Questions on: Petunia

Ron Smith, Horticulturist, NDSU Extension Service


Q: I planted several wave petunias a couple of weeks ago. Now something has eaten all of the flowers. We are thinking it's rabbits. Do you have any suggestions or ideas? Do you think that it might be something else? If so, what would you recommend? Thanks. (e-mail reference)

A: Spray what is left of the plants with Liquid Fence or Plantskydd to repel whatever thinks of your planting as a free meal. Rabbits are good suspects because they seem to be everywhere in the suburbs these days.


Q: Can you tell me the difference between wave and trailing petunias? Which would you recommend for flower boxes? Thanks very much. (e-mail reference)

A: I prefer the wave petunias because they simply are overwhelming in energy and flower show. Any of the new petunias on the market these days are fantastic, so I'm sure you would be happy with either one.


Q: We have wave petunias that are blooming and look ready to plant. The plants are in a small, farm greenhouse. We have noticed that some of the leaves are turning black, but have good texture. Thank you in advance for some help. (e-mail reference)

A: This sounds like a pythium fungus getting started. This is the same fungus that is related to seedling damping off. Increase the air circulation, avoid overhead watering and spray with a fungicide, such as Subdue, Maxx, Alude or Aliette. Hopefully, you've used sterile or pasteurized soil.


Q: When you were on the Prairie Pulse show, you talked about wave petunias, some kind of zinnia and another plant that you said bloomed all summer long and you liked the plant as an annual. The name sounded like narcissus or something. Would you be able to recall? I'm looking for annuals that would do very well in patio pots on the west side of the house with no shade. Thank you for your interesting talk. (e-mail reference)

A: I might have thrown in Echinacea, which is a perennial that loves full sun and heat. It is a prairie native that attracts butterflies. Annuals, such as portulaca and vinca, are champions with full sun and heat. They also are prolific bloomers. A very showy flower that you might consider is the Indian summer rudbeckia. Thank you for the nice compliment about the presentation!


Q: I bought quite a few flats of petunias. I planted, watered and fertilized the plants, but now I've noticed that the flowers have white spots. What are the spots and how do I get rid of them? (e-mail reference)

A: These could be some fertilizer burns that are not harmful to the plants. Future flowers won't have these spots. When you fertilize, be sure the material is totally water soluble. If you do use a dry fertilizer, be sure to water it in completely and keep the fertilizer off the foliage and flowers.


Q: I planted some petunias, but many of the flowers have lost their color. The flowers have white splotches and some seem almost completely bleached. Any thoughts? (e-mail reference)

A: It could be due to very high salts in the soil. Have the soil tested. If that is the problem, dilute it with generous amounts of sphagnum peat moss.


Q: The leaves on my petunias are turning yellow and drying up. This happens every year. They are in planters or hanging baskets. The plants get fed about every two weeks with Miracle-Gro. Is there something I can do to stop this? The problem starts at the bottom of the plants and by midseason about half of the leaves are gone, but still producing flowers. I have asked several garden centers what might be causing this problem, but they have no idea. I have purchased a liquid to mix in my sprayer to stop mildew and mold spores, but that hasn't helped. I have tried spraying the plants with a mixture of milk and water, but that hasn't helped, either. (e-mail reference)

A: Could they be planted too deeply or in too much shade? Are you using pasteurized potting soil? Are the hanging baskets free-draining? These are all the reasons I can think of as to why the leaves are turning yellow. Otherwise I have no idea what the cause may be.


Q: I collected seed from my petunias last year in hopes of having more plants this year. I don't think the petunias are hybrids, but I am not sure. I've started the seeds, which are growing nicely. Is there a way to know what the flowers will look like? What can I expect to see? (e-mail reference)

A: At least 99.44 percent of the petunias sold on the market are hybrids. Collecting the seed and sowing it from hybrids is going to give you a "Fibber McGee's Closet" of plant types and color combinations. They may not be rewardingly attractive, but it will be a good object lesson in Gregor Mendel's work with hybrids.


