Question
Hello, LIG!

First, let me say you've painted a wonderful picture in your profile.  Congratulations on your creativity and passion!

One of my own passions is the traditional red geranium.  I've never heard of this problem from anyone else, but one recurring problem I have is the tiny petals that make up the buds not all opening at the same time.  They appear healthy, but they don't seem to ever bloom as one big cluster...  One by one they open, and one by one they die off with no eagerly awaited show of spectacular color.

I let the soil get dry to the touch before watering, and then I will water til it runs out the bottom.  I realize that you are in Long Island, but I'm guessing that the rules are probably pretty much the same (?).  These are outdoor plants and I am in northern Texas where they get a mixture of full sun and partial shade -- about a half day of each.  I feed them Miracle Gro about once a week.  They are in plastic pots, as I find the terra cotta ones dry out the soil too fast and get too hot in the Texas heat.

I must be doing something right, because they are loaded with buds right now, and the days have been in the low 100's...  Haven't had the problem yet with these plants, but want to take precautions to prevent it.

Any advice you can give me will sincerely be appreciated!

Nancy

Answer
Hi Nancy - Days in the low hundreds? Holy moly! And it isn't even summer yet.

I assume we are talking about "Pelargonium hortorum", the Geranium called by horticulturalists Zonal Geraniums, typically large red flower heads with scallop-shaped leaves and sometimes a burgundy band across the leaves that are native to South Africa.  I agree, potted Geraniums are most likely the same in Texas as in New York, although growers have developed different strains that look to us identical but better suit the growing conditions, which I guess in Texas means extended periods of extreme heat.

Geranium growing is a major industry in the state of Michigan, which ships them all over the place.

Sounds like you have the watering, light and fertilizing down. Believe it or not, a lot of people can't get past the basics. This sounds like something more unusual.

Botanists say Geraniums prefer a pH of 5.7 to 5.9. I don't think that's your problem. A bad pH would show up as leaf symptoms and you have not mentioned anything wrong with the leaves. But if I'm wrong, please correct me.

Now, under common growing conditions, Nancy, Geraniums are a piece of cake.  But you mentioned your temperature, almost incidentally, and yet, this is an extreme environmental variable that most people rarely deal with.

Temperatures at day and night trigger many plant hormones.  In Geraniums, temperature controls growth and development.

It sets the rate of photosynthesis.  It slows or speeds up respiration.  And it controls flowering.

Geraniums typically set buds anywhere from 45 degrees F to 80 degrees F.  The ideal temperature for optimum growth rate, habit, and flower formation is 70-72癋 day and night. Above 85 degrees F, chlorophyl production stops. Among other things.

And as I said, some cultivars have been developed to withstand extreme heat and these must be growing in Texas.  They do a lot to get branching Geraniums that flower in one big flush, with a 50% open-flowers rate.  

Some cultivars are treated with a growth regulator called ethephon ("Florel") to stimulate branching and create more compact plants.  

Ethephon has several side effects: Smaller leaves.  Very short spaces between nodes. Increased branching.  Disruption of bloom by causing premature fading and dropping of buds and floret petals. Some cultivars are more prone to reactions than others. You probably don't remember the name of your Geranium from the plant tag when you purchased it, but just in case you saved it, I'm asking.  

If ethephon is used close to retail sale, a treated Geranium will still be shedding petals when you take it home. This habit slows down as the chemical slowly leaves the system.  

Let's consider one other possibility: Ethylene.

This is a gas you may have heard of that develops naturally around ripening fruit and as flowers fade.  Zonal Geraniums are some of the most ethylene-sensitive plants we have.  

Geranium flowers during shipping or even when you have them home produce small amounts of ethylene gas as they finish blooming.  This gas accelerates the fading of other blooms and is one reason we remove spent flowers from, say, a blooming Rose bush or a vase of Oriental Lilies.  It is not practical to remove individual florets from a Geranium head, but they do normally produce small amounts of ethylene, and this is not under normal conditions a problem.

But in your case...

Heat is a stressor even for Geraniums.  Your green thumb somehow manages these plants to flower where no other thumb will achieve that.  Exposed to extreme heat, for long periods of time, day and night, most Geraniums just stop flowering altogether.  But not at your house!

So you actually manage to do the impossible, getting a Geranium to bloom under conditions that give new meaning to the term Heat Wave.

At least, to a New Yorker.

But the petals, try as they may, cannot keep up with the task.  They open, burn out, and are "abscised" -- poof!

If no one else is having this problem, maybe it's because you are the only one in the state of Texas who knows how to get a Geranium to bloom on days when you could fry an egg on the sidewalk.

I have to say, I am impressed.  

But I understand, you want this to stop.  You get SO close.  And you're SO far.

So there's one more possibility.  You don't seem to have any other symptoms of this, but just for the record, we'll put it down. Maybe other symptoms will come up and you'll recognize it.  It's something called Botrytis Blight and it comes with high temperatures and, usually, humidity.  

Botrytis is a common fungus.  It lives on dead and dying tissues -- flowers, leaves, injured stems.  Affected flowers turn brown and drop.  Geranium heads are made of many florets; we don't see entire spent heads drop the way a Rose would drop, say, but dropped petals would, like a Rose, still harbor hundreds if not thousands of Botrytis spores waiting for rain or waterdrops to splash and carry spores to another leaf or flower.  

And so, since they depend on wind and rain and people to transfer them to a nice place to grow, control consists of not getting foliage or blossoms wet. This is most important during the evening and when humidity is high. Dropped leaves and petals must be removed.  Hands or instruments that touch diseased plant parts should be cleaned before touching healthy plants and leaves.  

Given your Texas-sized weather, Nancy, you might consider introducing yourself to European Balcony Geraniums.  These were bred in European by growers to take the place of ivy geraniums, which can't tolerate high summer temperatures.  They have smaller, thinner leaves and single flowers. Examples include "Balcons", "Cascades" and "Decoras" strains. You can see some at Wheeler Farm Gardens website (www.wheelerfarmgardens.com/faqs.htm), one of probably many that sell these hybrids.