Q&A Material
as of Tuesday October 07, 2008
Q. We are maintaining some Bambusa vulgaris in a hotel's atrium planter.
They are always getting brown tips and leaf spots. I thought it might be due
to the coolness of the air in the atrium. What do you think?
A. I think you are partly right. They do prefer to be warm with good
ventilation, but it also sounds like you may have a problem with very hard
or fluoridated water. I would have the water tested to find out exactly what
you are dealing with.
Q. For three years, I have been maintaining two lilac trees for a client. They appear to be very healthy but they do not bloom. I have limited experience with these plants. What am I doing wrong?
A. It could be any number of reasons. Most lilacs prefer nice cold winters followed by growing seasons that provide at least 6 hours of full sun daily. Lack of sun is the most common reason for not blooming. Lilacs should not be planted too deeply, and they prefer an alkaline soil. If they are planted near azaleas or a lawn, they may be receiving too much acid or too much nitrogen. You shouldn't need to fertilize them, but if you do, fish emulsion and bone are good organic foods. Lilacs set their buds on the old growth, so don't prune them any later than July or
you'll destroy their future flowers.
Q. We maintain twenty 15' Ficus nitida trees in a mall. Eight
of them have something wrong with them and I have never seen this before.
The bark seems to be peeling off and in some branches there are clumps of
leaves which are turning kind of gray.
A. A few years ago, someone pointed out this disease to me
and said it was Phomopsis, a slow growing fungus which often attacks ficus
trees. This disease is very easily spread from one tree to another by using
contaminated clippers, scissors, and other pruning equipment. If left
unchecked, it will spread throughout the entire tree.
Q. How do I get rid of small wasps living in a corner of the moss of my staghorn fern without getting stung and without damaging the fern?
A. I don't have any experience with this, but I would probably start by spraying the waspy area of the moss with a regular wasp spray, towards evening when the insects are less active. It might take a few sprays every couple of days to get them under control. Then I would submerge the stag in a 30% or less dilution of insecticide to kill off any live larvae that might still be in the nest.
Q. I take care of four 7' tall Ming Aralias immediately inside the entry of a highrise building. They've been in that location for almost a year. They receive indirect light and they have ongoing leaf loss. If it continues at this rate, they will eventually be bare. I can't figure out the cause. Could this be a location problem?
A. Probably. Mings are very sensitive plants, and in their present location they may be getting stressed from drafts, dry air, and fluctuations in air temperature. They normally like to be warm and moderately moist. Perhaps replacing them with dracaenas might be a solution.
Q. One of my clients has a very large Asparagus sprengerii in a 12” pot
sitting in a corner window that gets indirect light. It dries out every week
because it is so rootbound, but the client loves the plant and doesn’t want
me to pot it up a size because he likes the container it is in. Can I trim
the roots?
A. You can trim the roots but you can probably just divide the plant, which
might be a better alternative if it is very full. Your client will then have
two favorite plants.
Q. We are maintaining some Bambusa vulgaris in a
hotel's atrium planter. They are always getting brown tips and leaf spots. I
thought it might be due to the coolness of the air in the atrium. What do
you think?
A. I think you are partly right. They do prefer to be warm
with good ventilation, but it also sounds like you may have a problem with
very hard or fluoridated water. I would have the water tested to find out
exactly what you are dealing with.
Q. I find that the lower leaves turn brown and dry out on every Phoenix roebelinii at my biggest account, a mall. My supervisor says I am
overwatering, but I say I'm doing just the opposite. What do you think?
A. I think you are right. You may be underwatering. Overwatering usually
affects the new growth, and long after the problem is in an advanced stage.
Malls are pretty dry and P. roebelinii needs a humid environment. More
frequent watering in smaller amounts might help. And, of course,
subirrigation containers/devices would be the best solution.
Q.
Can I cut back a Dracaena warneckii and root the cuttings? What is
the best way to do this?
A. Yes, you can cut it back, and if it is in good light and
otherwise in good health, it should sprout some new crowns. However, I
recommend that you do this using the air layering method of propagation.
This column is too short to explain it, but read a book or check around on
the Internet for full instructions.
Q. If my cat eats one of my plants, will he die? I have dieffenbachias and codiaeums.
A. It is unlikely that your cat will eat these plants at all since they don't taste good and will burn his tongue and mouth tissues if he bites into them. My cats have never shown any interest in my "poisonous" plants -- but they have feasted on my marantas and calatheas. I'm always more concerned about a cat digging in the soil of a plant, since it may contain harmful chemicals that a cat can then ingest when he's bathing himself. Same thing with toddlers eating dirt from a house plant.
