Northern & Central Midwest
Purchase bulbs for planting before a hard freeze (although you can usually plant beyond that time since the soil is still warm). Plan the garden with drifts or groupings instead of "soldiers" in straight lines, and use a mixture of large and small bulbs for a nice effect.
Keep the Vegetable Garden Going
Keep harvesting vegetables that are producing in your vegetable garden. As plants finish producing, pull and dispose of them in your compost pile or city composting facility. Plant the empty spaces with spinach and greens for late fall harvest. Top with a cold frame as the weather cools.
Seed a Lawn
This is the ideal time to seed a lawn. Rake the seedbed smooth, add a layer of compost or topsoil if necessary, and broadcast an appropriate grass seed for your climate. Apply straw mulch and keep the seeds moist until they have germinated and grown a few inches, even if you have to water every day.
Clean Up the Orchard
As apples, pears, and plums fall, pick up the fruits and bury or use them to make excellent cider and sauce. Fallen, rotting fruits are great havens for German yellow jackets, and overwintering spots for insects and diseases. Keeping them out of the orchard will go a long way toward preventing problems next year.
Plant and transplant evergreens such as pines, yews, spruce, and firs by the end of September. Their fibrous root systems need plenty of time in warm soil to put out new roots for winter. Water them well and continue watering until the ground freezes.