Generally speaking, you should apply 20 pounds (or 320 ounces) of worm castings per 1000 feet of root growth if you're using VermaPlex®; or 40 pounds (or 640 ounces) of worm castings per 1000 square feet of root growth if you are not using VermaPlex®.
For calculating smaller garden plots, it's probably simpler to find the amount of castings per square foot. So, you would use .32 ounces worm castings per square foot with VermaPlex® and .64 ounces worm castings per square foot without VermaPlex®.
Worm castings for raised bed garden
When you build your bed and at the beginning of the growing season, a good mix for your square foot or raised bed garden is 30% worm castings added to your growing medium. Then apply side dressings of castings a few times through out the growing season.
If you're raising vegetables in a raised bed, particular an "intensive" planting where the entire bed is used by the plants, you can measure the length and width of the bed, then multiply by the number of beds to get the square feet of your planting area. Multiply the total square feet of planting area by .32 (or .64) to get the amount of castings required.
For instance, to add a side dressing of worm castings fertilize to an 8 x 4 foot raised bed, you would need about 10 ounces of worm castings per application. (8 feet times 4 feet = 32 square feet times .32 ounces worm castings = 10.24 ounces of worm castings.)
This is a small amount, but if you're using pure castings like Pure Black Castings™, which are concentrated and 99.9% all castings, it doesn't take a lot. Fertilizing with vermicompost, which is worm castings mixed with organic material, requires much larger amounts. Here is an article on this site which describes the difference between vermicompost and worm castings.
More Garden Fertilizing Info
World renowned canine author Digger Jones, sharing wisdom and wisecracks.