Orchid Culture - 2009 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!
Q. My plant has these strange leaf deformities. What am I doing wrong?
A. We turned to Fred Clarke for an answer. Fred believes the most likely cause is weather stress from the very hot summer we had this year. It can also be caused by several other factors like genetics or chemical stress. If it occurs annually, it’s genetic; if randomly, it’s probably one of the other two.
Q. This is the second time this little Den has bloomed for me. Does anyone know her name?
A. I think it is possible, but by no means certain, that your plant is Den. Burana Stripe. Unless you get a better suggestion, put Den. Burana Stripe??? on the label so you know it's a possible maybe and someday you may see one with a plant label and know for sure.
Reduce Watering in Fall
Q. Everything I read says I should go to once a week watering in the fall for my phals. They’re growing inside in clay pots. Do I start now?
A. If your summer watering habit is to water twice a week, you should start increasing the time between watering gradually, pretty soon you'll be at once a week. Start by increasing to every fourth day, then fifth day, etc. Rather than adhering to a rigid schedule, try to judge when your plants look like they need water. Feel the weight of the pot, feel the potting medium, look at the leaves and general vigor of the plant and then follow your instincts. You will be surprised at how much you know!
Move Plants Slowly into Brighter Light
Q. I had beautiful leaves on my orchids but not many blooms. Knowing that insufficient light is the number one reason orchids don’t bloom, I decided to move them into a sunnier spot. Now look what happened, it sure looks like sunburn. What do I do now?
A. It seems that every year I move my plants too quickly into brighter conditions and some of my plants get sunburned. It’s not terminal, let the leaf wither until it can be easily removed. Let the plant gather its energy from the brighter light and you will be rewarded with new growths and leaves and then flowers later in the season.
Lower Phalaenopsis Leaf Yellowing
Q. I bought my son a white phalaenopsis with a double spike and now the bottom leaves are yellowing. What should he do?
A. It is not uncommon for phals to lose their bottom leaves this time of year. If they pull off easily, you could pour some hydrogen peroxide on the wound as a precaution. It is also a large plant in a 4 inch pot that looks a little dry. Try watering it a little more frequently. If another leaf yellows, don't be shy about knocking it out of its pot to check the roots and make sure they're thick and fat. Rotting roots could also cause the leaves to yellow.
Black Rot on Cattleya
Q. I look at my orchids every day and was very surprised to see this water soaked leaf and pseudobulb, it happened so fast. What happened and what do I do?
A. That is the dreaded Black Rot. It infects our plants during the hot humid weather even if the plants aren’t exposed to tropical rain storms. In your plant, it started in the middle of the rhizome and moved up the pseudobulb into the leaf, requiring only 2 or 3 days to do the damage. You can see it is moving in the rhizome to the adjacent pseudobulbs by the tannish discoloration of the rhizome.
More subtle is the beginning of the leaf yellowing, look at the junction of the pseudobulb and the leaf and that is where the yellowing begins. This is a fast, ruthless killer but you may be able to save your plant if you remove all infected tissue with a sterile tool. You will need a piece containing at least 3 uninfected pseudobulbs to replant. Then drench the repotted plant with a fungicide labeled for treating Pythium or Phytophthora, like Banrot or Subdue. Wash your hands before touching another plant. The cooler fall weather will give us respite from this disease.
Q. I noticed today that my C. Chocolate Drop had what appeared to be an aborted bloom pod and a flush of new roots that seem to have stopped growing when they reached the edge of the pot. Looking closely at the roots, I noticed that along the same roots, new root buds were forming. Then I noticed a lot of spots on the new spike which I thought were the beginnings of the coloration spots seen with happy plants getting plenty of light but then saw the coloration spots were not spots but tiny bumps that moved. I concluded that they must be thrips which could also explain the root growth problem. I sprayed the whole plant with Orthenex.
A. Well Sherlock, I think you figured it all out. You can also use the white paper trick Phillip Hamilton told us about to see if you have thrips. If you shake the bloom over a piece of white paper and elongated dark spots move around on the paper, you have thrips. Thrips are barely visible sucking insects that attack flowers and leaves and transmit disease from plant to plant.
Infested buds may not open and flowers may be deformed and have water soaked spots, appearing to have virus-caused color break. Leaves may appear pitted, stippled, silvery or bleached.
