Winter rest requirements for Dendrobium harveyanum?
 

I've had a Den harveyanum for a couple years, and while it does bloom each spring, the flower count is very low and I've read that this could be caused by an insufficient winter rest.

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This is a Den which comes from a monsoon climate with rather heavy rainfall in the growing season, followed by a dry, bright and cool fall and winter. Humidity at the tail end of winter is said to be rather low, with plants likely receiving very little moisture at all.

This is the winter rest info on travaldo's blog (and read elswhere):
Travaldo's blog: Dendrobium harveyanum care and culture
" Rest period:
A cool, dry rest is necessary for Dendrobium harveyanum and should last until new growths appear in the spring. You can completely eliminating water in winter, but the plants are healthier if they dry between watering in winter, but they will not be completely dry for too long. However, during the last 1-2 months of winter, the plants must dry out completely between waterings and stay dry for a bit longer. Occasional morning fogging will protect the plants of drying. Fertilization should be reduced or eliminated until regular watering starts."

I have been 'resting' it by reducing watering to once every 3 weeks or so between halloween and spike formation. The bulbs on this plant shrivel rapidly, so I've been afraid to lengthen the watering intervals. Mine is grown potted and indoors, and in the winter the humidity is between 35-60%, temperature 18-24°C and I have LED fixtures as supplemental lighting. Does anyone here have experience with this Den? Should I limit watering to occasionally heavy misting and skip the soaking entirely? I understand the advice above, but it's difficult to figure out how that works in practice.

I don't grow this, but something that helps me with culture over the resting period is to first figure out what the natural range of the plant is & the elevation it grows at--you can typically find this info on the IOSPE: in this case, SE China and the regions immediately around; elevations of 1100-1700 meters
Armed with that knowledge, use google to pull up an elevation map of the region; select a point that lies within the target elevation range. Guangzhou is in SE China, so I'll use a point in it; Tiantang Peak is the highest peak in this subtropical province, 1200 meters and a bit
Now run a weather search on the location; this will give you averages on humidity, precipitation, temperature, etc., broken down by month, for a calendar year. From this data, one can more closely infer what to do culturally. In the case of your dendrobium, I'd try shooting for substantially cooler temps during the winter rest phase; Dec-Feb the average temps are just above freezing 2C or so--plants are cold, with relatively low humidity & low precipitation...ie try treating them [culturally] like cymbidiums

Neither do I grow it but I would also suspect cool winter temperatures are important. It's hard to achieve in a home in a cold-winter climate. Years ago I did it by closing off the heat vents in a room, but not everybody can do this.

Thanks for the info and I was aware that the temperature part of the winter rest would be challenging for me (I can move it to a cooler room to 'win' a couple degrees), however I would still appreciate some advice regarding the watering aspect since that is something that is within my control...

Sounds like that is your problem. Letting a dendrobium dry out for 3 weeks during it's most crucial flower development time (winter) is asking for trouble.

I know lots of the guides say to do so but we don't give out orchids ice cubes, we don't stop watering our warm growing orchids in the height of summer for 3 weeks.

Some orchids do rest but the ones that flower in spring aer orchids that collect the energy to do so over winter.

If you stop watering it at such a crucial time it is no surprise. Your bulbs are even wrknkling. The orchid is losing all its energy reserves.

Bulbs are an emergency reserve for when there is a drought in nature. In our home environment we should never simulate a stressful environment.

The only reason care guides have traditionally advised to reduce watering is because orchids do slow down growing in winter and too much moisture combined with cold temperatures can cause root rot.

Since then I have concluded that root rot and stem rot is most often caused by a weakened orchid - not water or low temps (but low temps can kill a weakened orchid)

It is even perfectly acceptable to not subject an orchid to the low extremes it would experience in nature.

We know flowering is induced by a combination of the light hours and the temperature.

Stressing an orchid to flower is old wives tales. I thought you knew that by now Camille.

I am just showing my face again to point out such an obvious reason to you... Not in an insulting way. Just a bit of a sigh and the reason I don't participate no more. If nobody on here listens or learns and a day later they are back to doing the same old wives tales again then what is the point.

Ok you might say but SF, I do not listen to a word you say. If that is the case then you will never improve your flower count. Up to you.

The best flowering orchids (doesn't matter which variety) are the ones without shrivelled pseudobulbs.

Considering I would bet you that I could find an example of pretty much any orchid that flowered with and without shrivelled pseudobulbs that tells you that shrivelled pseudobulbs are not a requirement for flowering and like I mentioned if your flowering reserves are depleted by the time it comes to flowering then the flowering will be reduced.

It's like trying to take a trip to France on an empty petrol tank. If you just did a trip to Germany the day before and didn't refuel then you will not make the trip to France. With a dendrobium you can't just refuel the petrol tank. Plumping up dehydrated pseudobulbs takes a minimum of 9 months in my experience (either S/H or daily watering)

If every year you let the pseudobulbs shrivel over winter then you will be repeating the process every year and the plant will spend 9 months replenishing the energy lost the year before and then lose it all over winter again.

I'm sorry. I didn't respond earlier because I haven't grown this one and haven't talked to anybody who does. I didn't want to offer useless random speculation.

But I have found this article, which didn't appear the last time I searched on this plant, months ago. It is written by an orchid expert:
Dendrobium harveyanum

Thanks for the link, I had seen it as well. They grow in a greenhouse though, where I expect humidity is going to be different (higher) than indoors. I'm not looking for input from someone who specifically has this species, general watering advice for 'dry rest' in indoor growing conditions is fine too.

Like I said I can move the plant to another cooler room, and stick it between the window and curtains but it won't get cooler than maybe 15C there, still with low humidity (and no supplemental light).

And heck, worse thing that can happen is that it doesn't make larger spikes. I'll still be happy with the 2-3 flowers I get, since I know it's difficult to do much better. (and better than no blooms at all!)



ShadeFlower, while I do appreciate your input and do agree with you on your opinion for most orchids, for winter resting Dens I do not agree. Cool and/or dry is what these types of Dens naturally get in the wild, and it is well known that for many of the winter resting Dendrobium types, cool and/or dry are important triggers for blooming. See the link ES posted for a fine example of this.

Here is speculation. Monsoonal climate terrain I've been to in Mexico has very arid winters with low humidity unless the locale is quite close to the sea.

Some Dendrobiums do require the high light/lower temperature/reduced watering treatment to bloom well. When done correctly, it does not desiccate the plants.

The degree of reduced watering varies. In my greenhouse (with good humidity):
Den. kingianum: I reduce watering to once every 4-6 weeks..
Den. nobile: I reduce watering to once every 2-3 weeks
Den. aggregatum: I give it zero water from November till I see the buds.

For all of these, once the buds form, you start to ramp up the watering schedule.

The one detail, which most writers neglect:
For all the winter rest Dendrobiums, it is critical that you stop fertilizing. The general rule should be:
mid September: No more fertilizer
mid October: Reduced watering

I only start fertilizing these plants again, once the buds are within a couple of weeks of opening.

I did NOT know that, thank you for the information! I'll stick a brightly colored labelled in the pot as a visual reminder to not give fertilizer or Kelpak before spring.

To be more acurate, yes I had come across this information, but only in relation to nobile type Dens. I didn't think that this advice applied across the board to most/all winter resting Dendrobiums.