Instructions
Watch your garden until you see Seedos appear. Talk to him. He will come once per day, and eventually will give you a rose seed.
Visit Costolot's General Store and buy more rose seeds. They cost 62 coins each.
Dig holes in your garden soil and plant the rose seeds.
Note: You don't have to dig a hole first, but the roses grow quicker this way.
Head back to Costolot's General Store and purchase three bags of red fertilizer. They are 18 coins each. Add the fertilizer to newly planted roses.
Collect your roses when they fall off of their bush.