Yellowstone National Park is home to a variety of habitats, and typically the elevation determines when it's wildflowers will bloom. Areas at lower elevation start to bloom in early June, while higher elevations may not catch up until mid-July— making peak wildflower season early June to mid- to late-July.
Some park biologists say that the best place to see wildflowers in Yellowstone is in the Northern Range, including Mammoth and Lamar Valley, and even towards Dunraven Pass. The dry landscape is surprisingly hospitable to a variety of wildflowers.
Of course, at Nomadic By Nature, we think the best way to see wildflowers and experience their joy is on foot. Breathing in the same air as them, being able to look at them up close and personal, and seeing the expansive ground that they cover— that is where the real essence of the wildflower is experienced!
The following is a condensed list of some of the wildflowers you may encounter while visiting Yellowstone National Park:

Aster:
Characterized by it's long, thin pale purple petals, the aster can be found parkwide, and is one of the longest lasting wildflowers in Yellowstone, in bloom from May to September.

Alpine buttercup:
This common wildflower grows in moist meadows, subalpine and alpine. Characterized by its' small, five-petaled and bowl-shaped yellow flowers, the alpine buttercup is a common wildflower to see in Yellowstone, blooming from June to August.

Arrowleaf balsamroot:
This small and bright yellow-colored wildflower grows in close clusters, and is typically found in the Northern Range, from June to July.

Bitterroot:
As the state flower of Montana, the bitterroot is pink and grows in clusters low to the ground, can can be
seen in the Northern Range, from May to June.

Bull thistle:
Seen as a noxious weed in most areas, the bull thistle is characterized by its large purple, rounded flower heads protruding from spiny bulbs. They are seen flowering from July to September, in every area of Yellowstone.

Elephant head:
This wildflower is pink flowered and pink stalked, and grows most concentrated in meadows, but can be found in a variety of habitats in the park. It is most likely to be seen from June to July.

Fireweed:
As their name suggests, the fireweed is typically one of the first wildflowers to return after a wildfire. They are distinguished by their flashy pink flowers that grow upright on a tall stalk. Fireweed is found parkwide, and blooms from July to August.

Fringed gentian:
Blue and purple in color, the fringed gentian opens it's flowers on sunny days and typically closes them on cloudy days. They can be found in geyser basins, meadows and near Lake Yellowstone, typically from May to August.

Glacier lily:
The petals of this bright yellow wildflower seem to grow upside down, as if they are reaching up to the sky. You can find glacier lily around Lake Yellowstone and Dunraven Pass, from May to June.

Harebell:
This pale purple bellflower grows from July to August and can be seen all over the park. Although it has slender foot-long and delicate inch-long flowers, the harebell is much hardier than it appears.

Indian paintbrush:
Commonly found in all areas of Yellowstone, indian paintbrush can be distinguished by its bright red, and sometimes yellow or orange bracts (which are a type of modified leaf, not petal). They are hemiparasitic, meaning they have the ability to leach nutrients from neighboring plants. They can be seen June through August.

Ladies tresses:
Although the ladies tresses is part of the orchid family, it stands apart with its "geometric, braid-like design of tightly-spaced single white flowers ascending spirally along a single flowering stalk". You can find these amazing flowers near geyser basins and in meadows, from July to August.

Larkspur:
Primarily found in meadows, the larkspur is bright purple in color and is notable for the long "spur" sticking out behind the flower. In Yellowstone, larkspur blooms from May to August.

Lupine:
Named after the Latin word lupus, meaning "wolf", the lupine were originally thought to spread quickly and rob the soil, when in fact, the opposite is true. Lupine add nitrogen to soil making it healthier and richer. They are known by their purple petals that grow upright on its stalk, and bloom June through August.

Oregon grape:
This yellow, clustering flower blooms in a wide variety of habitats, from dry to moist soil, and foothills to montane. The oregon grape has stiff, holly-like leaves and grows low to the ground. You can typically see this wildflower from April to July in Yellowstone.

Pasqueflower:
The pasqueflower is a silky-haired, cup-shaped purple flower with yellow stamens, commonly seen in the meadows of northern Yellowstone. They are in bloom from April to May. In late spring and summer, once they have finished blooming, they will be seen as just feathery plumes.

Rabbitfoot crazyweed:
This vibrant purple flower is typically found in sagebrush meadows, as well as valleys to lower montane. It is characterized by it's dense, pea-like flowers, colored brightly purple. You can see rabbitfoot crazyweed from May to June in Yellowstone.

Shooting star:
This extremely unique looking wildflower is characterized by its pink flowers that seem to defy gravity and look like a shuttlecock. They are primarily found in meadows, but can be seen throughout the park, and bloom from May to June.

Spring beauty:
As one of the first signs of spring beauty, the spring beauty is one of the first wildflowers to bloom in Yellowstone. It grows small white flowers, striped with pale pink lines down the center of its petal. These are commonly found April through June.