Orchid Culture - 2008 Questions & Answers
by Sue Bottom, from the St. Augustine Orchid Society Newsletter.
Email us with any orchid question, if we can't answer it we'll find someone who can! Send photographs too!
Dynamite Slow Release Fertilizer
Q. Courtney was talking about Dynamite at the
last meeting. I am thinking about switching to that
slow release fertilizer and stop using my water
soluble fertilizer. Many of my cattleyas have roots
at the surface and I don’t know how much of the
good root zone is below the surface. Seems to
me that the roots at or above the surface of the
growing medium will get little benefit from the Dynamite.
So, how much of the total root zone is needed to give the
plant sufficient nutrients? Also, I have heard numerous
times of the importance of flushing the salts out with clear
water periodically. How is that accomplished when using
Dynamite that has some degree of fertilizer dissolution
whenever the plant is watered.
A. The Dynamite works by dissolving a small amount of
its fertilizer when you water so any surface roots above
the Dynamite would not be fertilized. However, I suspect
there are sufficient roots in the pot for fertilizer uptake and
the occasional aerial root will just seek out water. If all your
good green tipped roots are out of the pot, it may be time
to think about repotting. When you flush, you are trying
to flush the accumulated salts, those salts that have been
deposited from multiple previous fertilizing events, out of
the root zone. If you reach a steady state by flushing a
sufficient amount of water through your pot, even with the
Dynamite in the pot, you would have a salt load equal to
the salt in the dissolved water in that single fertilizing event,
and that salt level should be at an acceptable, low level.
After flushing, the salts will begin to accumulate again in
the root zone over time until the next flushing event.
photos by RePotMe.com
Q. I am thinking of switching away from coconut husks
in my growing medium and going more to a tree fern mix.
What are the proportions of aliflor, tree fern, charcoal, etc.
that you use for your Cattleyas?
A. The freely draining mix I use for cattleyas and dendrobiums is about a third aliflor, third tree fern, sixth charcoal and sixth sponge rok, although I probably mix it differently each time around. If you listen to Fred Clarke, he is an advocate of adding organic material (in this mix tree fern and in your prior mix coconut husk) into your potting mix for three reasons, to increase microbial activity, to buffer changes in pH (acidity and alkalinity) and to increase the cation exchange capacity (make nutrients more available to the root zone).
You will need to water more frequently with tree fern than coconut husk in your potting mix because the mix dries much more quickly, which is, of course, why the tree fern mix works so well with the cattleya and dendrobium type orchids that have pseudobulbs or canes to store water and food versus the more water retentive coconut husk mix that works so well with phalaenopsis type orchids that have only a fleshy leaf to store water and nutrients.
photos by RePotMe.com
Orchid Potted in Sphagnum Core Surrounded by Bark
Q. One of the first things I read about orchid potting mixes
in my Ortho book was to be wary of mixed potting media.
The topic was about a small orchid grown to market size
in sphagnum and then placed in a larger pot of bark for
retail sale. One could not see the sphagnum. If the orchid
is watered to keep the bark at just the right moisture
level, the sphagnum will stay too wet and rot the base of the
orchid. Shouldn't the potting media have uniform drying
A. Absolutely, and I think you have answered your own
question. You shouldn't’t repot most orchids unless you
have a good reason to repot them. Once a newly acquired
orchid has bloomed out, you can repot it if you find the
dreaded mixed potting media situation you describe or if
you simply want that orchid in the same mix as you normally
use so that all your similar type orchids can be watering
at the same time. Other than that, only repot when the
mix has broken down or the orchid has become unstable
by growing too much out of its pot. The exceptions to
this ‘repot sparingly’ rule would be for your phalaenopsis
that should be repotting by June every year or two or your
paphiopedilums that seem to love being repotted, possibly
because they are so sensitive to salt accumulation.
Q. I remember one of our
speakers saying that we
need to dry out our some
dendrobiums in the fall and
winter. When do I start? How
can I tell one Dendrobium
Great question. The first
thing you have to do is figure
out what type of dendrobium
you have. The big box stores
normally stock the phalaenopsis type dendrobiums, so
named because the flower is similar to a phalaenopsis
flower. These types of dendrobiums are treated similarly
to cattleyas, they do not require a cold dry winter rest
period, although most plants slow their growth in winter
requiring less fertilizer and water. For the more unusual
dendrobiums, you are going to have to check your
plant label. If it is a species, cross check it against the
spreadsheet to see what section it belongs to and what its
winter care requirements are. If it is a hybrid, you can email me
the name of the plant and I will check its genealogy in
OrchidWiz and let you know whether or not it requires a
cold, dry winter to flower best.
photos by RePotMe.com
Dendrobiums Resent Repotting
Q. My Dendrobium looks like it needs to be repotted. How
can I tell for sure? What’s
the best potting mix for
A. Most Dendrobiums like
being root-bound and dislike
having their roots disturbed.
