To “flock” a Christmas tree means to put imitation snow on it. Many people like the “white Christmas” look this creates. Flocking is more common on artificial Christmas trees, but it can be used on both real and artificial trees. Flocking can also be applied to wreaths and other Christmas decorations.
Some trees come with the flocking already on when you purchase them. Some retailers have the capacity to apply flocking to a tree on request for you, usually using a special applicator device attached to a hose which runs from a reservoir of flocking. You can also purchase flocking from craft stores and specialty Christmas stores to apply yourself.
There are a variety of styles of flocking, which have similar but not identical ingredients. Flocking can have a thinner or thicker texture, and it can be a realistic white in color or tinted. Most flocking starts with a base of cellulose, water, and wax or a spray adhesive. It is fairly common for it also to have a fire-retardant ingredient.
Coating your tree with something fire-retardant is a nice way to reduce the risk of fire, but it’s not a substitute for the usual precautions you should take with a Christmas tree, including keeping it well watered so it won’t get too dry, and keeping it away from the fireplace or other heat source.
One drawback to getting flocking with a fire-retardant is that the other ingredients typically are biodegradable, making flocking a green product, but the inclusion of the chemical fire-retardant adds a non-green element to the mix.
Commercial Christmas tree flocking has been around since the 1940s. It was always also possible to make a form of fake snow oneself with ingredients such as soap flakes, starch, and water.
It is advisable not to use flocking the whole time your tree is up if you intend to leave it up a long time, because flocking has a tendency to yellow as it ages. You should be fine for two to three weeks, but if you put up your tree right after Thanksgiving and flock it immediately, you may well have some discoloration by Christmas.
Beyond that, how and how much to use flocking (and indeed whether to use it at all) are aesthetic decisions that are up to you. Flocking is simply a decoration for you to use however you think looks best, or to forego entirely.
“What is Christmas Tree Flocking?” Ask Deb
“What is Christmas Tree Flocking?” Wise Geek