Q. Is it necessary to double-pot (with peat) the plants that I then submerge into the soil of large indoor planters?
A. It is not necessary, but it may be desirable, particularly if the plants are rootbound. But if that is the case, you should probably just transplant them first instead. In general, double-potting is more effective with freestanding decorative containers, if the method is to be used at all.
Q. If I put a low light plant in a dark office, will it continue to live but not produce new growth, or will it eventually just give up and die?
A. It depends on the type of plant, how dimly lit that office is, if the plant is pest-free and disease-free, if it was a hardy and healthy plant when first installed in the dark office, etc. But, in general, it will eventually die. How long you can keep it going is quite another story.
Q. I maintain two Phoenix roebellinii palms at a mall. They have good light and lots of new growth. I have recently sprayed both plants for mites, and I would like to know if the spray is what is preventing the new fronds from opening.
A. The spray isn't the cause, but the mites probably are. They are a cause of stress to any plant, and a stressed plant needs all its resources to fight the mites or whatever else is preying on it.
Q. Should you water an indoor plant with cold water or warm water?
A. Neither. The water should always be room temperature.
Q. I am maintaining indoor plants for a client who travels a lot. All the plants are growing in water only, no soil. The client says I need to check and adjust the pH regularly. Why?
A. For the same reason that you should know the pH of the water you use on plants grown in soil. Most foliage plants like water that is a little on the acid side for optimum growth, and most water sources tend to be more on the alkaline side. If the water in your client's plants is not the correct pH, the plants may be unable to use their nutrients and may become unhealthy or die.
Q. Some of my residential clients are now bringing their outdoor potted plants inside. What should I do to keep outdoor pests from the indoor plants?
A. Try to keep the outdoor plants in their own room, far away from the indoor plants. Remove any visible pests, debris, etc., from the outdoor plants. Give them one thorough watering to drive out any pests that may still be inside the pots. Be sure to thoroughly clean your tools off after working on the outdoor plants.
Q. Why do rhapis palms always get tips on them?
A. Palms tip when the roots burn as a result of overfertilization, lack of humidity, being rootbound, and erratic watering. Transplant rhapis palms up a size before you install them to ensure they are in soil that will retain moisture and drain well. Don't fertilize for a year or so, and after that only with a highly diluted fertilizer twice a year during growing season.
Q. I grew a coleus in water that looked gorgeous for ten years. I cut it back periodically to keep it full, got it a bigger jar. I moved and gave it to a friend. Two years ago I rooted some cuttings and they don't do a thing. Hardly any new growth, poor color. What am I doing wrong?
A. Try relocating the plant to a much brighter location and see if that helps. Also be sure you keep the water clean and that it is room temperature. You might also try adding a very miniscule amount of liquid fertilizer to the water once a month.
Q. Is it better to buy roses bare-root in winter and plant them, or wait until spring and buy them in pots?
A. I usually recommend bare-root because the plant has more time to establish itself, and also bare root is less expensive than potted roses. But, if you aren't sure what the rose will look like or what its growing pattern will be, you should probably buy potted.
Q. I live in southern Oregon. Can I relocate a Japanese maple in my yard at this time of year (early fall)? If yes, what is the best way to do it?
A. Yes, you can move it. Be careful when you dig it up so that you do as little damage to the roots as possible (although I have root-trimmed them at this time of year with no problem). Dig the new hole at least twice as big as the root ball, fill the hole with water and let it sink in. Add some soil, place the tree in the hole, add soil around it, add more water and let it sink in again, finish adding soil, water it again, cover the soil with some bark, and you're done. Keep it watered regularly until the fall rains come.
Q. I maintain two 10' Ficus lyrata in an office. The leaves are extremely dusty with no shine at all. A feather duster doesn't work and I'm afraid I'll crack the leaves if I wipe them with a rag.
A. If you're very gentle you should be able to wipe them without damage. You might also be able to lay down a drop cloth and spray them with a leaf cleaner, working from the top down. You'll still have to do some wiping, but it might minimize your contact with the leaves a little.
Q. I have all the plants in my den in terra cotta containers. The plants are fine but the pots are getting a white crusty film on them. What is causing this and how can I stop it?
A. That's caused by a combination of hard water and soluble salts that accumulate in the soil and then leach through the clay. You can scrub it off the outside of the pots periodically, but it won't all come off, and it is pretty much impossible to prevent. Some people think it gives a nice rustic look to the pots, so maybe you could try to appreciate it for its decorative look!
