QUESTION: I have six bathtubs in my back yard, in which I grow onions, tomatoes, fennel, cucumbers and other vegetables. I seem to be getting a lot of growth with my plants, but very few blooms. Am I overfeeding?
ANSWER: Most likely. Anything grown in a container (even a large one like a bathtub) needs regular fertilizing, but too much nitrogen will cause excess growth at the expense of flowers and fruit.
Some people fertilize at first with high nitrogen formulations--fertilizers with numbers such as 10-5-5 on their labels, the 10 being the percent of nitrogen--then switch to "flower and fruit" formulations, such as 0-8-8. These have little or no nitrogen, and are supposed to promote flowering and fruiting, but there is little scientific evidence that they do.
Tests conducted at Cal Poly San Luis Obispo suggest that there is no difference between fertilizing with nitrogen the whole time and fertilizing with nitrogen at first, followed by a no-nitrogen formula. To get more flowers and fruit, continue using a high nitrogen fertilizer, but simply use it less.
Controlling Mildew on Roses Near Trees
Q: Can you identify a rose that was in my garden? It was a Grandiflora, medium pink in color and a prolific bloomer. Also, please suggest a method of controlling powdery mildew that does not pose a problem for nearby fruit trees.
A: Since there are only a few Grandiflora roses, it was probably 'Queen Elizabeth,' the first rose to be called a Grandiflora. As for mildew, Ortho's Funginex is the control recommended by the American Rose Society.
It contains the active ingredient, Triforine, and also controls rust and black spot, two other common rose diseases. It will also control powdery mildew on calendulas, crape myrtles, dahlias, snapdragons and zinnias, which are all susceptible to this seasonal disease, usually seen only in spring and fall.
Since Funginex also has fruit trees on its label it should not harm them, or contaminate the fruit, but it would be wise not to spray once the fruit forms. Fortunately, powdery mildew is usually gone by that time of the year.
Camellia Ailments and Their Treatments
Q: I hope you can help all of us who have camellias that suffer from brown blight. Mine have increasingly shown blight, dropping of buds, sticky blossoms, dried brown buds or even failure to blossom at all.
A: You are actually describing a number of camellia ailments, though most gardeners tend to blame them all on a disease called camellia petal blight. According to Tom Nuccio at Nuccio's Nurseries in Altadena, the dropping of buds can be varietal--some kinds do it, such as 'Pink Perfection,' others don't--or it can be brought on by the weather--Santa Ana winds or rain.
Some camellias will "bullnose." The petals stick together, the bud looks wet and shiny and the flowers don't open. Overhead watering with sprinklers can be a cause, or it may just be the variety or weather.
Dried brown buds can also be varietal or cultural. It usually happens on plants that are not happy with their care or environment. Flowers that turn brown may just be old or getting too much sun. This often happens on plants that have outgrown their shady location and now grow up in the sun.
If the flowers become heavy with water, turn to mush (try rubbing the petal between your fingers) and the veins in the petals become darker than their surroundings, then you have camellia petal blight.
According to Art McCain, a university extension plant pathologist, there really are no sensible chemical controls, despite the fact that some books recommend PCNB, which must be applied to the ground in winter, or benomyl, which must be sprayed on the flowers "nearly every day."
The only control is cultural, and even this is not sure-fire because the mushroom spores can drift in on the wind, but give it a shot: Pick up every camellia blossom that falls to the ground and send them to the dump. The mushrooms that cause this disease sprout from the fallen blossoms. Incidentally, sasanqua camellias do not get petal blight.