How Do I Treat Damage Caused By Frost & Freezing?

Water the tree immediately as freezing temperatures pull the moisture out of the tree's roots.
Wait and determine the extent of damage before pruning in the spring or when the possibility of frost has passed.
Identify the graft or bud union, and make sure the fruiting wood above the graft is still green and healthy.
Photo of the graft can be found here:
https://lemoncitrustree.com/store/pest-disease

If it is viable it should produce new buds in the spring. If all the leaves are brown
and curled, remove them in the spring and water the tree with a quarter cup of bone meal mixed in a gallon of water for a potted tree.
It will take a few weeks for the appearance of new buds. After bud break, you can prune the branches if desired.
Preconditioning helps; trees exposed slowly to cold will fare better than those subjected to a sudden frost. Also, prolonged exposure to cold is more damaging than a brief plunge in temperature. Here are some methods we have used to help protect plants when freezing temperatures may pose a threat.

Listen for news of cold fronts, and be prepared to take action!
Water all garden plants thoroughly before a freeze since freezing soil will pull sustaining moisture from the roots.
Use antitranspirant sprays. Common brands: Anti Stress and Cloud Cover.
Put old fashioned, heat-producing Christmas lights in the trees or in landscape lighting under the trees. This method often yields excellent results for cold-sensitive lemons and limes.
Hot bulbs can scorch leaves, so take care to angle them so that they directly touch foliage as little as possible.
Use frost cover blankets, also known as floating row cover or Remay. This is a spun polyester material designed to cover trees and plants. It can be draped directly on the plants and secured at the ground to trap daytime heat. Unlike plastic covers, it can be left on during the day without fear of overheating the plants. Used in combination with lighting, it is a great way to protect cold-sensitive plants.