IN PLANT TYCOON,...(IMPORTANT QUESTION!!!! POINTS HERE!!!!!!!)?

In plant tycoon, I need to make a mela rare oak. I have different types of rare oaks, but just cannot seem to produce and plant with a mela. Can you tell me how to get a mela? I would like specifics, and also, can a mela be bought in the first tier plant seeds in the shop? I'm using the IPad version, so I have to use "plant bucks" to buy upper class seeds. If at all possible, I want to avoid using my Bucks to buy a seeds from tier 2, 3, or 4. Thanks!