How these lists are made

The data

The PLANTS Database is the USDA Natural Resources Conservation Service’s standardized list of U.S. plants. For each plant it records where it occurs (state and county distribution) and whether it is native, introduced or both in the lower 48, Alaska, Hawaii and Puerto Rico. For about two thousand species it also has a characteristics record: height, shade tolerance, moisture use, minimum temperature and more. This build was retrieved on November 4, 2026 through the PLANTS web services and its public map service.

Scope: 3,666 species, of which 1,686 have a characteristics record. Varieties, subspecies and forms are folded into their species. Species without a characteristics record are the most widespread natives in each state and nationally.

What “native” means on this site

A species is on a county’s main list only when all three hold: it is recorded in that county by USDA PLANTS (its county distribution file, matched by state and county FIPS codes); PLANTS gives it native status for the lower 48 states (or Alaska, Hawaii or Puerto Rico); and Kew’s World Checklist of Vascular Plants (WCVP) records it as native, not introduced, in that state. Species that USGS’s Register of Introduced and Invasive Species (US-RIIS) lists as introduced are left off as well. In short, every plant on a list is recorded as native to the state in Kew’s World Checklist of Vascular Plants and USDA PLANTS, and recorded in the county by USDA PLANTS.

Why two sources: PLANTS records native status for the lower 48 as a whole and repeats it for every state, so on its own it would call black locust native in California. WCVP records status state by state. Where WCVP says introduced, or has no record for the state, the species is left off that state’s lists.

These are state-level records, not statements about your county or your yard. Recorded native ranges can include long-established populations that spread from gardens; check your state’s native plant society list for local guidance.

Known limit. WCVP’s state records can include long-established spread. Northern catalpa (Catalpa speciosa), native to a small area of the central Mississippi valley, is recorded by WCVP as native in 32 states, including Massachusetts, so it still appears on Massachusetts lists. We know of no county- or state-level source with a clear license that would correct cases like this.

In this build 104,218 of 1,358,921 county-species records that PLANTS alone would have listed were left out (62,569: WCVP has no record for the state; 27,480: WCVP records it as introduced in the state; 8,147: species not matched to WCVP; 5,640: listed as introduced by US-RIIS; 382: WCVP record doubtful or extinct). 42 species could not be matched to WCVP by name and are not listed.

Native and introduced (“Both”)

PLANTS labels some species Both: some of their forms or populations are native and others were brought in from elsewhere. Where WCVP also records them as native in the state, they are kept, but only as a secondary group. Common dandelion and Kentucky bluegrass are examples. These species are never on the main lists. Each county and state page shows them in a separate, collapsed section, “Also listed as native and introduced here”. Most gardeners should choose from the main list.

Connecticut has no county records in this build. Its statewide list leaves out every species that PLANTS labels Both in any state, because Connecticut’s own label could not be separated from the county data.

Garden-ready

“Garden-ready” means the species has a PLANTS characteristics record, so the light, moisture, height and zone filters can work on it. It is not a recommendation: many garden-ready species are large trees or wetland plants, and many good garden natives lack a PLANTS record. The “Garden-ready only” switch is on by default; turn it off to see every native species recorded in the county.

• Type comes from the PLANTS growth habit. A species with several habits gets one: tree, then vine, then shrub, then grass or grass-like (graminoid), then wildflower (forb/herb), then subshrub as shrub. Ferns include horsetails, clubmosses and quillworts.
• Sun or shade uses PLANTS shade tolerance: tolerant = shady spot, intermediate or tolerant = part shade, intolerant = sun-lovers. The PLANTS web service reports this trait as high, medium or low with the scale reversed (prairie grasses are “high”, hemlock and maidenhair fern are “low”), so we read high as shade-intolerant and low as shade-tolerant, after checking it against two dozen well-known species.
• Moisture uses PLANTS moisture use (low, medium, high).
• Mature height uses PLANTS mature height in feet.
• A plant with no value for a filter is left out while that filter is on. Unknown never counts as a match.

Estimated cold hardiness

PLANTS gives a plant’s minimum temperature (°F), the coldest it tolerates, not a hardiness zone. USDA zones are 10°F bands split into 5°F half-zones, starting with zone 1a at −60 to −55°F. We assign the coldest half-zone whose lowest temperature is at or above the plant’s minimum: k = ceiling((minimum + 60) ÷ 5), zone = k ÷ 2 (rounded down) + 1, “a” when k is even and “b” when odd. A minimum of −33°F gives zone 4a (−30 to −25°F).

A plant suits a ZIP when the ZIP’s zone is the same or warmer. There is no upper limit, because PLANTS records no heat limit. ZIP zones come from the 2023 USDA Plant Hardiness Zone Map ZIP table published by PRISM / Oregon State University. This is our estimate, not the official USDA map, and it ignores summer heat, humidity and soil drainage.

The ZIP lookup

ZIP codes are matched to counties with the Census Bureau’s ZIP Code Tabulation Areas and the 2020 ZCTA-to-county relationship file. A ZIP that crosses county lines shows the county with most of its land and names the others. PO-box-only ZIPs have no area and are not found.

County lists exist for 3,166 of the 3,232 counties in the ZIP table. The median county has 372 species counting native-and-introduced ones; the main lists exclude those. Counties with fewer than 30 garden-ready natives (251 of them) still have a page, but it is kept out of search indexes because the records are thin.

Limits

• County records show where a plant has been documented, not every place it grows. Fewer species in a county can mean fewer surveys, not fewer plants.
• Native status is per state. Large states such as Texas and California hold very different climates; use the county list.
• PLANTS has no reliable pollinator data, so this site has no pollinator filter.
• Ecoregion-level lists are planned for a later version.