November 1996 - Indiana Yard and Garden - Purdue Consumer Horticulture

November 1996

Q. I would like to know why my garden phlox gets this white flaky substance on the stems and leaves. I’ve put different dusts and sprays on them. Nothing helps. I keep thinking every year it will go away, but it always comes back. Should I dig them up and plant new plants? They are only 3 or 4 years old, so I don’t want to do that if I don’t need to. The flowers are nice. – Marjorie Leaders, Hudson, Ind.

A. Tall phlox is susceptible to a white powdery covering on the leaves called powdery mildew. It is most severe where air circulation is restricted and humidity and moisture is abundant. To increase air circulation, plant phlox where a breeze can reach them, allow ample space around each plant, and pinch out one-third of the stems as they come up in the spring. Reduce moisture by avoiding overhead watering. Finally, clean up all plant debris from the garden in the fall to reduce reinfection next year.

Newer cultivars of phlox are bred to be resistant to powdery mildew. Look for resistant cultivars, including ‘David,’ ‘Alpha,’ ‘Miss Lingard,’ ‘Omega,’ and ‘Rosalinde.’

Q. In addition to your recent response about peony blight, a friend of mine told me that ants are necessary for peonies to bloom. She said peonies have a sticky coating that ants must eat away before the bloom can open. She had an elderly neighbor that sprayed to kill the ants, so she had to go collect some ants for her neighbor’s peonies.

I checked mine this summer and, sure enough, there were ants on the buds before they opened. So just in case it isn’t botrytis blight… – K. Lingafelter, Zionsville, Ind.

A. This is a popular garden myth, but it isn’t true! The ants neither harm nor help the peony. They eat the sweet secretion from the buds, but it doesn’t affect the bloom. You’re right – the ants are almost always present, but they’re minding their own business.

Q. I’m writing for an answer on why my snowball bush (Viburnum) doesn’t bloom. It is about as tall as I am, at least 5 years old, and it has bushed out well, but never has bloomed.

I purchased one of the same for my neighbor and my daughter at the same place, same year, and none of them have bloomed. It couldn’t be soil, as all three are at different locations. Can you help me on this? Also, I have a 5-year-old blue hydrangea that has never bloomed. – Mrs. Keith Spurr, Greencastle, Ind.

A. Several factors can affect flowering, but it is odd that they wouldn’t bloom in three different locations. Are you all trimming the flower buds off? Viburnums flower from buds that formed the previous year. Prune only in late spring, after other viburnums in the neighborhood have finished flowering. Most viburnum species, including the common snowball, require full sun to blossom and fruit. My final guess would be excess nitrogen fertilizer. Too much nitrogen promotes leafy growth at the expense of flowers.

The hydrangea is easier to figure out. The bigleaf hydrangea is a popular florist plant, but it is not reliably hardy beyond Zone 7. The roots overwinter each year, but the tops are killed back to the ground. This causes a problem, since flowers are produced on the previous year’s growth. Other hydrangea cultivars are more reliable, including Hydrangea arborescens ‘Annabelle’ and ‘Grandiflora;’ H. paniculata ‘Grandiflora,’ called the PeeGee hydrangea; and H. quercifolia, the oakleaf hydrangea.

Q. We have moved into an old farmhouse. The man who lived here before us evidently loved flowers. My problem is a hibiscus bush that comes up every year, has nice big green leaves, but never blooms. It gets plenty of sun, so that’s not it. There was another bush way in the backyard that was destroyed putting in a pole barn. It had no blooms either. I wonder if I need two bushes, or is there something in the soil it might miss? – Nancy Campbell, Bloomfield, Ind.

A. Hibiscus blooms on new wood (formed in the current growing season), so overwintering is not a factor. Since you’ve ruled out sun, and the plant does not require two plants to flower, that only leaves improper pruning or fertilizing as I mentioned above. Pruning in late spring or early summer would remove the blossoms we expect in July or August. Again, excess nitrogen, whether intended for the surrounding lawn or for the shrub, will give you a nice, green bush with no flowers.

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