When a garden is slimy and mildewed, move the air and
change the watering
Mold is taking over! I have a number of patches in our
mulched areas that are light yellow and turn to dark brown. By
early September my plants were turning white in the leaves and
looked bad. What caused this and how can I help?
- L.W. -
You're looking at two separate problems.
The mold is slime mold, a mulch decomposer that sometimes has
enough energy to "bloom" yellow. It's harmless except when large
enough to lap over ground-hugging plants during hot weather,
killing the covered foliage. You can't get rid of it except by
removing all mulch, which is not a good move for the garden
Slime mold is most likely to occur in thick wood or bark mulch,
and isn't seen where other soil microorganisms are working well
enough to decompose mulch within a year. So don't keep piling on
mulch if you use wood that persists from one year to the next, and
switch where you can to finer-particle, quicker-decomposing
materials like fall leaves.
Your whitened plants are probably infected with powdery mildew,
fungal diseases that disfigure but rarely kill. Mildews were not
prevalent during the hottest part of the drought but began to crop
up once temperatures dropped and we got a bit of rain.
Some plants including zinnia, tall phlox, bee balm, and lilac
are simply prone to mildew. They don't "give it" to each other,
however. Each plant species is prey to its own fungus species. We
simply see the same symptom on different plants.
When mildew is prevalent among several species, we look to poor
air circulation and watering problems as the real culprits.
Where air doesn't circulate well, mildew spores have more time
to grow and take hold on a leaf. Poor air circulation can be a
whole-neighborhood problem -- cleansing breezes are more likely on
hilltops and in meadows than in low lying areas and woods. However,
you can have dead spots in a yard near solid fences and thick plant
growth. Pruning to thin overgrowth can help, as can replacing solid
fencing with airier structures.
Some species, such as zinnia, are more prone to mildew if their
leaves stay moist for long periods. Other species, like bee balm,
are more susceptible when grown too dry. Reduce mildew by
rearranging a garden to group plants by their varying water needs,
then irrigating more carefully. Replacing what you already have
with disease-resistant varieties is also a good move -- throw out
'Starfire' phlox and plant 'Franz Schubert' instead. Research
plants in garden encyclopedias and on the Internet before you buy,
to learn the disease resistant types in each species.
Winterizing a water garden...
... revolves around keeping fall debris out of the water. The
less organic material there is in an ice-covered pond, the less
decay and more oxygen there will be to keep fish and plants in good
Cut back water plants and put that foliage on the compost. Keep
fall leaves skimmed off a pond's surface or stretch a
leaf-collecting net above the water.
Stop feeding fish. They can't even digest food once temperatures
drop to the 40's. Clean your filters. Make a commitment to keep an
opening in the ice or divert the flow of water from your pump to a
bubbler to keep oxygen levels up.
You washed plants before you brought them in for
...and that's good. A thorough cleansing of the foliage and pot
is more effective than an insecticide for fending off unwanted
houseguests. Yet neither approach is enough in itself if the plant
is prone to pest trouble.
Some insects or eggs always escape either sudsy soak and rinse
or toxic spray. These pests rebound within the first weeks, at the
same time your plants' natural defenses are down while they're
adapting to lower light.
A pest's presence may not be noticeable until it reaches crisis
levels in mid-winter. So for this first month back indoors, move
plants into the shower every week or ten days to rinse them with a
forceful stream of water. This sends pesty survivors and newly
hatched insects down the drain.
Green thumbs up
to those who aren't fooled by surface appearances and so
continue to water important plants. The soil may have lost its
crusty appearance and cool weather persuades us to think the
drought passed along with the heat, but below the top inch the
ground is still bone-dry in many places. Keep trickling the hose
under key trees and shrubs until fall leaf drop finishes.
Green thumbs down
to giving up on any shrub, tree or long-lived perennial after
just one disappointing season. Take a lesson from the Detroit
Lions' football fans! But don't go too far in that direction. If
one year of skimpy growth or lackluster bloom follows another,
don't hope for magic. Continuing lackluster performance calls for
major change, such as a move to better growing conditions.
Originally published 10/12/02