Manure was mentioned in an earlier post. Cow manure is typically what is available at the box stores in bags for single digit plant quantities. For 100's of plants, you'll need manure in bulk quantities. Bags of cow manure is not going to be practical. Cow manure in bulk i've found to be difficult to get, but horse manure is easy to get. Cows digest what they eat several times and as a result the plant seeds are killed and their manure does not generate weeds where it is applied. (It may help grow what is already there.) Horses have a different digestive system and seeds can pass thru them without killing the seed, so when horse manure is added to a garden you're adding all those weed seeds as well that will sprout. However, the compost process raises the temperature of the compost pile high enough to kill the seeds, so the composted horse manure can be applied without the problem with the weed seeds sprouting.
P.S. Chicken manure is high in nitrogen and will damage the plants if applied directly. So, same process - compost it first.
