Remember when the holiday shopping season ended when the holiday was over?

No more.

"It never ends!" laughs retail analyst Wendy Liebmann of WSL, a retail analyst firm. "It just goes ooooon and ooooon and ooooon."

In January, the nation's retailers used to rake out the aisles, restack all of the unsold sweaters and throw the sheets on a big table for the biannual White Sale. But now January is growing in importance. Retail sales rose 10.5 percent in January this year versus 2005, when they rose 7.5 percent. In 2004, January sales rose 6.1 percent.

Retailers are restocking shelves with fresh merchandise and selling early, early spring fashions before most consumers have tossed their Christmas trees out on the curb.

All because of a small plastic card — the gift card.

"January is no longer a dead month," says Dan Horne, a marketing professor at Providence College in Providence. "Now, retailers are holding back hot items to entice consumers coming into their stores in January bearing their Christmas gift cards."

This year, consumers bought $24.8 billion in gift cards, 34 percent more than in 2005. That growth is phenomenal. Gift card sales rose only 7 percent from 2004 to 2005, and 0.5 percent the year before. There's no end in sight. "We'll be buying more gift cards next year, there's no doubt," says Malcolm Fowler, general manager of Ernex, a company that manages card programs for more than 1,000 U.S. and Canadian retailers. "The only question is: Will sales rise 30 percent or 20 percent?"

The holiday shopping season used to end by New Year's Day or later that week when people exchanged their presents and maybe snagged a sale item or two. Retailers held their breath when counting up sales for the key month of December, when 40 percent to 60 percent of a retailer's sales can occur. If they didn't sell their stock at full price or near it in December, they'd have to sell it deeply discounted — and less profitably — in January.

But the popularity of gift cards is transforming the retailing industry.

Most people spend their gift cards in January and February. And because retailers can't count gift card sales until the cards are redeemed, those sales dollars are pushed out of December into the next year. Gift card sales now represent 5 percent of total holiday sales, so those dollars are having a significant impact on retailers' business in the months after Christmas. About 40 percent of card redemptions are made in the first week after Christmas. But the rest comes in January or early February.

"Retailers have finally learned that even if they don't get all the business by Dec. 25, they don't have to panic," says Marshal Cohen, chief industry analyst at NPD Group, a retail consulting firm.

"January used to be a throwaway month, but it's not anymore."

That could be good news this year because retail sales projections for December have been lowered recently by some key trend watchers, including MasterCard Advisors. It said this week that holiday retail sales would rise a "disappointing" 6.6 percent from last year compared with 8.7 percent in 2005. (The period is from the day after Thanksgiving through Dec. 24.) The National Retail Federation says sales will rise 5 percent in December, "not phenomenal but modest," NRF spokesman Scott Klugman said earlier this week.

Analysts have been worrying that a slumping housing market and higher gasoline prices have put a damper on consumer spending. But Cohen of NPD says retailers can blame gift cards for muted December sales. People haven't stopped shopping, he says. They've just "delayed" shopping.

"Everyone is worried about what happened to the holiday season this year. It was the retailers' gift cards," he says. "They shot themselves in the foot."

Retailers also continued to push this year for an earlier and earlier start to the holiday shopping season and so offered deep discounts on the Friday after Thanksgiving on some sexy electronics, such as high-definition TVs and new video gaming systems.