For years I said I didn’t have thrips. Was I ever wrong, I just did not know how to identify them. They did lots of damage to the flowers and girdled some of the vanda roots like you can see in the pictures. You can spray with Orthene or Bayer Tree and Shrub. I bought some Conserve based on Phillip Hamilton's suggestion and sprayed it on the plants and the flowers without damaging them and that eliminated the problem in the greenhouse.
Yellow Spot on Phalaenopsis
Q. One of my phals has a small spot on one leaf with a yellow rim. Didn't our last speaker say the yellow halo is characteristic of a bacterial infection, similar to the red surrounding a human skin infection? Is there a home remedy for me to try or should I just cut it out? I have 7 plants in my bathroom.
A. For a bacterial infection, break out the hydrogen peroxide and pour it on the spot just like you would use on skin infection. Watch the spot to see whether it enlarges. If it does, take a sterile razor blade and cut off to about an inch below the yellow halo around the spot. But if you're lucky, the peroxide will kill the bacteria and you will be able to save the leaf.
Bud Blast on Cattleyas
Q. I have had a lot of bud blasting on my cattleyas, on some plants up to half the buds. I'm wondering if the heat we've had over the last couple of weeks is the culprit, it went into the mid to high 90's and sometimes I wetted the plants and growing area down to keep the temperature down. Do you think the excessive heat is the cause?
A. We went to our Go-To Guy Courtney Hackney for an answer, he writes: Did the buds blast inside the sheath or after they had emerged? The heat is likely the culprit if the buds blasted after they emerged. If the buds were still in a closed sheath, you may have contributed to the problem when you wet your plants down and then they got hot again. If the temperature drops and then increases there can be precipitation within the sheath causing the bud blast.
My greenhouse is hot too, but I have only had a bud blast here and there. The trick is to keep lots of air moving around the buds, this will help keep them from overheating. You can also add more shade when temperatures get over 95F or spray the outside of the greenhouse with water to help cool it down.
Don't Divide Cattleya if You Want Specimen Plant
Q. There are 4 or 5 fairly young leads on my B. nodosa with no indication of spiking with 3 new leads just starting. It gets full sun through porch screen from sunup til noon. Should it be repotted? Must it be divided, my preference would be to try and cultivate it to have several blooms at once. Am I nuts?
A. No, I would say you’re a great grower! I think you'll get flowers on the nodosa if you wait for the growths to mature, you should see the sheaths within a month I would guess. I wouldn't repot at least until after it blooms. You've got some room left in the pot and they seem to bloom the best when they have filled or go a bulb or two over the edge. Should be beautiful when it blooms!
Scale Present Below the Media Surface
Q. As I was repotting my L. purpurata var. carnea I noticed a few large scale on the newest fully developed pseudobulb. They brushed off very easily so I believe they were dead from some previous spraying. I had to soak the pot thoroughly and use a knife to get the roots to release from the inside pot edge. There are lots of small white spots on the roots, unlike the white spots that sometimes remain after the wet root turns green. They wipe off with a little gentle effort. Sure looks like scale to me. Can scale reside on the roots below the media surface?
A. Yes, I think sometimes the scale buries itself in the pot, under the rhizome where it cannot be killed by foliar spraying (and possibly also on the root and/or pot). If you find scale during repotting, water blast all the scale you can see and then spray the plant and roots with Orthene or Malathion. After you repot it, drench it with a full strength insecticidal spray.
Algae on Vanda Roots
Q. When I picked up the vanda I bought at Krull Smith, I got some green stuff on my hands from the leaves. Jim said it was algae, no big deal. When I was watering it this morning I noticed the older roots were totally covered and the water was being repelled by the green powdery stuff. The newer roots were soaking it up. Should I do nothing, or try to blast it off with a strong stream of water from the hose?
A. If the algae is preventing the roots from hydrating, you can remove it by spraying with a dilute bleach solution (1 ounce per gallon) or dilute 10% pool algicide solution (2 tsp per gallon). Spray the plant being careful not to spray the flowers which will spot if the solution touches them. After 10 minutes or so, take your hose end sprayer set on flat and water blast the algae off the plant.
Q. My Sarcoglottis sceptrodes has an 8 inch spike and is close to flowering. It seems to have stopped developing new leaves during this spiking process. Since I have no experience with this genus, what happens after the flowers are through blooming? Will the plant start with new leaf production? It only has a half dozen sad looking leaves.
