I've actually experimeted. I should state that I have found probably a 100 or so 4 leaf clovers. Actually, many of them are 5, 6 and 7 leaf clovers. Back to my experiment. I found one in my yard and left it. I came out and looked at it every day or every other day for a week or so. It dropped the extra leaf!
One other thing and that is they are easier to find when they a sparse like the pic you show. When they are so tight in with each other it is much harder to see them.