Keeping the stems in a vase of water can help delay basil’s rapid deterioration, but fresh basil should either be eaten or preserved within a few days of harvesting because basil wilts very quickly, once picked.
Basil does not respond well to cold temperatures, so please don’t refrigerate it.
Like sweet basil, Thai basil doesn’t retain its flavor well when dried, so it’s best to use fresh Thai basil whenever possible.
Freezing chopped basil in ice cube trays filled with a little olive oil or preserving in salt are the two best ways to keep basil for long term storage.