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Ron Smith answers reader's questions about the world of plants and gardening.


By Ronald C. Smith, Horticulturist

NDSU Extension Service

Q: I live in Michigan and have a Thanksgiving cactus that is roughly 5 years old. It was a cutting from my mom's plant that was 20 to 25 years old at the time of the cutting. The plant seems very happy and healthy. It blooms at Thanksgiving, Christmas and around Easter. I can't count the number of blooms I get, but I would say close to 100 each time. I transplant it every year or two into a bigger pot because it has grown quite large. The last time I transplanted it was more than a year ago. I typically water it once or twice a month. More in the summer months as it dries out. I recently decided to determine if my plant was a true Christmas cactus or something else. I discovered that my plant is a Thanksgiving cactus because of its pointed leaves. I was disturbed to read a post about root rot and that someone mentioned that their plant was looking woody and wilted. I’ve noticed that the base stems are getting woody and hard. I thought this a normal part of my plant maturing, but after reading the other post, I am concerned it could be a sign of root rot. I have no other signs that the plant is having any health problems. It is continuing to grow and there are many shoots and leaves forming. The new leaf growth tends to have a purplish color, but as the leaves mature, they change to a deeper green. One thing that I may have done wrong is use the wrong type of soil. Would it be best for me to repot to a larger pot with the right soil mix or just use fresh mix into this same pot? If I repot, how can I determine if my plant has root rot? If so, what should I do? (e-mail reference)

A: Interesting story and thanks for relating it to me. Basically, you have nothing to worry about. The plant is really indifferent to the potting soil, as long it is pasteurized and drains decently. The woody character of the stem base is an indication of the maturity of the plant, since the stem appears to be firm and everything else is growing satisfactorily. You are close to the end of what is considered a normal life span for this species (please don't bury me with letters or phone calls about having had the same Christmas or Easter cactus much longer). I would advise you to take some leaf cuttings and root them this year. Do this about the time you repot in late summer or early spring. Otherwise, keep on doing what you have been because you obviously have discovered the secret to success with this species!

Q: (This is the response to my answer about the Thanksgiving cactus.) Thank you so much for your prompt reply. I did not realize that these plants had a life span. What happens at the end of their life? Do they get too large to hold themselves up? Would it help to prune it (I have never done this before)? I will take your advice and make some cuttings. Where should I make the cut and how big a plant area should it be? (e-mail source)

A: Mother Nature never planned for houseplants to exist genetically. When we move plants from their natural environment into an artificial one, the whole ball game changes. For example, your Thanksgiving cactus is an epiphyte, which means that it is found in association with other plants or on rocks. It clings to its support with aerial roots and gets nourishment from the atmosphere (tropical jungles of Brazil) or from the tree crevices in which it lodges. When the leaves get too ungainly, they can break off and lodge in another spot on the same or another tree and then send out very small roots and aerial roots to get a new life established. What’s sold in the commercial trade are hybrids that growers have developed for flowering characteristics. The success of this plant as a houseplant depends on the owner having the ability to approximate rainforest conditions. That is not completely true because I have seen some very beautiful Schlumbergera spp. plants thriving in anything but tropical forest conditions. Apparently the hybridizing results in far more adaptable plants for the indoors. The death of a plant occurs when one of the growth factors is eliminated, such as light, water or nutrients, or when an herbivore decides to have it for lunch or a pathogen takes up residency. Pruning would not hurt the mother plant and would assure perpetuation should anything happen to the original beauty that you have grown so fond of. Take stem cuttings consisting of two or three pads as spring comes around. Allow the ends to dry for a day, then plant in a moist, pasteurized, high-organic potting soil. Keep the plant in the shade or out of direct sunlight until new growth appears.

Q: I read and enjoy your answers to arborvitae questions in Hortiscope. I planted two rows of emerald greens 12 years ago. They are doing fairly well. The plants are about 15 feet tall. I am thinking of trimming the tops so they will be more stable during winter snows. How many feet can I safely take off the top? Will the arborvitae grow back after trimming? (e-mail reference)

A: From a rule of thumb standpoint, cut back about 2 feet off the top. Cut near to a lateral branch. Yes, they will regrow after pruning. I would suggest doing the pruning in early spring before new growth begins. You could avoid pruning by tying a cotton cloth about 2 to 3 feet from the top to keep the snow from splaying the branches apart.