Q. I have a Nandina ("heavenly bamboo") growing indoors. It is about 5' tall and very bushy and I've had it in the same place and the same pot for ten years. Lately the leaves are turning brown and falling off. Can you tell me what is wrong?
A. If it's been in the same pot for ten years it could be that you need to transplant it up a size with new soil. If it is rootbound and lacking enough soil to retain moisture, older leaves would die and drop. Or, if it isn't rootbound, an overly warm room could also cause the soil to dry out and leaves to fall.
Q. I have a potted staghorn with large upright leaves that are starting to fold and turn downward. The shield fronds seem fine and are firm. Is this natural or could I be overwatering?
A. In general, when the leaves get very large they can droop from their own weight. I prefer to let a stag go almost dry between waterings, but it depends on how much light and heat it gets during the course of a day. Hard for me to tell about watering issues without seeing a plant in person.
Q.
What is the difference between bulbs and corms?
A. Aside from their appearance, the main difference is how they use the food that is stored in them. The bulb uses and then replenishes its food resources every year. The corm uses up all its food resources and turns into a dry husk, then grows a whole new corm in its place.
Q.
We just took over maintenance of a small yard enclosed by a very mature but ugly Eugenia hedge that's been boxed to death. Can it be salvaged? Any advice on how to start?
A. It could take just as long to make it look good again as it would to install new plants and train them into a hedge. If you opt to salvage it, start by pruning the top so that it is narrower than the base, and so that the top is rounded or slightly pointed. You will need to remove about 10"-12." It will probably take a couple years to look good, but a new hedge would take at least three years to reach a mature size.
Q.
I maintain two beds under an inside stairway. The owners want marantas and aglaonemas, but it is too cold and dark for them. The owners know this and always pay for replacements, but it takes so long because I have to pull all the lava rock away and then dig up the plants and replant them and cover them with the lava rock. Any suggestions?
A. If these plants don't last a long time, why bother to plant them at all? I would just leave them in their pots, submerge them in the soil, cover them with lava rock, and then just remove them and insert new ones as needed. It's at least a little easier, and in time the pots will lift out more easily, leaving pot-size places in the soil.
Q.
My staghorn fern has yellow leaves. What could be causing this?
A. If the leaves are yellow from the center outwards it is probably being overwatered, is too cold, or both. If the leaves are yellow from the tips inward, then it is probably underwatered. Be sure that you thoroughly drench the staghorn by submerging the board and moss in a large tub or bucket of water. Then allow it to dry out almost entirely before drenching it again. If the weather or the room are very warm, move it to a cooler location. If it is in a cold location, move it to a warmer one. It should be in partial shade, not full sun or full shade.
Q.
Will a Phalaenopsis orchid tolerate being in a sunroom with tinted windows, getting some direct sunlight? I have a new plant and two buds have just fallen off, and one new flower is going limp. I am watering it weekly when the water meter indicates it is dry.
A. I have successfully grown phalaenopsis orchids in full sun without tinted windows. But if the buds are falling off, the plant is probably either too cold or too wet or both. Do not use a water meter as they do not work in bark. The bark should always be slightly damp, but never wet. The plant should also never sit in a saucer that has water in it. You can lightly spritz a little water on the bark surface a couple times a week and that should be sufficient moisture.
Q. We have a pond with water plants in it. The pond company sold us snails to keep the algae down, but the snails eat the plants and multiply like crazy. I don't know if this is in your area of expertise, but can you tell us how to eliminate algae and still have plants?
A. Aquatic ponds require a balance of plants and animals to be healthy. Snails are part of that balance. You need to have the type of snails that do not eat plants and eat only algae. Two of those are Neritina reclivata (Olive Nerites) and Viviparis malleatus (Japanese or Trap Door Periwinkles). It is unlikely that either of these will over-multiply, and you will probably have to buy more of them if they die off due to not having enough algae, as is the case with some ponds.
Q.
Is it okay to put small rocks or glass beads on top of the soil as "topdressing" for indoor plants? I have a client who wants both, and I'm concerned about the weight, and about moss growing or water sitting on top and the soil not drying out between waterings.
A. I use small rocks and gravel in all my plants to keep my cats from digging in them, and I've never had any problem. Most of my plants are in subirrigation, so no problem with the soil staying wet in those because it's always dry on top, but my plants that are in regular pots are fine too.
Q. I
have tried to get rid of fungus gnats without using chemicals, including removing the top couple inches of soil and replacing them with clean soil. I also tried a predator. No luck either way. What else is there?
A. Have you tried diatomaceous earth? I have not tried it personally, but I have been recently told that when mixed in with the top 2" or so of soil, it destroys the larvae. One thing you need to do is to make sure those top inches of soil dry out between waterings.
