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WHAT IS A NATIVE PLANT?
A native plant is one that naturally occurs in a specific geographic area without human intervention. For the Northeastern United States, native usually means that a plant occurred within an area at the time that European colonists conducted the first official botanical surveys in the 1700s. In some instances, though, evidence indicates that plants were brought into the area by colonists or native peoples before that time.
Plants that were brought into an area by humans are considered to be non-native even if they are native to adjoining areas. Plants that establish populations in areas to which they are not native are called introduced, adventive, or naturalized.
An invasive plant is a non-native plant that spreads quickly and cause economic harm, environmental harm, or harm to human health. Even though some native plants spread aggressively in cultivated areas, they are not considered to be invasive.
We often speak of plants as being native to a political area, such as a state or county, but biologists consider the relevant area to be a plant’s ecoregion. Ecoregions are geographically defined areas receiving uniform solar radiation and moisture, in which ecosystems are generally similar. Various species, subspecies, and varieties of organisms coevolved within these geographic boundaries over thousands of years, so the biodiversity of flora, fauna, and ecosystems within each ecoregion tends to be distinct from that of other ecoregions.
Ecoregions are defined by the U.S. Environmental Protection at different levels. Level III is normally used for classifying the native status of plants. Several Level III ecoregions occur within the political boundaries of Pennsylvania, as shown in the maps at https://gaftp.epa.gov/EPADataCommons/ORD/Ecoregions/reg3/reg3_eco_pg.pdf.
Even though the same species of plant might occur in multiple ecoregions or habitats, it might exhibit unique characteristics that enable it to adapt better to the conditions of a specific ecoregion. Such variants within a species are called ecotypes. The differences of an ecotype from other variants within the species are too few or too subtle, however, to warrant classification as a subspecies.
To find your ecoregion use the EPA map linked above or ecoregion locator at https://bplant.org/ecoregion_locator.php. For more information about ecoregions, visit https://www.epa.gov/eco-research/ecoregions. To read descriptions of all ecoregions in the U.S., including those in Pennsylvania, follow this link: https://gaftp.epa.gov/EPADataCommons/ORD/Ecoregions/pubs/NA_TerrestrialEcoregionsLevel3_Final-2june11_CEC.pdf.
WHY SHOULD I PLANT NATIVES?
The plants, animals, and other organisms within an ecoregion evolved together over thousands of years, creating a unique and intricate web of interactions among themselves and with their physical environment. For example, the nectar, pollen, fruit, seeds, leaves, and other parts of native plants provide specific nutrients to indigenous animals that non-native plants do not. In return, native plants receive “custom” services from those animals, such as pollination and seed dispersal. Native plants also develop unique relationships and nutrient exchanges with indigenous soil organisms. Utilizing native plants in our landscapes is, therefore, an important way to preserve biodiversity by helping to ensure the survival of plant and animal species that are otherwise threatened by habitat loss, pesticides, and other impacts of human development. In addition, because they are adapted to local soil types and site conditions, native plants do not require fertilizers or watering once they are properly established.
Because of native plants’ critical importance to wildlife and the preservation of biodiversity, we recommend that gardeners strive for 100% native plants in their landscapes.
For more information about the benefits of native plants and how to use them in your Pennsylvania landscape, visit:
HOW DO I KNOW IF A PLANT IS NATIVE?
Perhaps the easiest way to find out whether or not a particular plant is native to Pennsylvania or your county (a good proxy for your ecoregion) is to search for it on one of the following websites using the botanical name. Some sites also allow you to search by common name. Since multiple species can share the same common name, however, it is important to make sure that you find results for the actual species you are looking for.
http://www.bonap.org The Biota of North America Program site provides both state- and county-level maps of plant status. This is the most accurate site for distinguishing native from introduced (adventive or exotic) species, though it is important to understand the map distribution color codes, especially for county-level maps (see http://www.bonap.org/Help/BONAP%20Help.html). It does not contain any description or other information about the plants, though.
https://plants.sc.egov.usda.gov/home. The USDA Plants database also provides state- and county-level maps of the native status of plants. However, it considers all plants found in an area at the time of the colonial-era plant surveys to be native even if they were introduced by early colonists or native peoples. USDA provides informative fact sheets about cultivating some native plants, especially those with commercial value. You can use the State Search feature to generate a list of all plants found in Pennsylvania.
https://www.wildflower.org/plants/. Operated by the Lady Bird Johnson Wildflower Center, this site is probably the most user-friendly and popular of the three. It does not provide state- or county-level maps, however, only a list of states to which a plant is considered native. The list does not distinguish native plants from those introduced before colonial-era surveys, but the accompanying text often does. This site includes photos and useful information about growing each species, including the types of habitats in which it occurs naturally. You can use the Combination Search feature to generate a list of all plants found in Pennsylvania or only plants with the characteristics you specify.
