Shawn.... ooops... I was typing so fast, I mis-typed... Sunflowers are NOT a nitrogen fixer, but they are great for pollination, green manure, breaking up the soil, shading squash, and bush beans, and attracting pollinators.
And then there's this....
Author: BioBilly
"Sunflower; helianthus an annual plant [that at the time of this publication was considered by farmers as a weed]. The roots dive deeply to pull up minerals and fiberize the soil. Stalks breakdown quickly and add organics to the soil. A heavily planted field of sunflower will produce almost double the amount of green manure as compared to any other plant. Sunflowers make a wonderful mother plant for corn, whose deep diving root will grow in with the shallow corn roots to help stabilize the corn.
[This makes sense when one considers the physics of the two plants. Pound for pound a pipe is stronger than a solid, because a pipe has to have two surfaces deflected before it will bend, compared to one surface on a solid. A sunflower has a pipe like stalk, corn has a solid stalk. In high winds corn will blow over first, but a companion sunflower will catch a corn stalk in its arm like leaf petiole and ride out the storm together"
And this: (which I really love)
Author: Dan D Lyons
"Next, I would consider planting a ring of giant sunflowers under that mulch around your tender apple tree to give it some much needed shade from the coming July/August sun. I know it says to plant the apple tree in full sun, but please trust me on this one, I have had lots of
experience killing young trees by baking them in the sun Once your sunflowers are about 1ft tall, then plant a planting of pole beans/bush beans intermixed in the spaces around the sunflowers and apple tree. The pole beans will use the sunflowers (that are now about 2-3'' when the beans are sprouting) as a natural lattice and also quickly add nitrogen to the soil and give you an edible crop. The birds will give you some very rich 'guano' fertilizer when they show up to eat those mature sunflower seeds. You can even save a few of the sunflowers and beans to use as seeds for next year . This planting will look very nice a be a good conversation piece in suburbia. After harvest you have a ton of biomass (leaves and stalks) to mulch your apple tree with. Then in the fall you could go with a more
perennial companion planting to accomplish the same thing that your sunflower/pole bean guild did but on a longer term basis, many of the things Tel Jetson mentioned in his post to you."