Bring plants indoors now, but leave the pests behind

September is the month to bring tropical and subtropical plants indoors, but make sure you inspect them properly first before bringing in unwanted pests.

Coleus, arrow leaf, shamrocks, spider plant and asparagus fern. Photo by Rebecca Finneran, MSU Extension
Coleus, arrow leaf, shamrocks, spider plant and asparagus fern. Photo by Rebecca Finneran, MSU Extension

Many gardeners decide to give their indoor plants a summer vacation outside for the summer. Smart gardeners situate plants out of direct sun so they don’t get fried into crispy critters. When temperatures are mild and rainfall is good, indoor plants enjoy their escape from captivity. However, the month of September looms with its first chances for light to heavy frosts. Tropical and subtropical indoor cuties cannot tolerate that nonsense and need to be back in their winter homes. Before any of the plants cross the threshold, they need to be checked for unwanted hitchhikers. This list can include flying, walking and scale insects, cocoons from moths, slugs, snails and the occasional “party favor” hidden inside the drain hole of the pot. Being an exotic plant on a Michigan deck does not give the plant any immunity from local insects. Insects like spider mites, scale and aphids have no problem widening their menu options to include your summer plant vacationers.

If only a cursory inspection is done, many things including insect eggs can get missed. Those things may be kept in check while they are outside by natural controls, but can be a major annoyance indoors. A quick and incomplete inspection and putting the pot into a bucket of water to float out any critters minimizes a number of problems. Your deck or patio is the perfect place to do plant tune ups before they are brought in. Get a bag of soilless potting medium, water and some clean pots and do it right. The time spent now will be just a fraction of what it will take to conquer an insect problem that migrates onto other plants or to track down an elusive tree frog indoors.

Before beginning your inspection, Michigan State University Extension recommends watering the plant thoroughly. Slide the plant out of the container and check the soil, especially at the bottom of the container. Often, there will be ants that have spent their summer vacation digging out the potting medium and carrying it away. Or there could be assorted sowbugs and pill bugs enjoying the organic matter. When a cavity has been created by the missing potting medium, small frogs can move into the space. Later, when the plant comes indoors, Froggy will exit and housecat hysteria will ensue. This is the perfect opportunity to pick off some of the old soil and use the new soil to repot the plant. However, if the roots are crowded, it’s time to pot up to a bigger container. Water the newly repotted plant well and let it drain well before moving the plant indoors. If the plants are on a deck that has spaces between the boards, your drop-in insects will just squeeze between the boards and move in from the bottom.

Inspect the leaves and stems for insects or eggs especially on the bottoms of leaves. Commercially prepared insecticidal soap is a good product to use if there are spider mites or aphids. For the unseen insect eggs lurking below the foliage, you can apply a systemic insecticide drench while your plants are still outside. The insecticide will move up into the canopy of foliage just in time for hatching eggs. The juvenile insects will not be able to become established on a treated plant. If the indoor plants were put into the soil in the garden, when digging them up look carefully for and remove earthworms. Outside, earthworms are valuable, but when confined to a pot, they can cause damage as they churn around in the restricted area of the pot.

In most places in Michigan, the date you want to have your plants inspected and moved back indoors is Sept. 15. Most years, this will be before it’s too cold, but if you don’t do the work of inspecting and repotting and leaving the critters outdoors, insects, slugs and tree frogs will just recolonize your plant hotel.

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