60 wildflowers were recorded blooming in Pennsylvania in August in our iNaturalist sample; 20 of the top 50 are at their peak this month. The list is ranked by number of research-grade observations.
Top wildflowers in August

Common Jewelweed
Cardinal Flower
Allegheny monkeyflower

American hog-peanut
Purple Loosestrife

Asiatic dayflower
Wingstem

White Snakeroot
Wild Carrot

Great Blue Lobelia

Flat-Topped Goldenrod

Cutleaf Coneflower
All wildflowers blooming in Pennsylvania in August
| # | Species | Scientific name | Family | Obs. | Peak in state |
|---|---|---|---|---|---|
| 1 | Common Jewelweed | Impatiens capensis | balsam family | 331 | Sep (rising) |
| 2 | Cardinal Flower | Lobelia cardinalis | bellflower family | 283 | Aug (peak) |
| 3 | Allegheny monkeyflower | Mimulus ringens | lopseed family | 239 | Jul (past peak) |
| 4 | American hog-peanut | Amphicarpaea bracteata | Legumes | 228 | Aug (peak) |
| 5 | Purple Loosestrife | Lythrum salicaria | lythrum family | 199 | Aug (peak) |
| 6 | Asiatic dayflower | Commelina communis | Spiderworts | 196 | Aug (peak) |
| 7 | Wingstem | Verbesina alternifolia | Sunflowers, Daisies, Asters, and Allies | 154 | Sep (rising) |
| 8 | White Snakeroot | Ageratina altissima | Sunflowers, Daisies, Asters, and Allies | 153 | Sep (rising) |
| 9 | Wild Carrot | Daucus carota | carrot family | 152 | Jul (past peak) |
| 10 | Great Blue Lobelia | Lobelia siphilitica | bellflower family | 151 | Sep (rising) |
| 11 | Flat-Topped Goldenrod | Euthamia graminifolia | Sunflowers, Daisies, Asters, and Allies | 147 | Sep (rising) |
| 12 | Cutleaf Coneflower | Rudbeckia laciniata | Sunflowers, Daisies, Asters, and Allies | 127 | Aug (peak) |
| 13 | Pale Jewelweed | Impatiens pallida | balsam family | 126 | Sep (rising) |
| 14 | Naked-Flowered Tick-Trefoil | Hylodesmum nudiflorum | Legumes | 121 | Aug (peak) |
| 15 | Chicory | Cichorium intybus | Sunflowers, Daisies, Asters, and Allies | 119 | Jul (past peak) |
| 16 | black-eyed Susan | Rudbeckia hirta | Sunflowers, Daisies, Asters, and Allies | 115 | Jul (past peak) |
| 17 | brown-eyed Susan | Rudbeckia triloba | Sunflowers, Daisies, Asters, and Allies | 113 | Sep (rising) |
| 18 | Virgin's-Bower | Clematis virginiana | buttercup family | 110 | Aug (peak) |
| 19 | Common Boneset | Eupatorium perfoliatum | Sunflowers, Daisies, Asters, and Allies | 105 | Aug (peak) |
| 20 | Indian tobacco | Lobelia inflata | bellflower family | 98 | Jul (past peak) |
| 21 | Swamp Rose Mallow | Hibiscus moscheutos | Mallow and Hibiscus Family | 89 | Aug (peak) |
| 22 | Panicled Hawkweed | Hieracium paniculatum | Sunflowers, Daisies, Asters, and Allies | 88 | Aug (peak) |
| 23 | Bird's-Foot Trefoil | Lotus corniculatus | Legumes | 79 | Jun (past peak) |
| 24 | Trailing Fuzzy-Bean | Strophostyles helvola | Legumes | 79 | Aug (peak) |
| 25 | Partridge Pea | Chamaecrista fasciculata | Legumes | 77 | Aug (peak) |
| 26 | Rosepink | Sabatia angularis | gentian family | 76 | Jul (past peak) |
| 27 | Swamp Milkweed | Asclepias incarnata | Dogbane Family | 75 | Jul (past peak) |
| 28 | American groundnut | Apios americana | Legumes | 72 | Aug (peak) |
| 29 | Bull Thistle | Cirsium vulgare | Sunflowers, Daisies, Asters, and Allies | 71 | Aug (peak) |
| 30 | Carolina horsenettle | Solanum carolinense | nightshade family | 70 | Jul (past peak) |
| 31 | Pearly Everlasting | Anaphalis margaritacea | Sunflowers, Daisies, Asters, and Allies | 67 | Aug (peak) |
| 32 | Blue Vervain | Verbena hastata | Verbena Family | 67 | Jul (past peak) |
| 33 | Common Toadflax | Linaria vulgaris | Plantain Family | 64 | Jul (past peak) |
| 34 | Common Hibiscus | Hibiscus syriacus | Mallow and Hibiscus Family | 62 | Aug (peak) |
| 35 | Ghost Pipe | Monotropa uniflora | heath family | 61 | Jul (past peak) |
| 36 | Common Selfheal | Prunella vulgaris | Mint Family | 61 | Jul (past peak) |
| 37 | Fall Phlox | Phlox paniculata | phlox family | 60 | Sep (rising) |
| 38 | Japanese knotweed | Reynoutria japonica | knotweed family | 60 | Aug (peak) |
| 39 | American pokeweed | Phytolacca americana | Pokeweed Family | 56 | Jul (past peak) |
| 40 | White Wood Aster | Eurybia divaricata | Sunflowers, Daisies, Asters, and Allies | 54 | Sep (rising) |
| 41 | Common Sneezeweed | Helenium autumnale | Sunflowers, Daisies, Asters, and Allies | 52 | Sep (rising) |
| 42 | Blue Curls | Trichostema dichotomum | Mint Family | 52 | Aug (peak) |
| 43 | Pickerelweed | Pontederia cordata | Pickerelweeds | 51 | Jul (past peak) |
| 44 | Bittersweet Nightshade | Solanum dulcamara | nightshade family | 48 | Jun (past peak) |
| 45 | Wild Bergamot | Monarda fistulosa | Mint Family | 48 | Jul (past peak) |
| 46 | White Meadowsweet | Spiraea alba | rose family | 48 | Jul (past peak) |
| 47 | Porcelain Berry | Ampelopsis glandulosa | Grape Family | 47 | Aug (peak) |
| 48 | Purple Crownvetch | Securigera varia | Legumes | 45 | Jun (past peak) |
| 49 | Butterfly Milkweed | Asclepias tuberosa | Dogbane Family | 43 | Jul (past peak) |
| 50 | Flowering Spurge | Euphorbia corollata | Spurge Family | 43 | Aug (peak) |