Treatments for a Greenhouse

A greenhouse allows gardeners to grow plants during the winter, when most plants are dormant.

greenhouse pests
Plants are typically more crowded in a greenhouse, making pests and disease more serious issues than they are in an outside garden.

These problems require aggressive treatment in an enclosed environment.

A greenhouse provides regulated environmental conditions, which also requires periodic maintenance.



greenhouse treatments
The clear plastic on the roof of a greenhouse allows it retain heat, making it much warmer than the outside environment.

A gardener may keep outdoor plants in the greenhouse temporarily during the winter, in a process known as overwintering.

Another use of greenhouses is to start plants early in the year before the last expected frost of the winter.

The plants can then be transplanted outside as seedlings.

Gardeners in cold climates may also keep warm-weather plants in a greenhouse throughout the year.


The higher concentration of plants in a greenhouse also means the concentration of pests tends to be higher. Common insect pests include

  • Aphids
  • Black flies
  • Mealy bugs
  • Slugs
  • Snails
  • Whiteflies


pest controlRodents such as rats and mice can also damage plants in a greenhouse.

General insecticides commonly used in greenhouses include copper, neem oil, pyrethrum and sulfur.

Mollusks such as slugs and snails can be treated effectively with aluminum sulfate.

Rodent populations can be kept in check with traps and poison.

Organic gardeners who do not use pesticides often must rely on keeping the greenhouse clean and removing pest by hand.


  • The enclosed, humid environment of a greenhouse allows diseases to spread much more quickly than they do with outside plants.
  • Common plant diseases in a greenhouse include bacterial blight, botrytis blight, powdery mildew and root rot.
  • It is especially important to treat these diseases proactively in a greenhouse, meaning the emphasis should be on prevention.
  • Destroy sickly plants to keep diseases from spreading to healthy plants.
  • Use only fast-draining soils to keep the roots from soaking in water for prolonged periods, and ensure that water on the leaves of plants is able to evaporate.
  • Keep pots, tools and work surfaces as clean as possible.
  • Disinfect the tools used in grafting and division with a mild bleach solution immediately before performing these procedures.
  • This is essential for preventing the spread of disease, as these tools come into direct contact with the exposed flesh of the plants.
  • Existing plant diseases can be treated with antibiotics such as mancozeb, propiconazole, tebuconazole and triadimenol.
  • These drugs should be applied by a licensed professional.


wooden greenhouseThe high humidity of a greenhouse causes wood to rot more quickly, especially raw lumber that has not been treated with preservatives.

Gardeners can minimize this problem by building the greenhouse with treated lumber on a site with good drainage to reduce the amount of standing water around the greenhouse.

Bare wood surfaces in the greenhouse should also be covered with paint to reduce the possibility of rot.

Some types of wood such as cedar and teak are naturally resistant to humidity.

Portable greenhouses should be stored in a dark location to prolong their life span.


  1. Pipes made from polyvinyl chloride produce gases in a process known as out gassing.
  2. These gases can be harmful to plants, so PVC pipes in a greenhouse should be coated with latex paint.
  3. Keep the air flowing through the greenhouse with fans and by keeping the vents open as much as the weather allows.
  4. Good ventilation will also lower the humdity, which will prolong the life of lumber and prevent molds from flourishing.


greenhouse glass panelsThe plastic or glass ceiling of a greenhouse must be kept clear to allow sunlight to enter the greenhouse.

Clean the ceiling with warm soap and water when they become dirty.

Use a mild, biodegradable soap to ensure it doesn’t harm the plants.

Open the vents of the greenhouse when you clean the ceiling to prevent any vapors from accumulating. A greenhouse must remain sealed in order for it to retain heat.

The walls of a greenhouse are often composed of plastic sheets, which can develop tears over time. Patch small tears with clear tape, and fix larger tears with hot glue. Severe tears in the plastic sheet may require you to replace the sheet.


  • Gardeners typically perform annual maintenance on greenhouses during the fall, before moving plants into the greenhouse of the winter.
  • This consists of a general cleaning, especially the removal of dead plant matter to prevent the spread of disease.
  • Gardeners should also use this opportunity to replenish the level of ground cover in the greenhouse such as mulch and pea gravel.


greenhouse maintenanceThe annual maintenance of a greenhouse should also include a check of the equipment.

Check sprinklers and soaker hoses for leaks.

Defective soaker hoses are typically not worth repairing and should be replaced.

A greenhouse usually contains timers for the watering, lighting and heating systems, which should be checked for proper operation.

Inspect the cords of any electrical devices for exposed wiring.

This is especially important in a greenhouse, where electrical devices may run unattended for prolonged periods.

Check the insulation around the windows and doors for drafts. Replace any damaged insulation with new weatherstripping.

Greenhouses may also use caulking to provide a tight seal around windows and doors, which must be reapplied periodically.

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