If you let your houseplants vacation on the back deck or front porch this summer, then by early September it's time to get them ready to move back inside for the winter. Letting your indoor plants spend their summer at "camp" is a great way to give them extra air circulation, increased surround lighting, and natural fluctuations in temperature and humidity. But when nighttime temperatures begin to dip below 50, have a plan ready for moving them back inside. Here are some helpful tips...
Because conditions differ widely between the inside and outside of your home, a gradual reintroduction to the indoors is best. Sudden changes in temperature, light, and humidity can be traumatic to plants, resulting in yellowed leaves, wilting, and even death. Start by bringing your plants inside just at night. Granted, if it's a huge plant that you'd rather not move more than twice a year, bring it in and leave it there; it's likely established well enough to cope with the change in conditions. Plant trays with casters on the bottom are a fantastic solution for large plants!
Try to have your plants' winter lodgings planned out in advance. Rather than stick all plants in a corner and hope for the best until spring, consider each plant's light and water needs. Maybe wipe down your windows for extra light, install some ceiling hooks for trailing plants, and rearrange furniture to make space for larger plants. Your plants are alive and not pieces of summer lawn furniture to be stored. Treat them with love!
Inspect plants for signs of hitchhiking insects and treat appropriately before bringing plants back inside. Horticultural Neem oil works well for topical application or use a houseplant systemic... these are safe to use since your plants will no longer be in contact with pollinators. Remember to wipe down the outsides of your pots as well.
If necessary, re-pot plants into larger containers. One pot size up (i.e. from a 12" to a 14") is big enough to allow a couple years of growth without being too big and causing root stress. Scrub the pot, add fresh bagged potting soil (not garden soil which may have diseases), and replant.
Usually, if your plants have been outside in bright light and you move them into much lower light, you can expect some leaves to fall off. New leaves should form as the plants re-adapt to the lower light. If they've been outside in high light put them in high light indoors, like a south window or under plant lights.
Don't overwater during the winter! Let the soil surface get dry to the touch before watering again. Water succulents even less often, waiting for the leaves to look a bit deflated and un-succulent. Since it is so dry in Colorado during the winter months, humidity trays can help keep your houseplants happy without overwatering. Simply use a saucer and fill with pebbles or rocks. Fill the tray with water halfway up the rocks, but do not fill so much that the plants are sitting in water. As the water in the tray evaporates it creates a lovely little habitat for your plant.
In your home and in nature, plants are starting to slow down and take some quiet dormant time over the winter. We recommend you stopping fertilizing your plant in the fall and winter to give it a rest from growing. But when you are moving a plant indoors it is ok to give it a weak dose of liquid houseplant fertilizer. Even better, mix a handful of worm castings into the top inch of soil. Worm castings aren't a fertilizer so much as a soil builder. They work by promoting and supplementing your plant's instinctual growth habit rather than acting as a growth-forcing fertilizer.