The Vascular Flora of Pennsylvania: Annotated Checklist and Atlas, by Ann Fowler Rhoads & William McKinley Klein, Jr. (American Philosophical Society) lists the native status and current geographical distribution of all vascular plants known to occur in the Pennsylvania.
ARE NATIVARS AND HYBRIDS OF NATIVE PLANTS STILL ‘NATIVE’?
A plant variety is a subgroup of plants within an individual species that exhibits different characteristics from the straight species. The differences are too few or too subtle, however, to warrant classification as a subspecies. Seeds from naturally occurring varieties usually come true to their parents. In binomial nomenclature, naturally occurring varieties of plants are indicated by the abbreviation “var.” after the species name. For example, the naturally occurring white variety of Eastern Redbud is Cercis canadensis var. alba. If you were to germinate seed from this variety, most, if not all would also be white flowering.
Among the native plants available today, a growing majority consists of human-cultivated varieties (cultivars) often referred to as nativars. Some nativars originate as naturally occurring sports or mutations on wild or cultivated native plants. Other nativars are crossbred from two plants within the same species to reinforce a desirable trait, such as flower color or disease resistance. To ensure true-to-type individuals, many nativars must be propagated vegetatively through cuttings, grafting, and even tissue culture. Such plants are clones with no genetic diversity from their parents. Propagation of nativars by seed usually produces something different from the parent plants. Nativars are usually assigned proper names by their developers or patent holders. In binomial nomenclature, the first letter of a cultivar’s proper name is capitalized and the name is never italicized. Cultivar names are either enclosed in single quotation marks or preceded by the abbreviation “cv.” For example, the botanical name of the ‘Forest Pansy’ cultivar of Eastern Redbud is Cercis canadensis ‘Forest Pansy’ or Cercis canadensis cv. Forest Pansy. For cultivars of naturally occurring varieties, the cultivar name appears after the variety, as for Sunburst Honeylocust, Gleditsia triacanthus var. inermis ‘Sunburst.’
The straight species of a native plant is always preferable in native plant gardening. Straight species, especially local ecotypes, provide the greatest range of natural interactions with local ecosystems and other native organisms and help preserve biodiversity. Even though some nativars may be more attractive to certain organisms, such as pollinators, it is often at the expense of benefits to other organisms and genetic diversity. Indeed, some features of nativars, such as changes to leaf color, are purely aesthetic and decrease their benefits to other organisms. Because nativars are botanically classified as varieties of native species, though, they are still considered to be ‘native’. It is up to the individual gardener to decide whether or not to use them in their own landscape.
A hybrid plant results from crossbreeding two plant species of the same genus or from different genera. Hybridization occurs rather frequently in nature when insects or the wind cross-pollinate plants of different species. Natural hybridization seldom produces new plant groups with long-term viability. Sometimes, however, over the course of many generations, repeated natural hybridization produces open-pollinated plants that grow true to type and create new varieties, species, or genera. Most of the hybrids sold commercially are the results of painstaking crossbreeding by humans, and their seeds do not grow true to type. The correct nomenclature for hybrid plants includes the genus name followed by an X and the name given to the cross. For example, Quercus X deamii is a hybrid of Quercus alba (White Oak) and Q. muehlenbergii (Chinquapin Oak). In the commercial trade, the X is often omitted and the genus name followed directly by the hybrid name in single quotation marks, e.g., Agastache ‘Blue Fortune’ – a cross between A. rugosa (Korean Mint) and A. foeniculum (Blue Giant Hyssop). Because they are not true species and lack genetic diversity, cultivated hybrids are not recommended for native plant gardening, whether or not both parents are native species.
HOW DO I KNOW WHICH NATIVES TO PLANT IN MY YARD?
