Grammar can be taught in conjunction with these essential skills; it does not have to be one or the other. It is important that students have the vocabulary to talk about language, and grammar is the language they need in order to do so.
In reading, students can talk about why a particular author's work is effective if they know what grammar conventions the author followed. In writing and giving/receiving feedback, students will have a better understanding of what to look for to improve in their writing if they have the vocabulary to talk about the grammar rules they need to be following. In speech students can grade one another on how well they understood their classmates' speeches based on whether the speaker used proper grammar or not.
Grammar is an integral part of language learning and should be interwoven with other essential communication skills, not segregated from it. If incorporated in the lesson properly, it would take no extra time to learn the grammar rules alongside the essential skills.