Hi!
I have in mind a story where there were torrential rains periodically flooding the place (don't remember if it was a town, a planet, or what exactly), and the people had to get out or climb up on trees--otherwise, if they got under the water, they grew roots.

I think the story was Bradbury's but I'm not certain. Can anyone help?

Could be in the vast "similar, but not Bradbury" category.

Bradbury did write two stories about torrential rains--"All Summer in a Day" and "The Long Rains," both set on Venus. This isn't either of them. "The Long Rains" contains a notable scene about fast-growing fungus but no people growing roots. Orson Scott Card also wrote a story about a guy rooting into a jungle but I don't think rains were involved.

This is what I have done in the past with these story IDs and will do again whenever I have time, (which I MUST tell myself I will...someday) but in the meantime it REALLY helps if people do their own.

1. Go to the Abebooks forums. Make sure you are in the "Booksleuth" forum.
http://forums.abebooks.com/abesleuthcom
Post under "Science Fiction." If I were you, I wouldn't crosspost there, although some stories fall into more than one category, i. e. Children's and Science Fiction. This forum houses the most friendly, helpful, useful, knowledgeable folks I've been able to find online.

2. Go to Google Groups (or, if you REALLY MUST, Usenet--same groups in a different form, only Usenet preferers seem to have a less efficient system coupled with a superior, know-it-all attitude.) Start with this one:
http://groups.google.com/group/alt.books.isaac-asimov?lnk=lr
because Asimov is the author most frequently mistaken for Bradbury. Even if the story isn't one of Dr. Asimov's, his fans are polite, helpful, and widely read in other Science Fiction.
When you post there, crosspost to the following groups: rec.arts.books, rec.arts.books.childrens, and rec.arts.sf.written
The worst that will happen is some obnoxious troll, most likely on rec.arts.books.childrens where a number of them have taken up semipermanent residence, who has nothing better to do, will call you rude for crossposting (WHY, I have never determined and refuse to argue it with them.) The best that will happen is you only have to type your question (or copy and paste the one you already typed) once, and it will simultaneously appear in all four groups. If the people who answer just hit "reply" without stripping out the other addresses, all answers will appear in all those groups, so you only have to check one instead of opening up four groups separately. Usenet has a smattering of knowledgeable and helpful folks along with a community of idiots with too much time on their hands, but a lot of people see questions posted there and you may receive semidecent answers.

3. If all these free sources fail, go to:
http://www.logan.com/loganberry/stump.html
They are the ultimate authority and if the question can be solved nowhere else, it is well worth the $2.00 they charge to have it posted to their site, where it will stay on the unsolved pages until solved, without getting "bumped down" the way things do in message board format. It will then go permanently to the solved pages in case anyone else ever has the same question.

4. Lastly, most important! When you get your answer, whether it be right away or months or years later, PLEASE come back and post it here! If your post is no longer near the top, you can find it by clicking "Find" at the top of the page and searching for your username or some other unusual term. It would also be nice to mention from what source the answer came. If it's not posted here, it will end up on my "unsolved" list if and when I do get time to go back through all these, and I'll end up doing all of the above (except for paying for other peoples' stumpers, at which I draw the line) unnecessarily! Thanks!

Hope this helps!

Sounds very similar to "Parasite Planet" by Stanley Weinbaum. A Ham Hammond story; takes place on Venus. Eat your can of food within a minute after opening it, or it goes bad with a vengeance!

There is another story about a missionary trying to convert a native life form that goes into a second, underwater, plant-like stage - unless they stretch the juveniles by hanging them updide down for a while - but that is so many years ago I may never find it.