The gardener in Rose Town is looking for the legendary "Seed" and "Fertilizer". You can get the Fertilizer once you beat Valentina. Go to the far right of the town, and you can walk off the ground. Talk to the Shy Away and he gives you the item. You can get the Seed once you beat Megasmilax. Read the piece of paper that floated down and take the Seed. Now go to Rose Town, and go past the Item Shop to the gardener's house. Give him the items and he grows a beanstalk. Climb up to get the Lazy Shell weapon for Mario and the Lazy Shell armor for anybody!
Credit goes to: http://www.rpgclassics.com/shrines/snes/smrpg/secrets.shtml