The card has a series of pleats across the center to hold the flowers, which stand straight up when the card is opened flat.
See some more ideas--and a instructional video (!!)--at Valita's Fresh Folds. Note that her design has only two center pleats, adhered together. I added more pleats to keep the center from falling over once the standing elements were added.
Make the pleated card
On the back side of an 8.5" x 11" piece of paper, in landscape orientation, score 9 vertical lines 1/2" apart, beginning at the center of the card. (On my card this is the green grass paper.)
Mountain fold green lines, valley fold red lines.
Spread glue between all the pleats on the back (wrong) side of the paper. Close pleats. Clamp or weight. Allow to dry.
Turn paper right side up.
The pleats will form three valleys on the right side of the card (numbered 1, 2,3).
Make the flowers
Download flower and stem templates: PDF, SVG, Silhouette Studio, DXF.
Size the flowers so that the largest pieces, like the yellow daisies, are about 2" across. The smaller flowers should be about 1.5" across.
Cut flower parts from colored card stock and assemble. I used DaPino's illustrations for inspiration. Remember your flowers will be viewed from both front and back so make them two-sided.
Assemble flowers and card
You will need three rows of flowers. I arranged each row separately and then laid them on top of each other in three layers to see what they would look like in the assembled card. Add extra leaves as needed to fill in between the flower stems.
Start with the middle valley (marked #1). Glue the flowers in the valley and then glue the valley shut. Let dry.
Glue a row of flowers in crease 2, and another row in crease 3, but do not glue these valleys shut. If you glue the folds together the combined weight can cause the entire center to flop over instead of standing up straight.
Do glue together just the ends of all the folds. Clamp or weight and allow to dry completely.
Trim the pleated paper, lengthwise and width wise, to a pleasing proportion.
Base card
To accommodate the pleats of the flower card, make a base card with a book-like spine down the center rather than a single center fold.
Lightly mark the center line of the base card. (My base card is blue.) Do not fold on the center line. Measure out from the center line, both directions, a small amount, somewhere between 1/16" and 1/8". Score and fold.
Center the pleats of the flower piece on the base card. Glue the flower piece to the base card. Allow to dry with the card fully opened. Prop up the center flowers to keep them upright while the card dries.
Here's one made by Eunice from A Star for Chiemi.