I love me some green manure! Specifically, I love nitrogen fixing plants like alfalfa. Do you think your only choice is to grow plants for harvest, or cover crops? Why not both?
I built a new garden space this year to add to the Liberty Garden. I use the term Liberty Garden to refer to all the outdoor space devoted to growing useful plants at my home. The new garden zone is a small raised patch surrounded by a wooden frame. It is only about twelve by six feet1, so space is precious. The plan was to completely fill up the frame as is done with square foot gardening. Well, things do not always go according to plan. When it became time to plant, I was not ready with enough plants to fill the space. In fact as I write this I still have Amaranth2 and other babies in the windowsill nursery.
Since I did not have enough plants, and because I like to experiment with things like this, I planted what I could and filled the remaining space with alfalfa. Experiment is not the right word here as there was nothing scientific about this process, a gamble would be a better term. I selected alfalfa because it has deep, robust roots to really work the soil, it is a nitrogen fixer so a nice organic nitrogen source, is non-toxic (actually rather nutritious), has flowers that attract pollinators and other beneficial insects, and other nice qualities. The following is a picture showing part of the patch.
The results have greatly exceeded my expectations. The alfalfa has crowed out weeds, improved the soil and attracted pollinators as I hoped, but it has also attracted other beneficial insects such as lady bugs. You may see one or two if you look closely in the following picture.
What I did not expect was a beautiful herd/swarm/crowd/abundance of really impressive spiders. I do not have any pictures of them but they could be what is pictured at the following link. They must be a hunting spider of some kind as I have not seen any web. They are bigger than the wolf spiders I typically see; these measure about the size of a silver dollar. The garden patch has been nearly pest free with these babies patrolling. The spiders must need a little cover from birds as the population has been richer when the alfalfa is not trimmed lower than one foot.
Another pleasant surprise has been how the alfalfa has provided a wind brake for the tender young plants. Once the plants get to be about ten inches tall they are able to handle the sometimes brisk wind. Until that time, they have alfalfa to protect them. The following is a picture of some sage happily thriving surrounded by alfalfa.
The net is that I am really pleased with the alfalfa test. Filling the available space with alfalfa provided all the benefits I hoped for and more.