Definitely too late. Transplanting in the fall usually works, but for best odds you need to wait for spring. Ideal transplanting time for ferns in temperate areas is after frost but before the fronds emerge.

Patrick Alexander

It can be done now, but it's risky. I prefer to transplant in the fall rather than the spring. If in the spring I would wait until the fronfs have matured and hardened off.
Two conflicting opinions. Take your pick!

Make that three! I'm a mom with two kids and a crazy life, and I move my plants when I have the time as opposed to when it suits the plants! I should emphasize that I may be able to get away with this more easily due to my forgiving climate. The key in any case is to be aware of the trade-offs. For example, move or plant something in high summer, and be ready to water at least every two to three days. In colder areas, plants that aren't well-established by winter may require more protection to get through winter. And so on.

With respect to ferns in particular, when you move them in full growth you inevitably (trust me on this) break fronds. Some will provide replacement fronds the same year, others won't. So if you're moving these tall ferns into a showcase position, they won't do the job until next year anyway, and will look like poor cousins until then.

As Karin suggests, the gist is if you move them when they've got leaves, you'll generally lose some leaves, either because you break them or because the root system isn't strong enough to support the leaves after you've transplanted it. You also have much greater odds of losing the plant, though more often than not you'll be fine.

When there are no leaves, disturbing the root system causes no stress--the root system isn't doing anything right then anyways.

Transplanting in spring after they leaf out sounds like the worst option, to be honest. It's the time of year when the plant has the least resources, since it's just used up a lot of them producing leaves. It'll probably work a fair amount of the time, but just involves a lot of unnecessary stress on the plant, and is likely to leave the plant looking crappy the whole year.

Patrick Alexander

I too am a mom with 3, busy, busy kids. I have moved ferns at various times throughout the summer to fall. I often intend to try it in the Spring but always get so busy with other things I don't get around to it until Summer. Bring as much of the soil as you can , treat them gently, water them well. Often they have died back after transplanting, only to fool me and come back in their full glory the following spring. My vote is to go ahead and transplant.