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NDSU Agriculture CommunicationArchive

March 24, 2005


Ronald C. Smith, Horticulturist
NDSU Extension Service

Q: There are little, black bugs flying around my jade plant. What can I do to get rid of them? In addition, I was rather grossed out by all the worms, bugs and molds that I read about on your jade plant Web site. Are these common problems? Is there anything I can do to reduce the chance of getting these pests? (e-mail reference)

A: The black bugs could be fungus gnats or fruit flies, depending on where the plant is located. They are knocked down easily with a pyrethrin-based spray, preferably from an aerosol can so they can be killed while in flight. The material has a very low mammalian toxicity (extracted from the mum family) and is not harmful to the plant, as long as you don’t spray it directly on the plant. The insecticide is under pressure, so it comes out cold. If concentrated on the foliage, it could cause tissue burns. Fungus gnats originate from potting soil mixes. They more frequently are found in highly organic potting mixes because, in part, that component of the mix does not go through a sterilization or pasteurization process like the inorganic part of the mix. You can repot with a quality potting soil. The label should indicate that the contents are sterilized or pasteurized. Fruit flies are common at this time of year, especially around garbage disposals in the kitchen. It’s not a reflection on your housekeeping, just an unpleasant fact. The best treatment is to fill the sink up with hot, soapy water and run it through the disposal while it is running. Jades are very popular because of their beauty. In general, Americans care too much, emotionally speaking, for their houseplants and spend too much time watering, fertilizing, etc. Amazing as it may sound coming from someone well steeped in the horticultural sciences, most houseplants that look their best are ones that are benignly overlooked by their owners. I am not advocating this practice, but I do encourage people to attempt to follow what is right for a particular plant. Don’t give up in frustration if you have friends, neighbors or relatives who “do nothing special,” but their plant is doing everything you want yours to do!


Q: I planted several arborvitae trees in 2003 that are doing fine. I now want to replant some of them to make more room for a pit greenhouse. I’ll be using 4 feet of banked soil. Can I plant these trees up to the banked soil and trim the south side of the trunks as they grow? My concern is that the tree will suffer if it is up against the banked soil. My plan is to have an underground path from my basement to the greenhouse with about 2 feet or more of soil on top. How big is an arborvitae root system? How deep do they grow? How close can I plant these trees to my underground path or pit greenhouse? (e-mail reference)

A: “Up against” anything, such as a wall of soil, wood, brick, etc., can cause problems. Like any other plant, arborvitae need and better thrive when given breathing room. I don’t know the architecture of your dirt wall. If the wall is a straight vertical, it will cause problems. If the dirt wall is sloped sufficiently, it may not cause any problems. In fact, you could plant the small trees into the lower part of the bank.


Q: I thought I’d ask another question because you did so well answering my last question. I have a young aspen that is giving me trouble. There are three trunks in very close proximity (all one tree?). Oddly, one has very yellow-green leaves while the other two have dark green leaves. I assumed that this was due to chlorosis and added some liquid iron (planning to get the soil tested this spring before doing any further amending). Later in the year, the tree appeared to exhibit signs of shoot blight. I’m guessing that the decreased vigor of the plant and our cool, wet summer had something to do with it. It may have been infected last year, but I didn’t notice because we bought the house in June. Could you offer any suggestions as to an appropriate course of action? (e-mail reference)

A: Take out the problem tree trunk. If you don’t, it only will go downhill from here. The root system is damaged or diseased and will not improve. I speak from experience in attempting to correct maladies as you describe. I have tried iron injections, aeration, vertical mulching, etc., but to no avail.


Q: What is air-layering? I have a tall, skinny schefflera. You’ve talked about air-layering when you cut it back. In addition, can you root the plant cuttings in water? (e-mail reference)

A: That’s a good question. The answer is in the “Home Propagation Techniques” bulletin. The bulletin is available on the Web at You can root cuttings in water, but difficulties often come up when transplanting the cuttings into a potting soil mixture. You are better off rooting them in a media, such as sand/peat, and then moving the root mass and media into the container you will be keeping it in.


Q: We have two arborvitae next to our front door. They are about 8 feet high and look very out of place because of their height and location. Is it possible to cut them down significantly? (e-mail reference)

A: It is done all the time! If done properly, no one will ever know that the plants were a lot taller.