A. Marv Ragan reports that the stem and all the leaves on the Sarcoglottis will die back after blooming. New growth will start from someplace on the existing root system. The dorsal sepal and 2 petals are fused in this orchid. Marv says many of the orchids that are popular to grow do not have this fused flower structure but there are many orchids in nature that have this feature, we just don't usually see the plants.
Scale on Orchids
Q. I just brought an orchid home and noticed these white specks on it. What is it?
A. You have the dreaded scale. You should look at each plant every time you water. If you ever see a yellowish spot on the top of the leaf, look underneath the leaf and you may find scale sucking the juices out of the plant. Here’s how I handle scale. Get your water hose with the spray head set on flat and blast off all the scale as well as the papery sheaths on the pseudobulbs cause that is a great place for scale to hide from view.
Then, take a toothbrush and isopropyl alcohol and scrub it off or keep a can of Orthenex (now it’s called RosePride) handy so you can kill any hangers on. If you think the scale may be on the rhizome or into the potting mix, you can do a drench of malathion or Orthene.
Harriet Wright puts a special colored tag in her plants when she finds scale to remind her to check the plant going forward. When you repot, a good preventative step is to water blast the entire plant and remove the papery sheaths. This is particularly important if you repot your back bulbs because that is the most likely place for scale to accumulate. The insect growth regulator Distance will eradicate scale, but it is expensive ($250/quart).
Why You Repot Orchids
Q. How often should I repot my orchids?
A. Here's the short answer, don't repot unless you have a reason to repot because each time you disturb the orchid's roots, you will have some transplant shock though this can be minimized if you choose the best time to repot. Here are some good reasons to repot:
- You Want Mix to Match Your Normal Mix. You always have to match your watering habits with your orchid’s needs and your orchid’s potting mix. If you water all your plants at the same time, you might want to have them all in the same mix so you don’t have to think whether that plant in sphagnum really needs water while that plant in stalite is dry and crying for water.
- Two Types Mix Used. Often when you buy plants at the big box stores, you'll find that the plant is in an inner core of sphagnum surrounded by a bark mix. It is almost impossible to water these plants correctly because the sphagnum will stay wetter than the bark so you will either be overwatering the sphagnum core or underwatering the outer bark.
- Potting Mix Degraded. The organic matter in your potting mix will ultimately degrade. Here are some general rules of thumb. Sphagnum moss lasts a year or maybe two at the most before having to be replaced. Bark lasts for about 2 years. Coconut husks last for 1 to 3 years depending on how wet you keep the mix. Tree fern lasts from 2 to 4 years. Once the organic matter starts to rot, the roots growing in it will stay too wet and they will likewise rot. Once your roots rot, your plant will not have the strength it needs to bloom. You must repot before the organic material in your potting mix breaks down.
- Orchid is Unstable from Growing Out of Pot. If your plant is unstable from growing out of the pot, you may want to repot it. This is not to say that there is anything wrong with aerial roots or a pseudobulb or two out of the pot, often you will find that these plants bloom the best of all. But if the plant is unstable and unwieldy, you may want to repot it and get it set for the next 2 or 3 years of growth and blooming
Best Time to Repot Orchids
Q. I’m planning to repot my orchids, is there a best time to repot?
A. Here are the best rules for repotting:
- Cattleyas should be repotted right before the new flush of roots emerges because the plants will quickly reestablish with their new vibrant roots.
- Phalaenopsis should be repotted after blooming in the spring but in any case by the end of June so they can recover their strength and be ready to set their bloom spikes in the fall (the summer blooming Doritis types should be repotted in early spring).
- Dendrobiums should be repotted as infrequently as possible because they hate to have their roots disturbed, keep them in a nondegrading mix so you can drop them in a larger pot right before their new roots emerge.
- Oncidiums can be repotted at your convenience, normally after blooming.
If you are planning a mass repotting of all your orchids, do this in the spring from February through June. For those that are blooming or in spike during the spring repotting season, repot after they are done blooming but make sure the plants will have 3 to 5 months to reestablish and gain strength before the winter rest period.
Dark Pigmentation on Vanda
Q. I'm wondering if you can tell me what is causing the blackness on the surface of the leaves at the joints and what looks like sap beads on some of the leaves. Otherwise the plant seems healthy; it has put out 2 new big fat roots, one on each side of the plant. Can you help?
