Is it a new plant? Did you fertilize it in the last few days? What about over-watering? Are the leaves touching the metal? What color is the metal? It could be the car, but eliminate the other cultural possibilities first.

Al

Most likely not the car....but lack of water.....
Put the pot into a larger pot made of clay and fill the space between with damp sphagnum moss.....keep the moss damp ( water the plant when it needs it as well!) and that will keep the roots cool.
But fertilizer will burn a potted plant, and a plant newly placed in the hot sun may scorch.....and also under watering as well as over watering.
Sounds cute!
Linda C

It is a new plant. Beautiful and thriving at the nursery, of course. It was in full afternoon sun, as it is at my place. I haven't fertilized it, though I don't know if it had been recently.

How do I know if I'm overwatering? If the soil feels dry, I add water, right?

The little car is red, and the leaves touching metal aren't the dead ones. I will try the moss trick. I would love it if it isn't the car.

Where I was headed when I said it could be the car is root temperatures, but I wanted to eliminate other possible causes first. Most plants start shutting down in the root function dept. when actual root temperatures hit somewhere around 95* F. The cache pot suggestion is a good one & gravel can be used with the same effect.

Watering at midday, when pot temps are highest is a good way to cool down roots. Watering the cache pot in the AM, and then watering both the cache pot & the main pot (if it needs watering) in PM, is a good plan. If the pot isn't shaded, a light color (white, pastel) will go a long way toward decreasing heat from solar gain, too.

Al

In a pot with a hole in the bottom and potting soil it is just about impossible to over water a geranium in full sun.
You can water until water runs out the bottom 3 times a day....just make sure it drains.
And add water before the soil feels dry! In full hot west zone 8 California sun, the difference between just dry and stressed out is very small.
Linda C

Linda & I seem to fall at odds about watering containers properly. I'll offer up my thoughts for any reader's consideration, & listen in for any additional comment or conversation pertinant to Marcelli's thread.

It's extremely easy to over-water any plant in a container, especially when temperatures are high. In addition, there are too many variables to take into account to allow offering specific advice w/o all the info necessary to make informed decisions. Two important considerations are the size of the container in relationship to the degree roots have colonized the soil (size of plant), and the speed (aeration/drainage) of the soil. A gas permeable container (terra-cotta) also would need to be factored into the equation as would other variables like location (sun/shade), air movement, etc. Watering many containers, even with what many consider to be "good" commercially available soils, three times per day if the plant does not need additional water can easily become a death sentence via Phytophthora, Rhizoctonia and/or Pythium infections. That water drains from the drainage hole is inconsequential in determining the level of saturation in container soils. I'm suggesting that it is dangerous to prescribe watering three times daily without knowledge of the above mentioned conditions.

Plants do not sip or drink water like we do. Water in liquid form (as in droplets or water occupying soil macro-pores) actually slows water absorption by roots. (Complicated, but I'll explain if you like) Plants absorb moisture molecule by molecule from a microscopic coating of water on soil particles. Even when soil appears completely dry, if the plant is not wilted there is still enough water on the surface of soil particles to satisfy hydration requirements.

Actually, from a plant health perspective, the best time to water is at the first signs of the onset of wilt, but since for most that's a little too chancy to be comfortable with, it's better practical advice to say "It's best to water after you allow the soil to become very dry, but before the plant wilts". (I'm not saying this is true for all plants, but it is for at least 90% of what readers here grow in containers - probably more.)

In a bonsai workshop with a Japanese master (Ben Oki), one of the participants asked a question, pertinant to this discussion - "How often should I water my ...?" His (Mr. Oki's) expression never changed at all as he answered, "Wait until plant become completely dry - then water it the day before." To this day, I'm not sure if he was serious or it was his brand of humor, but the advice is sound for most plant material.

Overwatering in the hopes of keeping soil cool is just roulette. As noted above, saturated soils + heat is a perfect environment for any number of root rot fungi. If roots need to be cooled, excessive watering is not the answer. Any container gardener's number one priority (that's #1) should be to insure soils are properly aerated for the life of the planting or from repot to repot. Without aeration, land plants will not live & the possibility of those plants growing at anything close to potential genetic vigor is as closely dependant on aeration as it is on water, sunlight, or nutrients. We can control the water, sunlight, and nutrients in container culture with ease, but doing anything to alter aeration after the container is planted is a difficult task, indeed.

Al

I still maintain that a plant....in POTTING SOIL which assumes it's light and drains well.....in A POT WITH A HOLE is almost impossible to over water.
Remember we are not about keeping plants in a dwarfed state here.....we are aiming for full and lush growth.
Yep....I know the physics and biology or roots taking up water......but I also know that different plants with different leaf strructures transpire more moisture than others...and a plant that is large for the pot will need more water than another.
I say don't make it difficult.....water the geranium every day....twice when it's hot and windy!
No wonder people are nervous gardeners.....just put the roots in the soil and water it. It's a freakin' geranium for heaven sake....not a 100 year old bonsai.
Linda C

What I said has nothing to do with bonsai. 95% of the plants I have growing in containers are just that - plants, not bonsai. It's just good practice to water when a plant requires it & not x number of times per day, simply because it's hot out. I noticed you reduced your prescription to "once, or twice a day when it's hot and windy". That still may or not be appropriate, depending on how much water the soil holds.

Many, many potting soils that are said to be premium soils drain far too slowly for use in any container w/o substantial amendment.

You say, "... don't make it difficult.....water the geranium every day....twice when it's hot and windy!" I say, " Never disadvantage your plant(s) by watering on a schedule. Water when they need water & they'll reward you with healthy roots & more vigorous growth." This isn't just a fine point, or splitting hairs. It's a very important aspect in a container gardener's search for methods that yield vigorous plants in containers.

It might be good for beginning container gardeners to be nervous - it indicates they're paying attention. I think I would prefer a little "nervousness" to "complacent and without a clue" as to what's happening in containers. Of those two groups, the nervous ones are going to be better gardeners in the end because they care & want to succeed.

BTW I noticed you started making assumptions about potting soil - "which assumes it's light and drains well". That information isn't provided & it's best not to assume it to be true when giving one size fits all advice. In talks/demonstrations about container soils, I use "straight from the bag" potting soil to illustrate just how poor some potting soils can be. Some border on impossible to grow in because of the huge amounts of water they hold.

Al

I live in Spain -- roughly zone 8 -- and wish to landscape my terrace-deck with suitable container planting. However, the deck hardly receives any shade at all. Can you recommend some good-coverage, hardy plants, shrubs and trees that will tolerate up to 26f in winter and 100f in summer? I bought a Monterey Cypress (about 9 feet tall) which I've put in a 2ft pot. Does anyone know whether they burn easily in hot, summer sun?

Quote: "I still maintain that a plant....in POTTING SOIL which assumes it's light and drains well.....in A POT WITH A HOLE is almost impossible to over water."

LindaC- You've never grown geraniums before have you? they flower the best when you allow the soil to get so dry it pulls away from the sides of the pot.

while your oppinions are as valid as anyones here, i believe you are mistaken in what you are talking about and anyone with experience growing potted plants will agree with me that over watering is far more harmful then underwatering.