Perennial ryegrass heading dates – 3 facts you need to know

There is some confused opinion as to what is the ‘right’ ryegrass heading date for pastures being sown this autumn. This is a relatively straightforward decision, although some of the things we are hearing seem to be making it very complex! So, to help you answer your queries, here are the 3 key facts we think you need to know about heading dates.


1.    Do you need early heading for early spring growth?

The short answer is no. It might have been the case 10 years ago, but the use of Spanish genetics in perennial ryegrasses such as Trojan has allowed us to deliver both early spring growth and a later heading date in the same cultivar.


To illustrate this we’ve graphed what is probably the best industry-agreed yield data for the upper North Island, the DairyNZ Forage Value Index. In this there is a rating for ‘Early Spring Performance’ for each cultivar from 1 (=poor) to 5 (= excellent).


FVI early spring yield vs heading date for Upper North Island*

* Early Spring DM yield from DairyNZ Forage Value Index (1-5 rating, where 5 = highest DM yield). Standard endophyte lines excluded because of their animal health issues. Source:



We think there are two main points in the data. First, there’s no real relationship between early spring DM yield and heading date for the Upper North Island. If you were asked to draw a line, it might be the green one we’ve sketched in (??) which could maybe support the argument that cultivars which flower +10 days later are slightly better yielders.


Second, and much more importantly, is the performance of individual cultivars. For example from within the late heading cultivars you can both get excellent early spring DM growth (e.g. Trojan and Alto AR37) and poor growth (e.g. Abermagic).



2.    Do you need varying heading dates so farms don’t all seed at once?

We’re not sure where this one came from, but heading date is typically quite variable across paddocks for the same cultivar, because it is greatly influenced by grazing.


Timing of grazing influences seeding, and good pasture management in October and early November will nip new seedheads off before they emerge, so this delays heading in some paddocks.


The real advantage in late heading cultivars has been the improved feed quality through this period, with pastures being better grazed. In other words, they produce more milk, with less need for mowing/topping.  


3.   What about aftermath heading?

Aftermath heading (AMH) is what happens when ryegrasses keep setting seed through summer, which is no good for feed quality or palatability. The important thing to note here is that as a general rule later heading cultivars not only seed later, but have better summer quality and less aftermath heading – particularly those which include the Spanish germplasm. That’s one of the other big reasons why farmers like later heading ryegrasses, and why they’ve been so successful.


Take home message

Several decisions are involved in matching the right ryegrass cultivar to a farm, including DM yield, seasonal growth pattern, persistence, endophyte, and a good dose of previous experience in what you have seen of it.  


All things being equal, you’d choose later heading ryegrass for their better late spring and summer feed quality, and easier management.




A strip of an early heading cultivar (left) between later cultivars at St Peters School dairy farm on 25 November – a key time for feed quality through mating.