Making your own herb salt is easy.
Herb salt from dried herb
1 part (by weight) salt
1 part (by weight) dried herb
If you have small amounts you can pound them up with a mortar and pestle. If you have larger amounts blend them in a mixer.
Pour into airtight jars, label.
Herb salt from fresh herb
1 part (by weight) sea salt
4-5 parts (by weight) fresh herb
Chop up herb, mix with salt (use a spoon).
Drying in the oven: pour onto parchment paper (or whatever kind of paper you put under your bread when you bake), put into oven on 50 C (the lowest possible), keeping the oven door open so moisture can escape, and so your herb doesn't get burnt to charcoal. Let sit in that oven for a few hours or overnight - until dry.
Drying in room temperature: cover with another piece of parchment paper, let sit in a shady spot for 7-10 days.
Drying in a dehydrator: use parchment paper that's smaller than the dehydrator trays, let dry on 40 C for 1-2 days.
Drying in a microwave oven: I haven't done that, nor will I. A microwave dries by boiling the water out of the herb; some people tell me they get great results, but I've been taught that 40 C is max for herbs. If you do decide to try the microwave: start slow. You might end up with charcoal if you hurry things too much.
Once the blend is dry: pour into mixer, blend. Pour into airtight jars, label.
Herbs to use for herb salts
Most commercial herb salts contain celery (leaf and/or stalk). Other popular ingredients are parsley, lovage, and one or the other kind of onion.
Here's a few commercial herb salt ingredient lists:
- Labby's "Yrttisuola", the herb salt of a local biodynamic herb grower:
salt (60 %), parsley, basil, thyme, marjoram, lemon balm, dill, lovage.
- Bioforce's "Herbamare", the herb salt of a large organic Swiss herb house:
sea salt (94 %), celery, leek, cress (watercress? garden cress? another cress? no clue), onions, chives, parsley, lovage, basil, marjoram, rosemary, thyme and kelp.
- Meira's "Yrttisuola", the herb salt of a large local spice house:
salt (85 %), onion, parsley, glucose, celery leaf, marjoram, rosemary, basil, thyme.
- Knorr's "Aromat", the herb salt of a large German food house:
salt (56 %), monosodium glutamate (MSG), lactose, yeast extract, onion, hardened vegetable fat, spices (celery leaf and others), calcium silicate.
What herbs do I use then?
When I make fresh herb salts I use anything found in abundance in my garden. I do try to include at least celery leaf, parsley and lovage.
In addition, these may or may not get included: chervil, thyme, black currant leaf (has to be Ribes nigrum - the leaf is scented, and tastes great), French tarragon (or Mexican mint marigold), hyssop (that's Hyssopus officinalis, not an Agastache), caraway leaf, chives, dill, lemon balm, ...
... those are from memory, and there's lots of others, but there's half a meter (1.5') of snow on my garden right now, so I can't go out and have a quick look-see.
When I make dried herb salts I use anything found in abundance in my cupboard. I have dried parsley, lovage, and celery leaf, in addition to a well-stocked spice shelf (and lots and lots and lots of large herb jars, including a few culinary herbs. Mmmmm, thyme.). I also have dried onions - I love onions.