In a sure sign of spring, tree sap for maple syrup is starting to flow.

But just how long it will last and how quickly it will flow depends on the weather.

Warm daytime temperatures followed by freezing weather at night have been the perfect scenario to start tapping tree sap to make maple syrup. This year’s syruping season, which usually would have started at the beginning of March, was delayed until this weekend because of the cold weather.

Chris Ransom is a hobbyist who taps about 60 trees on his lot and neighbor’s lot in Vadnais Heights. He is also president of the Minnesota Maple Syrup Producers’ Association, which has more than 130 members.

It can be difficult to predict how fruitful a maple syrup season will be because the time to collect sap is typically two to four weeks, and weather patterns vary from region to region, he said. An average year would allow him to make 15 gallons of syrup, which he gives away to family and friends.

“I’m on track for a normal start to the season,” said Ransom. “But sap run is entirely weather-related — quantity and quality. Last year was a good year for me and for producers from about the Twin Cities and further south. Farther north they had a tougher go of it.”

Tree tapping is also in full swing at the Minnesota Landscape Arboretum in Chanhassen, where more than 400 maple, black walnut and birch trees will produce thousands of gallons of sap. The painstaking boiling-down process takes 35 gallons of sap to make one gallon of syrup. In 2017, the arboretum hit 130 gallons of syrup, the most in nearly four decades.

The large amount of snow that fell this winter doesn’t appear to be affecting sap flow, said Richard DeVries, who is in charge of sap collection. Almost all the trees were tapped this weekend using several different methods. On half of the trees, a gravity system pulls the sap downhill. The other trees are attached to a vacuum pump that carries sap to a large vat — the more efficient method used by commercial producers. The sap is then boiled in a large stainless steel evaporator that can cook up to 80 gallons of sap an hour.

While the arboretum runs a modest commercial operation, some of the maple syrup production comes from a popular educational program that attracts 1,500 students from around the state each year.

Since this weekend, the arboretum’s three 300-gallon sap collection tanks were already full, said DeVries. The birch tree tapping is an experiment this year, and he said the sap run has been slow.

The arboretum sells its syrup in the visitor center. It often sells for double or triple the price of commercial syrup brands, many of which only contain maple flavoring. People can sample the syrup at the arboretum’s MapleFest on March 30 and take a tour.

Minnesota produces less than 1 percent of the country’s maple syrup, far less than larger players in the Northeast such as New York and Vermont. Minnesota has 10 million tappable maples scattered throughout the state, said DeVries. It’s the most westerly state in the country that can produce maple syrup.

Syrup-making continues to be a growing hobby in Minnesota, he said. And this would be a good year to start because the last snowstorm turned into rain and melted much of the snow, enhancing the sap runs, he said.

But if the weather gets too warm and doesn’t drop back down to freezing at night, the syrup season is over, he said.

“It looks all good on paper, but I’ve been fooled before,” said Ransom. “One thing for sure, though, is that there will be a season and syrup will be made.”