Q: I added a new screened porch this fall and left my house plants out there a little too long. My fig tree dropped all of its leaves after that. It’s an heirloom with a long history. Slowly, new leaves have come back. The tree is 6 to 7 feet tall. I did not trim it at all. Should I have trimmed it? The top branches have no leaves as of yet. The house faces northwest, so the plant does not get direct sunlight until late spring or summer. I’ve watered it fairly regularly, but only when dry to the touch. I’ve had the tree for more than 40 years. I have pruned the tree on a regularly basis until now. Does the tree need more light? Tell me what to do! (Fergus Falls, Minn.)

A: Thanks for the informative letter and photos. The tree will recover where it is, but would do better if you could provide artificial light until you can move it back to a sunnier location. As for pruning, I'm certain that some will be needed, but you can decide on that later this year. At that time, you will need to decide if the plant is worth keeping based on what it may look like after all the dead branches are removed. As I have said in previous responses on this subject, usually the first nip of cold damages the foliage, but the foliage protects the cambial tissue for the most part. In a defoliated state or with the leaves dead, there is no transpiration taking place around the foliage that could act as any kind of protection. Consequently, the cambial tissue and leaf buds are killed. In summary, you have not lost your heirloom, just shook it up a little.

Q: I have two benjaminas (ficus). Both are 20 years old. One is about 5 feet tall and is spindly. For the first 16 years of its life, it was in a bathroom with a west facing window. Now it is in a south to southwest room. The larger ficus is 8 feet tall and in a room with floor to ceiling east and west windows. The plant is located next to a west window. For the past three summers, I have put the larger tree outside in the summer. It grows a lot of leaves. However, in the winter the leaves turn yellow and fall off. I would say that 20 percent to 40 percent of the leaves fall off. This problem started about nine years ago. I use a water meter and fertilize. How can I get the smaller tree to leaf out more? What can I do to prevent the yellowing and leaf drop problem? How long do these plants live? (e-mail reference)

A: I would encourage you to move both plants outdoors during the summer. This will help the smaller of the two plants overcome its spindly characteristics. When you bring them indoors, they are going to go through some leaf shedding because of the major environmental change. For example, typical outdoor summer days can register a 10,000 foot candle reading easily and frequently. Indoor lighting is no more than 1,000 foot candles at best. With so little light, the plant cannot support the sun- or high light- developed foliage, so it sheds a significant amount. You can lessen the impact by investing in a plant light or two during the winter months. The lights are inexpensive and can be put on a timer for 12 to13 hours a day. The plants will remain more stable in appearance and have a better chance of shedding off any stresses from insect, disease or cultural practices that may come up. As to longevity, ficus potentially can outlive a human being when given proper care. For more information on ficus care, go to my Web site at

Q: I have a peace lily plant that concerns me. The leaves get areas that are black and seem dead. I have many new shoots of leaves coming that also have these dead spots. It is a houseplant that is kept in the kitchen with fluorescent lightning and an average temperature around 72 degrees. Any suggestions? (Fargo, N.D.)

A: This could be due to overfertilization or too much salt content in the water. Allow the soil to dry down to the point that wilting almost takes place. Then completely water the media with distilled water. Pour off any excess water that collects in the dish under the pot within 15 minutes. If it is the high salt content as I suspect, future leaves should grow without any marks on them. From your description, I'm fairly certain that there isn’t a pathogen at work, so no fungicides need be applied.

Q: Our office purchased several dozen Black Hills spruce in containers for Christmas. Because I live on a 40-acre parcel, I have inherited about a dozen plants. I plan to line my dirt driveway which runs north to south. The drive curves a bit and runs about 1,200 feet. From reading the Extension Web site that you have, I believe I need to plant the spruce about 15 feet apart. How far away from the driveway should they be planted? Will 10 feet work? My house is north of Laurel, Mont. The elevation is 3,400 feet. The land is somewhat broken and has numerous pines growing on it, but I'm not sure of the varieties. The drive itself runs through a fairly bare stretch of ground with lots of grasses, but no trees. I will have to carry water to the trees, so I am wondering how many gallons I should apply at a time. Finally, do I need to protect the young trees from animal grazing? We have an abundance of deer and turkeys on the property, but I don’t know if these trees are or could be a part of a deer's diet. (e-mail reference)

