Crops which like warm soil, such as tomatoes, squash and pumpkins, should not be mulched in a Northern garden until the soil has warmed up completely. I kept these Beefsteak Tomato plants cultivated until it was time to mulch. I put a layer of black paper mulch down, and covered it with chopped straw. Both are biodegradable, and can be just plowed in after we pull the tripods of fiberglass 'electric fence' posts to support the plants. It is a lot of work to mulch carefully, but it saves far more time weeding later. The top of the chopped straw dries out quickly even in our damp climate, making plant diseases less likely.