When do you use -tch or-ch?

The suffixes "-tch" and "-ch" are used based on the phonetic and spelling rules of English. Generally, "-tch" is used after a short vowel sound, as in "catch" or "watch," to indicate the preceding vowel is short. Conversely, "-ch" is used in Words like "march" or "beach," where the vowel sound is typically longer. The choice depends on the specific Word and its pronunciation.