Money really will grow on trees in New England this fall, as millions of “leaf peepers” flock to the region to view its colorful foliage and inject billions of tourism dollars into local and state economies.

Vermont’s 3.5 million foliage tourists spend about $460 million — a quarter of the overall annual visitor spending — during the six-week foliage season, according to the Vermont Department of Tourism and Marketing. The haul is even bigger in New Hampshire and Massachusetts, where state officials estimate that combined visitor-spending totals more than $4.6 billion during foliage season.

“You can’t get great foliage without a good setup in spring or summer. This year the setup is not terrible, but it’s also not ideal.”

- Jim Salge, foliage expert, Yankee magazine

But just having exceptional foliage is not enough. All the New England states — Vermont, New Hampshire, Maine, Massachusetts, Connecticut and Rhode Island — invest in foliage marketing, and some create special apps and websites.

This year Vermont is spending $280,000 to advertise its “World’s Best Foliage” campaign, and the state’s tourism website, VermontVacation.com, will provide weekly foliage reports, best bets for driving tours and a foliage tracker.

Leaf peeping is akin to a sport in New England, and no two seasons are alike.

“To get really vibrant colors, we need a great setup,” said Jim Salge, foliage expert at Yankee magazine. “We need a nice, reasonably mild, reasonably rainy spring. We need a summer that has ample rainfall. And the biggest factor is a fall season that has a lot of sunshine, warm days and cool nights.

 “The nice thing about New England is that’s what is normal. So in an average year in New England, we get pretty spectacular foliage.”

Still, nobody knows for sure where and when the colors will peak. “Predicting fall’s color changes is part science and part luck,” said Michael Snyder, commissioner of Vermont’s Department of Forests, Parks and Recreation. “We know the science of color change and the factors that influence it, but we don’t know exactly how it will unfold in any given year. The good news is, our foliage is like a day on the slopes — when it’s good, it’s great. And even when it’s a bit off, it’s still really good.”

So what’s the forecast this year? “I’m expecting that it’s going to be patchy,” said Salge. “You can’t get great foliage without a good setup in spring or summer. This year the setup is not terrible, but it’s also not ideal.”

“Much of New England had a really dry spring, and then we had variable rainfall this summer,” he said. “Some areas have gotten rainfall that’s well above normal, and we have some areas where rainfall has been below normal. Some places are still running a huge deficit for rainfall, while 10 miles away they are right on target or ahead. So it’s going to be a patchy year.”

Want to maximize your chances of finding the best fall colors? Follow these tips:

• Time it right. Hitting the colors at their peak is a crapshoot, but you can up your chances. “If people give themselves a nice window in early October in the northern part of New England or mid- to late October in the southern part of New England, they’ll be perfectly fine — this year or any year,” Salge said.

• Be flexible. “It’s only a half a day’s drive from the earliest peak to the latest peak in New England,” Salge said. “So if you have the ability to get in a car, and some flexibility in your plans, you can find the peak.”

• Follow the crowd. Classic foliage routes include Route 7 in Vermont, coast road U.S. Hwy. 1 in Maine, Kancamagus Highway in New Hampshire and Route 2 through the Pioneer Valley in Massachusetts.

• Get off the beaten path. “Really, there’s great foliage everywhere, as well as fine country stores and great New England farms,” said Salge. “That’s why people come here; there’s something for everybody and it’s really easy to do.”

• Download Yankee Magazine’s free LeafPeepr app, which uses crowdsourced foliage reports to tell you where color is about to peak, at peak or past peak.

Suzanne Rowan Kelleher is the family vacations expert at About.com.