Q.
About six months ago I relocated a Euphorbia trigona for a client. It went from a sunny atrium to a small office that gets sun for about half the day. I had to cut it way back because it was so big, and I haven't seen any sign of new leaves. Should I be worried?
A. Probably not. Wait until spring and see what happens then. I have drastically cut these back before and they have always grown back.
Q. How can I eliminate scale from my staghorn fern (Platycerium). I've tried alcohol on a Q-tip and they just come back.
A. You are only killing the adults and not the eggs and immature adults that are still in the moss and that are too small to see with the naked eye. Drench the staghorn in water until there are no air bubbles. Remove the stag. Put on gloves and add pesticide to the water at about half-strength. Drench the stag for about five minutes. Remove it and hang it up to dry. In about a week or so, right before it is totally dry, repeat the entire process. Also, treat any neighboring plants that have scale.
Q.
We installed some Craigii compactas at a bank three months ago. They immediately began losing their lower leaves, which dried out entirely without tipping and fell off. No sign of any pests, not even in the soil. They are almost completely bare now, some having only a leaf or two on each stalk. I cannot tell what is wrong. Do you know?
A. I can't really tell you what is wrong without seeing the plants, but such a sudden loss of leaves on Dracaenas is often related to abrupt changes in temperature or too much water, possibly soil that is not draining adequately. Perhaps a combination of these things. Since it is winter, my first question would be, does the bank turn off the heat at night or lower the thermostat drastically? And how wet is the soil and are the plants getting adequate light?
Q.
No matter how often I spray plants for insects, the pests always come back. Are they just immune to the spray or is there something else I should know before I spray again?
A. The pests could be immune if you're not alternating sprays often enough. You could also be spreading insects around as you maintain plants, by not cleaning your tools or switching rags between infested plants or between maintenance accounts. You might also not be spraying properly: you need to spray the tops and undersides of the leaves, the nodes, the stems, the soil surface, the saucer/liner, the pot -- everything -- for full coverage.
Q.
When my moth orchid (Phalaenopsis) quit flowering, I cut the stems back and now there are leaves sprouting from them. What does this mean?
A. It means that your orchid is in a good growing location, and it is putting out new plants from the stem, a common way of propagating this type of orchid. Once there are some 2"-3" long roots growing from under the leaves, you can cut the little plants off and plant them in bark. They should be ready to bloom in a few years if kept in the same environment.
Q. I am the client of an interiorscape company. We have aralias that produce a sticky substance that drips on everything. I have asked that they fix the problem or replace the plants. Nothing is being done. What is the normal procedure for dealing with this type of plant problem?
A. Your plants have either scale or mealybug, plant pests that produce a sticky substance called honeydew. By the time there's enough of it to drip, you've got an infestation that is probably impossible to control indoors. The plants should be replaced, and your contractor should know that and act on it immediately.
Q.
I have what appears to be a fungus on some large staghorn ferns (Platycerium). What can I do to get rid of it?
A. You need to be sure it really is a fungus. These ferns get a soft white downy underside to their fronds and to the flat leaves that cover the moss. It's not a fungus. But, if there really is a fungus and the ferns are planted/mounted on a moss-covered board, let the moss dry out fully between waterings and that should kill any fungi or pests. If there is definitely a fungus on the moss or board, you can soak the board/moss or pot in a big pan or bucket or bathtub filled with an extremely mild dilution of fungicide and water. Don't get the leaves wet with the
fungicide unless you hose them off with water before you put them back in their original location. If they are potted and are rootbound, you may also need to transplant them into fresh soil or onto a moss board.
Q. I have two plants with a powdery black mold on the leaves. How do I get rid of it without using any deadly chemicals?
A. You probably have sooty mold, which grows on the honeydew secreted by aphids, scale, or mealy bug. Get rid of the pests first by spraying thoroughly with an insecticidal soap or by dabbing them with a Q-tip soaked in alcohol. Clean the mold off the leaves with a soft cloth dipped in the insecticidal soap or in a very mild dilution of soapy water. Prevent the spread of pests and diseases by always cleaning your tools and using clean rags on each plant.
Q. Is there any way that I can stop my cats from chewing on the leaves of my indoor plants?
A. You can try to offer them something green to eat that's more palatable and just for them by purchasing some grass or catnip planted in tubs. Let them nibble on those instead. You can find them at most pet supply stores.
Q. I have just taken over maintenance of an office that has about 200 sansevierias in subirrigation planters between the cubicles. The plants ar
