Will salting the ground kill insects and spiders?
Dusting the area with a diatomaceous earth based insecticide ought to do the trick, while being essentially non-toxic. If you want to prevent plant growth there too then of course salt the earth.

See Efficacy of modified diatomaceous earth on different cockroach species (Orthoptera, Blattellidae) and silverfish (Thysanura, Lepismatidae)