How To Quarantine Plants

Houseplant sales have surged in the past few years, according to the National Gardening Association. Some plant owners, new and seasoned, refer to themselves as plant parents and buy houseplant insurance, indicating just how dedicated they are to growing indoor greenery.

Certainly, that dedication extends to carefully selecting new plants, and knowing how to quarantine sick plants to keep their “siblings” healthy. The process typically starts at introduction.

Inspect the Houseplant

Look for insects and diseases before you add any plant to your collection.

When shopping for plants, check the tops and bottoms of leaves, the stems and stalks. Move the potting soil around to check for bugs there. Needlessly to say, if you find insects or any signs of disease, don’t buy the plant. Keep in mind if one plant is sick, the others displayed around it may be, too.

Also, keep an eye on all the plants in your collection. When you water them, look for insects and leaf spots. Every month or so do a more thorough inspection, as you would with a new plant.

If you receive a plant as a gift, inspect it well. If you spot trouble, don’t add it to your collection just yet.

What you’re looking for

Some common plant diseases:

• Fungal leaf spots: A sign of anthracnose disease. These are white and can decrease plant longevity, growth and overall appearance.
• Bacterial leaf spots: Common in cold and wet environments. They appear as black areas with a yellow circular pattern.

Some common insect plant pests:

• Mealybugs: Resembling pieces of white cotton and wingless, often found in moist, warm environments.
• Whiteflies: Soft-bodied white-winged insects, triangular and resembling soft, smooth leaves.
• Spider mites: Tiny, reddish-brown insects with light-yellow legs.

If you find any sign of disease or insects, better safe than sorry — quarantine the plant until you’re sure it’s healthy.

Set Up a Quarantine Spot

Quarantining means keeping the sick plant in a different room from the others. According to Dr. Gladys Mbofung-Curtis, plant scientist for Garden Safe, the ideal quarantine time is three or four weeks.

Tips for finding the best quarantine spot:

• Emulate conditions where the plant thrives and will eventually be placed, such as bright, direct sunlight or partial shade. Ask your local garden center and/or read the information that came with the plant about optimal conditions for growth.
• Choose a place you go into every day so you don’t forget to check on the plant. Out of sight, out of mind!

Apply Insecticide

If you’ve found insects, remove them with a damp rag, tweezers or a cotton swab dipped in vegetable oil or insecticide spray. Or put the plant under a light spray of water or insecticide in the sink to wash off the bugs. Also spray the soil; the insecticide kills the insects on contact. Remove any dead bugs you see on the plant or soil.

If you find leaf spots, remove and destroy the infected plant material, Mbofung-Curtis says. Then spray the insecticide in the same manner outlined above.

Continue insecticide treatment throughout the three- to four-week quarantine. “Treating [the plant] once a week or every two weeks can control common houseplant bugs and prevent fungal infection,” Mbofung-Curtis says. She recommends Garden Safe Brand Houseplant and Garden Insect Killer.

Spray the tops and bottoms of the leaves and the stems, stalks and the top of the soil. Then water the plant as usual.

Two additional insecticide options:

• Debbie Neese, a horticultural expert at Lively Root, a San Diego plant nursery, suggests Arbor Bio Insecticide. It’s concentrated, so one bottle goes a long way. “Mix [it] up as needed and use a spray bottle or drench the soil,” she says.
• If you’d rather avoid chemicals, make a DIY insecticidal soap from common ingredients.

How Do I Know My Plant Is Ready to Leave Quarantine?

After three to four weeks in isolation, do one last inspection before bringing the plant out of quarantine. Don’t be shy about geeking out with a magnifying glass or moving the plant directly into sunlight for a closer look. You don’t want to repeat the quarantine cycle. If all looks good, add that healthy houseplant to your collection.