A. The reddish black coloration looks like normal pigmentation from good bright light. The liquid looks like honeydew, a thick syrupy sap that is sometimes exuded from inside the plant and can be harmless. It's possible that a sucking insect (scale, aphids, mealybugs) has pierced into the plant and drawn out its sap so look into the crevices closely for some critter. As a precaution, you can water blast the plant with a sprayer set on 'flat' to dislodge any hidden pests. Then do exactly what you were doing before because that plant looks very healthy.
Sterilize Used Pots
Q. I am getting ready to repot and want to re-use some old pots. I usually soak them overnight in a bleach solution to kill any unwanted organisms. What can I use to get the white powdery stuff off the outside. I know this is salt accumulation on the pots my sister-in-law gave me.
A. As I repot, I drop the used pot in a plastic tub that is filled with water. When it gets filled up in a day or two, I pull the pots out one by one and use a scouring pad on the water saturated pot to scrub off any salt or algae accumulation on the outside or roots on the inside. After that, I wash out the tub and make a fresh 10% bleach solution, sometimes with some pool algaecide mixed in (2 tsp/gal). I return all the plastic pots to the tub and soak them for another couple of hours. Clay pots are porous so they should be baked in an oven for an hour or two at 400F. This should kill any pathogens lurking in the pot.
Bacterial Soft Rot on Phalaenopsis
Q. I had my Phalaenopsis inside during the cold weather and noticed a watery spot on one of the leaves. What should I do?
A. That looks like a bacterial infection, most likely Bacterial Soft Rot caused by the Erwinia bacteria. Small water-soaked spots appear on the leaves and often are surrounded by yellow halos. If unchecked, the infection will rapidly rot the leaves and roots and spread more slowly into the rhizomes or pseudobulbs. A quick response is required, cut out all the infected tissue down below the advancing yellow margin with a sterile razor blade.
Drench the entire plant with a bactericide like hydrogen peroxide, copper compounds or Physan (or Consan if you have some or diluted pool algaecide in a pinch) and repeat the treatment in 3 or 4 days. Then disinfect the area in which the plant was growing with a 10% bleach solution. If the disease has reached the crown of the plant, you may or may not be able to save it. If the crown is affected but you can kill the bacteria and the roots are healthy, you may eventually be rewarded with keikis at the base of the plant below the damaged area that you can repot and bloom next year.
Leaf Drop on Dendrobium
Q. I have an ailing Dendrobium which I hope you can help me with. The leaves are turning yellow and dropping off. Some folks suggested I spray it with Liquid Copper fungicide, but I am hesitant because nowhere on the container does it mention orchids.
A. Normal yellowing and leaf drop would normally affect the leaves on the back canes, not the front lead like this plant. Normal yellowing is also a fairly slow process though yours are yellowing and dropping in a matter of days. Leaf drop can occur if the plant gets too dry or too cold, but looking at this plant, the first thing to check is the status of the roots, are they healthy and tightly bound in the potting medium?
If not, knock the plant out of the pot and check whether the roots are vibrant and alive or dark and rotting. Often times the bark mix dendrobiums are sold in will only last for a year or two before it becomes sodden and starts to decompose. Even worse is when the mass grower has the plant potted in an inner core of sphagnum moss surrounded by a bark mix. In both cases, the roots will stay too wet for too long and ultimately the roots will begin to rot.
If the problem is root rot, don't despair because dendrobiums are incredibly hardy. Even if
it loses all its leaves, once you remove the lifeless roots and repot it, the plant will develop new growths from old the leafless canes. Dendrobiums don't like to be repotted or overpotted, so get a pot that will allow about 2 inches or so of new growth and use a potting mix that won't break down for many years (no bark please!). Place the oldest growth against the clay pot rim to allow the new growth the greatest room to spread in the new pot. Secure the plant with a rhizome clip, water and wait for it to come back to life.
A few words about using copper fungicides on orchids. Liquid copper and Kocide (copper hydroxide) can be used on most orchids and are particularly useful for bacterial diseases on phalaenopsis. However, the copper will cause floral damage so it should not be used on a plant in bloom, should not be applied with an oil based product and should not be applied to dendrobiums. Check the website links for information on pesticides
and fungicides & bactericides
for use on orchids.
Winter Care of Catasetums
Q. When my catasetum lost its leaves I put it on a high shelf in the garage for the winter. I recently had the thought that since it is mostly dark in the garage maybe it would be better in the house with a little light. I moved it into the house hoping to remember to check it every couple of weeks. Now I wonder if it is too warm and dry being in a heated part of the house. Seems you just leave yours in the greenhouse and don’t water but there is good humidity. Any thoughts on where I should have mine?
