I just bought a new house and have decided on where the garden is going to go. My soil is mostly clay so I built some raised beds with 2x4. I'm using 2 year old sheep manure mixed with wood chips and straw (with some lime added). My plan is to make plastic domes over them to allow them to warm up quicker in the spring and add a month to the growing season here in Iowa. Does this sound like a good plan?