Salt has no volatile oils and flavour compounds to combine with other ingredients, so you cannot make a flavoured salt by ‘infusing’ it with another ingredient as you can a flavoured sugar. Celery salt, for example, is made by grinding dried celery seeds with salt, and this is the method to use if you want lavender salt, which cannot be made by simply burying a few lavender sprigs in a jar of salt.
Use about one part flowers to about ten parts coarse sea salt, which responds best to grinding. The flowers need to be absolutely dry or they will cake with the salt; I always put a few grains of rice in the bottom of the jar to help keep the flavoured salt dry.