Without the context of a full sentence I will say it depends.

I find it difficult to learn tenses in English grammar:

because it is English grammar in general.

The way I was taught the different tenses in the English grammar I was taught at school isn't proving very effective:

because it is not English grammar in general but the particular grammar I was taught.

Note that not using the word "grammar" would not change anything, you can say "tenses in English" and everybody knows what it means.

The clearest and quickest formula would be "English tenses", I think. But "tenses in English" is good and sufficient. To express the idea that tenses are in a grammar book is actually not necessary, it is self-evident.