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

By Ron Smith, Horticulturist

NDSU Extension Service

Q: I have some plum seeds that I would like to start growing. Can you give me some tips, such as what type of potting soil I should use? I live in Tennessee. I enjoy reading your columns on the Web! (e-mail reference)

A: Plums are a challenge to grow from seed. If the soil is not frozen where you live, the easiest approach is to plant the seeds where you want the trees to grow in your yard. There is a cold treatment that is needed for the seeds to break dormancy and start germinating. If your soil is frozen, store the seeds in damp sphagnum moss in the crisper of your refrigerator. This will create an environment similar to what Mother Nature would do. After 90 days, some embryonic roots should emerge that would indicate that the seeds can be planted in pots. Get some standard, sterilized or pasteurized potting soil and carefully plant the seeds. The emerged root should be placed just below the soil surface. Place the pots in a sunny location. Water every 10 to 14 days or when the soil surface is dry. When in doubt, don't water for another day because overwatering is the No. 1 cause of containerized plant loss. I trust that the soil is not frozen in your part of Tennessee, so you can plant the seeds about 4 inches deep and stand back!

Q: I have a jade plant that I put in a container with some cactus and put it outside. The jade plant went wild. It is now winter here in Indiana, so I put the plants in the garage. So far, they look fine. Can I leave the plants in the garage? What about watering? I have not watered the plants since October, but they still look great. (e-mail reference)

A: You are coming close to getting away with murder! Unless your garage is heated, they will get wiped out by frosty temperatures. I would suggest bringing them indoors and providing a little more tender, loving care. However, I've received countless e-mails from people who have given their jade plant lots of tender, loving care, but then the plant starts dropping leaves, gets scale and spider mite infestations and then rots away or dies. Perhaps you are on to something or the plants are frozen in time since October and will collapse when they are brought into a more hospitable environment.

Q: We have property in the state of Washington with three huge black walnut trees. The trees are approximately 150 to 200 years old. Since the area has built up and the trees are taking over many of the neighbors, properties, it would be best for us to have them removed. I’ve been unsuccessful in finding someone who would appreciate the wood from these beautiful trees. (e-mail reference)

A: I would suggest contacting the American Black Walnut Association at to see if it can help. Black walnut trees used to be poached in Ohio and New York for making veneered furniture. It is hard for me to believe someone wouldn't be interested in taking the wood!

Q: I have two ficus trees here in Texas. I was away for three months and during that time, we had a cold spell. My friend brought the trees inside the house. Now both do not have leaves and are looking pretty bad. I am wondering if they will snap out of it. Should I move them back outside now that the weather is in the 60s? Can I cut them back? The trees were watered once a week while I was away. (e-mail reference)

A: It all depends on how cold it got and for how long. All I can tell you to do is check the cambium with your thumbnail to see if it is still green. If so, then there is a chance that the trees will recover. If not, dump them. If the cambium is green, I wouldn't be too anxious to set them outdoors again until the potential for freezing weather goes away. As for cutting them back, you can, but don't overdo it or leave any stubs.

Q: We planted a ficus tree in our yard that is growing extremely well and providing excellent shade. However, we've been told that its roots may travel through the dirt and cement of our pool in search of water. Is that true? (Orlando, Fla.)

A: Think for a moment about what you said about the roots traveling through the dirt and cement of your pool in search of water. Please understand that I'm not making fun of you. This is a common, mistaken perception that people have of plants and their roots, so your question is anything but unique. Roots grow through spaces in the soil and are stimulated by the presence of water and mineral nutrients in and around those spaces. If the soil is compacted, the roots will proliferate in a noncompacted area, which has by comparison a generous supply of air, water, and mineral nutrients. If your cement pool is leaking water and draining into the root zone, that is where the roots will develop. The roots grow toward a water source. If the root tip reaches the crack in the cement, the root could exert sufficient pressure to damage the pool. In other words, the tree's roots have no means, other than the presence of a balance of water, air and nutrients in the soil pores existing in the root zone, to find a way to your pool. If the pool doesn't leak water, the roots have no way of knowing that a water supply exists there and will not grow in that direction. There is no "aha" coming from the roots that will allow them to recognize a reservoir of water that is not leaking! If you still are worried about it after all of this explanation, then you can install a root barrier that a local landscape contractor will be glad to install for you. These barriers are used on golf courses to keep deciduous and evergreen tree roots from growing into the greens and fairways. I hope all of this helps clear up your concerns.

