If your goal is to transfer all files from `local_dir` the `*` wildcard does the trick:

    $ scp ~/local_dir/* user@host.com:/var/www/html/target_dir

The `-r` option means "recursively", so you must write it when you're trying to transfer an entire directory or several directories.

From `man scp`:

    -r 
    Recursively copy entire directories. Note that scp follows symbolic links encountered in the tree traversal.

So if you have sub-directories inside `local_dir`, the last example will only transfer files, but if you set the `-r` option, it will transfer files and directories.