With the newer couch grass varieties like Tahoma 31, what is the best grass seed for oversowing couch grass? We ran a trial in 2023 with both annual ryegrass and a turf type perennial ryegrass to see what is the best grass seed for reseeding.
Why oversow?
On sports turf and home lawns, you use annual and perennial ryegrass grass seed for oversowing or overseeding.
The improved turf-type perennial ryegrasses like Intense ryegrass, have greater cold tolerance, wear tolerance, disease resistance and persistence than the older types like Caravelle.
Annual and perennial rye are cool-season grasses, and you can use these as a permanent grass cover or a temporary grass seed for reseeding in winter, when warm-season turfgrass is dormant.
In Australia, oversowing warm season turfgrass, like couchgrass, occurs from Brisbane, south to Canberra.
Every year, temporary oversowing improves the colour during warm season winter dormancy, improves surface traction and ensures recovery from wear.
Read more about their generic differences below.
Annual vs Perennial Ryegrass Grass Seed for Oversowing?
Annual and perennial ryegrass are sub-species of ryegrass and annual rye is a bunchgrass and is also known as Italian ryegrass. It is native to southern Europe (Mediterranean).
- Annual ryegrass usually has a more limey green colour than the perennial.
- Perennial rye tends to have a much finer leaf texture.
- Annual rye has less uniform growth than perennial rye.
- If you allow annual ryegrass to grow too high, it tends to grow in a bunch-like pattern. So don’t allow it to grow higher than 50mm.
- You can mow turf type perennial rye at 15-20mm.
- Annual rye is only moderately wear-tolerant.
Why use Annual Ryegrass
Both annual and perennial rye provide a rapid green cover and germinate in 5-7 days.
As both types compete with weeds, they can help decrease weed pressure on dormant warm season turf.
Annual ryegrass seed is less expensive than perennial due to it lasting one season. Annual ryegrass germinates quickly and provides a green colour, then dies out as warm-season grasses exit dormancy and summer heat returns.
This lower cost, means annual ryegrass is used as a “filler” in lawn seed packs.
The Disadvantages of Annual Ryegrass
Because annual ryegrass only lasts for one season, it is not the best choice to use if you want to keep a permanent ryegrass cover and without mowing and proper maintenance, annual ryegrass flowers prolifically.
Annual ryegrass has poor heat and drought tolerance, so if you cut off the water with annual ryegrass, it won’t recover. Also, be aware annual ryegrass is more susceptible to disease than perennial ryegrass. So prepare to spend up on fungicides!
The Best Ryegrass Seed for overseeding
Our blog on improvements in perennial ryegrass shows how the US germplasm outperforms NZ genetics in NZ turf trials. This is despite the marketing suggesting it is the complete opposite.
However, annual rye doesn’t often get a look in, and it is not viewed in a favourable light as an overseeding grass.
However, advances in breeding have meant that some of the newer annual varieties are worth looking at. One of these is Breakout II from Mountain View Seeds.
A historical issue with annual ryegrass, has been it seems to die in drought, and when the water comes back on regenerates. The result is a messy transition, which needs chemical treatment, wasting valuable time and money.
When you use Breakout II grass seed for oversowing it claims to overcome this, so we put the transition claims to the test.
However, concerns exist with which is the most suitable choice for the best lawn seed for oversowing couch. These concerns are due to the negative impact of certain grasses on the growth of the overseeded grass.
This is the result of allelopathy. Allelopathy occurs when high endophyte turf-type perennial ryegrass produces one or more biochemicals that influence the growth of the couch grass. But are these concerns still valid with the newer couch grass cultivars?
Trial outline
A replicated block trial looked at three treatments on Tahoma 31 plus an untreated control. Two treatments were seeded, and one was a pigment application. The control (C) was untreated. The trial was maintained at 37 mm for the duration of the trial.
Oversowing was with Breakout II annual ryegrass (ZE) and Grand Slam GLD (HE) turf-type perennial ryegrass. Both seeded at 300 Kg/Ha.
Our choice of pigment was Vertmax Duo turf pigment (P) at a rate of 1L/Ha.
Results of The Trial into Grass Seed for Oversowing.
1. The null hypothesis is that none of these products affect turf Coverage (Green cover), Dark Green Colour Index (DGCI) or Colour Quality.
2. The Vertmax Duo turf pigment gives an instant colour response for the duration of the trial. The pigment response is highly significant, in comparison to all other treatments, with it still evident 195 days after the trial starts.
Close mowing shortens turf pigment longevity. Under a low frequency mowing regime such as council grounds, turf pigments will last longer. This is in contrast to a golf course fairway or golf green. Our 2023 work on turf pigments on golf greens shows that the best you can hope for is 17 days.
3. The Breakout II gives a significantly lower turf colour quality than the control. Turf type annual ryegrass, is bred to establish quickly, and stress out when temperatures increase.
4. All the treatments reduce couch cover in comparison to the pre-treatment. However, none of these reductions are significantly different from each other. Future work should look at how the couch performs when under a wear regime when you use ryegrass grass seed for oversowing.
5. The Breakout II grass seed for reseeding, gives an excellent non-chemical transition and is worth serious consideration for low cost oversowing without the need for chemical transition.
Graduated from Newcastle University with an Hons Degree in Soil Science in 1988, Jerry then worked for the Sports Turf Research Institute (STRI) as a turf agronomist before emigrating to Australia in 1993.
He followed this by gaining a Grad Dip in Business Management from UTS. He has worked in a number of management roles for companies as diverse as Samsung Australia, Arthur Yates and Paton Fertilizers.
He has always had a strong affinity with the Australian sports turf industry and as a result he established Gilba Solutions as an independent sports turf consultancy in 1993. Jerry has written over 100 articles and two books on a wide range of topics such as Turf Pesticides and Nutrition which have been published in Australia and overseas.