Where possible or were possible?

Answer 1

You most likely want "where possible".

To say "in every situation for which it's possible", you would write "where possible" (using "where", sounds like "wear").

The alternative, "were possible", can be correct English, but in completely different situations: talking about things that could be done previously, but maybe not now. (This is "were", sounds like "whirr".)

"I travel on horseback where possible."

"Tying up your horse outside the store, and going inside to buy a saddle, were possible when horses were more common as transport."

Answer 2

where possible-location-I put roses where (it is) possible.

were possible-time-Were (it) possible I would dance all the time