Backyard gardens seems a bit broad whereas the rest focus in on a certain subject relating to gardens.
I think its the first one the sentence looks fine with out a comma.
try but your mom chanel is gliching
You would need to introduce a list.
For example you could have: My shopping list contains of; milk, bread, and yogurt.
Another purpose is to separate clauses.
<span>There are 27 grievances listed in the Declaration of Independence against the King of England. One is dissolving the House of Representatives. Another is keeping standing Armies in a time of peace. The most famous one is having taxes without giving the people a voice.</span>
