If you plan on pinning arrangements end to end, you can insert stakes into the end and slide one arrangment to another.
Two bricks create an arrangement almost 18 inches long. The arrangement will be even longer when you extend greenery and flowers beyond the sides and ends.
One brick is approximately 9 inches long.
I'm going to attach a sphere to the center, by hollowing out an area in the middle and sliding the wet sphere onto the wooden stakes.
I'm going to insert a couple stakes first - and add more if needed until I feel the wet ball is firmly held into place.
Leave the extra length - it can always be cut off at the edge of the foam.
I'm placing a second stake on the other end as well.
You have to have your design in mind as you are building the structure for your flowers.
If you are adding more spheres on the ends - you'll have to include wood stakes for them as well. The design down the head table is going to be a long line of greenery with flower spheres buried at different heights and places down the table.