I was fortunate enough last week to be invited out to Helsinki in Finland to talk to a group of course managers. It was brilliant to go and visit a different area with some different challenges. They've been having a very different year to normal with very mild temperatures and more rainfall (sound familiar?).
Helsinki is about 650 miles North of my home in the South of England and about 1100 miles East.
Temperature and light are significantly different in this region to what I'm used to - very long summer days, very short winter days. Snow is a common occurrence in fact the generally talk over coffee was "can you remember when we last had a snow free winter?".
The two below light maps show light mapped out using 2019 data (I've used the 7 day accumulated light figure that I wrote about in this blog) First thing I notice is how obviously the shorter days in Finland lead to lower levels of light and equally longer days in the summer equal more consistent light.
I've used Mike Richardsons article in GCM on DLI and minimum light levels to add in some light level figures. The Orange line shows Mikes suggested figure for minimum amount needed to grow Ryegrass and Bentgrass.
The Ryegrass figure is shown in Orange and when we did some shade trial work at STRI last year we came up with a very similar figure. The Bentgrass figure is shown in yellow.
In the South of the UK we hover around the light levels suitable for growth all winter but are generally below the required figure from Early November to Early February.
In South Finland the Ryegrass figure is like turning of a light switch in Early October and the light doesn't lift again until mid February. So at least 5 weeks less suitable light than in the South of England.
For Bentgrass it's a slightly different story - Finland and the UK reach the required figure at a very similar time at the end of March and both drop of the same kind of time in Mid September.
The main difference is that in the UK we hover around the required amount of light all summer long and it's very feasible at any time to be short of light in the summer months - However Finland - has much stronger summer light which is far more suitable to manage Bentgrass in.
Of course this is only part of the picture the temperature obviously has a huge influence on plant growth. I've looked into that here.......
So to summarize Finland very clear cut - not enough light / enough light. Uk - We hover around the awkward levels both in the winter when we don't want growth and hover around the minimum required light all summer long (for bentgrass)
As far as I can tell this kind of light level work hasn't been done on Poa and I would guess that there are so many biotypes that it would be very difficult to do. It would be really interesting to do.
Take a look at my blog on the temperature in Finland and how to manage turf disease and turf care in Winter.