After reading some of the books and papers on Biodynamic Agriculture, this year I am planting a leguminous cover crop of Australian Winter Peas, Psium arvense, in the current vegetable garden areas.
Usually I have the fall/winter garden area fully planted in mid-October for next year's garlic and shallots, and then I mulch in late fall after they have sent out a few leaves. This year I plan a much smaller amount of garlic and shallots, so the remaining area will get the peas to fix nitrogen. (I have a fence line where I grew spring peas 2 years ago, and I noticed an increase in healthy production there last year, which I attribute to the nitrogen-fixing abilities of the earlier peas.)
I have also been researching temperate climate perennial shrubs and trees that fix nitrogen. Most of the trees that fix nitrogen are tropical, but there actually are a few temperate zone trees I've come across that fix nitrogen. Fortunately the shrub list is longer! It will be a lengthy process of time and money to get some of each planted over the next several years, but it's do-able.
After seeing the success with inter-planting vegetables in the flower beds this year, I'm definitely moving away from "rows" or "plots" of annual vegetables and into mixed bed areas that combine perennials like herbs, bulbs, flowers and fruit/nut trees/bushes with my annual vegetables.
I did notice that as productive as the veggies in the flower beds were, the Brix (nutrient density) in the tomatoes was below par. I don't think I have amended the flower beds since I first built them 4 years ago although the flowers have been lush, but clearly the soil is deficient in some minerals or at least mineral balance. Planting some nitrogen fixers (maybe peas next year?) in those beds will help the soil fertility in general, and I'll add some minerals before this winter sets in, and some organic fertilizer (5-4-3).
The bigger challenge is to move my mindset away from "only vegetables" in a specific area, and get my mindset onto areas that are mixed with a variety of perennial and annual plants that support each other in many ways. With some careful planning over the winter, I hope to get started next spring with mixing up my vegetable and flower garden areas. It will take several years to fruition I'm sure, although no garden area is ever static.
I just got the book Gaia's Garden yesterday via inter-library loan, and it will help point me in the right direction(s), esp. when mixed with my own research. The library book is the original edition but I do have the newer 2nd edition on my Wish List. From just the few pages I read last night, it is well worth the money!