Alkaline Soil May Be at Root of Princess Plant’s Problems
Question: I would like to have any suggestions for my princess plant. It appears it does not grow, although it has some flowers. What are its food and watering needs?
--N.P., Tarzana
Answer: The princess flower, or Tibouchina urvilleana, has simple needs. This Brazilian shrub likes ordinary watering, warmth and prefers to be kept out of constant or strong breezes.
Tibouchinas also like a slightly acid soil, and this may be the problem if you garden in a highly alkaline soil. Alkaline soils reduce the availability of some nutrients necessary for growth. Tibouchinas normally grow to become lanky shrubs 10 to 18 feet tall.
It’s difficult to quickly change the pH of a soil (the measure of alkalinity or acidity), but you can do it over time. Start by mulching the soil with acidic materials such as pine needles or redwood composts (soil amendments). Working gypsum and soil sulfur into the soil will also help; follow label directions.
When you fertilize, use an acidic fertilizer, a category that is usually mentioned on the label. Fertilize in spring and then lightly after each cycle of bloom. Once the plant starts to grow, it’s a good idea to pinch the new growth to force the plant to branch and become more bushy. Prune it more heavily each spring.
Another option might be to replant the tibouchina in a raised bed or mound where the soil has been heavily amended with acidic materials. This is a good time of year to dig up plants and move them, as long as they haven’t grown too big.
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Q: I bought a plant at a swap meet called yesterday-today-and-tomorrow. It was in bloom but hasn’t flowered since. Help!
--F.B., Los Angeles
A: Like many shrubs, Brunsfelsia pauciflora ‘Floribunda’ blooms once a year, in spring and early summer. In colder areas it may even lose most of its leaves in winter.
You bought a good plant, however, that is not used enough in gardens. It blooms along with late camellias. The bush looks similar and likes similar conditions--some shade, moisture and a slightly acid soil. In time it makes a 10-foot-tall shrub, usually taller than it is wide, with handsome, glossy leaves.
The name comes from the way the flowers change color after they open, starting out purple, then changing to lavender and finally to white, although there are other kinds of brunsfelsias. Wait until spring, and it will bloom.
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Q: I have a 1-year-old brugsmansia (angel’s trumpet) in a large outdoor container that is afflicted with white flies to the point that the leaves are yellowing and dropping. Is there some kind of systemic soil drench that might work, and is there a risk that the infestation might spread to a big brugsmansia in the ground nearby?
--L.C., Santa Monica
A: I’m not a fan of systemic poisons, but you can check at the nursery and see whether one is labeled for ornamental shrubs other than roses. In my experience, there’s no sure-fire organic control or poison for whiteflies, although there are lots of things in the garden that eat them, from lacewings to ladybugs.
You can try hanging yellow sticky cards (available at better nurseries) on the plant, but stay away from poisons since they tend to aggravate the problem. Whiteflies quickly become tolerant of poisons. In the meantime, you’re also killing the predators.
The fact that there is a big, healthy brugsmansia nearby should give you a clue that the plant’s problems have to do with it being grown in a container. Otherwise, the whiteflies would be all over the other one as well. The whiteflies are probably picking on it because something else is wrong.
It might be “overpotted,” which means it’s been put in a container too large for the rootball. In pots that are too big, the soil tends to stay wet too long since there are not enough roots to remove the excess water. This leads to roots rotting, which can cause leaves to yellow and fall off.
Generally you want to increase the size of the container gradually, a couple of inches at a time. If you start with a plant in a gallon nursery can, it should go into a pot about 2 inches wider and a little deeper. After it fills this pot, move it again to a larger container and so on.
The plant could also need fertilizing. While fertilizer is seldom the solution to problems with plants growing in the ground, container-bound plants (at least those growing outdoors) frequently suffer from malnutrition. They are completely dependent on the gardener for food, because there is little built-in nutrition in the artificial potting soil.
If the plant is not growing in too large a pot, try fertilizing every two weeks with half-strength fertilizer, or at least once a month with full-strength and see whether the whiteflies move on. Watering container plants constantly washes away fertilizers, so they must be replaced on a regular basis.
Use a liquid, or the kind you mix into a liquid. Or try timed-release kinds, which slowly dissolve and fertilize every time you water. They need to be reapplied much less often.