Within any given ecoregion, the specific site conditions, such as soil pH, soil moisture, and the amount of sunlight, influence which species of native plants will succeed in a particular location. Matching plants to their preferred growing conditions is embodied in the motto “right plant, right place.”
There are many good sources of information on selecting and growing native plants. These resources often cover a wider geographic range than Pennsylvania, so be sure to verify that any plant you are interested in is native to your ecoregion.
Native Trees, Shrubs, and Vines: A Guide to Using, Growing, and Propagating North American Woody Plants, by William Cullina (Echo Point Books & Media)
Native Ferns, Moss & Grasses, by William Cullina (Houghton Mifflin Harcourt)
The New England Wild Flower Society Guide to Growing and Propagating Wildflowers of the United States and Canada, by William Cullina (Houghton Mifflin Harcourt)
Native Plants of the Northeast: A Guide for Gardening and Conservation, by Donald J. Leopold (Timber Press)
Websites with Lists of PA-Native Plants for Specific Site Conditions or Use
https://www.dcnr.pa.gov/Conservation/WildPlants/LandscapingwithNativePlants/Pages/default.aspx (lists for sunny/moist; sunny/dry; shady/moist; shady/dry)
https://bhwp.org/grow/garden-with-natives/right-plant-right-place/ (lists for sun; shade; trees & shrubs; attracts birds; wet meadows; dry meadows; wet sites; dry sites; deer tolerant; black walnut tolerant)
https://edgeofthewoodsnursery.com/our-plants/plant-lists (lists for salt tolerant; for song/game birds; for hummingbirds; butterfly larval; butterfly nectar; deer tolerant; shrubs 3’ or less; for native bees; under black walnuts; wet areas; groundcovers; windbreaks/screens; slopes/hills; rabbit resistant; rock gardens; rare/threatened/endangered; dry sites; alkaline sites; septic/sand mounds; street trees; hedgerows; for bats)
Websites with Tools to Search for Native Plants by Zip Code or Ecoregion
https://www.nwf.org/nativeplantfinder/ (zip code search for plants that host the most caterpillars)
https://www.audubon.org/native-plants (zip code search for plants to attract birds)
https://xerces.org/pollinator-conservation/pollinator-friendly-plant-lists (regional lists for plants that attract pollinators)
https://www.pollinator.org/guides (zip code search for pollinator plants by ecoregion)
http://www.nativeplantcenter.net (search for native plants by ecoregion and site conditions)
Websites with Comprehensive, Searchable Databases of Native Plants by State, County, Site Conditions, and Plant Characteristics
Smart Phone Apps
Pennsylvania Wildflowers (helps search for plants and has links to detailed cultivation information)
HOW DO I KNOW MY SITE CONDITIONS?
Site conditions generally refer to the amount of sunlight, the soil moisture level, and the soil acidity.
Full sun means six or more total hours of direct sunlight each day, part sun or part shade between three and six hours, and full shade less than three hours.
For gardening purposes, soil moisture is the total amount of water in the soil regularly available to plant roots, usually within the upper 6” for turf and pasture grasses, 18” for herbaceous annuals and perennials, and 36-80” for trees and shrubs. It is affected by many factors, including the amount of precipitation or irrigation, soil type and texture, surface and subsurface drainage patterns, and the quantity and water usage of existing vegetation. In dry soil conditions, the soil within the root zone does not retain perceptible moisture more than two or three days after watering. When rolled in the hand, dry soil does not easily form a ball. With moist soil, also called average or mesic soil, you can feel moisture in the soil for up to a week or more after watering, and the soil will form a ball that is easily crumbled when rolled. Wet soil remains damp or sticky most of the time. A ball of wet soil does not crumble easily.
pH is the measurement of the hydrogen ion activity in the soil and affects the availability of nutrients to plants. Acidic soil has a pH less than 6.2, circumneutral soil from 6.2 to 7.2, and alkaline greater than 7.2. The most accurate way to test your soil pH is through PennState Extension https://extension.psu.edu/soil-testing.
WHAT’S A HARDINESS ZONE? HOW DO I KNOW WHICH ONE I’M IN?
