The weather was the toughest part.

Brandon Gardner, coming from the south, wasn’t used to the frigid temperatures of the New York City area. It took his body time to acclimate.

“I used to get sick every week,” the St. John’s signee told The Post after practice Friday at Christ the King High School in Queens.

That, along with the food and speed of the fast-paced city, were adjustments for the gifted 6-foot-9 forward from Waynesboro, Ga.

It happened fast.

In late June, Gardner verbally committed to St. John’s. By August, he had moved to New York City with his entire family, finding a place in Kew Gardens. He later enrolled at Christ the King, joining one of the most prestigious high school basketball programs in the country. The school has produced the likes of Lamar Odom, Jayson Williams, Speedy Claxton and many others.

“I felt, if he could play basketball in New York City, he could play basketball anywhere,” said his mother, Tameka Gordon.

It has been a transition for the consensus four-star, top-100 recruit who attended Word of God Christian Academy in Raleigh, N.C., and Gray Collegiate Academy in West Columbia, S.C., for his first three years of high school.

He said he was initially confused at some of the concepts. Coach Joe Arbitello and his staff have worked with Gardner — the jewel of St. John’s coach Mike Anderson’s recruiting class and a bright spot for the future during a disappointing season — on basics that he was lacking at both ends of the floor. That included offensive and defensive positioning, his responsibility as a weak-side help defender, the best spots for him to catch passes and need to move without the ball. For all his natural ability, and it is considerable, those little things may speed up his development at the next level.

“I’ve actually learned a lot,” the 18-year-old said. “This is going to help me in college because some of the defensive things that I’ve learned here, I wouldn’t know.”

Gardner’s overall numbers — 8.3 points, six rebounds and 1.2 blocks — aren’t eye-popping. He struggled somewhat early in the season, battling illnesses and ankle soreness. He didn’t start in a couple of games. But he has played much better of late, dating back to his selection to  the all-tournament team at the Bass Pro Shops Tournament of Champions in Springfield, Mo., a couple of weeks ago. His best game was his most recent one in a win over St. Peter’s: 17 points, five rebounds, two blocks. He threw down monster dunks, hit a 3-pointer and shut down Eagles star Qadir Martin. He has helped Christ the King rack up a 14-4 record and 11-1 mark in the ultra-competitive Catholic League.

“Since Missouri, we’ve seen a lot of progress,” Arbitello said. “Obviously, his athleticism, finishing at the rim, dunking on people, that’s the first thing you notice about him. He grabbed a couple of rebounds at St. Peter’s. I felt like he was above the top of the backboard.”

One anonymous college coach familiar with Gardner described him as an “NBA athlete.” Another raved about his motor and the energy he plays with.

He’s a highlight film, a human pogo-stick who credits his time running hills over the years for his athleticism. Archbishop Stepinac coach Pat Massaroni has been impressed with Gardner’s shooting ability — he does have 3-point range — and unselfishness. On a loaded team with several Division I prospects, patience is required.

“When you’re ranked as high as he is, and good as he is, you can do things that you want,” Massaroni said. “He’s bought into their team mindset, and that’s why they’re having so much success.

“He’s one of the best big men in the league, if not the state.”

Gardner has been keeping tabs on his future school, St. John’s. He has attended several games. The Red Storm haven’t lived to preseason expectations, and have struggled to put more than a few solid games together. They need to catch fire over their last 10 Big East games to get into the NCAA Tournament mix. They are currently 3-7 in the conference, much closer to the basement than the penthouse in Anderson’s fourth season as head coach.

Those struggles haven’t turned off Gardner. He remains excited about his future at the Queens school and joining his close friend, current freshman AJ Storr.

“I don’t have any second thoughts,” Gardner said. “I’m all-in.”

He was at the recent loss to Villanova at the Garden, which was attended by more than 13,000 fans. That spotlight is part of what drew him to the program.

“That excites me a lot,” he said. “I like games like that, when it’s a lot of people. That’s what I live for.”

For now, his focus is on finishing out his final year of high school strong. He has made friends at his new school, in particular current teammates Brandon Williams, Dwayne Pierce and Devin Vanterpool. He wants to enjoy everything about his one season at Christ the King.

“We’re not losing any more,” he promised. “I just want to win this [championship] so I can have another ring.”