Q: How did the farmer mend his pants? 
A: With cabbage patches!

Explanation: To mend a pair of pants, such as jeans, is to fix them.  If there is a hole in the knee you will need to patch the hole with a patch.  Yes, “patch” can be used as a verb and a noun.  “Patch” also means a small area of land that is planted with a the same type of vegetable such as cabbage: a cabbage patch.  This joke plays on the multiple meanings of the word “patch.”