Q: My petunias turned yellow in August. It looks like iron deficiency. My purple wave plants do not get this problem as easily as other waves or other varieties. I also have wave petunias in baskets in soil substitute. They are fine. The area with the petunias had fresh peat moss incorporated into the soil this spring. This yellowing is a yearly problem. I had hoped that watering with rural water would help, but it didnít. I fertilized every 10 days with Miracle-Gro. Is there a product that I can utilize before planting that will have long-term results? Should I also spray with a stemic to control leafhoppers? As I said, the purple waves growing in soil are not affected. (Langdon/Wales, N.D.)

A: When most people add peat moss, they donít do it in sufficient quantity. The mixture should be 50 percent soil and 50 percent peat moss. Be sure it is sphagnum peat, which has a pH of about 4.8. Miracle-Gro now has a slow-release product on the market that may help as well. See if you can find that in your part of the country. If not, go to its Web site to see where the product can be obtained or order the product.


Q: I have been growing wave petunias for several years to plant in hanging baskets. Trying to beat previous years, I have been adding more and more plants in the containers. I placed 10 plants in a 14-inch basket and six plants in a 12-inch container. They are not doing well even though I water them daily and fertilize weekly. I suspect that I have too many plants in the containers. How many plants should be placed in such baskets? (e-mail reference)

A: Good heavens! I promise that four plants per container will do a fantastic job of overflowing the basket. Each plant spreads 4 inches in every direction.


Q: This year I decided to buy wave petunia plants and create my own hanging baskets. The plants were full of flowers when I planted them, but over the course of two weeks all the flowers dried up. I now have green plants with no flowers. I have been using Miracle-Gro Bloom Booster once a week, but it seems to have had the opposite effect. The plants were sometimes put in direct sunlight for part of the day, but mostly hung in indirect sunlight. Any suggestions? (e-mail reference)

A: It sounds like you planted petunias outside that had not been hardened off. Treat them normally, but donít overwater or overfertilize. They should begin to recover in a couple of weeks.


Q: Iím going to try raising wave petunias in a hanging basket. I planted the seeds Jan. 1 and then transplanted the plants into pots Feb. 19. I give them 12 hours of fluorescent light per day. I need to know how many hours of light per day they need. Do I trim the plants? What is the best room temperature, feeding practice and should I use bottom heat? I would like these to be ready for Motherís Day. (e-mail reference)

A: Increase the lighting period to 14 to 16 hours. More light will make a big difference on plant vigor. Fertilize with Miracle-Gro every other week using a diluted solution. The room temperature should be in the mid-70s, if possible. Petunias are tough and forgiving plants, so they should respond well.


Q: I know someone who is having trouble with her petunias. They are planted in black dirt mixed with compost and well-decomposed manure. Every year about the first of July the whole plant turns yellow. She puts liquid iron on them and they seem to recover. Is it possible that they need to be fertilized earlier? I told her that it would be a good idea to send in a soil sample. She plans to do so. Am I missing something? (Hettinger, N.D.)

A: If she is getting a positive response after applying the iron, then there must be a deficiency there for some reason. It could be too wet or cold, too much alkali in the soil, a combination of these, or something entirely different. I suggest applying the iron before the symptoms appear next year. A soil test is also a good idea.


Q: My petunias are getting really spindly looking. Is it too soon to cut them off? If I do cut them off, how far down the plant can I cut without killing it? (Ellendale, N.D.)

A: Cut them back to a leaf node and give them a shot of Miracle-Gro at the same time. If they are getting spindly, they might not be getting enough direct-sun.


Q: Because they predicted a possible frost, I brought in my petunias and placed them on the floor of the garage. I had three pots and all were petunias. This morning every flower had spots on them. It almost looks like they are water spots that turned brownish. Could it have been something with the rain we had and then bringing them in? Also, can I put super phosphate around my tomato plants at planting time? Does it do any good? What is the best way to care for them? Some articles encourage the use of tomato cages or stakes while others say let them grow naturally. (e-mail reference)

A: I have no idea what happened to your petunias! As to your tomatoes, you can mix super phosphate into the soil at planting time. Everyone has their own views on how to plant tomatoes. I personally like them staked or treated as a vine, which most are. If they are the determinate form, they will grow pretty much as a bush and will not need any support. In my observations, there seems to be fewer problems with disease on staked tomatoes than the other way around. Every greenhouse tomato grower I have visited has them vined.


