I mulch my beds with salt marsh hay during the growing season and I leave it in place over winter. In the spring there is an additional layer of leaves and pine needles. I am wary of leaving these layers in place since every year my garden is afflicted with powdery mildew, aphids, squash vine borers, etal. This layer can become rather thick as well. Therefore, I have been removing it in the spring before turning the soil, adding compost and applying a new layer of salt marsh hay. I have been tempted to work it into the soil, but do not want to keep the potentially diseased material and insect larva. Would you advocate just putting a new layer of compost on top of it all and fresh hay?