The answer to your question depends on your school's requirements for honors/advanced placement classes. I recommend calling the school office this week and speaking to the counselor. More than likely, you do not need a teacher's recommendation to take an honors course at the high school level. If you are planning on making a schedule change, then it is always better to ask for it as soon as possible. Do not wait until the first week of school.
You should also inquire if the honors course which you are thinking about taking has any required summer reading list or not; many freshman level advanced English and history classes often require students to read a novel or nonfiction book over the summer.