Cooler temperatures indicate it is time to tend to your container garden. Bring inside any plants that are not winter hardy and care for the pots left out in the cold.
Houseplants in pots should be brought in before turning on the furnace for winter. Find a place for the plants where they will receive maximum amounts of sunlight, but keep them out of the way of cold drafts. A humidifier will help houseplants tolerate dry air; if you do not have one, use a spray bottle to mist leaves.
Inspect plants for insects and mites before bringing them inside. Remove whiteflies with a small, handheld vacuum. Rub scale insects and mealybugs from the plant with your fingers or a toothbrush. Wash spider mites and aphids off with a spray of water. (Mites and aphids have piercing/sucking mouthparts that will break off in the leaf tissues, killing the pest but not harming the plant.) You can also control insects and mites with insecticidal soap. Always read the label before applying any product.
Even if you don't see any insects on your plants, examine the entire plant and container closely. Last year, a toad made a home next to the roots of my peace lily. I was transferring the plant to a new pot when my new friend announced his presence. Once I recovered, I was able to catch the toad and return him to the outdoors, but I would have rather removed him from his home before he explored mine.
Trim dead leaves from the plant. Cut back vining plants if you wish to reduce their size.
Once inside, the plants will adjust to low light conditions and different temperatures. My plants typically lose leaves for 3-4 weeks after they are moved. Water only when the soil is dry 1 inch deep in the pot. Preferably, water until excess moisture comes out of the bottom of the container. Use trays to catch the excess or set the plants in the sink or bathtub when watering. Fertilize minimally as the plant is absorbing nutrients very slowly. Salts from the fertilizer can accumulate in the bottom of the pot and burn the plant.
Re-potting is best done in the spring or summer when the plant is actively growing, but a plant that has outgrown its container can certainly be moved into a larger one.
Containers that will be left outside need a little care too. Small trees, shrubs and perennials can survive in containers over the winter, but keep in mind that the soil will not stay as warm above ground. Large planters may have enough soil to protect plant roots, but small pots will likely freeze. Dig a hole and set the container in the ground for the winter, or wrap thin foam insulation all the way around the container. Make sure to water the plants when the soil is dry 1 inch deep and temperatures are above freezing.
Annuals can be left alone until they freeze. Remove plants as they die.
Terra cotta pots may crack if left outside all winter. To protect them, store in a location where they will not freeze, or insulate as described above. Containers made from other materials are less susceptible to freezing and thawing. Leaving soil or potting media in any container increases the risk of breaking. Preferably, empty all pots and store them in a basement or garage.
Keep an eye on the forecast to determine exactly when plants should be brought inside. Many houseplants are not hardy below 40 degrees. My own plants will move from the porch to the inside of the house this weekend, and I'll be on the lookout for hitchhikers.