist orchid books I would recommend. Books devoted to one group of orchids tend to be more useful. If you can find it I do recommend The American Orchid Society Guide to Orchids and their Culture: Products

[Dimples]

Originally Posted by Stefan Petersen

And when I repotted it it seemed like the bark in the bottom was a bit humid while it was dry on top

Not sure how you've been soaking the plant but wanted to make sure you knew that when you soak plants that are growing in bark, you need to make sure the water level is quite high so all of the bark can absorb water. Bark does not wick moisture up from the bottom like sphagnum moss or traditional houseplant potting soil/potting compost does. Setting a pot of bark in a shallow tray of water will only moisten the bark sitting in the water and maybe a little of the bark immediately above it, but the rest of the pot will stay dry.

If you have been soaking it in a deep container and it's still this dry, it's a sign that it's going too long between waterings. Good luck!

[Stefan Petersen]

Thank you very much for your adcvice. I started out by being very unsure if it was overwatered, underwatered or was burned by the sun.

I will soak it straight away. Would you do it with or without fertiliser the first time. A Danish lady suggested, that I should use two tea spoons of sugar when soaking it the first time? But I think you guys seem more informed on orchids :-)

Sorry for all these questions, but it is a very important heirloom from someone who was dear to me, and I am very anxious that I might have done something wrong to kill it.

---------- Post added at 07:57 PM ---------- Previous post was at 07:47 PM ----------

PS. What temperature should the water be? Cold, room temperature or warm?

[Roberta]

The bit of sugar in the soaking water (just the one time) may help the dehydration, and will do no harm. About 1 teaspoon (5 g) in 4 L should be enough. Don't worry about fertilizer at this time... orchids use very little, only when they are growing. They mostly survive on the carbohydrates that they make by photosynthesis, only need the minerals in fertilizer to make new tissue and not much even then. Think of fertilizer as "vitamins" not "food".

Room temperature water is fine. (Whatever comes out of the tap unless it is very cold... these are not particularly sensitive)

[estación seca]

This kind of Dendrobium is very easy to grow if kept warm and well watered.