You have to grow flowers and trade for the furniture. According to another forum, you don't have to match the flower type, so you can trade for all the same type of easier fences and they'll get you a passing score. I'm stuck on this level and don't really grow flowers, so I can't help much more.
This is good to know. I just started planting all the common seeds in bulk to get one of each furniture piece/item from each category. I suck at cross breeding so I won't fuss with that.