There are times when a florist is asked to create centerpieces in "non standard" containers. This just means something that really isn't meant to be a flower container and doesn't always fall within a specific size.
The first thought is always to protect the container. If it is not waterproof, you will need to add a rectangle pot liner to prevent water damage (especially to wood or baskets).
A customer approached me with the need to buy floral foam so that small wooden boxes could be used as the container. I knew she would need a liner, so I needed the exact (inside) dimensions of the wooden box.
The decision had to be made whether or not she would need bricks of foam or the larger (Grande) brick which is equal to two standard size bricks.
I taped together a prototype of the wooden box, since I didn't have the actual container. This is actually a wooden shoeshine box to be turned into a centerpiece for a large benefit that my customer is involved in.
The next challenge was to find a liner that would fit inside the box and protect it from the moisture. I do have a liner that the measurements are pretty close.
Liner sides usually slant outward so they fit down inside baskets. The Grande brick will have to be cut in order to fit inside the liner, plus extend above the top edge of the container.
At first I considered using standard Oasis bricks - but decided that would be too much cutting and waste.
The Grande brick is just about the right height, although some cutting will have to be done.
Using my template and a long sharp knife, I will cut the block into the correct size. You may have to allow for angled cuts if your own liner is angled.
Cut cleanly down. A smooth edged knife will make a cleaner cut than a serrated knife.
Don't discard the smaller piece, you may be using those pieces fitted together for some of the containers. Used dry, it can also be used to wedge the liner more tightly into the container.
I'm now cutting off the other side because the brick is still too large.
The cut brick now matches the template. It is always a good thing to fill the container with as much foam as you can. Remember - this is what holds the water that keeps the fresh flowers alive. You'll be amazed how much water flowers can drink in one day.
You see the the cut Grande brick now fits into the liner that fits into the wooden box.
The height is a little more than I would like to have, so I'm going to cut it down some. You can skip this step if you've like . . . but I usually like to have about two inches above the lip of the container.
You should not cut in down level to the container edge. If you do that, you won't be able to insert flowers from the side. This would result in the greenery and flowers sticking in an upward angle and not look good from the sides.
After scoring the block lightly, I place it on my cutting surface to make the actual cut.
Cut down cleanly and set the trimmed piece aside with the others.
The pieces that you trimmed away can be used as wedges to tighten the fit after the soaked brick is in the liner in the container. Don't soak these pieces in water, since they will be between the liner and the box to keep it from sliding around.
These leftover pieces can slide between the liner and the box to keep the liner in place in the container.
Use waterproof floral tape to tape the Oasis foam to the box. Where the rectangles are show places you can wedge dry pieces of the leftover foam to keep the liner from sliding around.
Flower food is important. Florists always take extra care that their arrangements have both the water and the nutrients that fresh flowers need to extend their life as long as possible. Use the right amounts dictated by the label. Too little won't do much good. Too much won't hurt the flowers - but it will waste product.