Most of the food a plant produces is made in the leaves via photosynthesis. What comes up through the roots (as minerals/fertiliser) is mainly to support that process in one way or another. Taking off green leaves is a bit like having a feed and then getting your stomach cut out and thrown away. Well, multiple leaves are like multiple stomachs, so you still have those that are left, but food production/intake is reduced. I've never been a fan of pruning palms, not even a fan of topiary in general. Giving them fertiliser will ensure they have all the supplements needed to keep the plants' processes performing at optimum levels. Other than that it's up to the remaining leaves to get the palms back to normal, a waiting game basically. Anyway, that's my take on the issue. Good luck with them.

Basically the only thing you can do is make sure that they have nutrients available by giving them some occasional monthly or bimonthly palm fertilizer, and just waiting. It will probably take the rest of the growing season for them to look full again, but they will look good again by this time next year. Next time you should either find someone else to trim your trees and/or show them pictures of Washingtonias that are pruned the way you want them (properly). I hate seeing palms over pruned (or any plants) and it's a common problem by me too (not with palms, but with other plants that shouldn't be pruned as much as they are).

I hope your palms have a fast recovery!
Good luck!
-Alex

I hate over trimmed palms! I see them here in Southern California and it drives me insane! They look so weak and frail. I don't know why they do this. I suspect the gardeners don't really know what they are doing, they just cut and cut without knowing the damage they are doing to the palm, all because they think it makes palms look cleaner. I don't like cleaner palms, I like them full and bushy. Give your palms tons of quality nutrients, be patient and do not let the gardeners mutilate your palms again. I'd be so pissed!!!

In Florida it has been such a problem with landscapers giving palms the hurricane cut that they are considering fining them if it continues as it is killing the trees here.

Hope you don't have to pay them.