These two facts both suggest
the best potting medium is
one that will not decompose
easily, so bark and sphagnum
moss are not the potting media of choice. A better mix would
be one with aliflor, charcoal, sponge rock and tree fern (or
coconut husk if you can’t find tree fern). Don’t repot your
dendrobiums unless you have a reason to repot them. The
best reason to repot is if the potting mix is decomposing,
which if left in place will likely rot the roots along with the
mix. This is easy to tell if you push your finger into the
pot and the media feels moist and it tends to hold water.
If the plant has become unruly and is pushing out of the
pot, wait until the new roots are getting ready to grow and
emerge from the lead cane. Then you can repot with the
least potential for transplant shock because the new roots
will establish the plant quickly.
Unifoliate and Bifoliate Cattleyas
Q. Is there any correlation between bifoliate
and unifoliate and once per year blooming vs.
multiple blooming cycles? I have Slc. Jewel Box
‘Dark Waters’ which has 5 leads. I have been
told that it won’t bloom until next spring. Another
thing about this plant is that it has both unifoliate
and bifoliate leads.
A. Most species bloom once a year although
bifoliates like C. aclandiae, C. schilleriana and
C. violacea might bloom twice
a year as might a unifoliate like
C. walkeriana. Your Slc. Jewel
Box ‘Dark Waters’ is a hybrid
between the bifoliate species
C. aurantiaca and the unifoliate
hybrid Slc. Anzac, so it is not unusual for it
to have both unifoliate and bifoliate leads.
It is a spring bloomer and based on the
habits of its parents will probably bloom
once a year. With 5 new leads, it should be spectacular
when it comes into bloom!
Healthy Roots Are Key to Healthy Plants
Q. Some growers
say that orchids need
to be somewhat pot
bound. Others says
that they grow better
with no medium at all
- just plunk them in a
basket and let them do
their thing. Provided
that they are both watered and fertilized appropriately,
why do these two methodologists swear by their personal
routines - and they both have wonderful plants?
A. Great question. Orchid growers always say that in
order to have great flowers you have to have healthy
plants and in order to have healthy plants you have to have
vibrant roots. So the happy pot bound orchid and happy
medium-less orchid must share one thing in common,
healthy roots. The pot bound plant is an established
plant that has a root system filling the pot, so when it is
watered the water is quickly absorbed and air refills the
void spaces. The orchid in a medium-less basket can
be watered heavily without rotting the roots because
the basket dries rapidly and the roots are reexposed to
air. The difference between the two growing strategies
would be the amount of water required to keep each
plant happy and healthy, more water for the medium-less
basket, maybe wetting daily, while the pot bound orchid
would be watered every 2 to 4 days during the summer
growing season. The bottom line: you can grow and
bloom orchids under a wide variety of conditions if you
adjust the three most critical elements, water, light and
air, to match your growing environment. Look closely at
your plant each time you water, if the exposed roots are
growing actively with a long green tip and look healthy,
rest assured, you are doing everything right and will be
rewarded with beautiful blooms.
Bacterial Infection after Tropical Storm
Q. After the extended
rains from the tropical
storm, I am seeing
damage on my
vandas. What do you
think it is?
A. It looks like
either a bacteria
or a fungus. The
black necrotic spots look like damage from the bacteria
Pseudomonas (Bacterial Brown Spot). You will have to sanitize the plant by cutting
out the infected tissue with a single edged razor blade and
then reduce leaf wetness. Spray with Banrot (if you have it) or Consan or Kocide,
you don’t have to worry about phytotoxicity because the
plants are not in bloom. If you can’t find Consan, try 10%
pool algaecide applied at the rate of 2 tsp/gal. The Kocide
is a copper compound and will leave a blue residue, don’t
apply it to dendrobiums and don’t apply if the temperature
is above 90.
Spots on Vanda Leaf
Q. I have small yellow
spots starting to
appear in the leaves
of several plants. It
spreads very slowly.
Eventually a black
spot develops in the
A. The yellow leaf
spotting you describe sounds like the fungus Cercospora.
The description in Home Orchid Growing is “these usually
appear as yellow spots that become sunken and turn dark,
or small brown spots that become darker and sunken, or
as brown streaks. In all cases, the spots enlarge and
the affected issue dies, sometimes with the death of the
whole leaf.” To treat for Cercospora, sanitize plant by
cutting away seriously infected tissue with a single edged
razor blade and reduce leaf wetness. Then alternate
applications of a systemic fungicide like thiophanate
methyl (like Clearly’s 3336 or Banrot) and a protectant fungicide like
mancozeb or dithane (labeled as Daconil in the store).
The leaf will never lose the spotting but you will stop the
spread of the disease.
Honeydew and Sooty Mold on Buds
Q. Several of my Brassolaeliocattleyas and related others have developing or mature leads with a sheath like a snow pea. They exude the clear sticky stuff which I have been told is a good thing. The last few days I have noticed sooty mold starting to grow on some of the sticky. I have wiped it off but I know I am just smearing the spores around. What do you do for this situation?
