Criteria for inclusion: trusted sources such as universities, government agencies, or non-profit organizations. No attempt is made to be comprehensive.

University of Maryland Extension (UME)

UMd Extension (UME). A statewide, non-formal education system within the College of Agriculture and Natural Resources and the University of Maryland Eastern Shore, providing a wealth of information and resources for the public.
UMd Extension (UME) in Spanish. Written by Anahí Espíndola, Assistant Professor, Department of Entomology, University of Maryland, College Park.

Specific UME sites of interest

Home and Garden Information Center (HGIC). Provides access to a wide variety of subjects relevant to home gardeners.
Additional information on gardening, plants, and pests.
Montgomery County Master Gardeners. Trained volunteers of UME; information on what they do and how to become one.

Diagnostics

Home and Garden Information Center (HGIC). Ask Extension: Submit questions or photos for diagnosis of problem or plant ID.
UME Soil Fertility. Explains the whys and hows of soil testing, revised Feb 2021. (UMd no longer offers soil testing services.)
University of Delaware Soil Testing Program. Order kits online and learn how to take a soil sample.

Pesticide use

Montgomery County Lawn Care Law. Information on allowable use of pesticides in Montgomery County.
Maryland State Department of Agriculture Pesticide Information for Consumers
U.S. Environmental Protection Agency Mosquito Control. About mosquitoes, preventing bites, repellents, and control methods.

General interest

Cornell University. Information for home gardeners on flowers, vegetables, and garden design.
Missouri Botanical Garden Plant Finder. Allows searching of over 7500 plants by scientific name, common name, or plant characteristics. Includes photos, descriptions, requirements, problems, resistance, etc.
Deer-Resistant Plants. List of deer-resistant plants compiled by Mt. Cuba Center and the Pennsylvania Wildlife Preserve.
Invasive Plants. Information about alternatives to and control of invasive plants in the home landscape.
Sustainable Landscapes. University of Delaware Botanic Gardens provides links to information on sustainable landscapes practices.

Native plants

Criteria for inclusion: trusted sources such as universities, government agencies, or non-profit organizations. No attempt is made to be comprehensive.

Audubon Native Plants Database. Find native plants by zip code.

ChooseNatives.Org. Focused on the Mid-Atlantic region (DC, DE, MD, NJ, NY, PA, VA, WV), provides comprehensive list of native plant nurseries and plant sales in the region, plus a list of invasive plant resources.

Mt. Cuba Center. A garden devoted entirely to native plants located in Hockessin, DE, the Mt. Cuba website provides links to its research trial results of various native plant cultivars including aster, baptisia, coreopsis, echinacea, helenium, heuchera, monarda, and phlox; a native plant finder; and a list of native plant nurseries.