Successfully Establishing Turfgrass is Best Done by Mowing Higher

Cut high to help turfgrass establish seems to be the rule.

The most resilient turf has deep roots that can reach the deep water in the soil profile. New turf must be watered regularly until the deep roots develop, but regular watering discourages the turf from rooting deeply, because the turf gets all the water it needs at the surface. All the while, you’re wasting water.

 

So what can you, as the turf manager or home grower, do to speed up the deep rooting and so minimise the irrigation?

 

Researchers at the Texas A&M University, North Carolina State University and the University of Florida asked this question. To answer it, they grew plugs of turf (couch, zoysia grass, bahia grass and buffalo grass) in tall clear tubes, and tested combinations of nitrogen (N) fertiliser and mowing height. Two rates of N approximated the lower and higher ends of the normal recommended range. Two cutting heights (which depended on species) represented heavy and light mowing.

 

Two conclusions were evident:

 

• The higher N rate encouraged faster rooting.
• The higher cutting height encouraged better rooting.

Cutting height had no effect on the rate of root growth, although it had a big effect on root mass: the low cut greatly reduced root mass.

 

Bahia grass achieved the best root growth (depth and mass) in the high N, high cut combination. But Zoysia grass did best in the low N, high cut combination. The results depended as much on the species as on the treatments.

 

Overall, maintaining a high cutting height did far more to encourage rooting than applying high N fertiliser. The authors recommended that turf managers cut establishing turf to the highest height recommended for the species.

 

This is especially relevant for zoysia grass, where we are already recommending half of the nitrogen rates that appear on most fertiliser bags.  Zoysia does not respond to high nitrogen particularly well, as it is naturally a slower growing grass.  We would suggest a cut height of around 45 -50mm initially, reducing to the more conventional cut height of around 20 - 25mm.

For Bahia grass, a high cut is 65 -75mm, and low cut 35mm, with commercial operators using 45mm.  For Bahia, one might need to also temper cut height and frequency with a need to remove seed heads, which direct fertilisers into reproduction, which is not needed during estabishment.

This also fits well with convention that says that a higher cut height during stress periods is beneficial - for this you could interpret stress as high temperatures and low water availability eg September - mid December in north Australia.

[partially sourced from SESL Newsletter September 2012]  

Further reading
Wherley BG et al. 2011. Nitrogen and cutting height influence root development during warm-season turfgrass sod establishment. Agronomy Journal 103: 1629–1634.

Bahia Grass - Best Turf for Water Efficiency

In the rush to use new turf species and new varieties sometimes this old stalwart is overlooked.

Bahia grass - Paspalum notatum is one of the very best grasses for water efficiency in the monsoonal tropics.  In areas with an extended dry period, it will stay green for the longest, and quickly rebound after extended dry weather - even as long as 7 or 8 months - to continue to thrive.

In the NT, it is best to avoid using the more readily available variety - Pensacola - as it is not as tough as others, tends to be more clumping, often appearing to have bare areas betwen plants and most importantly, it produces abundant seed heads year round so you are always needing to mow.

The older areas of Darwin often have a locally adapted ecotype, of unknown origin.  It produces seeds, but is usually sown by runners [ the other varieties can be too].  It was the predominant lawn in Darwin from the 1950s to about the 1980s, but less used today.  This line is ok as a turf species, and is very tough, and water efficient, but does tend to have a lot of spicules on the leaves - silica spurs that can irritate skin, especially where kids are rolling around on the lawn.  Argentine has less of these spicules, and so does Pensacola.  Its disadvantage is planting by runners, a time consumimg job.

The preferred seed sown line is Argentine.  We originally organised testing of this variety in the early 1970s in the Top End, importing seed from the USA, and first seeds were sown at Berrimah Farm.  It is still there, looking great. 

From the original evaluation, Argentine was selected and used in a lot of the early development around Palmerston in grassed waterways, and in park and landscape development after Cyclone Tracy in the reconstruction of Darwin.  Seed sowing is relatively low cost and a lawn can be developed in 10 -12 weeks.  No Australian production of seed has occurred and all Bahia grass seed is imported from the USA [ so is all couch, zoysia seed etc too].

The advantages of the Argentine variety of Bahia grass include:

• almost no seed head production, except a small amount around January in the north of Australia
• excellent spread and forming a dense surface cover
• very tough, reasonably resistant to wear
• low water needs
• excellent drought resistance and quick recovery when water is applied
• easily mown at around 30 - 45mm high, although it does grow moderately quickly in warm, wet weather - weekly mowing needed in the wet season for domestic lawns; maybe every three weeks in the dry season
• very little thatch development
• mostly free of pests and diseases

All of the Bahia grass types tend to become invaded by the awful weed grass "red seedy grass" or "Mackey's pest", which is botanically Chrysopogon acicularis.  This spreads by very insidious runners and produces huge numbers of seed heads.  There are herbicide solutions available for the control of this weed in Bahia grass, but products are not easily available for domestic use because of commercial packaging sizes - we can do this work if needed.  Efforts to eradicate it will pay big dividends.  Often seed is carried on legs, clothes, equipment and similar items so a biosecurity approach is needed to keep it out in the first place.

For a large lawn or open space area and especially where there is a need to be prudent with water use in the dry season.......Argentine Bahia grass is a good option.  It is also widely used as a water efficient turf in Florida [which is where the photo was taken].  Do not over water, as this induces ingress by other water loving species, including broad leaved carpet grass in our environment.