My oregano plant drying up now my lavender and my tarragon have start to dry I don't know what is the cause of it.
Herbs Plants Drying Up
The plants you mentioned like hot, dry conditions so overwatering is more likely to kill them than under-watering. Both have about the same effect on the plant, leaves shrivel and die. If these plants are in clay soil, the soil must be amended to let it drain faster. (They must dry out between waterings or the roots will rot.) Adding perlite, sand or pea gravel is a must down at least 8 inches. If grown in containers, make sure they have drainage holes in the bottom and add sand or perlite to the potting mix so it is about 1/4 sand/perlite. Do not use fine grain sand like play sand. Look for coarse "builders' sand". If my hunch doesn't seem right, please repost with a picture and tell us how you are caring for your herbs.