In May, gardens across the U.S. are at their peak bloom, so it probably comes as no surprise that National Public Gardens Day takes place on May 10, and the month is filled with special festivities. One of the most-anticipated garden-related events will be the reopening of Longwood Gardens' Main Fountain Garden, which underwent a two-year renovation. Another can't-miss event is Ballet Arizona's aptly named "Topia" series at the Desert Botanical Garden in Phoenix. Plus, these are no mere gardens; they are also filled with significant art and history. Some green spaces, like South Carolina's Brookgreen Gardens, which doubles as one of the world's largest sculpture gardens as well as one of the biggest botanical gardens, have been recognized as National Historic Landmarks. So, if you want to explore spectacular gardens this spring, commune with nature and admire beautiful floral displays in these sanctuaries across the country.[See: America's Top 7 Scenic Spring Road Trips Under $500.] Longwood GardensKennett Square, PennsylvaniaLongwood's Main Fountain Garden features more than 1,700 fountain jets and streams, and will stage a grand reopening celebration from May 27 to 29 as part of its "Summer of Spectacle," with theatrical fountain shows, fireworks and fun programs continuing through Sept. 30. The Main Fountain Garden, Longwood's crown jewel, is a European-inspired five-acre expanse with sculpted plantings, sculptures, plus a new hidden grotto. What's more, Longwood is a highlight of the scenic Brandywine Valley along the Pennsylvania-Delaware border. Industrialist and philanthropist Pierre du Pont established Longwood 111 years ago to save historic trees from being sold as lumber. He designed many of the gardens himself. Now, Longwood's more than 1,000 acres include a beer garden, meadows, woodlands, a conservatory and even an Aeolian organ. Chanticleer EstateWayne, PennsylvaniaThe garden estate Chanticleer (which translates to rooster in Old French), was founded by pharmaceutical company owner Adolph Rosengarten, Sr., whose name translates to rose garden. Mr. Rosengarten actually named it after "Chanticlere, though one of the finest castles in England...is mortgaged up to the very castle windows," as described by William Makepeace Thackeray in his 1855 book "The Newcomes: Memoirs of A Most Respectable Family." Chanticlere, in Middle English, and Chanticleer in Old French, translates to rooster, so rooster symbols are found throughout the more than 5,000 plants on 35 acres of Chanticleer. Best of all, visiting this garden is easy, as it's located in the suburbs of Philadelphia.United States Botanic GardenWashington, District of ColumbiaGeorge Washington, Thomas Jefferson and James Madison led the groundwork for Congress to establish a national botanic garden in 1820. The United States Botanic Garden on Capitol Hill is one of the oldest in North America, continuously open to the public since 1850. This delightful free oasis consists of a Conservatory, a National Park and Bartholdi Park. Named for Frederic Auguste Bartholdi, who designed the Statue of Liberty, this namesake park features his graceful Art Nouveau "Fountain of Light and Water." Another major draw is the Conservatory's rotating display of hundreds of orchids from its 5,000-species collection, plus a reconstructed Jurassic Age landscape of ferns and other plants. Also well worth a visit is Washington's United States National Arboretum, about four miles northeast of the U.S. Botanic Garden. You can get a bird's-eye view of the arboretum's resident bald eagle family, "Mr. President" and "The First Lady" and their eaglets, "Honor" and "Glory," through a live camera, complete with sounds.[See: 7 Top Spring Flower Festivals Around the World.]Brookgreen GardensMurrells Inlet, South CarolinaBrookgreen, America's first outdoor public sculpture garden and now North America's largest, with a total 1,900 sculptures, celebrates its 85th anniversary this year. About 500 sculptures are set in the quintessentially Southern landscape composed of azaleas, camellias, magnolias, live oak trees dripping with Spanish moss. No surprise because Brookgreen Gardens is comprised of four former plantations, totaling 9,000 acres. This exquisite National Historic Landmark was co-founded by railroad heir Archer Huntington, who also established the Library of Congress's U.S. Poet Laureate position, now celebrating its 80th anniversary. The co-founder was his wife Anna Hyatt Huntington, one of the most prominent, successful 20th century American sculptors. Renowned especially for her dramatic animal sculptures, she founded Brookgreen's Native Animal Zoo to preserve and protect native species. This great family destination is only 20 miles south of Myrtle Beach.Longue Vue House and GardensNew Orleans, LouisianaEight acres of gardens created by Ellen Biddle Shipman, the "dean of American women landscape artists," surround this 20-room Classical Revival-style mansion in New Orleans. Shipman began designing Longue Vue's gardens in 1935 in collaboration with architects William and Geoffrey Platt to create a garden estate for Edgar Bloom Stern and Edith Rosenwald Stern, a high-profile philanthropic New Orleans couple. The Sterns supported worthy causes from the arts to civil rights. Their former estate, a National Historic Landmark, contains original opulent furnishings, art and antiques. Two highlights of its gardens are the Spanish Court, inspired by the medieval gardens of the Alhambra in Granada, Spain, and the Louisiana iris collection in the Wild Garden.Missouri Botanical GardenSt. Louis, MissouriThe Missouri Botanical Garden, a National Historic Landmark in St. Louis, is one of the country's oldest gardens, and has been in continuous operation since 1859. It offers many unusual features, especially The Climatron, the first geodesic dome to be used as a greenhouse. It was inspired by the principles of R. Buckminster Fuller, the inventor of the geodesic system. The garden has created Therapeutic Horticulture Programs for blind or visually impaired people, children and adults with autism, ill people and their caregivers, among others. Many of the unique programs are held in the Zimmerman Sensory Garden, which specializes in sights, smells and textures of plants. Another highlight is the Victorian District, which features a maze and founder Henry Shaw's home, Tower Grove House. [See: 7 Top Places to Catch Spring Blooms Across America.]Desert Botanical Garden PhoenixThe Desert Botanical Garden in Phoenix is the world's only garden focusing solely on desert plants. The 50,000 plants scattered across 55 acres include rare, threatened and endangered species from around the Southwest, mainly from the Sonoran Desert. Beginning in spring, you can enjoy unusual events in the garden. Ballet Arizona's aptly named "Topia" series in the Desert Botanical Garden begins on May 23. Flashlight tours to catch sight of night-blooming plants and nocturnal animals start on May 27. Another fun program is "Cactomania!," which draws attention to the garden's crucial mission to save cacti, the world's fifth most threatened group of living things, according to the International Union for Conservation of Nature's Red List of Threatened Species.