Q: I have quite a few black walnut trees. I pruned the lower branches on some of the trees several years ago. The unpruned trees had a good crop of walnuts this year for the first time. I have not noticed any walnuts on the pruned trees. The pruned trees have a much nicer shape than the unpruned trees. I didn't finish the pruning because I was afraid I was doing it wrong at the time. Do you have any information on the correct time and method of pruning? I would like to do it now because I have time. Thanks very much for any guidance you can give me. (e-mail reference)

A: It all depends if you want fruit or lumber from the trees. If you want lumber, then prune them to have nice, long trunks with branching beginning as high as possible. For fruit production, let them grow on their own. Prune in the spring, but not until after the trees have leafed out completely. This will cut down on sap flow. If pruned while they are dormant in the spring, the result would be a heavy sap flow that may cause some concern on your part, but is not harmful to the tree. You might be interested in joining or associating with the American Black Walnut Association. Go to for more information and support in your pursuits!

Q: When is the hydrangea season? I am planning to marry in September and want to know what type of hydrangea is best for that time of year. I live in Illinois. (e-mail reference)

A: I would strongly suggest that you look into getting the Annabelle hydrangea. We love it in North Dakota because of its dependability and longevity. Its flowers are sometimes up to 12 inches across and flower for six to eight weeks from late June into September. Check with local nurseries to be sure of the flowering time. The timing should be fine as long as the wedding isn't too late in September. A new introduction, endless summer, also would be hardy for your area. As the name implies, it flowers all summer long on old and new growth. It can produce pink flowers in acid soil or blue flowers in alkaline soil. If you can find a nursery or florist that would cooperate, it would be neat to have red (pink), white and blue flowers at your wedding.

Q: We have four miniature blue spruce trees in pots in front of our garage. I’m not sure if the pots should be wrapped with tarps to keep the roots warm or if the pots should be brought inside. I know they need light, but the garage has no windows. I can’t seem to find any literature on the subject, so I’m hoping you might be able to “shed some light” on the subject. (Cincinnati, Ohio)

A: Here is the light I can shed. Dig the potted plants into the ground around your property somewhere. This will keep the roots from reaching lethal low temperatures. Water them in well and then mulch with straw. They easily should survive under those conditions. The trees probably could survive out of the ground if you want to take a chance. The winters in southern Ohio are wimpy compared with what we have to put up with in North Dakota!

Q: Google didn't help me find the answer to my question. My aunt in Stanton said someone told her the neighbor's cottonwood trees were more than 900 years old. I thought cottonwoods lived about 70 years. How long do native cottonwoods live? (e-mail reference)

A: I really doubt the trees are that old. Cottonwoods are subject to a wide range of insect and disease problems. The real age of the trees can be determined by the use of girth measurement and a core sampling of wood taken from the trunk. This is not as easy as one might think. There is a science to making this determination accurately. Dendrochronology is the systematic study of the age of tree species. Cottonwoods (poplar) are not known among the older "champion trees" of the world, such as the sequoias, yew and others. Typically, cottonwoods will go through two phases of growth. Juvenility is a period of fast growth followed by senescence, which is the gradual decline of the tree leading to death from some cause mentioned earlier. This whole species could be considered one of the pioneer species common on the Great Plains. They establish easily, grow fast and are weak-wooded, which makes them easy prey to wind, ice and snow damage. My best guess is that cottonwood trees more than 70 years old might be rather rare unless established in a protected site and given lots of good attention.

