Cool Season Grasses
Fall yard maintenance is crucial where the turf grass is a cool season grass such as fescue. Fall is when cool season grasses should be seeded and it is the best time to apply fertilizer. Fall is also the best time for applying lime where soils are naturally acidic. Overseeding at the wrong time wastes the effort and the seed, but it does not cause long term problems. Applying lime at the wrong time has the same effect. Fertilizing cool season grasses at the wrong time can be disastrous, however. It creates conditions favorable to the development of fungus diseases and can lead to the need to use fungicides or even start over with a new lawn.
Though warm season grasses such as bermuda grass, zoysia, centipede and other southern grasses benefit best from spring and summer fertilization, cool season grasses should be fertilized between September and November and again in February or March. In no case should a cool season grass be fertilized between April and August. Spring fertilization can produce lush spring green growth that is very attractive, but that lush growth also makes cool season grasses susceptible to developing persistent fungus diseases such as brown patch. (image here: http://www.turffiles.ncsu.edu/diseases/Brown_Patch.aspx). The goal of cool season grass fertilization is to build up the roots so it can better resist the onslaught of diseases and summer heat. Growth continues underground until winter arrives and resumes in late winter and early spring. Grass plants need to have nutrients in the soil during those times.
The weather can turn wet and cold quickly, plastering any leaves that fall at the end of the season to the ground. Leaves block out the sun that grass needs to stay healthy during the winter and inhibit air circulation. This weakens the individual grass plants, making them less able to successfully compete with any weed seeds that may be present in the turf area. When turf grass is less robust, it is easier for weeds to become established. Keeping the lawn clear of fallen leaves can allow the homeowner to avoid having to fight fast-spreading weeds in the future. Persist with fall yard maintenance until after leaves are finished falling.
Protect Landscape Plantings
Clean up planting beds in the fall. Leaves accumulated around the base of shrubs can hold moisture that can encourage disease development. Where there are annual flowers or a vegetable garden, yard maintenance that includes cleaning out the remains of those plants after the first frost eliminates a disease route and can guard against insect pests during the following growing season. Insects often overwinter in plant debris, the dead plant material left after the growing season and fall frost have finished with ornamental or vegetable garden plants. Collect all of that material and put it into a compost pile where possible. The pile will heat up to kill insects and disease organisms, leaving the gardener with beneficial compost full of nutrients and necessary organic material.