You can apply compost on top of the soil anytime of year - I just added some today around my squash plants and sweetpeas. There are advantages to each season. Waiting until the soil warms up in the spring, then adding compost, means you have warmer soil for heat-loving crops like tomatoes and peppers. Applying compost in the fall means the weather will break it down and the worms will take it down, so the garden will be ready in the spring. In summer, the compost will shade and cool the soil. Dig in and spread that compost. Keep Growing, Marianne Binetti