Questions on: Phlox Ron Smith, Horticulturist, NDSU Extension Service

Q: I have a fairly large area of creeping phlox on a side hill in the front lawn. It has bloomed well the last few years. Some of the plants are getting too long and there was some winter kill in spots. Should phlox be trimmed? If so, how often, when and how much? (e-mail reference)

A: Trim it back after it has finished flowering and give it a shot of Miracle-Gro or a similar product. It can be done annually, but it is not needed. I would suggest doing it when the plants start to get that ragged look that you describe.

Q: I accidentally sprayed portions of my large, beautiful phlox with Weed-B-Gone. The entire plant is not dead, but the large center area is brown and appears to be dead. I have tried saturating the plant with water once a week. It has been 2 1/2 weeks and I am worried that I will have to replace the whole plant. It's beautiful and has been growing for four years. Can you recommend anything to save the plant? Will it come back next year? (e-mail reference)

A: The only answer I can give you is to wait and see. Once the herbicide has been absorbed by the plant, very little can be done to reverse the action.

Q: I have a creeping phlox that I planted last year. It was blooming last year, but this year everyone else’s phlox is in bloom except mine. Do rabbits eat phlox? I read that phlox is not a rabbit’s favorite food. (e-mail reference)

A: Rabbits like creeping phlox like teens enjoy pizza! Spray the plants with a rabbit repellent, such as Hinder, Liquid Fence, Plantskydd or pepper spray (capsaicin). Reapply on new growth as it emerges or after a heavy rain.

Q: Which perennials should be cut to ground level in the fall? Specifically tall yarrow, purple coneflower, mums, and garden phlox. (E-mail reference)

A: The guidelines depend on where you live. In North Dakota, we like to let perennials remain with the flower stalks to help trap snow. Cut them back in the spring before new growth begins. I suppose in the more southern regions of the country trapping snow is not a concern while a neat looking perennial flower bed is, so cutting back in the fall would be appropriate.

Q: I planted orange perfection phlox last spring in the back of my garden because the tag said it would grow 3 to 4 feet tall. It's blooming now but it's only about 18 inches tall so it's sort of hidden. Should I transplant it to the front of the garden? When would be a good time to do that? And if not, do you think it will grow taller? (Moorhead, Minn.)

A: You might want to wait another year. Sometimes it takes a couple of years for herbaceous plants to reach their full potential height. If it isn't up to height expectations by this time next year, then move it the following spring.

Q: Is there a cheap household way to treat flowers that develop fungus? I'm having problems with geraniums and summer phlox. Someone mentioned baking soda, but I don't know how much to add per gallon. I suppose I could buy a well known fungicide and have it for next summer. (E-mail reference)

A: Sorry, but I don't know of a baking soda cure. I would recommend the use of an organic fungicide such as Safer Fungicide and Miticide. Another one on the market containing Neem, another organic, is Schultz Expert Gardener Fungicide 3. It is a miticide, fungicide, and insecticide. All fungicides work better as preventatives than as cures.

A. First, be sure it is getting plenty of sun--at least four to six hours of direct sunlight. Then try fertilization with Miracle-Gro. We use it once a month on our plots to maintain vigor and bloom-ability through the growing season. If it doesn't show any flowers next year, dump it and start over.

Q. The leaves on my phlox are turning yellow and drying up all the way to the stem. What is wrong with it, and how do I treat it? (McLaughlin, S.D.)

A. Phlox are subject to a number of what I call "high humidity" diseases—powdery and downy mildew, leaf spots and stem blights.

Control these diseases by cutting back the frosted stems this fall and removing them. As new growth emerges next spring, keep a wary eye out for any development of the mildew and dust with sulfur or other appropriate fungicide. Sometimes increasing the spacing between the plants helps cut down on the spread of the disease, along with a reduction in overhead watering.

