Your pup can have a haircut anytime. Cutting the hair will not make it grow faster. You can snip the tips of the hair to prevent split ends/breakage, and that will encourage healthy, strong growth.
If your goal is a longer coat, be very careful choosing your groomer. Many groomers will cut/shave Yorkie coats shorter than instructed, especially if the dog is dropped off with any hair tangles or mats.
__________________ Kristin, Max and Teddy |