Groundcovers

In Tsubo-en we have intentionally not planted any mosses as groundcover. This was a design requirement originating from prior experience. Most mosses that we do have, did grow there by natural causes.
Not to elect for mosses as groundcover has two important reasons:

The environmental and location conditions are not well suited for large area´s of moss.
There are to many (black)birds that see it as a challenge to turn over and rip apart each and every square centimeter or inch of moss. This we know from experience in previous gardens and reconfirmed in this one.

For elaboration on this choice see: Mosses and lichen.

Tsukuyama groundcovers in principle are moss replacements. When planted together in large numbers to form a carpet that covers the soil, many plants can serve as groundcover.

Preferably a "moss replacement" shows great resemblance to or is a look a like of, moss used in Japanese gardens. Having said this one should be aware that a great variety of mosses can be found in even a single garden in Japan.
As an example, in the Saihõ-ji temple (or Koke-dera, or Moss Garden) the area around the pond is said to be covered with more than 120 varieties of moss.
One of the most favorable perennial groundcovers for Tsubo-en is one that, when growing on a tsukiyama area, looks like a Cryptomeria woodland or mountain side as seen from great height or great distance. This is the omnipresent Polytrichum commune, sugigoke (Common Haircap Moss, Common Hair Moss, or Great Goldilocks). The individual stems each appear like a Cryptomeria tree. The name part sugi is taken from Cryptomeria Japonica and koke from moss (ko changes to go). Unfortunately this moss requires high humidity and rainfall and still has birds as its listed enemies (item 2 above). In [12] it is stated that Soleirolia soleirolii (mind-your-own-business) could be a substitute. We do not have any experience with that as this book dates from 2007.

Requirements for suitable perennial groundcovers

A groundcover plant is one that, planted en masse, effectively covers the soil to form an attractive tapestry of color and/or texture. No one particular group of plants is better than another at covering the ground, but particular individual plants within a group perennials make better groundcovers because of their specific characteristics.

Apart of the esthetics and foliage described above the desired characteristics of a perennial groundcovers for the tsukiyama's are:

Grows compact in sunny and more shady spots.
Will grow in low-lying areas with less drainage and more soggy soil but should also survive on higher area's and during drought in periods when rainfall is scarce.
Should not be too demanding with regard to the soil.
Must grow well on flat area's and slopes.
Spreads quickly by runners or widening clumps to forms a mat of plants.
Spreads with discipline (e.g. not multiply by seed).
Is easily removed if it grows beyond its boundaries.
Discourages weeds.
Does not need constant watering, feeding or grooming and raking.
Looks good (see esthetics above) all seasons and for many years (perennials) with little care.
Either not flowering or inconspicuous flowering. Flowering ot not the odour (smell) must be acceptable.

	In the whole Tsubo-en garden **Leptinella potentillina or squalida** (prev. Cotula common name: "Water buttons" or "Buttonweeds", Green Brass Buttons, (Dutch: Goudknopje ook wel Vedermos), is the primary "moss substitute" groundcover. This plant is more or less evergreen and a moderate Sun-lover. It has feathery evergreen leaves that form a nearly flat carpet, perfect for the Tsukiyama as a moss substitute and in flagstone pathways. Tiny yellow flowers appear in spring. This could even be a good lawn substitute in average to moist areas. It has a nice bronze winter colour. It is easily divided year round, by ripping into small pieces or cutting small plugs for transplanting.
	This photo is more or less real size. The size and hight are very much habitat dependent. During flowering, the odour is very strong and may not be loved by everyone. We find it a smell to get used to that then gives a feel of recognition. Also see: Keeping the groundcovers out of the gravel and Unwanted mosses and lichen in ground covers.
On the higher tsukiyama grounds in full Sun area´s it grows smaller and gets less bright green. This as such is no problem. What can become a problem is that unwanted mosses overgrow the Leptinella.
	A smaller of the above, also evergreen version, is Leptinella minor (prev. Cotula) (Alpine Brass Buttons, Dutch: Speldekussen) very much like Leptinella gruveri (Miniature Brass Buttons) ), is also used on some places. Depending on the habitat, even when looking from close range this could easily be mistaken with a moss. It can very well be used in between flagstones as a moss replacement. This species has tiny, feathery evergreen foliage of deep green, sometimes a little bronze in summer. Flowers are green and insignificant. Easy to grow in any soil that does not completely dry out. Easily divided by digging up the clump and ripping into smaller pieces, year round. This very tiny species is ideal as a (moss replacing) groundcover, or as a moss-like carpet in a bonsai container.
In a corner of the front garden and in an area behind the O-karikomi we have Acaena magellanica (New Zealand Burrs, Dutch: Stekelnootje). This is a low maintenance evergreen plant that performs well. This species forms a mat of lacy grey-green foliage, bearing interesting greenish flowers that mature into copper-red burrs during the summer months. They can grow beyond where you want them, so be sure to inhibit its growth and be strict. Only a few times per year. It is easily divided in not too small pieces early fall or spring.

Photo above and top of above-left:
On part of the Hõrai-jima (Turtle island) in the front garden, Armeria Maritima (Dutch: Engels gras) grows around the "mountain-lake" or lower-pond. In essence this is a low maintenance plant.

Once a year we need to remove the dried flowers that contain lots of fertile seeds, before they populate the Ginshanada.