Q. What causes the whitish spots on my lilac bushes and my phlox? (Fargo, N.D., e-mail)

A. The white cast, or spots, on your lilacs and phlox are from a topical fungus known as powdery mildew. This is generally not a serious enough problem to be concerned with. These two species are especially prone to this fungus, which shows up in late summer or early fall, when the humidity is especially high, along with the temperatures.

Simply clean up the leaves, and if you wish, spray the foliage next season with a fungicide to inhibit the development of the mildew.

Q. I have phlox plants that just don't bloom. They are quite thick and I plan to thin them this fall. Would this help? Also, when is the best time to transplant lilies and mums? (LaMoure, N.D.)

A. Definitely thinning would help the phlox bloom. Wait until several frosts have hit them.

I have transplanted lilies any time the spirit has moved me when the soil isn't frozen or the mosquitos too thick. Mums can be moved anytime as well. Many people will have a "mum garden" where they grow them during the early summer, then move them where they want for show around the time they come into bloom. Just make sure the site is in full sun.

Q. I've not written to you before, but I turn to your column before any other on Fridays when the Farmers' Forum arrives. May I ask a few questions, please?

(1) Do small evergreens like lots of water? I bought two small (about 1 foot high) bushes earlier this summer. I delayed transplanting the bushes, but they seemed to thrive and then suddenly both died. Someone told me I need to use Miracid on evergreens, but perhaps I bought the product too late. I did water the bushes a lot.

(2) I wonder why my 15- to 18-year old Bridal Wreath died back to the ground. It is a foundation planting and was huge and gorgeous until three years ago, when branches began to die. All branches are now dead, but new growth is coming from the ground. Should I use Miracid?

(3) My beautiful 12-year-old white old-fashioned lilac bush (about 9 feet tall) is dying. Several large branches have leaves that are totally withered and brown. I began to notice the withering about Aug. 1. Might I have overwatered?

(4) My dogwood bush looks rather sick, too. The leaves have strange spots on them.

(5) I have an old (about 25 years) phlox that flourished and produced beautiful rose-colored flowers until about four years ago. Now, it begins with green sprouts (in the spring) but fairly quickly the stacks become brown and shriveled. It does not get much sun.

I would appreciate any suggestions you might make. I'mhopeful you will continue your column. (Fargo, N.D.)

A. Oh, brother! Your questions could launch a thesis! I'll do my best to provide you with direct, accurate answers based on what you have told me.

1.Evergreens do not do well under continuously wet conditions. They are generally upland plants, able to survive extended waterless periods. You most likely killed them with too much kindness.

2, 3, & 4. Spireas should be pruned each spring to remove the oldest woody canes; lilacs are hosts to borers and scale insects, and at least a half dozen fungal diseases, any of which could be causing the symptoms you describe. Ditto for the dogwood.

5. A phlox plant that is 25 years old? That has to be a world record! Dig and divide, reset in sunny locations. I am surprised powdery mildew and spider mites didn't take their toll.

Fertilizing with Miracid or Miracle-Gro certainly won't hurt anything. While it will help plants along, it won't resurrect the dead ones. Thanks for writing and for the nice comments.

Q: I have had two different garden phlox that I have tried in five different spots (full sun) over the past 10 years and still have not had any luck in getting it to bloom. I have tried Miracle Grow and thinning the stems. (E-mail reference, Lisbon, N.D.)

A: I really don't know unless there are some cultural gaps you are missing. Watering -- phlox need to be consistently moist. The old theory of "keep the feet wet, the clothing dry" refers keeping the roots moist but the water off the foliage. Mulching -- all phlox respond well to an organic mulch such as peat moss, compost, or pine needles. Mulch helps control the weeds and keeps the soil moist. Fertilizer -- use a 10-10-10 at time of planting and sprinkle around the plants as new growth emerges in the spring. I would think that your Miracle-Gro would take care of that need. Other than these basic suggestions, I have nothing else to offer you as to why the phlox will not flower.

Back to Flowers Menu
Back to the Hortiscope Table of Contents