Lisa Marie Presley claims she's disappointed at the "empty space" surrounding Michael Jackson's tomb -- so she's now challenging MJ fans to flood the place with sunflowers ASAP.

LMP just posted a message on her MySpace page describing her recent visit to Michael's grave site at Forest Lawn. Presley -- who was married to MJ back in the '90s -- says she believes Michael "deserves more" than the "few bouquets, candles and gifts" that currently surround Michael's grave.

Read more at TMZ.