Give the rhizoids (slender root-like filaments that are used for attachment and nourishment) of mosses the opportunity to attach to a rough surface, and they quickly will! If you want to, and or have the time, many aquatic mosses are quite capable of self-attaching. You simply ‘show’ the moss a growing surface, place them together in your aquarium, then the fronds will, sooner or later, attach themselves to the growing surface. If you don’t want to wait for this to happen, then there are other simple and effective ways to achieve the same effect.
One of the best ways is to spread the aquatic moss over the surface you wish to cover, and then use fishing line or black thread to attach it. These methods of attachment will be visible to begin with, but the aquatic moss will grow over them very quickly. Some experts in this field recommend using 100% cotton thread as it will, ultimately, dissolve and disappear. If you are using any method of attachment, please do consider the other life forms in your aquariums. Fish especially may get stuck or injure themselves on loosely tied threads, and may attempt to eat loose pieces once the knots have dissolved. Keep an eye on your aquarium and make any adjustments when they need to be made.
Pruning and Lighting
In general, aquatic mosses will grow in most lighting situations. The hardier mosses can actually thrive in lower ambient lights. Lighting is an especially important issue to consider when it comes to aquatic moss growth. If you have chosen different types of moss for your aquascape, then make sure you know and understand how each of these mosses grow. If one aquatic moss grows much more vigorously than the others, the new growth in the more vigorous moss can and will overshadow the slower growing mosses, thus preventing them from receiving light. This will mean that the slower growing mosses will die if you do not spot and rectify this occurrence very quickly. The simplest way to deal with this, if you want to use aquatic mosses that have different growing patterns, is to prune the faster growing aquatic moss before it becomes an issue, or move clumps of it to different parts of the aquarium. It is good practice to prune mosses regularly as this will help to prevent the mosses becoming stringy.