If your mother was interested in flower arranging, or you are a particularly attentive florist patron, or for some reason or another you have had to dismantle a flower arrangement, you may have encountered a green, spongy substrate into which all the cut flower stems had been thrust. Like Kleenex®, this product is often known by its brand name, Oasis®. Generally speaking, however, it is called “floral foam.” Floral foam performs the dual function of keeping a cut flower in the orientation that you desire and keeping the flower hydrated.
Vernon L. Smithers of Akron, Ohio, who made it as a phenol-aldehyde, invented it in his lab in 1954. The often repeated story is that he had a flower arrangement in his lab that he was about the bring home to his wife, and he opined (in the way of chemists), “Wouldn’t it be nice to create substance that would keep this arrangement watered and upright?”
Apparently floral foam can also be made with a saturated solution of urea and formalin, combined with sulfuric acid to produce a mixture that quickly hardens into a ‘cross-linked thermostatic plastic,’ which is to say, a foam that is stable at room temperature. These substances – whether derived from urea or phenol-aldehydes – are referred to technically as “open- or close-celled foams”
The open-celled foam absorbs and retains water. It can be bought either already wetted or still dry, depending on the type of arrangement it is intended to hold. If bought dry and then wetted, it is advised that you set the dry brick of foam in a large container of water and let it absorb it at its own (fairly rapid) rate. Let it slowly sink into the water rather than forcing it under. The latter method will leave air bubbles in the areas of the foam; a flower stem in contact with a waterless area will immediately dry out and ruin an arrangement.
Floral foam replaced an earlier method of maintaining an upright flower arrangement with all stems in a fixed position called the floral frog. The frog is a weighted object crowned by vertical spikes and/or a matrix of wire. They sit (squat) in a pool of water at the bottom of the flower vase, hence the name.
The older invention never went entirely out of style and because arguments based on sustainable use of resources are becoming more widely accepted, the frog may be poised to make a comeback. Some expert arrangements never gave up on the frogs because they felt that they worked better than foam blocks.
Wen Zientek-Sico argued that the foam actually impairs the ability of flowers to absorb water and nutrients, although she cites no reference for this. Her real reasons are admittedly personal: she likes to collect frogs because they come in so many interesting shapes and sizes. Zientek-Sico also points out that it is cheaper to use and re-use frogs than to continually buy foam, which, once full of holes from flower stems, does not work as well a second time.
The status quo, however, seems to be floral foam. In an online video at eHow.com, Amelia Tallman notes that floral foam makes it possible to put arrangements into all sorts of odd shaped containers. This is not a very good argument for using foam over frogs, because frogs permit the same (or nearly the same) versatility. Tallman seems to be speaking to an audience that has been simply sticking flowers in an upright vase over and over again.
Styrofoam® is also used for flower arrangements, although Connie Krochmal suggests that because it doesn’t hold water as well as the Oasis® phenolic foam, you are better off using it for autumn and winter arrangements of boxwoods and evergreens (“topiaries”), which can be kept green by just spraying them regularly.