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Don Kinzler, Published June 22 2012

Hortiscope: Pot-bound plant contradiction explained

Q: You have a very interesting website. I read in one of your answers that a hibiscus plant won’t bloom until it’s root-bound. In another answer, you said to put it in a bigger pot so it doesn’t get root-bound.

I have a hibiscus that is about six years old. Two years ago, I repotted it into a 20-inch pot. The plant now looks like three separate plants. The roots have grown to the top of the pot and I have to water it twice a day when the weather is hot.

I am wondering if I should try to separate the plant or if I should just try trimming the bottom roots and putting it back in the same pot. It is loaded with buds and has six to eight blooms every day. Any ideas? Thanks much. (email)

A: Sounds like what I said is a contradiction. Here is the official interpretation: Repotting should be done when the plant is overly pot-bound, even if it has flowered. It also should be repotted if it is pot-bound and not flowering. It never should be repotted while it is flowering because the plant will become stressed to the point of dying.

Root-bound or pot-bound plants will tend to flower with more intensity and frequency than those plants that are not because “life is too good” for a plant to bother with flowering. Keep in mind that flowering, which is the reproductive stage of a plant’s lifecycle, requires a great deal of energy. Living in a container environment that drains well and has adequately moist soil, plus ample nutrients to continue vegetative growth, lulls the plant into thinking that there is no rush to produce flowers and fruit.

Change the plant’s environment a little where the roots occupy almost all of the available air space and are beginning to grow around the inside of the container. This presents a stressful situation because there is no nutrient “bank” left in the soil to draw upon. Water simply flushes through the container because there is no water-holding capacity in the remaining soil.

This stressful situation is sent throughout the plant to get with it and begin attempting to save itself by producing flowers. When plants are in their native habitat, they tune in to the changes in their environment.

Warmer days with longer daylight hours will elicit a reaction of vegetative growth, flowering or both. Shorter sunlight hours and cooler temperatures will signal an end to the growing season, so any fruit the plant may have set will be pushed into maturing. For example, allow a tomato plant that has tomatoes on it to be killed by frost in the fall.

The following spring, tomato seedlings will emerge to carry on life for the species. Sorry for the excess verbiage. Once I got started, I just couldn’t stop. I think I’ve answered your question.

Q: What fungicide should I use on young apple and pear trees to save them from cedar apple rust? We noticed that the juniper trees also are showing signs of the problem. (email)

A: Pick off all the fruiting bodies that you can locate on the junipers and destroy them. Next, go to a local garden center or garden supply store and look for a fungicide such as Heritage, Mancozeb, Immunox, Banner or Bayleton. The fungicide should be used on the apple trees, not the junipers.

Q: Large numbers of leaves are falling from my sugar maple. The leaves appear to be snipped off along the stem. What could be causing this? I can’t see any pests. (email)

A: There could be several reasons for the leaf drop. The most likely candidates are leaf stalk or petiole borers. Both insects burrow into the leaf petiole in the spring and cause the leaves to fall. The larvae remain in the leaves when they fall to the ground. They burrow into the ground and remain dormant until the following year.

Water stress is another possibility. A spring full of generous rain showers, which suddenly is followed by elevated temperatures and no water for a couple of weeks or more will cause stress.

From your description, it sounds like it might be the leaf petiole borers causing the problem. In either pest case, you have nothing to worry about because they usually stop as the summer comes on. The result is more cosmetic than threatening to the tree.

I’d appreciate knowing where it is you live because it would give me some sort of clue as to what else might be causing your problem.

Q: I have had a goldfish plant for several years. It hangs in my kitchen window over the sink. It has bloomed every year. However, in the past year, it has produced only one “fish,” but the leaves keep growing, so I have had to cut it back several times.

I have kept the cuttings and planted them in different media. Some are in water and stones, some in soil and some just in a glass. They are growing nicely but not producing any blooms. I fertilize the plants regularly and water when needed.

Is it possible they have turned into male plants and won’t bloom or will they bloom again sometime in the future? I have become very discouraged. I look forward to your answer. (email)

A: You obviously have a very green thumb because you were able to get so many cuttings to root in such a wide range of media. Typically, mature goldfish plants are covered with blooms during the spring and summer. Some plants also may bloom at other times of the year.

You’ll get the most blooms by providing plenty of bright, indirect light. Keep the soil slightly dry during the winter to help promote heavy flowering in the spring. Be careful not to allow the soil to dry out completely.

You probably are guilty of being too kind to the plants, so they lazily languish in a vegetative state. A little moisture stress in late winter will prompt the plants to go into their reproductive stage of life.

Q: My husband planted a tree that has a 4-inch caliper. However, the tree is declining. The tree was balled in burlap by a nursery.

We tried to amend the clay soil by using peat moss and black dirt. Do you think we would have a chance to save the tree if we dug around it and amended more of the soil or do you feel that it could be the roots declining?