Q: I’ve had a spider plant for more than two years. I think it is a variation on the standard spider plant because it has more curly leaves. When I bought it, I probably had 20 babies shooting out of it. I keep it in the kitchen window where it gets light most of the day. I do not think I am
overwatering, but recently all the babies died. Within the last month, all the stems to the babies turned brown and some babies fell off. I would like to revive the plant and get the spiderettes growing back. I have other spider plants that have not produced babies in years. What specifically causes spiderettes to grow? (e-mail reference)

A: Spider plants best thrive in a pot-bound situation and have access to sunlight. A spider plant should be in a room where the sun shines through the window at some point in the day. It doesn’t matter if it is direct or indirect sunlight, as long as the sun coming in can brighten the room. The production of spiderettes is tied, somewhat, to day length. In response to increasing daylight, the plant should begin producing flowers and spiderettes sometime this spring. Don’t overwater or overfertilize this plant species. Both are needed, but not in any abundance. That may or may not have caused the demise of the spiderettes on your plant.


Q: I received a zebra plant for Christmas. I would like to know how to take care of it. I’ve heard it is a difficult houseplant to grow, but mine seems to be doing well. (e-mail reference)

A: By zebra plant, I assume you mean calathea zebrina. They do not do well in direct sunlight, so it should be shaded continuously. Watering should be watched closely because the potting soil should not dry out. This group of plants is particular about humidity. Surround the plant with damp sphagnum peat on a tray of pebbles filled with water. That will help a lot. You also could purchase a humidifier for the room. The room temperature should not be allowed to go below 60 degrees. Fertilize only when the plant is showing active growth. Calathea zebrina make good terrarium or bottle plants.


Q: When is my kalanchoe supposed to bloom? It bloomed all summer in my greenhouse, but I would like to see it bloom for Easter. I read that the plant should be covered for about a month. I did that, but it budded within a week. How long should I leave it covered? (Onaka, S.D.)

A: These are short-day plants, which means they should be getting 12 1/2 hours of total darkness a day. All I can tell you is to go ahead and cover it. When you see buds forming, no further cover is necessary. Plant vigor, temperature and the growth stage the plant is in also are factors, but the main triggering mechanism is the lack of light exposure.


Q: I bought a jade plant approximately three years ago. It has proved to be a rather hardy plant. I keep it outside during the summer and bring it inside during the winter. Twice I have forgotten to bring it in before the first frost hit. Surprisingly, it recovered quite well each time. It has spawned a few smaller plants in the pot. I decided to take one of these smaller plants and put it into a large terrarium with my pet lizard. The lizard eats insects, which are mostly superworms and crickets. After placing the plant in the terrarium, I realized these insects probably are going to eat the plant. Is that the case? (e-mail reference)

A: Unless you have the terrarium swarming with insects, the plant should be safe. I assume you have other plants in the terrarium as well. For the most part, the insects you place in there for lizard consumption are disoriented and “out of season,” so they are not in a foraging mood. However, isn’t this what you want to create, a miniature ecosystem only with the fittest surviving? Even if the plant should become an object of desire for the enclosed insects, any plant worth its salt should be able to survive an occasional nibble now and then.


Q: My son threw a sandal at my Yucca cane plant and broke the stem about a quarter inch from the dirt. What can I do to save the plant? It truly is a beautiful plant. (e-mail reference)

A: Make a clean cut to remove the top of the plant and stick the cutting in a rooting medium. The base also eventually should send up new shoots. In theory, you should get two plants out of this little accident! Go to my Web site at to learn more about home propagation techniques.


Q: I have a large section of lily of the valley that I planted 12 to 15 years ago. The plants are healthy and spreading. Last year, they turned brown and looked dead. Any idea why? Also, I have hosta of all sorts growing around my yard. I’ve had quite a problem with tiny holes in the plants. I was told slugs caused the holes. By the time the lilies were withering last year, the plants were full of holes and looked extremely frail and lifeless. (e-mail reference)

A: I have no idea why your lily of the valley turned brown. Overwatering is a possibility. Your guess is as good as mine is. You may want to contact your local Extension agent to find out if a horticulturist or plant pathologist is on staff who can diagnosis the problem. Slugs and hosta go together like peanut butter and jelly. Remove the foliage before new growth begins this fall. At the same time, place several dishes or traps of slug bait that is available at most garden centers. This should at least partially control them. As best you can, avoid any excess moisture on the plants. Also, try to remove all slug hiding places, such as boards, rocks, rotting foliage, etc.


Do you have a gardening or houseplant question? Write to Hortiscope, Box 5051, NDSU Extension Service, Fargo, ND 58105 or e-mail to Ron Smith at Note to e-mail correspondents: please identify your location (city and state) for most accurate recommendations.


Source: Ron Smith, (701) 231-8161,
Rich Mattern, (701) 231-6136,



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