Boy I hope this doesn't make me sound dumb, but here it is. I've read about fertilizers, alfalfa tea, ph, and a million other things, but I've missed the answer to this. Why does a few days of rain cause massive growth spurts, but watering does not? Am I the only one that sees a huge difference between them? Is it bad tap water? If I caught rainwater would it be like getting rain? Am I imagining the difference? Is it possible the plants feel the vibration of the rain hitting them and respond in a different way? Magic or voodoo? I see roses growing huge in places that have droughts, so I know they can grow without rain, but here it seems like they need it to grow. Maybe it's because it's cooler when it's raining, and that triggers the growth? Does anyone know for sure?

Rainwater brings nitrogen with it.

I'd like to know the answer to this one as well. I suspect it's a difference in the composition of the two different types of water. Tap water has many added chemicals, but it also might remove some chemicals that are normally present in rain water. It seems that no matter how much I water my plants, everything in the garden perks up and looks better even after a short rainfall.

I see that Porkpal added a post before I was through typing this one. Yes, the nitrogen could be the answer.

I'm going to say voodoo.

Look at that cat! It looks suspicious!

Witchy, Lightening fixes nitrogen that is present in the air into a form that can be used by plants. Rain is great but lightening is free food.

ohhh now that is interesting! Lightening is definitely missing from the tap. So it is part voodoo.

There is no comparison between rain water and city water in my garden. I Water with city water to keep the plants alive, but I depend on rainwater to make the plants grow and bloom. I have always felt that the lightning supercharged the water . So that makes me feel that my garden is short on nitrogen, and that I should be adding more.

We don't have much lightning here, so that can't be the only reason.

The chemicals in the city water can cause nutrient lockout, so the plants can't take in the nutrients they need. I guess a lot depends on what is put into the city water system.

I have an Ocotillo in my yard. This year I was watering it regularly because we've been in an extreme drought. A few days ago we finally got the first rain we'd had in 6 months. Before the rain, the Ocotillo didn't leaf out or bloom. Now that it's had the rain, it's leafing out and looks beautiful. I've never been able to figure it out. I'm guessing that the well water has too many minerals.
I'm finally setting up rainwater harvesting barrels so I can use more of what the plants want.

I would think the pH of rain might have something to do with it along being chemical-free.
We get a LOT of rain here without lightening a lot so IDK about the electrically charged rain theory?

Agree Karen @plantmanager This is the year of the rain barrel for us, too. There is just too much difference in plant growth and performance not to ignore the differences plus the water savings. I hope the aluminum gutter collecting it doesn't male a difference. I had to make adjustments to barrel #5 as it wasn't getting any water. 1) had to close the spigot and, 2) shortened the connecting hose so that it didn't have to travel upwards. I still have one lone barrel collecting ever slowly directly from the sky.

Rain picks up nitrogen from the atmosphere (air is about 78% nitrogen); the energy from lightning just makes it easier.

I've been wanting to set up a rain barrel for a while. I was trying to use some pond water, but I can't get it out myself with any efficiency, and would probably fall in if I did. That's going to be my next project. Shouldn't be too hard.

porkpal said:Rainwater brings nitrogen with it.

Porky hit the nail on the head.
Lightning creates Nitrogen Oxides that is carried to the soil as nitrates when it rains.
The nitrates are in the moisture in the clouds.

Lightning does not really occur in some of the most lush areas, such as Oahu, Hawaii. There is not enough land mass.

I thought it is the dissolved oxygen in rainwater that is the big boost. Acid rain affects the dissolved oxygen. I have heard you can add a little hydrogen peroxide to your water for a small oxygen fix. Plants seem to really like it. I worried that along with oxygen I was killing bad bacteria...which is ok too! But a chemical does not know good bacteria from bad and down the road was I causing a bigger problem?
So I am unsure what to do.

May gardening bring much joy and happiness to you!

I wonder if the increased humidity accompanying rainy weather would also help the plants grow?

There, maybe, but here there is never a lack of humidity and the rain still has miraculous effects.

Chlorine and other substances in mains water inhibit the uptake of nutrients and thus reduce plant growth and health. Rain water has a neutral pH. It's usually softer than tap water and soaks in the ground deeper than a hose watering; people don't water long enough to equal the soak of a good rain.
This is from gardening.stackexchange

I have to remember to grab my bottle of test water strips from the other house. The tap water here really sucks, and I know it's gotta be pretty alkaline, or super hard, or something. Soap will hardly lather here. I've been thinking about a water softener. I brought my dishwasher to this new place because it was excellent, but not here. I wonder what the people driving by would think if I went out in the rain to get a decent shower myself? I don't blame the roses, I resent it too.