Q: I planted some wave petunias in a pot on the deck rail. They were doing great, but now they are starting to get a little leggy. I'm not sure how to trim them back. Could this be happening because I was cutting off dead flowers? Can I cut back the whole stem after it gets too long? Should the plant grow new stems from the center? (e-mail reference)

A: Wave petunias getting leggy? It shouldn't be possible because these are spreading, densely flowered plants that grow almost with a vengeance. We have them in containers and hanging baskets all over our campus. All that is done to them is watering and fertilizing on a regular basis. It could be that you donít have a wave petunia.


Q: My mother bought us a nice hanging basket containing two cascadian bi-colored petunias just over a week ago. In the last few days, the leaves in the middle and around the edge started going limp and curling. Can you tell me what the problem is and if I can rectify it? The plants get a lot of sun and I water twice a day. At the moment, there are still plenty of healthy looking flowers on the plant. (e-mail reference)

A: Most likely it is Botrytis fungus getting started. To help clear it up, back off on the watering to once a day. You may also want to spray the plants with an all-purpose fungicide.


Q: I recently bought a hanging basket with petunias in it. The plant looked wonderful when I bought it, but now it has turned brown and brittle, almost like it hasn't been watered enough. I started to prune the dead areas and noticed a ton of black little balls all over the plant. They come off pretty easily so I thought maybe they were aphids, but I can't find a direct answer on any Web site. What should I do? (e-mail reference)

A: Dump the plant and get another one. What you are seeing are the spores of a fungus disease that killed the plant. It is not your fault, just something that happens. When I say dump it, I mean in the trash. Don't put the soil in your garden.


Q: I planted petunias and zanias in an outdoor bed and planters. This year the plants started to turn yellow at the outside of the leaf and then into the main steam. I also have several small violas that turned yellow and then brown. I use only rainwater with no fertilizer. These plants were blooming well and healthy looking until just recently. (Bison S.D.)

A: It could be a simple fertilizer need. Give the plants a shot or two of Miracle Gro or something similar a couple of times during the growing season. While rainwater is excellent for watering, if the soil is devoid of nutrients they are not going to thrive.


Q: After I fertilize my hanging petunias they stop producing flowers and get green bulbs that have little black seed-like things in them. How do I prevent this from happening? (E-mail reference)

A: I have never heard of this happening before. Usually just the opposite occurs. The petunias hanging in baskets on the NDSU campus bloom profusely after they are fertilized.

I can only suggest that you remove the "black seed like things" when they appear. New growth should produce new flowers. I would also take note of the variety of petunia and not use it again in the future.


Q: I have some wave petunias that I am growing under flourescent light. They are about six weeks old and are nice stocky-looking little plants. The light is on them about 15 1/2 hours a day and I fertilize about once a week. Recently some of the leaves started turning yellow. I had the same problem last year with my geraniums. I water them when the soil feels dry. (E-mail reference)

A: I suspect that the soil may be poorly drained or that you have them in containers that are not free-draining. I am assuming that you are using pasteurized soil media that you purchased at a local garden store. If you have done all of these things, then it could simply be mature leaf senescence.


Q: Please help, I bought some petunias from a garden center about eight weeks ago, put them into hanging baskets, and they were doing really well. Suddenly, the leaves have gone brown, and the flowers are all very damp and not opening. I have watered them lots, then left it thinking maybe I have watered them too much, but they are still the same. They are in the sun for about six to eight hours when it is sunny, but lately we have had very windy and rainy weather. Is there anything I can do to save them? (E-mail reference)

A: It sounds like they might have been hit by a frost. Dump them and begin again.


