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Hortiscope

Ron Smith answers reader's questions about the world of plants, trees and gardens.

By Ron Smith, Horticulturist

NDSU Extension Service

Q: I have a willow tree that I planted four years ago. I faithfully wrapped the trunk for winter during the first three years. However, last fall I forgot to wrap it. Sadly, this spring I noticed extensive rabbit damage to the trunk. The trunk is completely stripped of its bark about 5 inches up from the base to about 18 inches. Can this tree be saved? (e-mail reference)

A: Once we forget or have a memory lapse on something like this, it is amazing how quickly nature takes advantage of our lapses. With the tree completely girdled, it will not survive. It may leaf out this spring, but then everything will dry up and die because of the cambial tissue destruction. Water or nutrients can’t reach the top part of the tree anymore.

Q: I’ve had a white oak tree for approximately seven years. While similar trees in my yard have grown well, this tree has yellow and underdeveloped leaves in the summer and does not drop many of its leaves in the fall. Our local nursery suggested using liquid chelated iron around the base. I did read the directions, but I am worried I misunderstood them. I used 16 ounces to 1 gallon of water around the base. I watered for about 15 more minutes after that. It is spring here in eastern Nebraska and I see buds on the tree. Will the tree die because of the probable overdose of iron? What should I look for? Is there an antidote? (e-mail reference)

A: Enjoy spring's arrival and your oak tree budding out because you have nothing to worry about. Iron is one of those elements that plants have a hard time getting toxic doses of, so your tree likely will be fine. If it does die, it will not be from an iron overdose.

Q: My memory is bad, but I think you told me to cut back a clematis vine in the spring. Should I do it now? (e-mail reference)

A: Now would be a good time.

Q: My neighbor has three large ficus trees in his backyard. One of the trees is about 5 feet from our common wall that is constructed of cinder block and stucco. The trees are about 16 years old. The common wall, as well as my planter next to it, has shifted and cracked. The wall is shifting toward his house. Is it possible that the root structure has invaded my planter? (e-mail reference)

A: I doubt the roots are migrating under the wall and invading the planter. However, you need to get this checked out by a local International Society of Arboriculture certified arborist. The arborist would know the local situation better than I do.

Q: I recently discovered your Web site while searching for information. I would like to ask a question regarding techny arborvitae. We planted 10 techny arborvitaes in July 2004. They are doing well, even after surviving a severe drought in 2005. I water them when necessary. They have grown to double the original size. The plants are located on our west property line and exposed to wind and sun. I have not used any wrap or antidesiccants. Heavy snow this winter bent them to the ground, but they have straightened up. I cut off about six branches that were broken by the snow. While doing that, I noticed that the two largest northern arborvitaes have several long splits in the bark on the main trunks. The bark has peeled back to expose the wood inside. These areas are deep within the trees. They do not appear to be the result of typical damage from deer antlers that we get on some of our other plants. The deer have not eaten these at all. Is this splitting condition typical of techny arborvitae? Could it be caused by a disease or from having been bent to the ground? Do you recommend any sort of treatment? I am attaching several photos. Any information you can provide would be greatly appreciated. (Riverwoods, Ill.)

A: Those splits are caused by weather fluctuations and appear to be healing normally. As these trees continue to mature, the wounds will heal, so the trees will be fine. If you want to protect the trees during the winter, I suggest a coarsely woven burlap canopy on the south to southwestern side of the plants. This will protect the arborvitaes from the winter sun for a couple of years. Don't use any antidesiccant sprays.

Q: Last year my hosta plants got very large. How do I make them smaller? (e-mail reference)

A: Dig and divide the plants as soon as possible. That will make them smaller for the time being. These plants are as tough as a crowbar, so they can tolerate a little something less than total tender loving care!

