Trees / Shrubs – Keep planting
Flowers – Dig tender perennials such as canna, dahlia, and elephant ears before a hard frost. Store in garage or root cellar where temperatures are cool but not freezing.
Lawns – Lawns can be seeded easily in September due to increased rainfall and decreased temperatures. Weed seeds are not as likely to compete in fall seedlings also. Remember to use a starter fertilizer with your seed. Depending on rainfall, watering may need to continue into late September.
Vegetables and Fruit – Harvest squash and allow them to dry thoroughly before storing. Frost can occur this month so cover tender vegetables with plastic or cloth to prolong your harvest season of tomatoes and peppers. Vegetables like cabbage, parsley and spinach can tolerate cold well.
Pesky Bugs – Wasp nests become very visible once the leaves start falling off. If the wasps are not bothering you, leave them alone, as they will complete their life cycle naturally & move on. Yellow jackets are more aggressive and will invade your picnic, so be careful of them.
Planting-Plant balled & burlapped, balled & potted, and container-grown ornamental plants.
Transplanting – Dig plants that were root pruned in the spring. Deciduous plants may be moved bare root, but narrow leaf evergreens should be moved balled and burlapped or balled and potted. Plants that are to be transplanted in the spring should be root pruned now.
Fertilizing – One of the first priorities after selecting a fall planting site and before planting is to test the soil. Soils in established landscapes should be tested every three years and corrective action taken as needed.
Watering – Irrigate newly planted or established ornamentals any time there is less than 1 inch of weekly rainfall and plants are actively growing. Apply water at the rate or 1 quart per square foot of planting area on poorly drained soils. On well-drained soils, use a half-gallon of water per square foot. Be sure to maintain adequate moisture levels this month to ensure good root growth prior to winter dormancy.
Plant protection – For newly planted ornamentals, you may apply a pre-emergence herbicide before spreading a 2- to 3-inch layer of mulch over the soil in the bed or around trees.
Source: Rebecca Finneran – MSU Extension & Bulletin E-1947