Peel and clean out a small pumpkin, reserving a slice of the rind to lend bacteria to the fermentation process. Add salt, pumpkin rind sliver, and cardamom seeds to a pint-sized jar.
Slice the pumpkin into small sticks just tall enough to fit into the jar, leaving about 1" of head space. Pack tightly into the jar, much like making cucumber pickles.
Pour water over the pumpkin, salt, and cardamom until the pumpkin is entirely submerged. Place a lid on the jar so that it is airtight and leave to ferment at room temperature for 2-3 weeks. Check the jars daily, opening the jars to release pent up carbon dioxide each time pressure has built up.
After 2-3 weeks taste the pumpkin. If it is sufficiently tangy, you can eat it right away or move it to cold storage.