The sky was cloudy Friday morning with rain in the forecast, not ideal weather for a garden tour. But when Pat McGuire opened the front gate to the Minnesota Landscape Arboretum at 9 a.m., he found 25 vehicles lined up with people just waiting for the chance to drive through the grounds.

And as they passed him, they waved and clapped.

“That was just a really cool feeling,” said McGuire, an assistant gardener on the staff, one of a skeleton crew that has been working hard to maintain the arboretum’s 1,200 acres while it’s been closed by the pandemic.

The arboretum, part of the University of Minnesota’s College of Food, Agricultural and Natural Resource Sciences, shut its gates in mid-March along with other U venues. It typically draws about half a million visitors a year.

But on Thursday, word came via e-mail and social media that the arboretum would partly reopen Friday — to vehicle traffic only. Visitors would not be allowed to leave their cars (except at the few open restrooms) and buildings would remain closed. Admissions were limited and advance online registration was required, $15 per car for nonmembers.

By midafternoon Thursday it was fully booked through the weekend. The car tours will continue indefinitely.

Traffic is being allowed only on Three Mile Drive, a winding one-way that meanders past collections of trees and neatly groomed shrubbery, forests and ponds, rolling prairie landscapes and some of the arboretum’s 100 gardens. Visitors are allowed to pause here and there to admire a view or snap a photo.

“Just being out here and having the windows down feels really good,” said Kate Thomas of Minneapolis as she approached the end of her tour. In a normal year, she said, she visits the arboretum several times a month.

“It sounds a little cheesy but I actually teared up a bit driving through it,” she said.

The annual tulip gardens are starting to bloom — 39,000, in a spectrum of reds ranging from palest pink and peach to fire-engine red and deep magenta. More than 200 varieties of daffodils add splashes of yellow and white.

Pear trees are covered with fluffy white blossoms, delicate cream-colored petals are still clinging to the magnolias, and trees in the arboretum’s crab apple collection will soon burst out in bright pink.

“It was just as I thought it would be — perfect,” said Kathy Reason of Chanhassen, who in a normal year visits the arboretum at least once a week. “It was just comforting to see everything.”

Arboretum officials weren’t sure how smoothly the reopening would go. But Friday’s visitors were so responsible about following the rules that around midday, officials extended the hourly vehicle capacity from 75 to 100. By late afternoon, even with the extra admissions, the arboretum was booked through Monday.

If all goes well, officials may soon let visitors walk around the grounds — while social distancing of course, said Director Peter Moe.

“Some other arboretums had opened and had so many people they couldn’t monitor social distancing and closed again, and that’s the last thing we want to have happen,” Moe said.

Annual gardens will go in after the tulips are done, said Alan Branhagen, the arboretum’s operations director. Wheat, corn, soybeans and other Minnesota crops are being planted at Farm at the Arb, a new interpretive attraction designed to educate the public about agriculture.

When it shut down on March 13, the arboretum was working with about a fifth of its usual gardening staff. More employees have been brought on since, but they’re still going without the help of about 800 volunteers who normally assist the gardeners and perform other tasks.

The nonprofit arboretum continues to struggle financially. Much of its $14 million operating budget comes from gate fees as well as programs and events, all of which have been canceled through June.

Still, arboretum enthusiasts have been renewing memberships and even kicking in donations, Moe said.

Friday’s partial reopening had even the skies cooperating, with patches of blue and periods of warm sun.

“It’s just a really exciting day for the arboretum,” Moe said. “Every day we get into May it gets more spectacular.”