If possible, put your houseplants outdoors for the summer. Even in the best of cases, our homes never quite equal the conditions that exist in nature and therefore our houseplants are essentially under constant stress. Just as humans adapt better to a stressful or boring desk or factory job when they have an annual vacation, plants grow best when they receive two or three months of summer respite during which they can enjoy better light, higher air humidity and cooling rain that opens pores and removes dust and grime.
Wait for Warmth
The vast majority of indoor plants are tropical plants that are not very tolerant of cold. Even a night temperature of 50˚F (10˚C) can be harmful, especially when the plant is used to indoor nights that were never below 70˚F (21˚C). Not only should you wait until there is no more risk of frost, but for night temperatures stay above 60˚F (15˚C) most of the time before putting them outside for the summer. In many climates, that means mid-June or even later.
Before placing your vacationing houseplants outdoors for the summer, however, remember they need a period of acclimation before they will be ready to tolerate the sun, otherwise their foliage may burn badly. Put them them first in the shade for about a week and then in part shade for another week. Only after that will they be ready for full sun.
Note that this applies even to plants that may have been getting full sun indoors, like cacti. Window glass filters out ultraviolet rays, so even a plant that has been growing in the sunniest spot in your home risks a bad sunburn if you transition it outdoors too rapidly.
The Right Plant in the Right Place
Of course, just as you do indoors, it’s important to give each plant the conditions it likes when it goes outdoors: shade for ferns and philodendron, part shade for begonias, pileas and phalaenopsis orchids and full sun for cacti, most succulents, bougainvilleas and others.
You can learn more on about the needs of houseplants in my book Houseplants for Dummies.