Moss lawn

Traditional Japanese garden aesthetics avoids contrasts, symmetries and groupings that would create points which dominate visual attention, instead creating scenes in which visual salience is evenly distributed across the field of view. Stand-out colours, textures, objects, and groups are avoided. The size of objects, groupings, and the spacings between them are arranged to be self-similar at multiple spatial scales; that is, they produce similar patterns when scaled up or down (zoomed in or out). This property is also seen in fractals and many natural scenes. This self-similarity may be extended all the way down to the scale of surface textures. The mottled texture and colour of moss (like that of rocks) can be used as part of such self-similar, evenly-distributed-salience designs.[10] Moss is considered to express a wabi-sabi aesthetic.[11]

Moss lawns can grow in anything from blazing sun to full shade, but different species are specialized to different light levels.[2] Year-round sun exposure is important; space under deciduous trees may be seasonally sunny, and require sun-tolerant species.[9]

Mosses do not grow roots into the soil, but most mosses need to attach rhizomes to the substrate in order to grow and remain in place; this is assisted by clearing and smoothing a lawn substrate and fairing a fillet between vertical and horizontal surfaces. Loose debris and sharp angles discourage moss growth.[8] While preparing for the moss, curves and mounds may be sculpted (this is easiest in clayey soil), and a hose may be used to erode the edges of shapes.[18] Established moss can resist flowing water[8] and secure steep slopes.[9] While some beach species specialize in growing on shifting sands, and may grow on sandy, salty roadside soil in cities,[8][21] most mosses are very slow to colonize loose-shifting surfaces.[22] Depressions in moss lawns may fill with debris.[8]

There are moss species that grow on almost any substrate, including rocks, wood, or soil.[2] The rhizoids do grow into any soil, in some cases about as deep as the moss is tall, in order to hold the moss in place.[3] Generally, mosses does not absorb nutrients from the soil, so soil amendments do not benefit moss.[2] Many mosses are ombrotrophic, fed by rain.

Melting snow provides moisture and cool temperatures, which encourage moss growth.

There are moss species that are suited to the full range of soil pHs,[2][8][14] but some gardeners adjust the pH to discourage other plants which might compete with the moss.[23] Many other plants do badly in acidic soil;[9] moss thrives in acidic soil conditions.[1] This also reduces the risk of limescale deposits on the moss, which can wick water up from waterlogged soil; regularly rinsing with rainwater from above will wash off deposits. Mosses absorb water through their leaves, and are watered more like air plants than common vascular garden plants. Watering with hard tapwater may also cause lime deposits; soft tapwater may contain dissolved metals, which can kill moss.[14] Japanese moss gardens largely rely on natural precipitation,[24][11] with the garden creating conditions where the moss will spontaneously grow.[25] Shelter from wind will reduce evaporation, which helps keep mosses from drying out.[26]

To photosynthesize, moss needs sunlight (not necessarily direct), moisture, and temperatures above about -5 degrees Celsius (20 Fahrenheit) simultaneously. Unlike most other plants, it cannot store energy for use later (except for in a storage protein used to repair cell walls).[27] This means that watering moss will not increase growth unless it will stay wet, unfrozen, and at least slightly lit for some hours afterwards.[16][14] Moss has little ability to retain water; it is poikilohydrous. If dried-out or frozen, it becomes dormant.[27] Becoming dormant takes energy, so rapid wet-dry cycles can cause a net energy loss.[16] Light, frequent watering can allow moss to grow quickly, while leaving the lawn too dry for other plants, which need water to soak in to the soil.[2] Once established, moss does not required watering, and is more drought-tolerant than most plants.[2][16] Moss can survive frozen for centuries, and revive when thawed.[28] Moss has internal antifreeze,[17] which allows it to grow at temperatures a few degrees below freezing.[27]

Sekirakuen Garden in Hakone, Japan

Young mosses take a protonemal form, which is more like an algal film than a moss; small moss fragments may revert to this state. Moss in a protonemal state is much more likely to die if dried out. When it converts to the gametophyte form, after a few weeks, it becomes much more drought-resistant.[29]

A sprinkler or misting system, automated on a timer, is often used to get mosses established. Spray times of 2–5 minutes, thrice daily, are typical,[9] but this may vary with the moss species.

