Three-year-old Miss D.'s Christmas dress needed a bit of additional length, since she does not care to wear tights or leggings--so her mom and I decided to solve the problem by adding three inches of black tulle netting to the dress's underskirt.
This little dress already has a ruffle of red netting attached to its red taffeta underskirt, so we also stitched the new black tulle ruffle to the underskirt, with the top edge of the black tulle covered by the red tulle.. (In my opinion, such stiff ruffles should always be attached on the TOP of the lining or underskirt to prevent scratchiness against the skin!)!
In this case, the new ruffle is 6" wide. It's stitched to the lining 3" from the edge, so that 3" extends from under the skirt itself.
I cut the ruffle 3-1/2 times the width of the skirt hem, and 12 " wide. After seaming the ruffle panels together in a huge circle, I folded it lengthwise and gathered it along the folded edge.
Here's a great way to gather a long ruffle: Fold the piece to be ruffled in fourths along the width, and mark the quarters with pins. To ruffle, place a piece of sturdy cord (I used crochet thread) along the line to be ruffled and zig-zag over the cord with a medium stitch width and length. It's then easy to pull up and adjust the ruffle, with little danger of breakage. Mark the edge which the ruffle will be attached to in quarters, match the pins, adjust the fullness, and stitch.
The cord could show a bit, so I stitched the ruffle to the underskirt with a narrow zig-zag, next to the gathering cord, then pulled out the cord.
I have to say I think the ruffle really adds to the dress--and Miss D. loves the added twirly factor!