The December 12th USPS Postal Bulletin indicates that this issue will be released at AmeriStamp Expo 2014 in Little Rock, Arkansas, on February 14.
From my article from the October press preview:
Flowers figure big in the first half of the 2014 stamp program: A block of four Winter Flowers booklet stamps is due early in the year. …
Winter Flowers will be a block of four with dark blue backgrounds in booklet format. Says the USPS, “Each of four stamps depicts a close-up view of one plant — Christmas cactus, amaryllis, cyclamen, or paperwhite — with detailed and colorful renderings of its blossom and foliage.
“The stamps feature digital paintings in PhotoShop. Using a cordless pen or stylus, [artist William Low] ‘painted’ his brushstrokes on a pressure sensitive screen, adding dabs of color and weaving layers of texture into the paintings.” He used actual potted plants as his models. He also designed the 2013 Poinsettia stamp.
From the USPS on December 24th:
With Winter Flowers, the U.S. Postal Service continues its tradition of issuing stamps that present beautiful, floral-themed art.
Each of these four stamps depicts a close-up view of one plant — Christmas cactus, amaryllis, cyclamen, or paperwhite — with detailed and colorful renderings of its blossom and foliage.
These winter-blooming flowers are popular potted plants, especially during the holidays when people enjoy them as gifts or as festive decorations. Just as these flowers brighten our dark winter days, these stamps will add a decorative and cheerful note to all your correspondence.
Art director Ethel Kessler designed the Winter Flowers stamps, which feature art by William Low.
Here’s the Digital Color Postmark for this issue: 
How to Order the First-Day-of-Issue Postmark:
Customers have 60 days to obtain the first-day-of-issue postmark by mail. They may purchase new stamps at their local Post Office™, at The Postal Store® website at www.usps.com/shop, or by calling 800-STAMP-24. They should affix the stamps to envelopes of their choice, address the envelopes (to themselves or others), and place them in a larger envelope addressed to:
Winter Flowers Stamp
Little Rock Main Post Office
ATTN: Station Manager
600 East Capital Avenue
Little Rock, AR 72202-9998
After applying the first-day-of-issue postmark, the Postal Service will return the envelopes through the mail. There is no charge for the postmark up to a quantity of 50. For more than 50, customers have to pay five cents each. All orders must be postmarked by April 19, 2014.
Technical Specifications:
Issue: Winter Flowers Stamp
Item Number: 689100
Denomination & Type of Issue: First-Class Mail Forever
Format: Double-sided Booklet of 20 (4 designs)
Series: N/A
Issue Date & City: February 14, 2014, Little Rock, AR 72202 (APS AmeriStamp Expo 2014) (Field Event)
Art Director: Ethel Kessler, Bethesda, MD
Designer: Ethel Kessler, Bethesda, MD
Typographer: Ethel Kessler, Bethesda, MD
Artist: William Low, Huntington, NY
Modeler: Donald Woo
Manufacturing Process: Offset/Microprint “USPS”
Engraver: N/A
Printer: Banknote Corporation of America
Printed at: Browns Summit, NC
Press Type: Alprinta, 74
Stamps per Booklet: 20
Print Quantity: 500 million stamps
Paper Type: Phosphor Tagged, Overall
Adhesive Type: Pressure-sensitive
Processed at: Banknote Corporation of America, Browns Summit, NC
Stamp Orientation: Vertical
Image Area (w x h): 0.77 x 1.05 in./19.55 x 26.67 mm
Stamp Size (w x h): 0.91 x 1.19 in./23.11 x 30.22 mm
Full Booklet Size (w x h): 5.74 x 2.38 in./145.80 x 60.45 mm
Colors: Cyan, Magenta, Yellow, Black, Blue
Plate Size: 480 stamps per revolution
Plate Numbers: “S” followed by five (5) single digits
Marginal Markings: Front: Header: “WINTER FLOWERS” “Twenty First-Class Forever® Stamps” • Plate numbers in peel strip area • © 2013 • USPS in peel strip area • Barcode (015645689107)
i have ywo stamps of 2013 winter flowers. how much each???
Mahalo, Galinda
Each is now worth 49 cents (face value), the current value of a Forever stamp.