Is there a minimum quantity of harvest that requires terumot and ma'aserot?
Question
I have a basil plant growing in my yard outside. Since it's a herb, does it require a berachah? Also, I generally pick a few leaves each time. Is there a minimum amount of leaves that requires terumot and ma'aserot?
Answer
To bless or not to bless
Yes, there is a berachah since we actually eat the leaves (pesto and all). For produce growing indoors, however, or in covered porches, separate without a berachah.
Miminum amount
Any amount (even a leaf or two) requires tithing. Lechatchilah, it's best to separate T&M each time. Only if there is a concern that a family member will pick leaves without ma'asering, it's possible to take terumot and ma'aserot in advance.
See the bolded links in the similar QA here for the procedure and text.
There is, on the other hand, a minimum amount of produce you need to inaugerate a new coin to transfer the kedushah of ma'aser sheni or neta revay (this coin is called a perutah chamurah): the amount of ma'aser sheni/neta revay produce needs to be the value of at least a perutah (calculated based on how much the produce costs in the store; on our website we also have the value of a perutah). We handle this for members.