The park is located in the Carolinian Zone of forests in Southern Ontario. Due to the location of the park in the Carolinian Forest Zone, approximately 50% of the parks vegetation is considered to be exotic (Durley, 1997). The park is home to many rare plant species such as sassafras, and black gum trees. Other plant species that can be seen within the park includes: black oak, sugar maple, black walnut, white trillium, sharp-lobed hepatia, and wild leek. Much of the vegetation that is not under forest cover in Short Hills Provincial Park is currently characterized by post-agricultural succession.

One of the most noticeable plants in the park includes the Trillium (Trillium gandiflorum). You may recognize this flower as the emblem of Ontario. The trillium flowers in the spring time and bears 3 large leaves with a flower that consists of 3 white petals. The flower withers away and eventually returns as reddish-purple berries for the duration of the summer.

The Aboriginal People used these plants as food and aphrodisiacs. The plant was also used in a curse to wish bad luck on enemies. The green part of the plant may be cooked and eaten, however the plant will die and it is illegal to kill a trillium plant in Ontario.