I do not have a figure ,but I know that you can have much much more than enough for planting next year and years after that but maybe not eough for colinary use. last year I collected about one third spice bottle of seeds from one dill plant. That was an average plant.

You would need quite a few plants to get that much seed. But remember, you can put these herb plants in amoungst your border flowers if needed where they are quite pretty and add another demension to your flower beds.

Suggestion: When the seedheads start to set seed (green) I always carefully enclose the heads in small paper bags or bags made from nylon stockings to keep the seeds from falling off when ripe.

Or, you can watch them carefully, and when the seeds start to change color pull the whole plant and put the heads of each kind upside down in a paper bags to finish ripening and drying.

Conditions, plant variations, and plant varieties will all make seed production hard for me to crystal-ball exactly for you. But I'd have to guess 6-12 plants should maybe get you in the ballpark for the amounts you are looking for.

Westelle gave some good advice. Many people have dedicated garden beds - flowers here, herbs there, veggies some place else. But some plants, like the herbs you mentioned, are quite attractive mixed in other garden beds. Just be sure to use no chemicals in places you wish to harvest food items from.

FataMorgana

Thanks.

I've got tomatoes and eggplant in my flower beds due to a shortage of space, but we can probably manage to find space for a few of them.

It will be a start.