UPDATE: The book winners are Laura Bell, Leslie, and Heather. Congratulations!
Here is the final installment of plant docs Kathryn Wadsworth’s and David Deardorff’s diagnoses of Rant reader plant problems. It’s been fun and fascinating! I’ll be giving away 3 copies of What’s Wrong With My Plant? to those who submitted or commented later today.
The Plant Doctors Report, III
in Pennsylvania, sent photos of grayish-green “fungus”-looking stuff growing on
azaleas, dogwood and mountain laurel. She first noticed it on one of her
dogwood trees that died over the winter.
The “fungus”-looking growths you’re seeing are lichens. They
do no harm to plants. They are epiphytes, like tropical orchids and bromeliads,
which use trees and shrubs for a perch to sit on. Epiphytes do not parasitize
their hosts because they don’t steal nutrients from them.
Symbiotic organisms, lichens consist of a fungus and an
alga, two very different organisms, which live together harmoniously. Very
sensitive to air pollution, lichens prove very useful as air quality
indicators. Their presence suggests you enjoy excellent air quality in your
in Davis California, has a Meyer lemon that’s been growing in a pot for perhaps
six years. For the last few years it hasn’t been as happy as it used to be. It
isn’t healthy looking, the leaves get mottled with yellow, and there isn’t much
new growth. Very few flowers so far this year.
It was repotted
two years ago with fresh potting soil and it gets organic citrus fertilizer
every so often. It gets ample sunlight and Leslie is careful about watering. In
the winter it gets dressed up with piazza lights to ward off frost.
First, I’m wondering about the pH of your water source
because your tree shows some signs of micronutrient deficiencies. Citrus need
iron, zinc, manganese, and magnesium in larger quantities than many other
plants. These micronutrients can become unavailable to your plant as the pH of
the soil goes up. If you water with tap water, and if you have hard water with
a lot of calcium in it you may be raising the pH (making it more alkaline).
Your organic citrus fertilizer should be formulated at the right pH, and should
also have the proper micronutrients in it. But it’s possible that your water is
making those nutrients unavailable to your plant. Try flushing the pot out by
pouring a couple gallons of pure drinking water from your grocery store into it
and letting it drain away. Follow up with a couple doses of coffee grounds to
acidify the soil.
If you do not have hard water and you’re certain the pH of
the soil in the pot is okay, then the next thing I wonder about is watering
practices. The soil should be moist, not wet, and on the dry side of moist. I
know you’re careful about watering, but only water once a week and never let
the pot sit in a saucer full of water. Citrus do not like to have wet feet and
the symptoms frequently mimic the symptoms of nutrient deficiencies.
Ann Newcomer has Otto laurels “all chewed to crap by the damn vine weevil” (the
Otto laurel is Prunus laurocerasus ‘Otto Luyken’). And, as if that weren’t
enough to pull your hair out by the roots, now the leaves are half brown, half
green, and one shrub isn’t worth keeping even though it’s covered with buds.
Mary Ann is, quite understandably, cranky.
The half brown/half green leaves I see in your photos
suggest a serious interruption of the flow of water from the roots to the
leaves which could be due to a large number of different causes. However, since
we know you are plagued by vine weevils, dig up part of the root system and
look for white grubs eating the roots. If the grubs have brown heads and lack
three pairs of jointed legs they’re vine weevil babies. Because the adult vine
weevils devastated the foliage above ground it’s highly likely that their
babies (which live in the soil and eat plant roots) are causing the water
uptake problem by destroying Otto’s root system.
Vine weevil adults hide in the soil during the daytime, and
then come out at night to ruin your plants. The grubs stay in the soil until
they mature. You can nail these little buggers with an application of
beneficial nematodes which, like smart missiles, seek out and destroy all the
vine weevil adults hiding in the dirt as well as their offspring. Harmless to
humans, pets, birds, bees or butterflies, these microscopic little worms only
parasitize soil dwelling insects.
Thanks again, plant docs. We hope you’ll be visiting again.