Mindy - I'm assuming you got this from Groupon? FWIW, with the Groupons, you will never loose the value you paid, you only loose the promotional value after the expiration date. So you can always use for $40 worth of plants after the expiration date.

From the Groupon FAQ

"What happens if my Groupon's promotional value expires?

All is not lost! If your Groupon's promotional value expires, you can always redeem it for the amount paid. For more information about expiration dates and voucher values, read our Terms of Sale "

As another option, you could try to sell it on couprecoup.com - a clearing house for people to buy and sell all these unused daily deal vouchers.