Q: I have two spider plants that have fruit flies. How do I get rid of the flies? I have the mother plant in my kitchen, but they are not bothering that one. (e-mail reference)

A: Launch a double-barreled attack against them by using insecticidal soap and sticky (fly paper) tape. Also, when you start running your central heating system on a regular basis, the drier air will help to wipe them out.

Q: I stumbled upon your Web site while looking for information about planting walnut trees. I have a few walnuts from a tree that my grandfather planted when he was young. I would like to plant a walnut tree in his memory. I have never planted a tree before, so I’m wondering if you had any helpful information or if you could tell me of any books or Web sites that would have a step-by-step guide to planting walnuts. (e-mail reference)

A: No books are needed. Plant the nuts where you want the tree to grow. The nuts should be planted about 4 inches deep. Do the planting in the fall. If they are viable seeds (nuts), they will sprout and grow. Hopefully, the squirrels won't find them. Be sure the site receives full sunlight for optimal growth. Walnut trees have a very strong taproot system and typically don't transplant easily. That’s the reason for planting them where you want them to become established.

Q: I just bought four mission blue spruce trees as recommended by a local nursery. The trees appeared to be healthy after being delivered and planted, but all of the trunks were crooked. In fact, the trees were not very straight all the way to the top. They were planted so they looked as straight as possible. The individual from the nursery said this was normal and the trees would grow straight as they mature. There also were some broken branches at the bottom of the trees and a few that appeared dead. He stated this also was normal because the trees were kept very close at the tree farm. He added that the trees would correct this defect in time. Is this all true? I am not a tree expert. Thanks so much for your time. (e-mail reference)

A: What the nursery told you was a mixture of truth and marketing hype. Spruce trees are normally fairly straight-trunked, so the crookedness is not common. It could be the trees were subjected to varying strong wind forces and mechanical intrusions that caused them to grow in a crooked fashion. Dead or broken branches left on the tree at the time of planting is a poor marketing tactic. This would be analogous to purchasing a new car with a cracked window or flat tire, which would be totally unacceptable. If the company had good marketing finesse, it would have made a correctional pruning prior to or at planting time. The statement that they now will grow straight is pretty much a truism unless some disease, insect or mechanical injury causes them go through reorientation. The fact that the trees are or were healthy at planting time is a good sign. Since the trees were planted by the nursery, I hope there is some kind of guarantee that the trees will survive and grow. Chalk this up to experience and see what the trees look like coming out of the winter. Then do some correctional pruning yourself on the broken or dead branches to improve the appearance of the trees. When you prune, cut back to where the needles and lateral branches exist or cut the branch off completely back to the trunk. Closeness at the tree farm is an indication that the trees were kept on-site too long. This would cause some die-out or breakage during removal.

Q: I purchased soil this summer for transplanting my houseplants. I noticed a month ago that I have tiny gnats. Could it be from the soil? After purchasing Gnatrol and using it for two weeks, I still am seeing the gnats. I have been trying to let the soil dry as much as possible without losing my plants. Do you have a solution? If I do need to transplant all of my houseplants again, how do I sterilize the containers and plants so the gnats do not transfer to the new soil? (e-mail reference)

A: They should decrease in number or be wiped out completely when you start using your central heating system during the colder weather because the drier air that results usually causes an environment that is too dry for their survival. If that isn't something you want to wait for, you can try sticky tape. The tape will collect a significant number of gnats until the heating system is running on a regular basis. You also could go ahead and repot using pasteurized soil. A hot, soapy scrubbing usually will wipe out any eggs that may be adhering to the pot. You also could get new containers. A dip of insecticidal soap with the root system will finish off the cleanup, if you want to go that far. But I would save that last step as a move of desperation because I don't know how your houseplants would react to the treatment.

NDSU Agriculture Communication

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