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Plant Answer Line Question

Keywords: Orchidaceae (Orchid family), Dendrobium

I have a couple of Dendrobium orchids, and one other that I don't know the name of. Both the Dendrobium have lost all their leaves, and I'm worried that they will die if they are not repotted soon. There is white fuzzy mold growing in the potting mix (which is just bark) of at least one of them, and I researched a little online and found that it is a common kind of snow white fungus (that may not be the right name) that is common to orchids in general.

I'm worried about root rot, and I'm wondering what I can do to try to revive these two orchids back to blooming. I read that soaking the roots in hydrogen peroxide can often help kill the fungus and then repotting thereafter can possibly revive them. What would you suggest for a repotting mix, and do you have any tips on reviving orchids once that have lost all their leaves?

The roots seem to still be intact, and do not appear to be rotted, as far as I can tell. I'm also wondering about good types of greenhouses/shelters to keep them in, as well as heaters to keep them a little warmer in the house -- they seem to be having a harder time with the 60 degree temperatures that my apartment tends to be. Any advice you could give would be great!


Some Dendrobium are deciduous, so your plants are likely acting exactly as they should. However, now that they've lost their leaves, you should restrict watering them through the winter, watering them only enough to keep them from shriveling, until flower buds form. Then, resume watering again. The species of Dendrobium that are deciduous require night temps of 50-55 degrees F during the winter.

Dendrobium grow well in Osmunda fiber, a potting medium, or bark if they are carefully staked, though they shouldn't be re-potted or divided until new growth starts. Also, Dendrobium with 4 or 5 shoots will grow well in a 4-5 inch pot, so you don't necessarily need to increase the pot size when you do re-pot your plants.

If you cut back on the water you give your Dendrobium through the winter, you shouldn't have to worry about root rot/fungi, especially if you repot them when new growth appears.

The advice above is taken from Home Orchid Growing (by Rebecca T. Northen, 1990, pp. 209-212).

Orchid Growing Basics (by G. Schoser, 1993, pp.40-45) shows some ways you can create a good place for orchids inside your home. For Dendrobium, placing the plants in a window with southern exposure, a grow light that will give them 12 hours of light each day, and humidity (Schoser recommends standing the pots on upsidedown flower pots in a tray of water) seem to be the most important considerations.

The Miller Library has many, many books on orchid growing.

Also, you might want to investigate the Northwest Orchid Society.

Date 2017-05-11
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Plant Answer Line Question

Keywords: Phalaenopsis, Orchidaceae (Orchid family)

I have a question about a Phalaenopsis orchid. The orchid is a year old and at the top of last year's flower stalk has grown a new set of leaves as well as roots. Can this be cut off and re-rooted? Also, after the blooms fade, do you cut the stalk off and if so, how far?


Here is some information on propagation Phalaenopsis, from a commercial orchid grower:

"Phalaenopsis can be vegetatively propagated by cutting the flowering stem above a stem internode, the dormant growth 'eye' is covered with a triangular sheath. Cut, with a hot knife or shears, through the flower stem after the last flower has fallen. Then move the plant to a dimmer area. In most cases, new plants will start from the dormant 'eyes.' After the new plants initiate, the mother and 'keikis' (babies) can be move gradually back to higher light. When the keikis have 2-3 roots, the keikis can be removed, by slicing between the stem and the keiki, or cutting the stem above and below keiki's attachment point. The new plant can now be potted up and grown on. If more flowers are desired, cut the stem as above, but do not move the plant. In the second method, the mother plant is topped. As a monopodial plant, Phals continue to grow vertically. In time, they discard their lower leaves. The leaves have served as a storage vessel of water and nutrients. The leaves have outlived their usefulness and are discarded. New roots are produced above the leafless stem, as the Phal continues growing vertically. The stem can be cut below the new roots. The top part, with leaves and roots, can be repotted after proper care of the cut. The remaining stub can be left as is, for a few days/weeks. Soon, new little plants will be found growing out of the old stub. These keikis can be repotted in the same manner as the first method. They will grow on and eventually bloom. If left on the stub, they will often bloom sooner, than if individually potted."

The American Orchid Society has a video illustrating the potting of a keiki, as well as a host of other orchid care information.

You may find the following links to the Brooklyn Botanic Garden useful for general directions on orchid care. Here is an excerpt: "Some species will also produce plantlets on the flowering spikes, complete with leaves and roots. These small offshoots can be pruned and planted, but keep in mind that transition from plantlet to flowering specimen is a long process requiring several years and lots of patience." Here is another helpful link from the Brooklyn Botanic Garden website.

As for what to do with a spent flower stalk, here is what the Royal Horticultural Society recommends: "A flower spike can continue to bloom for up to three months. Once faded, cut the spike just above the second node (joint) beneath the spent flowers, and a flowering sideshoot may develop."

Date 2017-05-04
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Plant Answer Line Question

Keywords: Dendrobium, Orchidaceae (Orchid family)

I just got a Dendrobium, it is Dendrobium eima x impact. The flowers are pink and white. I was wondering how I can tell if it is a deciduous one or an evergreen one. I still have months before winter, but want to make sure I give it the rest it needs when the winter does get here.


