Garden Variety: Isolating outdoor plants before moving them inside prevents spread of disease, pests
Fall is a popular time for gardeners to give away plants as they move potted specimens indoors (and run out of space) and divide perennial flowers. Picking up plant freebies is a great way to expand a plant collection, but plants should always be quarantined and/or examined with caution before being moved into a new home or yard. They may transport insects and mites, disease pathogens, weeds, earthworms, and other undesirable creatures.
Examine plants for signs of insect activity first. Scale insects, mealybugs, thrips, spider mites, and other tiny insects often go unnoticed until populations are high enough to cause damage. They can easily spread to other plants in the vicinity and populations may balloon quickly in indoor settings. If possible, quarantine new plants by keeping them separate from the plants you already have for a week or more and continue to look for insects and signs of insect activity.
Scale insects are typically attached to stems and branches, or to the undersides of leaves. They range in color and size depending on the species and may look like a bud scar, lenticel, or other plant part. They can usually be flaked off with a fingernail. They may drip sticky honeydew on leaves below where they are feeding.
Mealybugs are white and more noticeable but often hide in leaf axils or on the undersides of leaves.
Thrips and spider mites are best detected by placing a piece of white paper under the plant and tapping the leaves. Look for black specks moving on the paper. A magnifying lens can aid in identification. Without a lens, round specks are most likely spider mites and elongated specks are most likely thrips.
Next, examine plants for signs of disease. Spots on leaves, lesions on stems, and discolored roots may indicate the presence of plant pathogenic fungi or bacteria. Remove infected leaves or prune out infected parts if possible. If the main stem of the plant has cankers, lesions, or other affected areas, or roots show heavy damage/decay, toss the plant. Treatment for fungal and bacterial diseases is preventative only and introducing infected plants only exposes more plants to the disease pathogens.
Weeds usually travel in the form of seeds or pieces of special roots called rhizomes. They are frequent hitchhikers on divisions of perennials such as hostas and daylilies. There are a couple of options here – remove soil from the roots of the plants prior to planting or take a wait-and-see approach. Removing the soil is the best option.
To bareroot plants, place them in a bucket or tub of water and tease roots apart to loosen soil and remove it. An alternative is to place plants in a basket or on a screen and wash soil from the roots with a high-pressure nozzle, taking care not to damage plants or roots in the process. Plant the plants in their new locations soon after root washing, taking effort to keep roots moist between washing and planting.
If barerooting the plants is not possible, go ahead and plant them, but watch diligently during the next growing season. Remove any unwanted plants that sprout amongst them as soon as possible. Bermudagrass is an especially troublesome hitchhiker that may not appear until mid-summer.
Earthworms are an interesting hitchhiker. Many gardeners like them, consider them to be beneficial, and generally find their movement with plants acceptable. However, the earthworms that are common in gardens and landscapes today in the U.S. are not native to this country and are some of the earliest invasive species. In recent years, experts have expressed increasing concern about the effects of earthworms on native ecosystems. Certain species, such as Asian jumping worms, are considered especially problematic.
Washing plant roots as described above removes unwanted earthworms and their eggs.
Finally, plants may carry along other creatures such as slugs, snails, roly-polys, frogs, lizards, mice, voles, etc. Movement of these creatures is most common with potted plants. They are easily found by removing plants from their pots and barerooting the plants or at least inspecting the soil closely. Remove any extra animals from plants and pots before bringing them inside.