Fill an empty vase with whole lemons and push them down into the vase so they hold each other in place against the glass. Shift the positions of the lemons as needed to get a tight fit. Add more lemons if needed to help wedge the arrangement firmly into place. Chill the lemons in the refrigerator and add water right before displaying the arrangement.
Cut lemons in half and arrange them in the bottom of the vase with the cut side facing the glass. Wedge in as many lemons as will fit. Getting them in tight helps to keep them on the bottom of the vase. Cut a slice of floral foam and wedge it into the center of the vase between the ends of the lemons. Trim it to fit, as needed. Add layers of cut lemons between the vase and the floral foam. Gently pour glass gems into the vase to conceal the floral foam. Add the water last.
Arrange whole or cut lemons in the bottom of the vase, filling the vase as far as desired, such as halfway to the top. Cut flowers or foliage so the stems vary in length, with the longest ones twice the height of the vase. Crisscross the stems of flowers or foliage to create a balanced arrangement and keep the lemons in place. Pushing strong stems between the lemons at an angle from each direction will keep the lemons at the bottom of the vase.