The PHS Philadelphia Flower Show is an annual event produced by The Pennsylvania Horticultural Society and held in Philadelphia, Pennsylvania at the Pennsylvania Convention Center in early March. It is the "largest indoor flower show in the world" attracting more than 250,000 people annually. The show features large scale gardens, which range from elaborate landscaped displays to individual and club entries of a prize horticultural specimen. Each year there is an official theme which serves as the inspiration for most exhibits. The exhibits are submitted for judging in many categories, and are highly competitive.

The amateur division of the show known as the Competitive Classes often have an assigned theme, related to the overall show theme. The 2007 Show, Legends of Ireland, featured Pressed Plant Material (i.e. dried flower pictures) that "..incorporated a Celtic Knot.". The first weekend's Medium Niche theme was Wish You Were Here "Exhibitors will be sent Irish postcards for inspiration. A copy of the postcard will be mounted next to the exhibit." Entrants for that class typically have a mockup of the niche at home, where they practice assembling and lighting their entry in the months preceding the show. In a Challenge class, entrants bring only pruning shears, and must use show-provided materials to interpret a theme within a limited amount of time. Three typical Horticulture classes are 142: Clivia, flowering. Pot 8" or under, 143: Clivia, flowering. Pot 8"-10", and 144: Clivia, foliage. (There was also a Clivia entered in 2007 under Exceptional plants 10–20 years old, to be judged against “perfection” for their species/cultivar.)

A popular part of the show floor is the Garden marketplace where visitors can buy plants and seeds, cut flowers, craft items, and other flower, landscaping and horticulture-related items.

The Show boasts fabulous floral and garden design, live entertainment, culinary events and extraordinary gardening how-to workshops and lectures by experts.