Master Gardeners Diagnose Plant Health


(Conservation Currents, Northern Virginia Soil and Water Conservation District)

The Fairfax County Master Gardeners’ Diagnostic Laboratory operates year-round. The lab is staffed by senior Master Gardeners who have many years of experience in solving plant, pest, and disease problems. Bring a sample of whatever is troubling you to any Fairfax County Public Library and ask the staff to send it to the Master Gardeners through the county’s mail system.

Your sample will be analyzed at the lab, and a detailed diagnosis with recommendations will be mailed back to you. This generally takes two to four weeks, depending on the time of year and the backlog of requests.

Samples are sent from the library to the laboratory through the county interoffice mail. It is important that you bring your sample suitably wrapped for this journey. Plant specimens should be sealed in a plastic bag; insects should be in a firm plastic container. Complete the Laboratory Diagnostic Sheet, and place the sheet and the plastic container in another envelope or box. Do not place the Lab Sheet inside the same plastic bag with the sample. (Moisture from the sample often renders the sheet unreadable.)

During the months of May through September, the Master Gardeners will hold plant clinics throughout the county.

Here are some tips for collecting and packaging samples:

  • For disease/problem diagnosis: Provide a sample showing both diseased and healthy tissue on the same sample. For proper diagnosis, samples should have stems or branches at least 6" long. Individual leaves are usually not sufficient. Include a small handful of fine feeder roots if you think the plant can spare them.
  • For plant identification: Provide as many parts of the plant as possible—the entire plant if it is small enough. In addition to stems and leaves, include flowers or berries if available. Attach a description of the plant’s size, shape and growing habits. (For example, does it drop its leaves in winter, is it a 5' shrub or a 1' groundcover, etc. If no flowers are available, describe when it last flowered and what kind of flowers it had.)
  • Sod: Submit a sample of sod 6" to 8" square from the margin of the affected area that contains both healthy and problem grass. Do not send grass that is already dead. Send the entire root system—it may be 2 or 3 inches deep. Place sod in a plastic bag inside a sturdy box. For identification of a lawn weed, do not send sod but follow instructions above for plant identification.
  • Insects: Collect one or more complete insect specimens and place them in a sturdy plastic container (such as old pill bottle or film canister) with diluted rubbing alcohol. Soak insects overnight to preserve them, then drain off ALL the alcohol and seal. Do this BEFORE you bring the sample to the library. Do not send insects in tissue paper or envelopes. Do not tape insects to a card or paper.

Please do not send snakes, rats, mice, or any other wildlife through the library system.


Contact Fairfax County: Phone, Email or Twitter | Main Address: 12000 Government Center Parkway, Fairfax, VA 22035
Technical Questions: Web Administrator

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