$re = '/(.*?),(.*)/m';
$str = 'Geranium, Ivy
Geranium, Zonal
Geranium, Interspecific
Impatiens, New Guinea
Petunia, Trailing
Petunia, Spreading
Petunia, Miniature Trailing
Impatiens, Interspecific New Guinea
Mum, Garden
Mum, Pot
Combinations, Vigorous';
$subst = "\2 \1";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php