These are before and after pictures of a porch--without and with the skirting I created. This instructable will give you some more details of how to do it.
Step 1: The Idea
I built a small porch for my daughter and daughter-in-law's house and needed some kind of skirting around it. I looked for alternatives to lattice and saw that boards used to be used with geometric shapes cut between the boards with gaps between them. I wondered if the same idea would work with flowers--with the gap serving as the stem. And it did!
Step 2: Create Stencils
First choose a flower(s) to use. I looked at flower silhouettes until I found some I liked. You may want to avoid using a many-petaled one due to the scrollwork needed. Copy the image and cut it out. Then trace it on some heavy cardstock (like the back of an old tablet) so that half of it is on one edge and the other half on another edge. Cut them out.
Step 3: Prepare to Cut
Measure the opening under the porch. I used cedar-tone treated lumber. 1x6s for the cut-outs and 2x4s for the frame. I made the lengths of the frames the width of the under-porch opening (minus 1/2 inch or so) and the shorter sides of the frame 7" shorter than the actual height of the opening (allowing for the width of the 2/4s). These are very simple frames. You could certainly build them better--but these worked. You'll have to figure out how to attach the frames under the porch--you may want to increase the height so that it will attach to the ledger board of the porch. You'll also want to check to see how square the under-porch openings are and allow for that in your construction.
I cut a notch on the inside edges of the frame so that the 1x6s sit inside the frame. This notch was cut 3/4" deep on all four pieces of the frame (the dimension of the 1x6s). Make the other cut of the notch at least 1" deep so that the 1x6s overlap each edge of the frame by at least 1". Building them this way (with a full-length notch) works as long as the outside edges of the frames don't show. See the photo that shows how the notch runs out to the end of the frame.
Cut the 1x6s so that they are 2-3" longer than the short sides of the frame. Lay out the 1x6s using pencils to maintain the spaces between boards. Cut the widths of the two 1x6s on the ends so that they are the same width.
Trace the stencils on the good sides of the 1x6s (the sides that will be seen). Make sure to line both halves of the stencils on adjoining boards.
Step 4: The Scrollwork.
Cut out the shapes. NOTE--how you do this depends on your tools AND the lengths of the 1x6 boards. If the board are longer than you can cut on your band saw or scroll saw (the limit for me were boards which were about 16" long), you'll have to use a jig saw. A jig saw would work on any size board but will take a lot longer. Or use simpler shapes such as hearts or patterns of circles cut with a hole saw. If you use treated lumber, be sure to work with ventilation and vacuums to collect the sawdust. I used a bandsaw with a 3/16" blade. I found it more accurate and quicker than anything else. I won't go into detail about how to do the scrollwork. You'll likely have to back out of your cuts a lot. Take your time and watch your fingers! The last photo is the heart template I used on a few boards.
Step 5: Create the Panel
Lay the frame upside down. Place the 1x6s in the frame good side down. Use pencils to maintain uniform spacing. Pre drill holes for the screws so you don't split the 1x6s. The frame is held together by screws through the tops of all the 1x6s as well as the sides of the end 1x6s. Use a square to make sure your frame stays square as you put in the screws. It doesn't hurt to use a little sandpaper to clean up the rough edges on your cuts--but be careful to not break any of the small pieces. Turn it over and smile.
This panel is not one from the porch, but it's made in the same way (though with cedar instead of pressure-treated wood.
I used black paint to paint over a couple of parts of the porch where the cutouts ended up being over those parts (not sure that makes sense--the idea is for the cut-outs to look black from shadow, but if there is wood directly under them, they wouldn't necessarily look that way.
I'm guessing that one could also make these by not building a 2x4 frame. It could work to just use 1x4s all the way around and screw the 1x6s directly to the backs of them. Might make attaching them to the porch a little more difficult.