Bring us your fungus, your weevils, and your growths—the plant docs are still here


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

8. Dawn,
in Pennsylvania, sent photos of grayish-green “fungus”-looking stuff growing on
, 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

9. Leslie,
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.

10. Mary
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.

Previous articleAquaponics in Buffalo: update
Next article2010: Are the Gods Smiling?
Elizabeth Licata

Elizabeth Licata has been a regular writer for  Garden Rant since 2007, after contributing a guest rant about the overuse of American flags in front gardens. She lives and gardens in Buffalo, N.Y., which, far from the frozen wasteland many assume it to be, is a lush paradise of gardens, historic architecture, galleries, museums, theaters, and fun. As editor of Buffalo Spree magazine,  Licata helps keep Western New Yorkers apprised about what is happening in their region. She is also a freelance writer and art curator, who’s been published in Fine Gardening, Horticulture, ArtNews, Art in America, the Village Voice, and many other publications. She does regularly radio segments for the local NPR affiliate, WBFO.

Licata is involved with Garden Walk Buffalo, the largest free garden tour in the US and possibly the world,and has written the text for a book about Garden Walk. She has also written and edited several art-related books. Contact Elizabeth: ealicata at


  1. Great advice. I was not familiar with what lichens really are…just love seeing them on the tree. I will look at them a bit different now.


  2. I’m so excited because I DO have hard water! I will be following doctor’s order immediately…thank you so much. And thanks to you Elizabeth for hosting this event!

  3. Lichens are nice, especially on stones. But on plants they indicate not just good air quality, but slow growth as well. A shrub or tree growing at a healthy pace is growing too fast for lichens to get a foothold. From the description the azaleas may be in dryer conditions than they like, so they are growing slowly enough for the lichens to get a grip and hold it. True, they aren’t a problem, but they do indicate a problem.

    As for the citrus, I have a small grove of potted citrus and got tired of repotting them, so I figured out a way to root prune, aerate and deep fertilize with organic fertilizer by using my soil probe I bought during my days as an organic farmer in the 80’s.

    You can read about it by clicking on the Citrus category at my new blog–

    Why the name? Because it’s easier to enjoy your garden if you’re not enslaved by it.

    Frank Hyman

  4. Citrus is pretty notorious (at least around here in Seattle) about getting infested with Spider Mites all winter long. They get stippling like in your picture. They lose a bunch of vigor every winter, until they either grow back in spring when the mites find better things to chew on, or else they eventually perish (or at least my grapefruit did… but the single grapefruit was delicious.)

    You might try spraying them down with water every other day – mites don’t like the humidity.

  5. I had considered sending in shots of my Meyer lemon, but since I didn’t, I’m really glad Leslie did. I live somewhat close to her & have the same situation – will work on correcting the hard water problem right away. Thanks !

  6. Thank you for identifying my lichen (a couple people also commented about them on my blog post). It’s good to know they aren’t a problem.

    We have had dryer conditions over the past year in my area of PA and this year doesn’t look like it will be much different so I can see how that could contribute to the lichens growing.

Comments are closed.