PDO 和 MySQL '之间'

I'm trying to get PDO to work with a MySQL 'between'. Below is my code:

$DBH = new PDO("mysql:host=$host;dbname=$dbname", $user, $pass);  

$start_date = date('Y-m-d H:i:s', mktime(0, 0, 0, 11, 1, 2009));
$end_date = date('Y-m-d H:i:s', mktime(23, 59, 59, 11, 30, 2009));

$STH = $DBH->prepare("SELECT * FROM `table` WHERE `start_date` BETWEEN ':start_date' AND ':end_date'");
$STH->bindParam(':start_date', $start_date, PDO::PARAM_STR);
$STH->bindParam(':end_date', $end_date, PDO::PARAM_STR);
$STH->execute();
var_dump($row);

返回的是一个带有0"或NULL"值的数组.当我硬编码结束日期时，它就像 start_date 设置为 -1，重新调整 end_date 之前的所有行.那么，我在这里做错了什么?

$STH = $DBH->prepare("SELECT * FROM `table` WHERE `start_date` BETWEEN :start_date AND :end_date");