Mosses can grow next to water features, but the unvarying level of artificial watercourses may not allow the moss to dry out, which can cause problems with mould.[30][16]

When transplanting moss on to soil, the soil surface is slightly loosened first. After the moss is in place, it is thoroughly watered and walked on or otherwise tamped down. This helps attach the transplanted moss to the soil.[8][9]

Transplanted moss may be secured to a new substrate with small twigs[9] or metal pegs. Pond netting or tulle, held with landscape staples or tent pegs, or sometimes suspended on stakes, may be used to discourage wildlife from digging up moss.[36]

Hillside pleurocarp lawn at Kenroku-en

Prostrate, creeping, branching; smooth sheetlike; fast to regenerate from fragments and faster-growing,[37] with maximum growth rates allowing them to double in size every six months. They are earlier-succession than acrocarps.[37] They can live constantly moist[27] or even submerged,[38] and may be watered as often as six times a day; however, if they become soggy they will grow fungi, including mould and mildew.[16] This is particularly common at temperatures above 24 Celsius / 75 Fahrenheit.[30]

• Hypnum sp.; deep to moderate shade, will resist some foot traffic.[13]
  • Hypnum cupressiforme[37]
  • Hypnum imponens (flat fern moss)[37][33]
• Entodon seductrix;[37] semi-sun [39]
• Climacium americanum (tree moss[9]); semi-sun, damp[39][17] Resists erosion, waterlogging; used for stormwater control.[9]
• Thuidium delicatulum (Common Fern Moss, Delicate Thuidium Moss);[37] sun to medium shade, moisture, shelter from wind. Will grow on logs and rough rocks.[40] Resists erosion.[9] Turns golden in the autumn.[17]
• Plagiomnium cuspidatum[37] (Toothed Plagiomnium Moss, Woodsy Thyme-moss)
• Bryandersonia illecebra[37]

Acrocarps are thick, upright, mounded/clumping in habit, and slower-growing.[37] Acrocarps need to dry out regularly.[27] If constantly moist for more than 2–3 months, they will rot,[16] and they will not grow completely submerged.[38] They are generally more drought-tolerant than pleurocarps.[2]

• Polytrichum commune (haircap moss, awned haircap moss, blue moss, blue hairy cap[9]); sandy, acidic soil; deep shade if dry, sunnier if wetter, will resist some foot traffic.[13][37] Can be mown lightly. Resists erosion, as it has unusually deep rhizoids.[9]
• Rock cap moss (Dicranum sp.); rocks or soil, deep shade only[13][37]
  • Dicranum scoparium (Broom Fork Moss,[33] mood moss, windswept moss, broom moss, footstool moss, cushion moss[9])
• Leucobryum species
  • Leucobryum glaucum (Cushion moss , pincushion moss, white moss[9]); silvery clumping moss that favours sandy soil, shade to light sun[13][37][39] Generalist species with a wide distribution.[9]
  • Leucobryum albidum[9]
• Campylopus introflexus[41] (an alien invasive in the northern hemisphere[42])
• Aloina aloides; likes sun, survives sand and salt; grows on sand dunes and at the margins of city roads.[39][21]
• Atrichum species
  • Atrichum undulatum (big star moss, crane moss, crown moss, starburst moss); adapted to shady, moist, areas; resists foot traffic well. Grows to an even height.[9]
  • Atrichum angustatum; similar to A. undulatum, but broader range of soil moistures.[9]
• Bryum
  • Bryum argentium[39]
  • Bryum caespiticium (tufted thread moss); indirect sun or shade. Dries to brown.[43]
• Ceratodon purpureus (fire moss, red roof moss); will grow in full sun and pollution. Robust and brightly-coloured.[39][43][44]