A: Planting the spruce trees 15 feet apart is good. Also, use 15 feet as a guide to planting the trees from the edge of your driveway. At 10 feet from the drive, you would be all right for about 10 to 12 years, depending on the rate of growth in your region. Addressing your concern about deer and other nibblers, spruce trees generally are not bothered. However, I have seen some cases where animals did become a problem. There are several good products on the market, such as Liquid Fence for deer and rabbits or a material called Plantskydd. If you are hauling water, the chance of you overwatering is not very high, which is good. However, I would suggest that you prewater the holes before planting. This will keep the dry soil from pulling the water away from the moist rootball. When you water, make it very thorough and complete. Keep in mind that the roots will follow the percolating water through the soil. The first year is the most important for keeping the roots in active pursuit of the moving water. Another point is that evergreens are susceptible to spider mite damage during extended heat and drought conditions. One of the best controls is to spray the trees with water a couple of times a week. Do a hard spray because spider mites don't do well under that kind of treatment.

Q: I have a beautiful Christmas cactus. Half of it bloomed before Christmas. The other half is blooming now. It is a very deep pink. I heard there also are red and white varieties. If I find slips of the other varieties, can I plant them in the same pot? (e-mail reference).

A: You certainly can, but I don’t recommend it. From a sanitation standpoint, it would be better to root any new slips in separate containers in case of disease problems that are not visibly evident. Once you see them successfully established and growing in your own environment, then you could do the integration to have the mixed colors.

Q: I had an inquiry about cottonwood branches breaking off. However, the branches that are breaking off are not main branches at the trunk. The homeowner said that the trees are watered. I saw a few samples of fallen branches that looked very healthy to me because the branches were green and wet. I asked him if the trees rub against each other or if he noticed more loss after heavy winds. He said no to both questions. Do you have any idea why a cottonwood would lose branches like this? (e-mail reference)

A: Branch drop or "free kindling," as I like to refer to it, is common with some species of trees. Poplars are among the most notorious for doing this. It generally is not associated with any disease or insect problems, although both can contribute to the branch drop as well. Willows and weeping birch also typically shed branchlets.

Q: What was the name of the book you cited about a husband-and-wife team who does the "welder" crafting for aboveground gardens that some handicapped people use? (e-mail reference)

A: The book I think I mentioned was “Square Foot Gardening” by Mel Bartholomew.

Q: We love the plants in our house. With some help from you, all are happy and healthy. However, we do have fruit flies. I realize you are not an entomologist, but can you tell me how to combat the fruit fly nuisance? (e-mail reference)

A: Fruit flies are an annoyance and difficult to control once they get established. They breed where there is rotting or overripe fruit, slow drains or wet surfaces, such as around high-organic potting soil. The adults can be trapped on sticky trap surfaces. Clean up the rest of the environment and replace the potting soil with material that is faster draining.

Q: We've tried to get Norfolk Island pine trees to look like others I've seen at the university I attend. So far, I haven’t had any luck. They systematically dry out and die, even after we learned we probably were overwatering. Any tricks with these buggers? (e-mail reference)

A: Norfolk Island Pines are native to Hawaii, which is a big clue. I have seen them fail where such care was given in homes on the mainland. I’ve also seen them thrive where they are not cared for in any particular manner. What is the secret to growing them successfully? Other than good cultural practices, the luck of the draw!

Q: I have a ficus that was planted outside about five years ago. It started growing in an 18-inch pot. Now it is as tall as our two-story house. We live in Houston, Texas. The weather service has warned us about a hard freeze and four to five days of ice. Should we worry about the tree freezing? I don't think there is any way to cover it up. (e-mail reference)

A: Sorry to be getting back to you this late. No doubt the tree was damaged by temperatures that got below 40 degrees for any length of time. Unless the temperatures got down to the freezing point and stayed there for hours, the tree should recover. I would suggest getting an evaluation from a local International Society of Arboriculture arborist. There should be several in your area.

Q: My husband and I want to plant something to create a privacy screen. We have land along a gravel road that is grazing ground for many whitetail deer. Vehicles are always stopping and parking along the road to watch and possibly poach the deer, so we would like to plant something to create a screen. We live in northwest Missouri. Would arborvitae be a good choice? If so, which variety? We need something wide, tall and fast- growing. If the deer like arborvitae, it may make matters worse if it attracts them closer to the road. (e-mail reference)

A: The deer will thank you for planting arborvitae! I would suggest contacting the local Department of Natural Resources for suggestions and possible contributions of deer- resistant plant material for you to use.

NDSU Agriculture Communication

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