Last year I dumpster dived a giant stack of white pharmacy trays that each measure 16 inches in length, 7 inches in width while being 5 inches deep. I tossed the stack in my Dodge minivan because I am John Starnes, compulsive pack rat/recycler.....I KNEW I'd think of a cool use for them. And I did!
I drill 8-10 holes on the sides, about 1 inch from the bottom, to create a miniature Water Wise Container Garden perfect for starting seeds in. The bottom half is filled with soil from my chicken scratch path/compost factory, then I add a few inches of commercial greenhouse potting mix. I snip miniblinds into 5 inch lengths to set edgewise into the soil to divy up the container garden for differing plants, then use a short length to label each section.
These have proved very effective, NON-THIRSTY havens for tomato, catnip, broccoli and many other seeds that stay damp a LONG time between waterings.
Many folks find the various Alliums (onion and garlic family) difficult from seed when direct sown into a garden, but I got GREAT germination from a leek variety called 'American Flag' (see photo). Once the seedlings are big enough to divide and handle, I transplant them into the garden.
Just remember the Dumpster Diver's Motto: "Peek, and you shall find!"