There are deciduous and evergreen types of Dendrobium. Unfortunately, I could not find information about the variety you are growing. If yours has soft canes, it is deciduous; hard canes are characteristic of the evergreen type. Here is information from Orchids Made Easy:
"Dendrobiums are separated into two main groups: hard-caned and soft-caned. Hard-caned Dendrobiums have tall pseudobulbs that are very thin and their leaves are generally a little darker in color than the soft-caned. Hard-caned Dens are evergreen and often keep their leaves for many years before they drop them. Hard-caned Dens grow spikes from the top of the cane and produce gorgeous flower sprays.

"Soft-caned Dendrobiums have leafy pseudobulbs that are long and slim. Their leaves are generally a little lighter in color than the hard-caned Dens. They grow leaves along the length of the cane and the blooms sprout from the individual stems that are along the cane itself. Soft-caned dendrobiums are deciduous and drop their leaves when the weather gets cold."

The American Orchid Society has a guide to growing evergreen Dendrobium for beginners.

There is also good general information on caring for orchids in the Brooklyn Botanic Garden guides on the subject. Generally, winter is the time to hold back on watering a bit, but also be careful about the plant's need for humidity--our heated homes in winter can be exceedingly dry. According to Orchids by Joyce Stewart (Timber Press, 2000), most orchids prefer 65-75% humidity during the day. She recommends "damping down last thing at night" during the winter (using a spray bottle or mister), if you have heat on in your house overnight.

Date 2018-05-04
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Plant Answer Line Question

Keywords: Orchidaceae (Orchid family)

All but one of my orchids are blooming this season! What could be the cause of the one orchid not blooming?


First of all, congratulations that you have all but one of your orchids blooming. Orchids are plants with very particular needs, as you well know. I have found two possibilities as to why your one orchid will not grace you with its flowers: light and space. However, there are other possibilities as well, which I will try to address.

Perhaps this one plant is not receiving the amount of sunlight it needs to bloom and the others are. Are all your orchids the same species or variety? If so, are they all in the same area of your house; i.e. same window? If they are not the same species or variety, then they may require different amounts and levels of intensity of light. Are they growing in a window with natural light or are you growing them under artificial light? If you are using artificial light, orchids do require dark as well as light. Orchids "should not receive more than 14 hours of artificial light a day. More than that will prevent them from blooming." (Orchid Growing Basics by Dr. Gustav Schoser, Sterling Publishing Company, 1993)

Are you using a fertilizer? If so, and the first number is a lot higher than the second or third (such as 15-5-5), it is likely that the plant is receiving too much nitrogen. This will do wonders for the green leaves but nothing to promote flowering. A fertilizer with the numbers closer together (such as 10-12-10) will be more balanced and would be recommended. Are you monitoring the temperature? "The effects of temperature changes are most clearly observable in the Cymbidium orchids. Flower production begins when daytime temperatures are about 68 degrees and nighttime temperatures are around 50-57 degrees. Phalaenopsis schilleriana and its hybrids will only bloom when the nighttime temperature is under 68 degrees for at least 2-3 weeks." (Orchid Growing Basics)

Here is an excerpt from a frequently asked question and answer web page from a commercial grower: beautifulorchids.com.

Q: I am growing my phalaenopsis orchid in the house but they never bloom. What can I do?

A: The most common reason for any orchid not to bloom is insufficient light. Move your phalaenopsis plants to a window where they will receive strong, but indirect light (near a south-facing window is ideal). You might also try lighting your plants with a fluorescent light fixture placed about 1-2 feet above the foliage. Give up to 12 hours of supplemental light per day. Phalaenopsis will also develop flower spikes in response to a cool period of about four weeks with night temperatures of 55F. After the cool treatment, raise the night temperature back to the normal 60-65F minimum. See if these changes to your growing conditions help to stimulate your plants to bloom.

Another page on the same site more clearly defines good vs. bad light. They explain that too little light may prevent the plants from blooming. They also list specific orchids that prefer low light and those that prefer moderate to high light.

The Brooklyn Botanic Garden All-Region Guides: The Gardener's Guide to Growing Orchids (2004) Handbook #178, (partially available online) has a lot of good information regarding light requirements on a variety of orchids. It is noted in this book that "light is undoubtedly the most important factor in determining whether or not an orchid will flower."

Also, there is a possibility that the one orchid has outgrown its pot faster than its companions and has a need for more space (and possibly more nutrients). "Most orchids usually only bloom from new growth" (Your First Orchids and How to Grow Them published by the Oregon Orchid Society, Inc 1988). "An orchid is in need of repotting when the leading pseudobulb or growth has reached the rim of the pot and there is no room for future development. (The Gardener's Guide to Growing Orchids by Wilma and Brian Rittershausen, David and Charles Publishers 2001) If you are getting new shoots but they are growing over the edge of the pot and breaking off, this would also be a sign for the need to repot.

The Gardener's Guide to Growing Orchids by Wilma and Brian Rittershausen, and The Brooklyn Botanic Garden All-Region Guide and Orchid Growing Basics by Dr. Gustav Schoser, offer good directions on repotting. The Schoser title even offers recipes on how to make your own potting mixes.

Date 2017-05-05
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May 31 2018 13:14:08