In article , "Anonny Moose"
wrote:

A few of my rhododendrons' leaves are showing a loss of color this winter.
They look almost white with green speckling. Anyone know what this is and
what I can do for it?

Thanks.

Karen
portland, or

When SPOTS appear on leaves in winter, it can be any number of problems
causing ill health to the root system -- such as borers or fungus -- &
winter spottiness is just the first sign of worse to come. But if the
whole leaf is just fading to yellow between the leaf-veins, the shrub is
chlorotic, which is repairable. This happens to all plants that prefer
acidic soil that end up in poor or alkaline soil. Some people induce the
problem if they add fireplace ashes to gardens, believing this is
beneficial when it can be very harmful to rhodies, roses, blueberries,
apple & cherry trees, by alkalinizing soil. If you've gone the "ashes are
good" route then you've injured the soil for rhodies. If that is the
case, rain & waterings will eventually wash out the alkalinity, unless
your local soils are naturally alkaline, then it's going to be a recurring
harrassment to ammend soils to acidic conditions unnatural for your area.

Over fertilizing or the wrong fertilizer can also cause chlorotic
conditions by interferring with rhodies' capacity to take in iron. Heavy
feeding of phosphorus intefers with iron uptake even if the iron quantity
in the soil is sufficient. Run-off from newly laid concrete or cement, OR
unstable deteriorating old cement, can alkalinize the immediate area
(stable well-cured cement is NOT a problem though). If you lime a nearby
lawn, this can leech into areas of woody shrubs, damaging the soil for
many perennials & shrubs & fruit trees -- what's good for lawns is not
always good for much else, so take care not to lime lawns too near
gardened areas.

The usual "fix" is sulfer or iron sulfate. This assumes the soil does have
iron in it but that alkalinity or other factor hinders uptake of iron. A
mere tablespoon of sulfer in the soil around the base of each shrub will
help it take in the iron it needs. If there's something continuously
keeping the area to the alkaline side of the pH scale, it will need a tiny
bit of sulfer EVERY spring. But this is a compensating method, not a real
restoration if the soil has been alkalinized. A great amount of peat
worked into the soil & heavy topcoatings of leafmold & composted manure
will help acidify the soil itself & increase plant health. Be VERY careful
with fertilizers that shoudl be low in nitrogen & low in phosphorus; until
alkalinity can be reduced, no amount of even a properly balanced
rhody/azalea fertilizer will help, because the problem is that the shrub
cannot take in iron when soil is limey.

Very rarely excessively acidic soil is the culprit, as even acid-loving
plants such as rhodies want only moderate acidity. In such a case a little
lime actually helps rather than increases the problem. So you need to know
your specific pH conditions before knowing which action to take, as lime
will increase the problem if the soil is alkaline, & help the problem if
the soil is super-acidic.

Though naturally alkaline soil or soil damaged by excesses of phosphorus
or lime or ashes are commonest culptrits, sometimes the soil is fine &
some other thing causes chlorosis, but the other causes would usually mean
the shrub did not do well for a few years before began to show stress, but
always struggled in the given location. Compacted, poorly draining,
clayey, over wet soil destroys a rhody's capacity to take in iron, as does
being planted too deep (their roots must remain "in the shallow." These
conditions usually cause root stress & disease or attract insect damage
the first sign of which will be either winter spottiness OR chlorosis. A
greater amount of peat or other organic material in the ENTIRE garden,
well-loosened for better aeration.

If soil is literally iron deficient or magnesium depleted, this can be
narrowly resotred. A feeding of liquid chelated iron according to product
directions will be the proper fix or iron deficiency. For magnesium
depletion, a high-magnesium low-nitrogen evergreen fertilizer, or just
epsom salts (magnesium sulfate) will fix that. Some recommend a
combination chelated iron with magnesium sulfate together as kind of
broad-spectrum approach. But tinkering with soil chemistry repeatedly will
in the long run do more harm than good & the original cause of the problem
should not be permitted to continue, so that organically rich slightly
acidic soils remain in prime condition by means of healthful annual
topcoatings of leafmold or manure compost. Without knowing the soil
conditions beforehand, & without knowing why the soil went wonky if it was
previously just fine, any action you take could turn out to be wrong.
You'll know fast if the action you take was helpful, as it takes only
about two weeks to begin turning back to green.

-paghat the ratgirl

--
"Of what are you afraid, my child?" inquired the kindly teacher.
"Oh, sir! The flowers, they are wild," replied the timid creature.
-from Peter Newell's "Wild Flowers"
See the Garden of Paghat the Ratgirl: http://www.paghat.com/