We would love to save this tree because it is one of our favorites. (email)

A: If your husband planted a tree with a 4-inch caliper, it would need a minimal rootball size of 42 inches. That would be quite big and heavy for even a very strong man with good equipment. The American Nurseryman standard manual says rootball sizes should be of a diameter and depth to encompass enough of the fibrous and feeding root system as necessary for the full recovery of the plant.

Of course, this is a general statement that would be rife with exceptions because of species, soil type, care in the nursery and more. My guess is that an insufficient amount of the fibrous and feeding root system existed at the time of planting for the tree to recover and establish itself.

Depending on how patient you are, you might luck out and have the tree recover, which would be right up there with minor miracles.

If I were the one to make the decision, I’d replace the tree because time is precious and unrecoverable. Life is too short to wait for a tree to either pull out of it or not. Create the beauty you want and enjoy it as soon and as much as you can.

Q: I have a 3-year-old lawn that is infested with crabgrass. I have heard there are some new and effective products for postemergent control. I would greatly appreciate your suggestions. (Bismarck)

A: A crabgrass invasion this early in the season? It seems unusual because crabgrass should just be in the seedling stage right now and not that distinguishable from other grasses, unless by close examination. You must have a bad invasion.

There are lots of crabgrass control products on the market. The most common herbicides available for postemergent crabgrass control are MSMA, DSMA, Acclaim Extra and Drive 75 DF. There used to be a product called Q4 that was labeled and hailed as an excellent postemergent crabgrass control product.

It has been discontinued by the company, but retailers are allowed to sell the rest of their inventory.

Another product that is on the market is Trimec Plus, which gives both broadleaf and crabgrass control. If there is anything more that is available on the market, I am unaware of it at this time. Good luck.

Q: I have a question about my emerald lustre tree. I planted the semimature tree three years ago. The first year, it looked beautiful and full. Last year, it had less foliage, and it is struggling again this year.

I have noticed that there is a white mushroomlike fungus on the bark. I have clay soil, but topsoil was added when the tree was planted. We purchased and planted another emerald lustre that is doing fine.

Do you have any suggestions on what I can do to help this poor tree? It is a beautiful tree, so I would hate to lose it. (Minneapolis)

A: When you say semimature, do you mean that someone came in and planted it using a tree spade or was it put in by hand? Was it balled in burlap? Was the tree in a container that you and someone else could handle and plant yourselves?

The reason I’m asking is because this is the usual pattern of tree decline that follows when too much of a root system is left behind when a semimature tree is planted.

For the most part, the decline is not reversible. Usually, the owner finally gives up and has it removed. Planting a tree with as much of the root system intact as is the best approach.

Many large nurseries will move trees that have been root-pruned carefully through the years before they get moved to a permanent location. This gives the tree a chance to develop a nice compact root mass that cuts the chance of a planting failure almost down to zero.

Q: I am having a problem with my cactus. When researching for answers, I came across your email address, so I’m hoping you can help me.

I’m struggling to identify the cactus. The closest image I’ve seen is of a cereus peruvians, but the spines are very different. They grow individually, not in clusters. They are very dark near the stem and a golden brown toward the end.

When I got it, they were all like this, but then some started turning red at the very top and the green was a much paler shade. These spines were bendy and broke off easily, not hard and sharp like the others.

I was told that it needed more sun, so when we had some nice days, I put it outside for a few hours. However, I think I may have left it outside too long. It has now lost color near the top of the stems and they are a slightly brown. One stem has gone partially black and shiny.

What should I do with it? I didn’t get any care instructions with it, so I don’t know if I’m watering it right or anything. (email)

A: Can you bring yourself to part with it? First of all, I don’t know the variety you are attempting to describe, and the symptoms you describe also leave me clueless. I’m sorry, I cannot help you at this point.

I suggest getting rid of the plant and starting new with something that is properly labeled and has directions on how to care for it.

Q: We have a couple of apple trees that we planted two years ago. Today, we noticed some of the leaves seem to be curling and browning at the edges. The apples that had started are dried out and crusty. None of the apples are larger than a dime.

I’ve taken a look through your website but haven’t seen anything that looks like our problem. Any help would be appreciated. (email)

A: This sounds like it could be a salt or herbicide problem. However, this is just a guess. You need to contact your county Extension Service agent to get the problem diagnosed. Go to www.csrees.usda.gov/Extension/ to find an agent nearest you. Someone there can line you up with a specialist at the land-grant university in your state who should be able to assist you.

Q: I received a question from a local producer who was growing a tomato plant in a pot and in the house. The plant was doing very well until just the other day.

It became droopy and was not drinking water. She said that she had a lot of grasshoppers on the window ledge next to the plant a day or two later. Is it possible that the grasshoppers could have eaten off the roots? (email)

A: Grasshoppers will eat just about anything in front of them. If the young grasshopper instars did, in fact, eat the roots, what stopped them from also going after the foliage? Something else must be going on that would cause a tomato plant this size to go limp suddenly.


To contact Ron Smith for answers to your questions, write to Ron Smith, NDSU Department of Plant Sciences, Dept. 7670, Box 6050, Fargo, ND 58108-6050 or email ronald.smith@ndsu.edu.