Q: I was wondering if 30-degree temperatures would hurt petunias, marigolds and impatiens that were planted outside now. (E-mail reference)

A: It depends. If they are close to the house, no; if they were hardened off, no; if the 30-degree temp comes for only an hour or so before sunrise, no; if a frost accompanies the temperature, most likely. The impatiens would be the first to go, followed by the marigolds, followed by the petunias. I suggest throwing a cover over them for the night.


Q: I planted several different varieties of petunias along with other flowers in containers this year. Several of the petunias have started drying up and falling over. I think aphids may be the problem, but I have sprayed and it seems to have gotten worse. Any suggestions? The other flowers seem to be fine. (E-mail reference)

A: I doubt it is aphids. Most likely it is a simple root rot that originated with the stock when you purchased it. When you planted them the site was ideal for the development of the pathogen. Be glad it was specific for petunias and not the whole planting.


Q: I have my wave petunias in hanging pots. My question is how often to water them. I have been watering them every day but I never know if this is too much or not. (E-mail reference)

A: Every day is a good start. Hanging baskets dry quickly and need daily watering. As the season goes on and the root mass takes over more of the soil ball, it is likely that twice daily watering will be necessary, depending on temperature, wind and other conditions.


Q: Our garden club has a garden plot that features a five-pointed star in the center. This year we're planning to use Antigua yellow marigolds in the star and surround the star with purple and lilac wave petunias. What's a good spacing for wave petunias for optimum coverage, and might we have a problem with petunias taking over the marigolds? (E-mail reference, Baudette, Minn.)

A: The petunias will grow into the marigolds, but not over them. I would space them about 2.5 feet apart and they will shortly grow together, making a dense and probably weed-free mat.


Q: Last year I sent you a question regarding my petunias with yellow leaves. I took your advice to add peat to the area. I also added cow manure, and with the combination of the peat and manure, I had beautiful petunias last year. Now I have another question. I have heard sunflower hulls do not make a good mulch because there is a chemical in them that retards growth. Do you have any information regarding this issue? I feed sunflower seeds in my bird feeders so have lots of hulls to dispose of. I would like to use the hulls in my garden but have been reluctant to do so because of what I have heard about them. (E-mail reference, Beach, N.D.)

A: Glad my past advice worked out for you. Sunflower hulls, to my knowledge, should not hurt the growth of your petunias. The hull is about as inert as you can get, so I don't know of anything toxic that could leach out and cause a problem. My advice: go ahead and use them where you want.


Q: My question concerns my "Wave" petunia. I rooted a cutting, which I am growing in a south window. It has started blooming, but not as well as it did outside. I expected this. I planned to root several cuttings to plant this summer, but after reading about letting plants go dormant when you're wintering them over, I wonder if my petunia needs a dormant period. (E-mail reference, Bismarck, N.D.)

A: No, you need not worry about making your petunia go dormant. It will continue to grow as long as it gets light, moisture, and nutrients, along with a decent temperature. Just plant it outside this spring, after hardening it off, and let it take off. It will reward you well, for the TLC you have given it!


Q: We are thinking of replacing some old trees with a poplar and a Russian olive. Do we need to worry about the roots that are left from the old trees?

Also I have been planting wave petunias every year since they came out, but this year they only had about half as many blossoms as other years, and the leaves were real slender. Other people we talked to had the same problem. We have saved some seed, but we are wondering if it could have been caused by the weather? (Litchville, N.D.)

A: You are OK! Any remaining root material will simply rot and eventually provide nutrients to the newly growing trees.

The petunia was a fluke. And, I doubt you will get anything at all like the wave petunia from the seed you saved.


Q. Why can't I get my petunias to bush out when I plant them in pots? I also would like to know how much manure I should add to a 6-foot x 6-foot raised bed? What is the best way to keep worms off of cabbage? (Litchville, N.D.)

A. Petunias need to be pinched before they will bush out to any degree. Do this at planting time. Use peat moss as a mulch around the vining plants and keep it moist. That should eliminate the drying. A five-gallon pail of manure worked into the top 9 to 12 inches of soil should not pose a problem. Use Bt or Dipel (same active ingredient) about every five days when the moths first appear. The material is harmless to humans.


