Gardening marathon has begun

Name the object?

I found this convex metal disk in the garden dirt. Around the rim it says "DRIVERS PERMIT" "Bellingham, Wash." In the center is a number 3. The back looks like it could possibly have had something soldered to it, maybe a pin clasp.

Potatoes! These are Reddales, a productive long storing red tater. We planted 2 rows of these and 4 rows of a high-protein russet named Butte. While I was digging in last year's potato patch I found 4 Ozette fingerlings, buries too deep to sprout. We roasted them with salt, pepper & olive oil and they tasted wonderful!

Raw materials - hay that makes manure (notice the diligent stablema'am) and the manure makes food. A nice little system. We ran short of hay and got tired of running to the feed store every few days, so we bit the bullet and had 15 bales of 2006 hay delivered. That and our greening-up pasture should see us through til this year's hay comes in. We need to have the 2nd barn half built by then so we can bring in a couple of tons this summer.