The journal Frogpond is an official serial publication of the Haiku Society of America. Its primary function is to publish the best in contemporary English-language haiku and senryu, linked forms including sequences, renku, rengay, and haibun, essays and articles on these forms, and book reviews.
Submission periods are one month long:
March for the spring/summer issue.
July for the autumn issue
November for the winter issue
Full submission instructions http://www.hsa-haiku.org/frogpond/submissions.html