At what size should you top your seedlings? Is it at a certain height or when a certain number of leaves have developed?
Hi Hot Charlie,
If you mean when should you prune the tops of your plants, well you don't have to if you don't want to.
If they are getting a bit leggy, you can always plant them a little deeper, so that less stem is sticking up above the topsoil, when you repot them into their next sized bigger pot.
dvg