Wilt Pruf Plant Protector Concentrate May Be Used Year Round To Help Plants Under Stress. We have used it most in the fall to protect evergreens from moisture loss resulting in winter kill. I also love it on wreaths and greens at Christmas. You can spray it on new transplants to reduce shock. Now I am going to use it to protect my shrubs and some perennials from drought damage this summer. One application lasts about 3 months. Apply with a pump sprayer. Do not use in hose end sprayer. 1 Pint.