how long does a dog have to be in season before she is ready to breed?

Never, if you get her spayed first, which you definitely should.

21 YEARS!!!If you are so ignorant as to be asking the BASICS *HERE*,you are too ignorant to be breeding HOUSEPLANTS,let alone dogs!PUPPYMILL WANNABE?SPAY IT ASAP!

Usually after about 4-5 days, when she is about in the middle of her heat

She will swell up and then start dripping blood. When the bleeding starts she will be ready to breed in about one -one in a half weeks. Watch her when shes actually ready she will scoot up to the male and she will move her tail to give him better axcess, and even sometimes she will lie down with her tail out of the way for the male to mount her. Hope this helps!!

Usually on the 10th day

You should only breed your dog if she is purebred and you have papers to prove it.If that is the case, she will be dripping blood when it's her time of the month. And you must be careful... every male dog in your neighborhood is going to know it and come for your dog. Keep her indoors and supervised outdoors.If your dog is not purebred with papers, DON'T DO IT. Spay your dog. There are enough dogs in this world, and not enough homes for them. If your dog is purebred.... can you guarantee that these puppies will go to good homes that have food, shelter, water and enough time for training? The last thing you want is one of your babies ending up at the shelter because the people who had him/her couldn't handle it.And besides, it's less painful for your beloved dog to get spayed... than it is to be chased down by various male dogs at all hours of the day when she'd rather be left alone.