The dangers of monoculture

My garden is cranking again this summer, and one of the most remarkable things about a garden is just how much it varies year to year.

You'd think, given how much remains the same, that a garden would be a consistent thing. The light and warmth of this latitude? More or less the same as last year. The drab Virginia clay to which I'm constantly adding mulch and nutrients? It remains identical. The crops? Pretty much last year's planting, meaning bush beans and strawberries, tomatoes and spaghetti squash.

Everything the same, yet the yield so different.