As we near the last frost date for most of the U.S., it's time to start the annual houseplant migration. Like many houseplant parents, I like to move my tropicals outdoors to enjoy the extra light, air and humidity. However, it's not as simple as just popping them outside when it's warm enough. Lisa Eldred Steinkop, the author of Houseplant Party and founder of The Houseplant Guru, shares her expert tips on how to get your houseplants ready to go outdoors.
Wait Until After the Last Frost Date
I live in the deep south. We have days during the winter when you get spring-like temperatures. Sometimes, it gets tempting to throw caution to the wind and put the houseplants outdoors before the last frost date. Don't do it—they are tropical species. Even early spring temperatures may be too cold for their liking. When in doubt, wait until the overnight temperatures are well into the upper 50s or 60s, and there is no chance for a surprise frost or freeze.
"If you are moving them out for the summer, you may want to up-pot them into larger pots if they need it before moving outside or right when you do so the mess is outside," suggests Steinkop, "Especially if they are rootbound because they usually need more water outside and rootbound plants would need even more."
Believe it or not, your potted plants still grew while indoors, and you probably didn't repot them during the growing season. Spring is the perfect time to refresh the soil and give them a nice new roomy pot to grow in.
Getting the Plants Acclimated
"Plants inside do not have as much protection on their leaves as they do when they are outside," says Steinkop. "They don't need it because they are trying to gather as much light as they can in our lower light homes." Consequently, an indoor plant needs to build up a thicker layer (cuticle) on their leaves before sun exposure, so they do not get a sunburn (yes, plants can get burned). "That is why plants should never be taken outside and immediately plopped in the sun," warns Steinkop.
How do you acclimate plants? "Put them on the north side of the house in the shade or under a tree for a couple of weeks to get it used to being outside, then move it gradually into the sun," Steinkop explains. She says it's comparable to going to the tanning booth a few times before you head to the beach so you don't get a sunburn from the sudden, intense exposure to the sun.
Also, protect them from the wind because the plants are not used to air movement, and the wind could stress them out and even damage them. "This acclimation process pertains to all plants, including cacti and other succulents," says Steinkop.
Not All Houseplants Should Summer Outdoors
Not all plants take well to the change in environment, even when you do it gradually. The most significant stressor is sunburn. "If they are not acclimated, they will sunburn, and with thinner leaved plants, it may be shocking enough to kill them," explains Steinkop.
Sunburned plants will wilt excessively or develop brown patches on their leaves. Research your plant before placing it outside to make sure you truly understand its light needs. Ambient light in a shaded outdoor environment is much brighter than many indoor areas.
"Some plants would rather not be in the full sun outside," says Steinkop. "High light plants are fine, but if you have a medium to low-light plant, such as an aspidistra, fern, or aglaonema, they will prefer to be in a shaded spot outside. Make sure the final location you want to place them out is a safe place for them."
Being outdoors means there's a chance for insects and other pests to reside in your potted plants. To help limit the chance for hitchhikers, use risers underneath your plants, so they do not sit directly on the ground. "This keeps the drainage hole off the ground and not only helps with drainage but will help keep insects, worms, centipedes and mollusks (roly polies) out of your plants," explains Steinkop.
Check Moisture Levels Daily
Potted plants in the outdoors will dry out faster. "Remember outside there is wind and more light, so your plants will need to be watered more often," says Steinkop. "Check them daily to see if they need water."
Plants in unglazed pots, like terra cotta, may even require watering every day. Remember to water thoroughly every time to ensure adequate moisture.