A hardiness zone is a geographic area that encompasses a certain range of climatic conditions affecting plants’ ability to survive (hardiness). In the United States, we use the hardiness zones defined by the U.S. Department of Agriculture (USDA), which are based on the average annual extreme minimum temperature during a 30-year period in the past. The USDA maps help farmers and gardeners know whether a plant will survive the lowest average winter temperature in their area. There are 13 hardiness zones in the United States, divided in increments of 10°.
The USDA map of hardiness zones, including those found in Pennsylvania, and a locator tool is at this link: https://planthardiness.ars.usda.gov/pages/view-maps.
Please keep in mind that winter temperatures sometimes dip below average and might kill plants that are normally hardy. Also, some microclimates are just too small to show up on the USDA maps.
Even though a plant is hardy in your area, it might not do well in your yard. Many other environmental factors, such as the amount of sunlight, soil type, and soil moisture, contribute to the success or failure of plants. Please use the resources above to find the right native plants for your yard.
WHERE CAN I BUY NATIVE PLANTS?
Native plants should never be collected from nature without the permission of the property owner, even from public lands such as roadsides. Whether or not you have permission, collecting native plants from the wild might disrupt their natural reproduction, reduce the availability of food they provide to other organisms, or compromise the success of the local population. It is better to buy native plants or seeds from reputable sources, such as dedicated native plant nurseries or non-profit organizations. There are many web-based vendors of native plants as well. Unless you are confident in the vendor’s knowledge, it is a good idea to verify the native status of a plant through a reliable source before buying it.
For a list of places to buy native plants in Pennsylvania, visit
HOW DO I IDENTIFY A PLANT?
The most reliable way to identify a plant is to use a field guide or desk manual. Smartphone apps and social media groups are helpful, too, but it is wise to verify the results with a field guide.
Traditional Field Guides
Newcomb's Wildflower Guide, by Lawrence Newcomb (Little, Brown and Company)
A Peterson Field Guide to Wildflowers: Northeastern and North-central North America, by Margaret McKenny (Houghton Mifflin Harcourt)
A Field Guide to Trees and Shrubs: Northeastern and North-Central United States and Southeastern and South-Central Canada, by George Petrides (Houghton Mifflin Harcourt)
Peterson Field Guide to Ferns: Northeastern and Central North America, by Boughton Cobb (Houghton Mifflin Harcourt)
Grasses, Sedges, Rushes: An Identification Guide, by Lauren Brown and Ted Elliman (Yale University Press)
Mosses, Liverworts, and Hornworts: A Field Guide to the Common Bryophytes of the Northeast, by Ralph H. Pope (Comstock Publishing Associates)
The Plants of Pennsylvania: An Illustrated Manual, by Ann Fowler Rhoads and Timothy Block, illustrations by Anna Anisko (University of Pennsylvania Press)
Flora of the Southeastern United States: Pennsylvania, by Alan S. Weakley (University of North Carolina at Chapel Hill Herbarium) download from https://ncbg.unc.edu/research/unc-herbarium/flora-request/
Weeds of the Northeast, by Richard H. Uva, Joseph C. Neal, and Joseph M. Ditomaso (Comstock Publishing Associates)
Web-Based Field Guide
https://gobotany.nativeplanttrust.org (covers New England, but most species are also native to Pennsylvania)
Flora of Virginia (includes most Pennsylvania plants)
Plant Identification and discussion
Plant Identification Group
County Offices of PennState Extension: https://extension.psu.edu/county-offices/
HOW DO I CONTROL WEEDS AND INVASIVE PLANTS WITHOUT HERBICIDES?
All herbicides (whether conventional/synthetic, organic, natural, homemade, or other) contain substances that might kill or injure non-target organisms along with their intended targets. Some also contain toxic ingredients that spread beyond the area to which they were applied and/or last in the environment for extended periods. For this reason, we do not recommend using herbicides of any kind, even “safe” ones.
Note: Be sure to properly identify any weed before you remove it. Some “weeds” are actually desirable native plants!
We recommend these eco-friendly ways to control weeds and invasive plants:
Competition from dense planting and native groundcovers
Bare soil open to light and precipitation is an invitation for weed seeds to germinate. Plant densely so that mature vegetation forms a continuous canopy and takes up as much available “real estate” as possible. This can be accomplished by layering plants (tucking shorter ones under taller ones) or using groundcovers as living mulches. Layered planting also simulates native plant communities and is more attractive to wildlife.
