We left an opening in our concrete countertop to accommodate our stainless steel tray. Our tray measures 16x24 inches and is 6 inches deep and has a lip all the way around to hold in place.
Step 2: Fill Tray
Create a substantial layer of gravel for drainage at the bottom of your bed and then fill with a rich organic soil/compost mix with a bit of perlite added sufficient drainage and aeration. (Can also drill drainage holes and use tubing to divert drain water to a bucket or back into your sink drain.)
Step 3: Plant
Pot up with plants that are easy to grow indoors such as herbs. Plant things you use on a regular basis. We did put a mint plant in ours and buried it in a separate container so we didn't have to worry about its' invasive nature in this small of a space.
Step 4: Lighting
Be sure to position your bed where you can get as much natural light as possible and if necessary, compliment with a growing light that can be positioned and installed underneath a cabinet. Water and feed as needed.
Step 5: Other options
You can also have fun with countertop salad bowls and the like. They give you easy access to fresh greens year-round and it encourages you to always make healthy, lively choices in the kitchen!