Okay so I noticed the other day that the cost for a single bee or water is about 3 green and a double (2 plants) is 8. So it is almost more cost efficient to them as individuals. The same is true for other spells I have noticed.
not always if you have four plants together you can use the double one if you have a bigger plot of say 25 you can use the large spell each of the spells have a max of what they can do small is one, the medium is 25 and the large is 69