When bare soil between plants cannot be avoided, covering it with 1-2” of organic matter can reduce the germination of weed seeds. Mulching more than 2” deep often attracts voles. You can mulch with compost, bark, wood chips, pine needles, grass clippings, straw, or other “breathable” organic materials. Be sure to keep all mulch away from the trunks of trees, allowing root flares to show just above ground level.
Manually removing weeds with a trowel, shovel, hoe, or other tool is very effective, though many weeds will come back from root fragments or seeds and need to be removed again. Consistent removal, however, will greatly reduce or eliminate their populations. Try to remove young weeds as soon as possible, before they spread or reproduce.
Mowing, String-Trimming, Flame Weeding
These techniques can be used to remove most or all of the above-ground portions of weeds and are most effective for annual plants that will not regrow from rootstock. For perennial plants, repeated treatment is usually necessary to fully deplete the roots of energy.
Smothering and Solarizing
You can kill all the plants in an area over the course of 5-6 months by smothering them with an opaque material such as black plastic or solarizing them with clear plastic. Detailed instructions can be found here: https://www.prairiemoon.com/PDF/Prairie-Moon-Nursery-Smothering-and-Solarization.pdf. You can also start an “instant” bed by laying cardboard or several layers of newspaper over mown turf or weeds, covering it with 2” of mulch, watering thoroughly, and tucking plants into the soil through holes that you cut in the cardboard or paper.
Controlling Specific Invasive Plants
Information about controlling specific invasive plant species can be found at these sites (though we do not recommend using herbicides):
HOW DO I REMOVE TURF AND START A MEADOW?
We recommend these sites (though we do not recommend removing existing vegetation with herbicides):
HOW DO I START NATIVE PLANTS FROM SEEDS?
We recommend beginning with this site, which includes many helpful links to other sites with more detailed information, including information on winter sowing:
HOW MUCH WATER DO MY NATIVE PLANTS NEED?
Before planting a new plant, it is a good idea to make sure that the soil is already moist so that it does not wick water away from the new plant. Once your plant is in the ground, water it throughly (about the same volume as the container or root ball) and slowly so that the water does not run over the surface away from the roots. Then, lightly mulch the soil out to the area of disturbance or to the drip line, whichever is greater. When the soil gets dry, which could be in a few days, a week, or longer depending upon the weather, water again with half to the full amount of the first watering. Keep this up through the end of the growing season.
Plants are generally not drought-tolerant until they are established, about one year for perennials and one to three years for woody plants. During this period, they should be watered during periods of dry weather. Water should always be applied slowly so that it soaks into the root zone. Remember that shallow surface watering discourages deep root development. Less frequent watering that thoroughly saturates the soil encourages the growth of deep roots.
Once they are established, properly sited native plants should not need any supplemental water to survive. When it gets hot and dry, they might drop some leaves or even go dormant, but they will usually survive to flourish when conditions improve.
But, it can get pretty frustrating to watch your plants wilt or go dormant, especially if you're counting on them for pollinators or other wildlife. So, you might opt to water even well-established plants when they are suffering from dry conditions. The general rule of thumb is that most garden plants in “average” soil need about an inch of water a week. That varies widely, of course, but it's a good place to start until you learn the different needs of your plants. Keep in mind that plants can suffer in extreme heat even if they're getting enough water. They might also have gotten used to heavier than usual rainfalls and need some time to adjust to normal ones. If the soil is moist, most plants usually don't need any more water.
To measure how much water your plants are getting, a good rain gauge helps. The gauges used by the Community Collaborative Rain, Hail & Snow (CoCoRaHS) program are the most accurate standard/funnel gauges. Once you start measuring precipitation, you'll be surprised how much rainfall amounts vary among events that seem similar. So often we hear "My plants can't need water. It rained all night." But, what seems like a torrential downpour or steady storm might result in just a fraction of an inch of actual precipitation. By regularly measuring rainfall, you can more accurately diagnose plant problems and adjust your watering regime as needed.
Even if you don't set up your own gauge, you should be able to find a CoCoRaHS monitoring station near you. The FAQs/Help page of the CoCoRaHS website explains how to find a local monitoring station, measure all types of precipitation, and become a citizen scientist yourself. https://www.cocorahs.org.
Prepared by Marc Radell for Facebook/PA Native Plant Gardening