See: Armeria Maritima clipping.

	Photo above: The flowering Thymus Praecox pseudo langinosus. There is great selection of evergreen Thyme that can be used as ground cover. All of them with some degree of spicy fragrance. This flat-growing Thyme has green leaves, smothered by mauve-pink flowers in early summer. A strong grower that tolerates moderate traffic. Creeping Thyme is easily divided in spring or early fall, and even small pieces will take root and grow. Attractive to butterflies and bumblebees. Thymus Praecox pseudo langinosus can also be seen on the right side of the left photo and on the picture below.
We have two species of Thyme. One is Thymus Praecox pseudo langinosus. This grows on part of the Hõrai-jima (Turtle island) where we not have Armeria Maritima (see above). Again this is a great low maintenance flowering groundcover.
	Opiopogon Japonicus "minor", "Nana" (Dutch: Slangebaard). Although "native" to the Japanese garden it is not what we most like. We have planted it more like a try-out. It grows very slow. After many many years it has grown to a very tight carped and we just let it go.
Chamaemelum nobile "treneaguei" (Dutch: Loopkamille) or Anthemis nobilis, commonly known as Roman Camomile, Chamomile, garden camomile, ground apple, low chamomile, English chamomile, or whig plant. This is the third groundcover we have tried in this area of the main garden. Prior ones where Leptinella squalida and Leptinella minor (see "What did not work"). So far so good. It is also suited for hot, dry sunny sites in mild winter regions. This special non-flowering selection forms a low evergreen mat of ferny leaves with a pleasant fragrant. In summer it spreads a pleasant smell that gets stronger when touched. Plants can be mowed or clipped if desired. Easily divided year round by digging up and ripping apart into smaller pieces. Note that our child Buddha, or better Jizo bodhisattva also "sits" in Camomile.
	We have two species of Thyme. This one is Thymus praecox "minor" (T. serpyllum "Minor"), it grows under the Pinus densiflora and we let it grow on the tsukiyama in the Main garden wherever it pops up. The green is darker than that of the pseudo langinosus and the growth is somewhat denser. This one is known to be the flattest, tightest and lowest form of creeping thyme. This flat-growing variety features fragrant dark-green leaves, smothered by light pink flowers starting in early spring but also during mid-summer. A slow growing specimen but still excellent as a drought-tolerant groundcover and moss substitute and for planting between flagstones.
This fast-growing creeping, and relatively low crowing shrub is an excellent groundcover for establishing on slopes and dangling over walls. Small fragrant white flowers appear in late spring, followed by bright red berries in autumn. These remain well into winter. The shrub is evergreen and very durable. It is drought tolerant once established. Cotoneaster "dammeri" grows on the surface that connects the wall to the water at the water front. One of the functions of this plant is to keep the ground together. Pinching growth tips in spring for the first couple of years will help to get a dense habit. Prune out any dead branches when noticed. In cold winter regions the leaves sometimes drop in late winter but are replaced by new ones.

Ground covers examples

We do not have authentic subject examples dedicated to and specific of this subject.
Nonetheless examples are available in a number of other "examples" sections. Most relevant:

For the complete "visual" examples see the applicable framed-list in: Visual Table of Contents.

Lessons learned and what did not work well

Here we document what went wrong with regard to the groundcovers that we used or wanted to use.

In the beginning we also used Leptinella squalida that was however replace because it grow too high for the purpose and was loved too much by snails.
In a less visible area we have had Pachysandra terminalis. After 8 years this has been removed because it proved too invasive and even got to the neighbours.
The Cotoneaster "Coral beauty", although not a groundcover as such, is used at the water frond. This is done to cover an area that is not really visible from the veranda and pathways. Although during the first years this was "low maintenance" it turned out to require a high maintenance effort. For this reason we have "thinned" it so that there is less growth and that it it can be more easily reached for clipping and pruning.
Leptinella minor is a great moss replacement. The problem we had is very specific. The minor species is very small and low. We got a small but very invasive weed, spreading through "exploding" beans, that we where/are unable to eliminate. The weed also grows abundantly in gravel. To finally get rid of it we have been moving to higher groundcovers.
In the beginning we also had Sagina subulata (Dutch: Vetmuur, Eng: Corsican pearlwort) in the garden. Unfortunately where given the wrong species. Wrong in that it spreads from (invisible) seeds. After we quickly removed it, it is still one of the most invasive "weeds" in Tsubo-en, often overgrowing the (wanted) mosses.
We forgot to use weed control fabric under the Cotoneaster "dammeri" on the water front. Now we have a lot of work to keep the weeds under control.
In the Left garden compartment we had Cotoneaster "dammeri" along one site of the path. After 7 years we have removed it and replaced by Leptinella potentillina. This was done so to achieve less maintenance and to get a more spacious impression.
After about four year we started getting (unwanted) moss (cypress-leaved plait-moss or hypnum moss) in the Cotula groundcover, mostly on the higher tsukiyama grounds in full Sun area´s, where the Leptinella remains lower.
Initially we did not regard this as a problem. However we should have started getting rid if it right from the beginning. After some six year it got to well established and now it takes a lot of effort to keep it under control.

Links related to groundcovers

Chapter: Bottom surface maintenance and
Training, clipping and pruning.
A brief overview of planting in hot and dry climates can be found at Plants for Japanese gardens.

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