It's time to start thinking about dividing those hostas that have become to big for the spot you want them to fit in. Do hostas have to be divided? No, despite what you may have heard, hostas do not need to be divided. The only time they really need to be divided is if they develop fairy ring, which is when the middle of the hosta starts to die out. Spring is the easiest time to divide hostas, because they are first emerging and are easier to get a handle on. In spring you can usually divide them and they will not skip a beat. However, hostas start to grow new roots not in spring, but in summer. Usually they are starting to grow roots around the time they are getting a second flush of new leaves. So it's actually better to divide them in August and September. Just make sure it's about 4-6 weeks before your area receives frost. Yes, I said it-Frost. Hard to think about frost during the dog days of summer.
Here is the Cheesehead Gardening video from spring of how to divide hostas.
Here is a video I created last year on dividing a reverted hosta, but it applies to all hostas. It shows how to tie up the leaves, which makes them easier to divide.