<?php
$months = array();
$currentMonth = (int)date('m');

for($x = $currentMonth; $x >=$currentMonth-12; $x--) {
    $months[date('F', mktime(0, 0, 0, $x, 1))] = 0;
}

echo "<pre>";
print_r ($months);
?>

<pre>Array
(
    [September] => 0
    [August] => 0
    [July] => 0
    [June] => 0
    [May] => 0
    [April] => 0
    [March] => 0
    [February] => 0
    [January] => 0
    [December] => 0
    [November] => 0
    [October] => 0
)