The rule of thumb is to plant winter pansies after September 15, when the weather cools. If you plant too soon and the weather is too hot, pansies will become leggy. Plant them in a well-drained, sunny location.
Late-summer is a great time to dig and divide perennials. In fact, many perennials should be divided every 3-5 years. Division is done by uprooting the entire plant with as much of the root ball intact as possible. Generally, the center of the perennial or grass will be dead, but the outer portions will be healthy, resulting in a clump with a doughnut-like appearance. Look for natural splits in the "doughnut" and begin teasing the roots apart into approximately six inch round hunks. If the roots are quite entangled, you can cut the plant into sections using a sharp shovel. Replant and water well. If you have extras you can share them with your friends and neighbors.
Coax Poinsettias into Bloom
Mid-September is the time to bring poinsettia plants indoors and condition them for holiday bloom by providing total darkness for about 16 hours each day. The method I prefer is to set the plant in a bright room for 8 hours and then either put a box over it or put it in a closet for 16 hours. In early December, when the leaf bracts begin to show color, stop the conditioning process and leave the plant in a bright location.
Move Houseplants Indoors
Valuable houseplants that have summered outdoors should be groomed and prepared for their return indoors. I bring mine indoors each evening and take them back outside each morning, gradually shortening their outdoor time and increasing the time they spend indoors. After two weeks or so, they're ready to remain inside full time. Some species exhibit leaf loss or browning of leaf edges after being moved indoors. This is usually temporary and improves after plants adjust to lower light and humidity levels indoors.
As the weather cools and the rains return, cover your compost pile with a tarp to keep the rain off. Too much water will slow the decomposition process. Remove the tarp each time you turn the pile. This will allow fresh air to enter which will keep the pile cooking.