From the U.S. Postal Service announcement on October 22, 2019:

With these stamps the Postal Service celebrates the beauty of American gardens. This pane of 20 stamps features 10 different photographs of botanic, country estate and municipal gardens taken between 1996 and 2014. The gardens include: Biltmore Estate Gardens (North Carolina); Brooklyn Botanic Garden (New York); Chicago Botanic Garden (Illinois); Coastal Maine Botanical Gardens (Maine); Dumbarton Oaks Garden (District of Columbia); The Huntington Botanical Gardens (California); Alfred B. Maclay Gardens State Park (Florida); Norfolk Botanical Garden (Virginia); Stan Hywet Hall & Gardens (Ohio); and Winterthur Garden (Delaware). Art director Ethel Kessler designed the stamps with existing photographs by Allen Rokach.

Additional information will be posted below the line, with the most recent at the top.

These stamps will be issued Wednesday, May 13th, in Winterthur, Delaware, presumably because of at Winterthur Garden.

Updated May 11th:
There will be a virtual ceremony for these stamps, open to the public, on the day after, Thursday, the 14th. Member Lefty Dundee got the information. See his message below for details (or click on “his message” in this sentence).

Updated March 23rd:
The first-day ceremony for this stamp has been canceled. The stamps will still be issued on May 13th. More details will be announced closer to the issue date.

Updated April 10th from the Postal Bulletin:
On May 13, 2020, in Winterthur, DE, the United States Postal Service® will issue the American Gardens stamps (Forever® priced at the First-Class Mail® rate) in 10 designs, in a pressure-sensitive adhesive pane of 20 stamps (Item 572700). The stamps will go on sale nationwide May 13, 2020, and must not be sold or canceled before the first-day-of-issue. The American Gardens pane of 20 stamps may not be split and the stamps may not be sold individually.

With this issuance, the United States Postal Service celebrates the beauty of American Gardens. This pane of 20 stamps features 10 different photographs of botanic, country estate, and municipal gardens taken between 1996 and 2014. The gardens include:

• Biltmore Estate Gardens (North Carolina);
• Brooklyn Botanic Garden (New York);
• Chicago Botanic Garden (Illinois);
• Coastal Maine Botanical Gardens (Maine);
• Dumbarton Oaks Garden (District of Columbia);
• The Huntington Botanical Gardens (California);
• Alfred B. Maclay Gardens State Park (Florida);
• Norfolk Botanical Garden (Virginia);
• Stan Hywet Hall & Gardens (Ohio); and
• Winterthur Garden (Delaware).

Art director Ethel Kessler designed the stamps with existing photos taken by Allen Rokach.

Automatic Distribution.

How to Order the First-Day-of-Issue Postmark:
Customers have 120 days to obtain the first-day-of-issue postmark by mail. They may purchase new stamps at their local Post Office™ or at The Postal Store® website at usps.com/shop. They must affix the stamps to envelopes of their choice, address the envelopes (to themselves or others), and place them in a larger envelope addressed to:

FDOI – American Gardens Stamps
USPS Stamp Fulfillment Services
8300 NE Underground Drive, Suite 300
Kansas City, MO 64144-9900

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. There is a 5-cent charge for each additional postmark over 50. All orders must be postmarked by September 13, 2020.

Technical Specifications:

Issue: American Gardens Stamps
Item Number: 572700
Denomination & Type of Issue: First-Class Mail Forever
Format: Pane of 20 (10 designs)
Series: N/A
Issue Date & City: May 13, 2020, Winterthur, DE 19803
Art Director: Ethel Kessler, Bethesda, MD
Designer: Ethel Kessler, Bethesda, MD
Typographer: Ethel Kessler, Bethesda, MD
Existing Photos: Allen Rokach
Modeler: Sandra Lane/Michelle Finn
Manufacturing Process: Offset
Printer: Banknote Corporation of America
Press Type: Alprinta 74
Stamps per Pane: 20
Print Quantity: 50,000,000 stamps
Paper Type: Phosphor Tagged Paper, Block
Adhesive Type: Pressure-sensitive
Processed at: Banknote Corporation of America
Colors: Pantone 554, Cyan, Magenta, Yellow, Black
Stamp Orientation: Vertical
Image Area (w x h): 1.42 x 1.085 in./ 36.068 x 27.559 mm
Overall Size (w x h): 1.56 x 1.225 in./39.624 x 31.115 mm
Full Pane Size (w x h): 7.5 x 7.9 in./190.5 x 200.66 mm
Plate Size: 180 stamps per revolution
Plate Number: “B” followed by five (5) single digits
Marginal Markings:
Front: Header: American Gardens • Plate number in bottom two corners
Back: ©2019 USPS • USPS logo • 2 barcodes (572700) • Plate position diagram (9) • Promotional text