A. We’ve had different advice. Jamie Lawson told us that once the plant goes dormant, you can pull it from the pot and just store it in the garage until new growth beings. Fred Clarke told us that keeping the plant in the pot surrounded by the old medium will help keep the old pseudobulbs from dehydrating.
I think it’s better to keep the plant in last year’s media and wait for the new growth to begin. If you keep the plant where you see it, you'll be able to tell when the new growth begins, the trigger for our repotting activity. First, you have to determine whether you plan to repot the catasetum this year (because the plant has overgrown its pot or the old medium is worn out).
If you plant to repot, knock the plant out of its pot when new growth begins, cut off most of the old roots, repot BUT DO NOT WATER. Wait for the new growth to be 4 or 5 inches before you water. Repeat, do not water until the new growth is 4 or 5 inches tall. I have repotted about a dozen catasetums so far this year after noticing new growth and have somehow resisted the almost irresistible urge to water the plants.
Q. What’s the best potting mix for Catasetums?
A. I use a mix of sphagnum moss and sponge rok and interlayer the media with the time release Dynamite like an Oreo cookie. Think about how catasetums grow, they are dormant during much of the winter months and then grow like mad during the 7 or 8 months of their growing season, so they need a ton of water and fertilizer to fatten up their pseudobulbs for late summer and fall blooming. I don’t grow many orchids in sphagnum but catasetums seem to thrive in it.
If you just plain hate sphagnum, use a coconut husk or bark mix similar to what you might use for a phalaenopsis. You want something that will provide a lot of water and nutrients to the root zone but is also airy enough to provide good drainage. Then water and fertilize like mad during the growing season and await your blooming reward.
Guignardia on Vandas
Q. I noticed this black stuff growing on my vanda. Do you know what needs to be done about it?
A. That looks like Guignardia Leaf Spot caused by Guignardia species, a fungal disease that attacks vandaceous and cattleya orchids. It can start on either side of the leaf as tiny, dark, purple, elongated lesions that run parallel to the direction of the veins. These lesions elongate into purple streaks or diamond shaped areas. To manage the disease, sanitize the plant by cutting out severely infested leaves with a sterile cutting tool like a single edged razor blade.
Reduce leaf wetness by altering your watering habits or timing to make sure the leaves dry rapidly.
A fungicide that will help prevent recurrence is mancozeb (sold as Dithane or Protect). Banrot or Cleary's 3366 would be even better if you can find them. A regular preventative spraying program can protect your plants from the pests and diseases that are always present in the outdoor environment. Dr. Martin Motes has an excellent article
on controlling this disease.
Best Way to Apply Pesticides and Fungicides
Q. What is the best way to apply pesticides and fungicides to my plants?
A. That all depends on how many plants you need to treat. If you have just a few, get a 1 qt spray bottle, mix up the chemicals for 1 quart and spray both sides of the foliage and pseudobulbs. A quart of isopropyl alcohol works well, even better if you add a tablespoon of summer oil to it. You can insert the spray attachment into the alcohol bottle when you’re using it and then cap it when you’re done to prevent it from evaporating. A toothbrush or Q tip will help finish off the little buggers. If you need a little more to do the job, get a hand sprayer that you can pump up to pressurize, mix your toxic soup and use the pressurized spray to hit all exposed surfaces.
If you have a need for 2 or more gallons, try an Ortho hose end sprayer. You can mix liquids or powders in it and use the force of the water pressure to cover all the exposed surfaces. Here’s a nifty calculator. You’ll want to use the highest volume in the sprayer and the highest application rate to get the best mixing of your chemicals. If you want to make 2 gallons, add the chemicals needed to make 2 gallons of mix, fill up the reservoir to the 16 oz line and set the top applicator rate to 8 oz. That means you will have 16 oz of mix that will be applied at the rate of 8 oz/gal which translates into 2 gallons of sprayed liquid (16/8=2). For 4 gallons of mix, fill the reservoir to 32 oz and use the same 8 oz/gal application rate (32/8=4). For 8 gallons of mix, fill the reservoir to 32 oz and use 4 oz/gal application rate (32/4=8).
Remember to add spreader sticker (or dishwashing soap) for better adhesion, cover your skin to prevent exposure, spray from upwind directions, wear a cartridge respirator if you must inhale fumes and shower immediately after spraying.