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The Root of the Matter

Martha Stewart Living, January 2009

What ails your houseplants may be easier to diagnose and cure than you think. This guide will help you determine whether your potted plants are suffering from insects, disease, or other problems and suggests ways to nurse your plant back to health. These simple solutions will turn caring for your houseplants into a joy rather than a frustrating chore.

Insects
Aphids
Symptoms

  • Clusters of tiny, soft, sticky dots, especially dense on young, tender growth. 
  • Insects may be brown, green, red, or black. 
  • The plant may feel sticky and may have shiny spots on leaves.

Solutions

  • Wash plants under a strong stream of water, rubbing the insects off with your hands.
  • Avoid overwatering and overfertilizing, which encourage the insects.

Mealybugs
Symptoms

  • Clusters of white, cottony-looking insects, most often found on undersides of leaves or where leaves meet stems.

Solutions

  • Touch sites of infestation with a cotton swab soaked in rubbing alcohol.
  • Plants under stress are most susceptible, so maintain their health and vigor.

Scale Insects
Symptoms

  • Small waxy dots or disks clinging tightly to leaves.
  • Insects may be brown, black, gray, white, or red.
  • Leaves are discolored and sticky.

Solutions

  • Wash entire plant with warm, soapy water and a soft cloth. For spiny plants such as cacti, use a skewer wrapped with a cloth soaked in warm, soapy water.
  • Isolate infested plant until scales have died and dropped off.

Spider Mites
Symptoms

  • Unhealthy-looking leaves stippled with tiny yellow or brown spots.
  • Light webbing appears over leaves and stems as infestation becomes well established.
  • The mites are tiny, but their brown fecal pellets can be seen, especially on undersides of leaves.


Solutions

  • Isolate infested plants immediately, and wash hands well after handling.
  • Spray plants with insecticidal soap, covering thoroughly.
  • Increase humidity by misting frequently as spider mites thrive in dry conditions.

Disease
Powdery Mildew
Symptoms

  • White or gray patches on foliage.
  • Plant appears pale and washed-out.

Solutions

  • Remove affected portions.
  • Increase air circulation.
  • A mixture of baking soda and water, sprayed on before fungus becomes firmly established, may be effective.

Botrytis or Other Molds
Symptoms

  • Soft, moldy patches on leaves or stems.
  • Black or rotting leaves and stems.

Solutions

  • Decrease watering.
  • Increase air circulation.
  • Remove damaged parts, and dust cut surfaces with cinnamon, a mild fungicide.

Cultural Problems
Overwatering
Symptoms

  • Wilted foliage feels flabby, indicating plant roots lack oxygen.
  • Moldy or sour smell from soil.
  • Black patches on leaves.
  • Algae growth on soil surface.
  • Fungus gnats -- small, winged insects resembling fruit flies -- may swarm around the plant.

Solutions

  • Check for drainage problems.
  • If possible, remove plant from pot and place it on layers of newspaper overnight in a warm, dry spot.
  • Once the plant is dry, repot it into a pot with good drainage.
  • To ward off fungus gnats, block access to soil surface with gravel or small stones.

Underwatering
Symptoms

  • Plant has wilted; leaves are withered, dry, and drooping.
  • Pot feels light.
  • Leaves may have brown tips or spots or may curl slightly.

Solutions

  • Plants that are very dry may require a 30-minute immersion in a tub of water.
  • Water more frequently.
  • Increase humidity.
  • Repot in a fresh, moisture- retaining potting mix.

Pot-Bound
Symptoms

  • Growth slows, and flowering may stop (although some plants, such as cacti, flower best when slightly pot-bound).
  • Roots protrude from drainage hole.
  • Plant or plantlets fill entire pot.

Solutions

  • Remove from pot; separate any offshoots if necessary.
  • Place into one larger pot or, if divided, several smaller pots.

Etiolation
Symptoms

  • Thin, weak, spindly growth.
  • Pale in color.
  • Growth may be at an angle while plant stretches for light.

Solutions

  • Increase light exposure.
  • If affected portions remain elongated or if plant becomes ungainly, consider beginning anew with cuttings, or trim be-low weak growth.

Sun Scald
Symptoms

  • Irregular brown or dry patches on leaves.
  • Pale, washed-out foliage.
  • Blisters on leaves.
  • Frequent wilting.

Solutions

  • Move plant away from strong light sources.
  • Remove affected portions if possible; they will not recover.

Not Flowering
Symptoms

  • Foliage is healthy, but plant does not flower.

Solutions

  • Increase light exposure.
  • Provide a significant difference between night and day temperatures.
  • Apply a balanced or blossom-boosting fertilizer.

Low Humidity
Symptoms

  • Brown tips on leaves.
  • Leaves fall off regularly.

Solutions

  • Increase humidity by misting regularly, placing plants on a tray filled with pebbles and water. Or use a cloche or a cake dome to cover plants (remove cover if it becomes foggy).

Cold Damage
Symptoms

  • Leaves are blackened entirely or in spots.
  • Discolored, flabby foliage and stems that won't stand up.

Solutions

  • Prune back affected portions to healthy, firm growth.
  • Keep plant away from low temperatures and cold drafts.
  • Maintain plant's vigor so it can outgrow damage.

Nutrient Deficiency
Symptoms

  • Leaves are yellow and sickly, sometimes around the veins or new growth.
  • Whole plant looks pale and unhealthy.

Solutions

  • Repot into fresh soil and a new pot.
  • Fertilize with a formula specially formulated for the type of plant.

Buds Drop Without Opening
Symptoms

  • Flower buds form but drop off the plant before they blossom.

Solutions

  • Avoid moving plants while in bud.
  • Keep them away from cold drafts or sudden temperature changes.
  • Increase humidity by misting.

Solutions in a Bottle
Baking-soda solution is effective against powdery mildew if applied at the first sign of the fungus. If you are growing plants that are especially prone, such as rosemary, spray them every two weeks.

1 tablespoon baking soda
1 tablespoon horticultural spray oil*
1 quart water

Mix well, and spray over plant, coating leaves thoroughly. Designate a spray bottle for this solution, and label it clearly.

Insecticidal soap is available at nurseries and garden centers. Read the label carefully before purchasing to be certain that it will treat your insect problem and is safe for your plant. Apply according to the directions. Remember that the soap is effective only if it makes contact with insects in its liquid form. After it has dried, there will be no effect.

*Horticultural spray oil is a light oil that helps the baking soda disperse in the water and stick to the plant. It is available at nurseries and garden centers.