The Center for Agriculture, Food and the Environment at the University of Massachusetts Amherst indicates fall is the ideal time to improve the soil for next season. Amending the soil in the fall allows it to react accordingly over time and reap the benefits in spring. Gardeners should till the soil and add compost or manure, which will counteract many nutritional deficiencies. Worm castings also are good to add, particularly for summer vegetable gardens. The gardening company Park Seed says that worm castings are high in minerals and effective at holding water — so much so that they even can be used alone in place of potting soil. Crushed egg shells, coffee grounds and banana peels also can be added in the fall.