Q. We plant petunias in our planter, which is located in the sun all day. In the fall when we dig them up, they have never established a root system. Can you tell me why? (Valley City, N.D.)

A. This often happens when herbaceous plants like petunias are planted when root-bound—which most are. The fibrous root system, developed in the marketplace container, fills all the available pore space. The grower kept everything alive through watering and nearly continuous fertilization.

You didn't say that your petunias looked poorly, just that they lacked an established root system, so you likely did a very good job of meeting their water and nutrient needs during the season.

If you want to correct this, split the rootball with hand pruners or a knife at the time of planting. This will encourage new roots to develop and move out into the surrounding soil.

When you are handling just a dozen or so plants—not too much of a problem; when it gets into the thousands, then all you want to do is get the job done!


Q.I am writing again! I have sent a sample from a perennialflower plant. It has done well for two years. Now this summer Inoticed one plant was all brown and gone seemed like overnight.Now, I see another plant is doing the same thing. What is theproblem?

I also seem to have trouble with petunias. The larger sample haslight green on the leaves. I am afraid they are going to dry up again. The smaller sample is from a plant that just seems to sitthere. What is the problem? I have sent a sample from our arborvitae bush. We have otherbushes in front of the house. This is the only one that has the "seeds." Why? Also, when is the best time to trim arborvitaes?

I really appreciate your column in the paper. Thank you. (Munich,N.D.)

A.Your samples arrived along with your questions, but the firstone had rotted and was beyond identifying or diagnosing.

Try fertilizing your petunias with a water-soluble material likeMiracle-Gro. If that doesn't color them up and stimulate growth,nothing will.

Since arborvitae are monoecious (separate sexes on the sameplant) I suspect that the one you are concerned with had anover-abundance of female flowers to produce so many cones. Itcould also be that the other plants are dominated by maleflowers, which do not produce cones.

Prune arborvitaes anytime in spring, summer or early fall. Justbe sure to leave some wisps of green shoots with each pruning cutto avoid permanent bare spots.


Q. I am looking for directions on how to plant a flower bed out of petunias, etc., in the shape of the U.S. flag. Do you know where I may be able to find directions? My son wants to do this for a 4-H project. (Kief, N.D.)

A. I suggest using white alyssum, red petunias and blue ageratum for the respective parts in the flag. Or, if the ageratum is too light a blue, use a dark blue petunia.

I saw versions of this done in Ohio in 1976. It was quite impressive.


Q: I have a flower bed where I like to put petunia plants. For the past two years the petunia leaves have been yellow with green veins and the plants have been small. This does not happen to other plants I put in this bed. I use an all purpose fertilizer and that has not helped. Do you have any ideas how I can prevent this from happening this year? (Beach, N.D., e-mail)

A: A number of things could be the cause. Petunias are sensitive to high pH, which leads to a shortage of iron (Fe) being available to the plants, resulting in a stunting of the growth. Another possible contributing cause could be the root systems are container bound in a knot when transplanted and the root system then has a limited surface area to uptake adequate nutrients.  I would suggest incorporating generous amounts of Canadian peat into the planting sites this spring prior to planting. This will help to depress the pH somewhat. Then, use Miracle-Gro as your fertilizer source right after transplanting to help make iron available to the petunias and other plants. Repeat on a monthly basis.


Q: I am having some problems with my petunias. I asked a local florist if it was aster yellows, but he had never heard of it. The leaves have become pale and you can see the veins clearly. Have I given the correct diagnosis, and if so, what needs to be done? (E-mail reference, Jamestown, N.D.)

A: Vein clearing, followed by general yellowing, twisted, epinastic growth, and deformed flower parts are the general symptoms of aster yellows. It sounds more like a problem with a delayed root rot that is not allowing your plants to grow properly. Ours are doing very poorly this year as well, most likely from the heavy rains in June. If the plants are not contributing to what you intended, remove them. Aster yellows is spread by leafhoppers, generally picking up the pathogen from surrounding weeds and transmitting them to healthy ornamental plants. So to control AY, spray to control the leafhoppers, and keep the weed population under control.


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