On our Centerville property, which is comprised mostly of old farm land, the soil is actually quite good for growing vegetables, especially on Cape Cod. There is at least 10-12 inches of loamy top soil, perhaps because the land around our old house has benefited from eons of decomposing plant material. Still, when we had a new septic system put in several years ago, I saw that the good soil lies atop pure sand, which is great for drainage, but tough for soil’s all-important water retention.
Optimal soil clumps easily with enough organic matter to hold some water, and also encourages all-important natural soil-building activities to occur, encouraging the growth of beneficial organisms like earthworms, good fungus, and other flora and fauna that create healthy soil conditions.
When we dug our first Cape Cod vegetable garden several years ago, we added a good six to eight inches of compost, purchased by the yard from a local supplier. (A yard is 27 cubic feet.) You can also buy compost by the bag from local garden centers like Country Garden in Hyannis—there are lots of good varieties, but our favorites are the completely organic varieties made in New England.
Compost is crucial for successful gardening on Cape Cod, whether your soil is a little light and sandy like our Centerville soil, or wet and full of clay like the soil on my son’s land, just one town over in West Barnstable. He had to laboriously pick, hoe, and double-dig his vegetable garden in unforgiving muck and then add reams of compost.