When do Japanese Spitzes start mating?

What reason do you have for wanting to breed? The only reason dogs should ever be bred is to better the breed. If you got any other reason, then please spay/neuter your dogs. There are more than enough pet quality dogs in the shelters who get euthanized daily, including purebred ones. Please do not add to this overpopulation. If you do insist on breeding, my best advice is to read, read and read some more, and then get a mentor who shows and breed dogs to teach you all that you need to know and will help you every step of the way. But for now you need to keep your male away from the female while she's in heat until she is at least two years old as she is still a puppy herself and not mature enough to handle pups. When they are 2 years, you will need to do extensive health checks on both (OFA, CERF, any other required genetical testing for your specific breed) to see that the dogs are genetically healthy. In the meantime you should also be showing the dogs to get their championships and make sure they fit the breed standard. Then, and only when they pass all this, can and should they be bred. You also need to know the homes for the puppies before the breeding even takes place, and you need to be prepared to take back the puppies at any time of their lives as you brought them to this world so you are responsible for them. So breeding isn't cheap, nor easy. You aren't going to make money on it. Those health tests are expensive, and cannot be skipped if you want to breed responsibly. You need to have money saved up for a possible c-section if she cannot deliver the pups and it could mean a lot of heartache, losing puppies or even the female. IMHO, breeding is best left for the professionals who have years of experience.