Zoysia choices for lawns

Zoysia grasses offer a new option in low-maintenance lawns for Australian home owners.

The best varieties are valued for their ability to form a lush, hard-wearing, high-quality turf when managed correctly. Their slow growth reduces the need for mowing and their nitrogen requirement is lower than that of green couch (Cynodon dactylon).

Zoysia grasses are reasonably drought-tolerant. In the tropics, even on a sand-based soil, they can remain green for four weeks without water. Zoysias established in a new mixed landscape adjust to shading as the adjacent trees and shrubs mature, coping well with deep shade in the tropics.

Growth rate

The slow growth of zoysia grasses, however, is a double-edged sword – it reduces the frequency of mowing, but it also means that zoysia grasses take more time to repair if damaged, and the longer commercial growth cycle makes the sod more expensive. In research trials by the Department of Agriculture, Fisheries and Forestry (DAFF), the best performing Zoysia japonica and Zoysia matrella varieties spread at less than half the rate of the top-performing green couches.

Zoysia leaves have high silica levels, a characteristic that makes them extremely wear-tolerant compared with other warm-season turf grasses. However, the growth rate of zoysias slows their recovery, making them best suited to intermittent use, rather than constant, heavy use.

Mowing

The hard-wearing leaves of zoysia will tend to blunt mower blades, which need to be kept sharp to prevent unsightly, straw-coloured, ragged edges on the cut leaves.

To avoid scalping, the grass should not be allowed to grow too long before mowing. Mow to remove no more than one-third of the sward height on each occasion. For best results, use a reel mower. Increase the mowing height by 10 mm under shaded conditions.

Soils and nutrition

Zoysias will establish on a wide range of soil types with acid to neutral pH, but do not tolerate anything more than very temporary water-logging, so good internal soil drainage is essential.

Zoysias are similar to blue couch (Digitaria didactyla) in tolerating much lower soil fertility than green couch, but will respond to nitrogen fertiliser by increased growth and deeper green colour. Slow-release fertilisers are effective in delivering the moderate level of nitrogen required by zoysias over an extended period.

Drought tolerance

This grass copes reasonably well with drought by in-rolling its leaves to conserve moisture and by developing a deep root system. However, the zoysia grasses are not as drought-tolerant as green couch or blue couch.

Lawn density

Zoysias form very dense lawns that resist invasion by weeds better than green couch. In time, thatch can build up and periodic (e.g. yearly in Darwin) de-thatching with a specialised vertical mower may be required with some varieties.

Seeded versus vegetative forms

The first zoysias to become available in tropical and subtropical areas of Australia were seeded varieties of Zoysia japonica, which are coarse-textured and prone to browning-off while forming numerous large, unsightly seed heads during winter. Due to their slow growth rate, seeded zoysia lawns in the subtropics can easily become overrun with weeds, including other grasses, before the lawn has fully grown in.

Away from tropical areas, it is much easier to establish zoysia from cut rolls of turf. A number of vegetative forms of zoysia have become available with fewer and smaller seed heads and improved colour retention in cooler weather. The most freely available form is Zoysia japonica, followed by Zoysia matrella. A third form, Zoysia tenuifolia, can also be used to form a fine-textured lawn grass, but is most commonly used for landscaping purposes as a low-growing, unmown groundcover.

Japanese lawn grass

Zoysia japonica (Japanese lawn grass) is native to tropical to warm temperate parts of South-East Asia, notably China, Japan and Korea. It is a medium- to coarse-textured grass that can be propagated vegetatively or by seed. It is one of the more cold-tolerant warm-season turf grasses and can be grown in the southern states of mainland Australia. Empire, ZT-11, Ozeboy and Empress are available as vegetative types, and Compadre and Zenith as improved seeded forms. The mowing height is 25 mm.

Zoysia japonica is prone to disease caused by Puccinia zoysiae. Zoysia rust develops under intermediate temperatures (about 15-20^°C is optimal for infection) and humid conditions where moisture remains on the leaves. Lawns should be monitored for rust in late winter to spring.

Manila grass

Zoysia matrella (Manila grass) comes from tropical and subtropical South-East Asia, and is only available as vegetative sod, not as seed. This fine-textured grass is tolerant of dappled tree shade (as low as 20-30% of full sunlight) and also shows good salt tolerance, which is useful in coastal areas. The mowing height is 15-20 mm. A selected form of Z. matrella is available under the registered name of ‘Shade Tuff’.

Zoysia rust has been found on Z. matrella in Queensland.

Dune couch

Zoysia macrantha (dune couch) is a fine-textured Australian native species of coastal origin. It tolerates salinity and temporary or short-term waterlogging. Itgrows in full sun or light shade, but is less shade tolerant than Z. matrella and Z. japonica. A fast growing cultivar ‘Nara’ has been released into the Australian and US markets. The recommended mowing height is 20-50 mm, but it can be cut up to 20 mm higher in shaded areas.

Acknowledgment

Thank you to Mr Peter Harrison of Above Capricorn Technologies, Darwin, for his valuable input during the preparation of this information.