Talk to Damien and Henrietta
Begin by speaking with Damien Salt, a pirate who hopes to woo a character named Henrietta. He seems to think that ice cream or flowers will do the trick. Henrietta is very close by; if you speak to her, you'll discover that she prefers flowers to ice cream. Henrietta doesn't want just one flower, though ̵1; she wants a whole bouquet. You'll have to track down enough flowers for her to be happy.
Find Clarabelle
After you've accepted the quest, head to OsTown and go to Clarabelle's house. Clarabelle is a gardener and knows all about flowers. She'll tell you that three flowers should do the trick, and you should return to her after you've found them. You have two options when it comes to finding the flowers: you can find all of them in OsTown or you can find them on Mean Street. Once you̵7;ve found three flowers, go back to Clarabelle and she will make a bouquet you can give to Damien.
OsTown Flowers
Use a bit of thinner on Clarabelle's lawn to remove the grass. You'll find a hidden cave that holds the first flower. Next, head to Ortensia's house. Use some thinner on the wall behind her house to reveal an alcove containing the second flower. Finally, use thinner on the wall behind the sunken boat. The final flower will be waiting for you there.
Mean Street
The Mean Street flowers are a little easier to find but they'll require some jumping. All of the flowers you'll need are hidden in the trees that line the Central Square. To collect a flower, jump up into a tree. The first tree that holds a flower can be found to the left of the Emporium. The other two flowers can be found in trees near the Museum.