A. The clear sticky stuff is called honeydew and if it looks like little balls or droplets at the base or tip of the leaf or bloom, it is probably just excess plant fluids being secreted by a healthily growing orchid. One problem the presence of honeydew can cause is attracting ants, and ants can spread scale throughout your growing area. To remove the sooty mold that grows on the honeydew, add isopropyl alcohol to a spray bottle and spray the affected area. The fear with honeydew is that it might indicate sucking insects like aphids, scale or mealybugs are present and causing damage by sucking the sugary fluid from your plant. Inspect your plant carefully for pests and treat appropriately. Spray with orthene, summer oil or malathion to control pests.
Water Before Fertilizing?
Q. Does it make sense, on the days I fertilize, to water first with clear water to get the roots plump and green and then water again with fertilizer? Prewatering should get the roots ready for feeding but does it make the roots less capable of absorbing any of the fertilizer solution because they are already hydrated?
A. If you have the time, watering 30 minutes or an hour before fertilizing is a good idea, particularly if in your first pass watering you water heavily until water runs out of the pot and then some. Not only will this help flush some salts from the root zone, it will open the spongy root so the fertilizer solution will be absorbed more easily. Then, in your second pass, you apply just enough fertilizer to coat the roots, this being the most efficient way to deliver nutrients to the root zone.
Orchid Sheath Stopped Growing
Q. I have a beautiful, healthy looking Cattleya that put up a sheath several weeks ago but I can see no buds and nothing seems to be happening now. Is this normal?
A. Maybe. There are a couple of likely possible explanations. If the plant was recently repotted, it may simply not have enough strength to bloom and you have a disappointing blind sheath. It is possible the plant is not getting enough light, the number one reason orchids fail to bloom. If this is the case, the plant will not have enough strength to bloom, move it to a brighter location and wait for the next blooming cycle. If your cattleya is getting 2000 to 4000 ft candles of light and your foliage is a pleasant slightly yellowish green, light is not your problem. Some varieties simply put up a sheath and then take a rest before going into bloom. If it is an awarded mericlone, you can check the month it was awarded to see what its normal bloom pattern is. Otherwise, have a glass of iced tea and wait. Many of those sheaths that were empty in July and August will be in full bloom in November or December.
Peel Open Cattleya Sheath to Prevent Bud Rot
Q. The sheath on my Cattleya is turning yellow. Is this any reason for concern?
A. Probably. Too many times moisture can accumulate inside the sheath and the results are rotten buds and no flowers. To be safe, you need to take action if the sheath starts to yellow and long before it turns brown. Gently pull the sheath apart from the top, sometimes there is a natural separation and you can pull it apart, otherwise get a single edged razor blade and slice off the very top of the sheath. Then, very gently, pull the sheath down to the pseudobulb (and remove if it easily separated) to allow any condensation or water to drain freely. It is possible to snap the bud off so be very careful and gentle. If the sheath does not separate from the plant easily, leave it attached to the pseudobulb, just make sure water and condensation drain away from the bud freely.
Light and Cattleya Leaf Color
Q. If I suspect an orchid is getting too little or too much light based on the color of the leaf, should I expect the leaf color to change after I have moved the plant to a new location?
A. Yes. If your cattleya leaf is a beautiful lush green, it needs more light. The leaf of a cattleya should have a slight yellowish cast and after the leaf hardens (about 3 months) should be as hard as cardboard. A leaf showing lots of red pigmentation is indicative of one getting great light but if the entire leaf darkens to a dark purple, or the leaves are really yellow, the plant might be getting too much light and would have to be moved or shaded.
You should see changes in leaf colors within 2 to 4 weeks of adjusting the light the plant receives. Avoid moving a plant into substantially more sun too quickly, or having water on the leaf during the bright midday sun, both of which can cause sunburn, which will appear as a scorched area fading to a dry, brown sunburn scar that will be present as long as the plant has that leaf. The SAOS has a light meter for use by members so you can determine how intense the light is in your growing area during the course of the day.
Color of Sheathing Around New Cattleya Pseudobulbs
Q. I have a Potinara that has 5 new leads all about 5 to 7 inches long that bloomed in April. I have been excited about the new growths on this plant but just noticed that 3 of the leads have a yellow/gold band near the surface of the potting mix. This almost looks like the sheathing (skin) around the sheath. It is very tight. Everything else looks OK but the other catt type plants are not showing the same condition. Should I be concerned?
A. Maybe. If you have 5 new growths, you are doing just about everything right! If the paper sheathing is gold but is tightly attached to the pseudobulb, not holding water and the lead is firm, there is no problem requiring action on your part. If there is any evidence of a place where water can accumulate, you have the potential for the new lead to rot. To prevent this, remove any paper sheathing that could hold water by peeling it back and away from the lead. If there is any softness in the lead with black or gray discoloration, you should be concerned that the rapidly progressing black rot is attacking the plant requiring immediate action on your part. Black rot is most prevalent during the hot summer months. It starts as a discoloration that can go from the roots up or the leaves down. If black rot is suspected, you must sanitize the plants by cutting away the infected tissue and then apply Banrot or Subdue, if you can find these fungicides.