One of the basic points of permacultural design and water usage is that bare soil is the single greatest source of loss of water in growing food. The principle of layering plants in space and time helps reduce the overall water consumption of a garden and also increase its productivity, as much as this goes against conventional (non-sustainable) gardening approaches. The overall goals are to prevent soil from being exposed, and ensure that plants mutually support eachother, and so forth.
I have been looking into applying this with asparagus, to reduce water usage involved in growing this food, but have been unable to find recommendations for plants to plant alongside (and given the spacing between plants, this leads to a lot of exposed soil). I would like to grow asparagus with as little external water input as possible. What can I plant next to asparagus to help cut down on the water loss, weeding requirements, and fertilizer requirements? I.e. how can I grow asparagus sustainably?