NEW YORK — It's lovely to visit a garden on a spring day, surrendering to the scents, colors, and even the sounds, of birds chirping or the breeze rustling a dogwood tree heavy with blossoms.

But there's also something to be said for taking a close look, guided by an expert who can reveal a garden's secrets and point out the wonders that a casual stroll might miss.

Many botanical gardens offer guided tours, from a docent-led walk to see seasonal highlights, to ticketed tours focusing on some aspect of the garden's collection. This spring, the Brooklyn Botanic Garden is introducing several types of guided tours for groups of 20 or more.

"It's a way to really get in contact with the plants," said Mark Fisher, a curator at the Brooklyn Botanic Garden.

Walking through the garden's Steinhardt Conservatory greenhouse with Fisher on the "Meet the Curator" tour, you see things that you'd miss on your own. He points out papayas clustered in a treetop; the architecture and artistry of a bonsai's pruned branches, and an orchid growing on a tree, its roots seemingly suspended in the air.

"See the vellum?" Fisher said, pointing to the soft, sticky, tiny hairs on the orchid's roots as it hung from a tree branch. "They get their nutrients by attracting leaf litter." This type of plant is called epiphytic, as opposed to terrestrial, Fisher noted.

Brooklyn Botanic Garden spokeswoman Leeann Lavin said there's an increased interest in these types of tours thanks to "baby boomers who want to keep learning" and other visitors who are looking for a "more intimate experience" than just taking a walk on a nice day.

Historic homes often have noteworthy gardens, too. No visit to Monticello, Thomas Jefferson's estate in Virginia, would be complete without a tour of the gardens. Jefferson grew hundreds of varieties of vegetables and fruits, and he filled his flower beds with a mix of European plants, like tulips, and native American specimens, including some collected by Lewis and Clark on their journey west. But part of the charm of the tour is learning that some of Jefferson's gardening experiments — including a vineyard and a dream of producing syrup from maple trees — failed.

Some locales organize tours of private gardens every spring, giving visitors a peek inside historic and often well-appointed homes that are not otherwise open to the public. Newport, R.I., hosts a "Secret Garden Tour," June 15-17. Natchez, Miss., has a "Symphony of Gardens Tour" May 4-5. Atlanta's Gardens for Connoisseurs Tour, May 12-13, is a fundraiser for the Atlanta Botanical Garden. Historic Garden Week in Virginia, April 21-28, sponsored by the Garden Club of Virginia, features 30 tours around the state, from 18th century James River plantations to walled urban retreats.