Lasagna gardening is wonderful.

For a different answer, I'd say mulch, lasagna-style or "otherwise":

It insulates from extremes of heat & cold, helps retain valuable moisture, protects little seedlings & rootlets from drying, adds a finished look to the flower bed, &, when it finally goes the way of all life & decays...it nourishes the soil.

I thought I'd pass this along - this site has a lot of good tips for gardening, really easy for me to waste a lot of time on there. Its got ton of info on plant nutrients and other stuff too.

Here is a link that might be useful: BHG