Even by now, if you've been growing parsley and cilantro this spring, even by seed, you'll probably notice that these plants begin to exhaust themselves early. The best thing to do is to replace the old plants with new starts.
If you cook with parsley and cilantro like most chefs, you use a lot of these two herbs. The thing to do is to keep two pots of each rotating between mid and late stages of maturity.
Between the two herbs, it's much easier to grow cilantro from seed. It sprouts readily and grows quickly. For either or both, some gardener/chefs avoid the patience necessary to grow plants from seed. Instead, they rotate with four inch starter plants. It's up to you.
There is something good about having parsley and cilantro growing close by, waiting for a moment when fresh ingriedients are especially important. Like any twilight evening right about now.