Q: I have a big, white oak tree in my front yard. We didn't pick up the acorns last fall, so now we have a bunch of little oak trees sprouting. I'd hate to mow them down and kill them because I would love to see them grow. Is there a way I can pull the sprouts and have them grow into full trees? If so, how would I go about it? How tall should the trees be before I uproot them? Is there any special soil I should use to replant them? How long before I can sell them or give them to a park? Also, do they need all of the roots to continue to thrive or will partial roots work? Thank you very much. (Sulphur, La.)

A: Pick a select few that have emerged beyond their cotyledons and are showing their first leaves. Carefully dig out the entire root system on a cloudy day or late in the afternoon or evening. Immediately plant the oak trees at their new site and water in thoroughly. Chances are that you will lose most of your trees because oaks are not known for their transplanting ease. If you do save a few, you are that much further ahead than doing nothing at all.

Q: I purchased a schefflera plant at a garden store last September. I believe it is the s. arboricola variety that has smaller, compact leaves. I water it about once a week or so when I feel that the top of the soil is dry. I discovered spider mites about a month ago. I took the plant outside and sprayed it with an insecticide that has clarified hydrophobic extract of neem oil as an active ingredient. The mites have since gone to mite heaven. A few months ago (before the mites showed up), the leaves started to secrete a sticky, shiny substance and then curl and fall off. Also, these leaves tend to have brownish bumps along the main veins of the leaves. This is mostly happening on the side of the plant that is facing the light, even though I have turned the plant several times. The plant does have vigorous new growth and the newer leaves don’t exhibit this problem. Can you help me with what to do to solve the leaf drop? (Columbia, S.C.)

A: It sounds like you have a scale insect problem. If they are few in number, they can be scraped off with the edge of a knife, but I doubt that you have only a few of these characters! To get rid of them will require some kind of systemic insecticide if contact with the neem oil doesn't do the trick. The adults attach themselves to the plant and insert a piercing-sucking mouth part into the surface cells of the leaf to suck the carbohydrate-rich fluids out. These insects have a waxy covering over their bodies. The covering almost makes them impervious to contact insecticides, so you need to use a light, oillike neem or a more potent systemic material. There should be some systemic available at local garden stores that can be used on houseplants.

Q: I just found your Web site and love it! I bought five tropical hibiscuses last year at a wholesale discount store. They produce large, orange (double I believe) flowers. Do you have any idea what variety this is? All the tag said was that the plant is a tropical. They were on clearance and lying on the ground completely dried out. I decided at the price they were listed at, I had nothing to lose. I repotted them in huge pots using Miracle-Gro potting soil. They wrap around bamboo sticks and are 5 to 6 feet tall. I decided to bring them in for the winter, but that idea turned out to be a lot of work! I constantly have to baby them, but it has been worth it because they produced gorgeous flowers for me almost all winter long. Every time I saw a leaf turn yellow or a plant not blooming, I seriously fretted and swore I would not go through this next year. Of course, I will. Every article I read said to prune them in the spring. Christmas was upon us and they had completely taken over my dining room, so after a little "Christmas cheer," I decided to prune them severely. What wonderful results that produced. At times, they all have up to nine flowers. One of them has become very leggy, so I was looking for advice on pruning once again and came across your Web site. I am going to use my pruning shears with the confidence that it will be OK! Another thing that I read was hibiscus trees only last for three years. Is this true or a myth? I have not given them any fertilizer since I repotted them last year and was thinking I would add more Miracle-Gro potting soil this summer. Would that be OK? I am afraid they will grow too fast if I do it in the winter. Before I brought them inside, I sprayed the plants with Bonide Tomato & Vegetable 3 in 1 Insecticide, Fungicide and Miticide. It seemed to deal with any bug issues. I am looking for advice on when I should repot them (they are in almost industrial-sized pots) and if there is a different product I should use to get rid of any bugs. I have a lot of time and energy into these plants, so I value your opinion. (e-mail reference)

A: I can't tell you what variety of hibiscus these are, but it sounds like you have their number for culture and blooming productivity. Repot when the plants take a breather from blooming. You don't need to use larger pots. Use fresh potting soil because most have trace nutrient elements that seem to be more than adequate for most containerized plants. If the product you are using is giving you satisfactory results, stay with it. From what you have told me, I think you and your tropical hibiscus plants have a “thing" for each other and you and the plants obviously are happy with the results! Keep up the good work!

