The easiest way to convert sod or weed areas to beautiful garden beds is by using a well known permaculture technique called sheet mulching. This technique suppresses weeds and causes the soil to retain maximum moisture.
A key material to suppress weeds and retain moisture is cardboard, which is the first layer to lay down. After this, various organic materials are added that act as both mulch and soil amendments. These added materials will break down over time and cause the soil to become extremely rich, especially when added on top of the clay that dominates the Northern Colorado region.
Organic soil amendments are very important, as our clay is very dense and does not support healthy root development. Some common examples include manure, leaves, compost, and straw. Wood chips can also be used, but they are slow to break down, which can be good or bad depending on your objective. Woody material buried deep can be good, as it will eventually decompose and provide rich habitat for worms and other soil organisms. Wood chips applied as a top layer can provide a long lasting weed barrier.
Generally, it is a good idea to wait a year after sheet mulching before planting. This allows materials to break down and for soil organisms (worms, bugs, microarthropods, bacteria and fungi) to become established. After this, tilling is not required; in fact, it is even discouraged, as it upsets the soil balance and releases carbon into the atmosphere. Thus, less work is ultimately required.
To maintain the bed, organic matter is added to maintain a thick enough mulch covering to suppress weeds. Weeds that grow through the top loose mulch covering are easily removed.
If you want to plant immediately, then it is a good idea to apply a healthy layer of plant bed mix, which is typically a premixed topsoil and compost blend.
Finally, if you are replacing sod, then you may need to modify your sprinkler system. This is something we do frequently, and we would be happy to explain the various options for you.
We are always very happy to help you accomplish your goals efficiently. Happy gardening!