My beard is growing, but in certain spots it is bald. What can I do to grow hair in the bald spots?

The degree and rate of Beard hair growth is genetic.  If you are still young, you may still have some growth In the future.  There is no medical treatment to grow hair in the beard area, however if your beard is still thin as you grow older, hair transplant is an option. In the hands of a skilled and experienced and restoration specialist beard hair transplant is very successful and natural. 

This is common in early beard growth. Many young men want to accelerate their beard growth and ask
about it. It takes age (genetic triggers which occur in family lines) so
if you want to find out when your beard will grow out, you need to find out
when your father or grandfather started to grow theirbeard. Hormones should have kicked in
nicely by the time a man reaches 18 but he must wait out his genetics
as hormone alone are not responsible for the onset of beard grown. Beard
transplants can be done when the young man is a bit older (over 25) if the
beard has not grown in yet