Q: I have a jade plant that is very healthy. It was covered with flowers when I purchased it, but has not bloomed since. I feed it just like I do all my other plants, but it just will not bloom. What can I do? (e-mail reference)

A: Do nothing. It will bloom again when it is good and ready to do so. Jade is considered a foliage plant, not a flowering one. The fact that it occasionally goes into a flowering cycle is a characteristic of all woody plants. The timing is controlled by cycles in nature and nutrient availability.

Q: Should I cut my raspberry canes off every spring or just the dead ones? Should I cut them to the ground or leave a few inches? (e-mail reference)

A: Cut off last year's fruit-bearing canes to the ground because they are dead. Also, remove any spindly canes that came up last year because they will not be productive. Look for canes that are pencil-sized or larger to keep. If you follow these suggestions, you should have a good crop of raspberries this year.

Q: I have a couple of plant problems. I have a well-established snow-on-the-mountain bed. In August, the tips of the leaves start to turn brown and curl. Within a week, the plants are brown and the bed looks dead. This has been going on for two years. I have checked, but do not see any bugs. In September, the whole bed starts to send up new shoots. Also, I’ve had a bed of peonies for 30-plus years. In July, the leaves become pale green and then get purple spots on them. There are no bugs on the plants. Some of the plants do not blossom as well as they used to since this started happening. I do not know what is going on, but to have problems in two flowerbeds every year makes me wonder where it will show up next year. Please help me out. (e-mail reference)

A: The problem you see with the snow-on-the-mountain is common with age. You are better off killing the entire ground cover and replanting with something else. This problem could be caused by excessive salts or from a fungal disease that has established itself in the planting. As for the peonies, they need to be dug up and divided. Do so every five years or so or when they begin to show the symptoms you describe. Be sure to plant so that the eyes (buds) are at the same level they were previously.

Q: I am most grateful for your Web site. I am a novice, somewhat fearful pruner and need more specific information on how to trim my two nigra arborvitae. I planted them according to the recommendations on the tag and from my state's Extension Service. They grew well, but are now too close to my house. Also, one is in a corner by my porch. It is not getting enough light in the back, so it is very bare. I don't know if I want to do something with that plant since it cannot be seen unless I am crawling between it and my house. I need to cut back on the height and rein in the sides, but I need them to stay a little full to hide the utility meter that is in front of my house. I'm getting ready to purchase my pole pruner and hedge shearer (right tools?), but I am looking for a little more courage. Knowledge is power (for me, it also is courage). I have cut deciduous branches, cut back spireas, severely pruned forsythias, but this is my first evergreen. I also need to do this in a week or two because spring is almost here and those trees serve as maternity wards for robins and cardinals. I don't want to disturb my moms. (e-mail reference)

A: You already are a pruning maven. Cut them back to the shape you want, but be sure to keep some wisps of green foliage remaining behind the cut. The pole pruner would be good for taking out the center stem to cut it down in size somewhat and encourage more spreading growth. In that instance, be sure to cut back to a lateral branch. Never leave a stub. As for the electric hedge shearer, use it with caution for the plant and yourself. Electric shearers make it too easy to get carried away with the shearing, so too much is taken off. The old adage of measure twice and cut once in carpentry applies as well to pruning. Be sure to know what effects the cuts will have before doing them. It is not what you take off that is important, but what is left behind after you are done. Good luck and don't clip the cord!


NDSU Agriculture Communication

Source:Ron Smith, (701) 231-8161, ronald.smith@ndsu.edu
Editor:Rich Mattern, (701) 231-6136, richard.mattern@ndsu.edu
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