Mood moss is a name off the shop shelf rather than a name from botany. It is the mounded, clump-forming moss sold in trays and sheets for terrariums, floristry and moss art, and behind the label sits one of our handsomest woodland mosses, usually broom fork-moss (Dicranum scoparium) or one of its close cousins. Working out what you have actually bought makes all the difference to keeping it green, because mood moss behaves nothing like the flat carpet mosses it is so often sold beside.
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What is really in the bag
Tip a tray of mood moss onto the bench and you get low, rounded mounds a few centimetres deep, every shoot standing upright and pressed tight against its neighbours, the whole cushion often swept gently to one side as though a comb had been drawn across it. That combed, all-one-way look is the signature of Dicranum, whose haunts and finer points have a page to themselves in broom fork-moss. It is an acrocarp, an upright, clump-building moss, and that matters more than it sounds. Acrocarps grow from their tips into slow domes and do not creep, so mood moss will sit and thicken exactly where you place it, but it will never knit sideways into a carpet the way a trailing moss does.
Sorting the shop names
The moss trade is loose with its labels, and three names get muddled all the time. Mood moss is the mounded Dicranum just described. Cushion moss usually means the pale, whitish domes of Leucobryum, greyer, firmer and far chalkier, which can fool the eye across a room but never up close. Sheet moss is different again, a flat pleurocarp such as Hypnum that lies in thin carpets and is what you want when moss must actually cover ground; the gulf between a mounding moss and a creeping one is set out in sheet moss and cushion moss. Frog moss and pillow moss crop up as well, both vague and generally pointing back at one of those three. When a listing simply says green moss, assume nothing and go by the shape.
Why it turned up in every terrarium
Mood moss became the darling of the terrarium shelf for sound reasons. The mounds bring instant depth and relief to a planting, a miniature run of green hills where a flat moss would read as a mat, and they keep that sculpted shape for months on end. Florists and moss-art makers reach for it on the same grounds, and it takes to a glass container more readily than most wild mosses because it comes from shaded, humid woodland floors and asks for that and little else. Against the real difficulty of keeping many mosses alive indoors, Dicranum counts among the more forgiving, which is a good part of why it sells so well.
Keeping it green indoors
Forgiving is not the same as carefree. The commonest way people lose mood moss is to stand it in a bright window and mist it now and then; it browns from the base upward, and a passing spray barely wets the crown of a cushion that has already dried. What it wants is steady humidity rather than the odd squirt, so a closed or part-covered terrarium suits it far better than an open bowl in a centrally heated room. Give it bright but indirect light and keep it out of direct sun through glass, which scorches it fast. Water the substrate and the cushion evenly with rainwater or soft water, since the salts in hard tap water gather and yellow it over time. Should a piece dry out and pale, soak the whole cushion rather than spraying it, and give it time; the general knack of bringing dried moss back is in reviving dried moss, and the container mosses worth trying are weighed up in best moss for terrariums.
Buying it, and a word on gathering
Nearly all mood moss on sale has been gathered from the wild, and in places that harvest has stripped woodland faster than it can grow back. If you buy, a supplier who can tell you where their moss was collected is worth paying a little more for. If you would rather gather your own, take only small amounts from ground you have permission to work, never from a nature reserve, and leave the bulk of any cushion in place to regrow. One healthy clump, kept humid and divided gently as it spreads, will hand you more mood moss in a year than a raid on a wood ever should.