Question
I have a container that is morning sun and afternoon shade. I love Geraniums in the old fashion red, but they do not do well in this container. I am stumped this year. What would be yor suggestion? Impatients? I have another question. Hanging Ivy Geraniums under Oak tree. For the past 2 years a black film covers the leaves and Kills the plant. Is this possibly from the Oak?

Answer
Sounds like you are saying your container is not the problem, it's the location of the container. Geraniums are spectacular container/pot plants.  But they need photons.  LOTS of photons.

Your plan to use Impatiens instead is a great idea. They have a different kind of chlorophyll in their leaves, they are made for the shade.  Just make sure you pinch them when they start to get too tall and thin.

Begonias are another option.  They need a little more light than Impatiens, but I think you've got that.  My favorites have bronze leaves with white flowers.  My daughter likes the verdant green leaves with pink flowers.  They would thrive in your container.

As for the black film under your Ivyleaved Geraniums -- "Pelargonium peltatum" to scientists -- you might be dealing with Black Rot, which according to Dr. James Partridge, Assistant Professor of Plant Pathology at Univ. of Nebraska, is a common afflication of this genus:

nu-distance.unl.edu/Homer/disease/hort/Non_woody/GeBacBlt.html

'Leaf symptoms on Ivy Geranium are different from other Geranium types.  Black streaks develop along the veins of newest leaves and spread down the stem.  Leaves also loose their lustre and turn yellow.  Stem Rot symptoms occur when the infection becomes systemic.  This phase of the disease is referred to as Black Rot. Vascular tissue becomes discolored. The exterior stem tissue turns from dull gray to black. Stems shrivel when dry rot ensues.'

Please confirm. If not, I need a more detailed description of where you see these symptoms most and the progression.

If however it does look like Black Rot, here's what I can tell you.

From the information posted by Dr. Partridge, we know we can blame a bacterium, Xanthomonas campestris, for this disease in Ivyleaves and certain other Geraniums.  One or more, perhaps even ALL your Geraniums were carriers when you brought them home, the malevolent microbes waiting for the perfect time to attack.

The perfect time comes with the right temperatures and humidity. Partridge explains:

'The bacterium survives in symptomless stock plants ... and in decomposed plant material. ... Disease development and symptom expression are favored by warm (70 to 80 degrees F) humid conditions.  Latent infections may occur at temperatures below this range.'

Xanthomonas campestris thrives when temps hit 77 to 85 degrees F.  When temps cool, the microbe sticks around, but remains at rest and goes completely dormant when temps hit 50 degrees F or cooler.  That makes it easy to spread by accident.  You may toss dead plants one summer, then buy new ones the next year and use the same Soil and/or container.  Once Xanthomonas has infected a plant, it's there for life.  Inactive, it remains a threat for a year or longer.

Plant Disease references often recommend using Copper to 'control' the disease. Fact is, the Copper won't eradicate it.  And Copper is risky to work with.

Consider that this bacterium needs at least 2 things to survive: (1) Air, and (2) Water.  Also consider that although the particular strain may prefer Geraniums, the population is capable of swiftly evolving with a dominant strain that attacks Impatiens (and Roses, Tomatoes, cruciferous vegetables...). You can run, but you can't hide.

Luckily, there is an awful lot of research being conducted on Xanthomonas campestris because of the economic damage inflicted on growers and farmers by its attacks.  Biological controls are very promising -- and I am a big fan of biocontrol, so this news is exciting for me, too.

Figure that in general, Bacteria and Fungi that cause disease are competing for the same resources.  So there are Fungi out there who want to eradicate Xanthomonas even more than we do. Results of tests of different Yeasts have been encouraging. One scientist noted, 'Yeasts as control agents of plant disease is a strategy with great potential mainly because of their ability to compete for nutrients and colonization sites.

Note that when scientists were measuring the numbers of Yeasts in soil they obtained them from, there were very few of them.  Pesticides used by well meaning farmers to control insects had also destroyed many of the disease-fighting Yeasts.

This happens a lot.

People think they're killing germs, fighting disease, and then some other unexpected disease erupts right behind the old one.  Yeasts are GOOD microbes.  Destroying them is BAD.

In fact, MOST microbes in the soil are in some way beneficial.  Those that are not fighting disease causing microbes, or causing disease themselves, are important to other organisms in the food chain.  Wiping them out is going to make some BAD microbes out there very happy.  Bad as in Xanthomonas.

The bad news is that you can't go out and buy a bottle of something that will kill the Xanthomonas.  Those bacteria are here to stay, unless you go to some extreme measures like bringing in the Center for Disease Control in spacesuits to sterilize your house and garden.

The good news is that you can:

1. Sterilize your soil in the oven before using it again.  If your container is terracotta, sterilize that too.  Let me know if you need instructions.  Change your clothes and wash in hot water; wash hands thoroughly (you know how surgeons scrub? THAT's what I mean by 'thoroughly'. These are REAL bacteria and you do not want a single one infecting another speck of soil.  You'll spread it with your hands and clothing.)

2. Keep soil and container BONE DRY before using again.  If you have to keep this stuff in the garage, put it in a plastic bag; don't let it get snowed on (moisture = GOOD for Xanthomonas).

3. No more chemicals.  You don't need fertilizer on good soil.  You don't need pesticides, fungicides, bacteriocides wiping out your friendly microbes population, setting the stage for more blights to come.  Ignore the advertising.  Use the scientific method.

4. Go out and find a nice organic compost mix.  Use substantial amounts in your container this time.  It probably contains Yeasts and other friendly microbes that will be completely effective against most diseases.  They'll also generate nutrients for your plants.

Finally, consider this: Although it may be murder on your Geraniums, Xanthomonas is not totally evil. It is emerging as an effective weedkiller against the most common Weed in the country, Poa annua aka 'Annual Bluegrass', the bane of Golf Courses coast to coast.

The world is a funny place.  The garden is full of surprises.  Science marches on.

Thank you for writing.

THE LONG ISLAND GARDENER