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Quarantining new plants

Also known as Isolating new plants, Plant quarantine

Growing know-howDepends
Houseplants for sale: inspect before you buy and isolate at home Photo: David Howard · CC BY-SA 2.0

In short

Many houseplant pest problems arrive on a newly bought plant. Inspect every new plant carefully and keep it away from your collection for a few weeks, checking it regularly, before letting it join the others.

How it looks

Quarantine means keeping a new or returning plant in a separate room or area, not touching your other plants, while you watch for pests and disease. Sources suggest from one to two weeks (Wisconsin) to at least three weeks (Colorado State); Iowa State suggests 3–4 weeks for plants brought back in after a summer outdoors.

Signs

What to look for during quarantine: small insects on new growth and under leaves (aphids, thrips, whiteflies), cottony tufts in leaf joints and on roots (mealybugs), bumps on stems (scale), fine speckling or webbing (mites), sticky honeydew or sooty mould, tiny flies over the mix (fungus gnats), spots or soft, rotting stems.

Life cycle

Many pests start as eggs or very small immature stages that are hard to see, so an infestation may only become obvious after a week or more; repeated checks matter more than one inspection.

What favours it

Risk is highest for plants from busy shops or swaps, plants that have been outdoors, and plants bought from greenhouses where pests breed year round. In warm tropical homes, pests can build up quickly.

Prevention

  • Inspect before you buy: look under leaves, in leaf joints, at new growth and, if possible, at the roots.
  • Keep the new plant in a separate area for a few weeks; do not let its leaves touch other plants.
  • Check it every few days with good light, a hand lens helps; yellow sticky cards nearby can reveal flying pests.
  • Wash hands and tools after handling it.
  • For plants that have been outdoors, rinse the foliage well before bringing them in.

Treatment

Start with the first step and move down only if the problem persists.

  1. If you find pests, identify them first, then start with the least harmful options: remove affected parts, wash or wipe leaves, dab mealybugs with alcohol on a cotton swab (test on a leaf first).
  2. If needed, use insecticidal soap or horticultural oil; follow the product label.
  3. Extend quarantine until repeat checks show no pests.
  4. Discard heavily infested plants when control is impractical; Colorado State advises discarding plants with cyclamen mite.

Pros and cons

Pros

  • Stops one infested plant from spreading pests through a whole collection.
  • Gives the plant a quiet place to adjust after purchase.

Cons

  • Needs space and patience; a few weeks' wait before displaying the plant.

Look-alikes

New-purchase shock
Leaf drop without insects, webbing or spots is usually adjustment, not a pest problem.
Springtails
Tiny jumping creatures in moist mix are usually harmless springtails, not plant pests.

Typical uses

All newly acquired plants, cuttings and plants returning indoors.

Sources

  1. Managing Houseplant Pests — Colorado State University Extension
  2. Houseplant Care — University of Wisconsin–Madison Extension
  3. Moving Indoor Plants Outside for Summer — Iowa State University Extension

Written in our own words from these sources. Check a product label before using any treatment.