Basil is a prolific herb and also a very preservable one! Every year for about the last decade we’ve been growing basil in the greenhouse. It produces more than we can use up over the summer months, even with weekly batches of pesto. Honestly, we usually manage to grow even more than we can preserve and use up over the winter months too!
The best way I have found to preserve basil is to gently (but thoroughly) rinse the whole plant and remove the leaves so that they are individual leaves. I like to run those through the salad spinner very gently so that the bulk of the water is off but the leaves are still a little damp when they come out. From there I place the leaves on the trays of the dehydrator, with a little room between them, but not completely separate, they can still be touching a little. Then I put them on the dehydrator base (you can do a stack of 10 trays, this will be on the very lowest heat setting, or even no heat if it’s warm enough in the house. After a couple of days of air flow the leaves will be dry and crisp and can be placed whole in a jar. (Any black or powdery looking leaves should be chucked… they didn’t dry correctly and might be gross.)