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  • Writer's pictureMark Hunt

March 29th, 2022 - A bit of a change on the way !!!!

All output from

Hi All,

Well, last week we had two conflicting weather projections for this week. The GFS output suggested an unsettled cold breakdown whilst the ECMWF output suggested high pressure would continue to prevail.

Looking at this week's weather, it is ultimately (and unfortunately), the GFS projection that is to going to prove the most accurate with a really chilly and wet mid-week / end of week spell I am afraid. In the GIF above you can clearly see the cold air pushing in from the east / north east. Taken into consideration the high teen temperatures at the start of this week, it will feel doubly cold as that colder air pushes in.

Difficult to believe that we will have such a transition, but transition we will. I passed a couple yesterday in Market Harborough and overheard them talking about the weather "Summers arrived early" said the man, "It'll be snowing by Thursday" said she..."Get away" was his retort or something similar :)

We can't complain though as March has been very nice and one of the sunniest on record I think with plenty of nice PAR light to get bentgrass moving. It is quite normal in my experience for us to experience a big change in the weather coming into April and this year will be no exception.

Talking about light, photoperiods and flowering plants, our minds will soon turn to seedheads and Poa annua if they haven't already.

I noted last week that the roadside verges are now lined with flowering Danish Sea Scurvy (Cochlearia danica). This is a really interesting plant, as it is a halophyte, that is to say, salt-tolerant and that is why you see it growing close to the edge of the road in the salt splash region because very little else does. These Danes are a hardy bunch you know !

Why the interest in this flowering plant ?

Well apart from the fact that it's a pretty successful Danish invader and therefore appeals to my Scandinavian heritage, I think the timing of this plants flowering by the roadside coincides very nicely with the commencement of the Poa annua - annual biotype seedhead flush, more on that later.

General Weather Situation

So Tuesday sees those light easterly winds pick up a tad in strength and that cold air begin to edge across The North Sea but Tuesday will be a transition day rather than a drop off a cliff day temperature-wise. It will be cooler though because those easterly winds will push in cloud cover and that'll drop the temperatures a tad. So Tuesday morning will see rain in The South West and along the south coast hang around most of the day and this will push up into the South Midlands during the morning. They'll also be showers pushing into the north east of Scotland and the Mersey Estuary. Later in the day that rain over Scotland will push southwards across The Borders into the far north of England. So not the end of the world but temperatures will edge down towards 12-14°C, with the brighter weather across the west. During the day the wind will edge towards the north east.

Wednesday sees that cold, unsettled air edge into the north east of the U.K and it'll introduce wintry showers and a pronounced temperature drop into Scotland. This ridge of rain and wintry showers over elevation will edge southwards into northern England. Further south and west it'll be a bright and chilly start with plenty of sunshine and as we go through the day it'll edge down into The Midlands reaching there by dusk and at the same time it'll push into the east of Ireland. A cooler, dull day for the north and Scotland with a sharp easterly wind and a pronounced wind chill. Difficult to believe sitting here typing this with a warm wind blowing through the open window. Further south the wind will be all over the place and temperature-wise, we will be down at 8-10°C. The same for Ireland and Scotland.

Thursday sees that moisture push down and it will fall as wintry showers overnight even further south into The Midlands and southern England. This bank of rain and wintry showers will be sitting across the southern half of the U.K and some will also edge into The North East. Ireland will start clear, bright and frosty. So a bit of an east-west split on Thursday with that colder, wetter front down the eastern half of the country and the brighter weather in the west. The wind will freshen from the north east and it'll introduce a sharp wind chill making Thursday the coldest day of the week. Right parky like with temperatures lowest in the south and east under that unsettled cold front. Ireland and Scotland will be a little milder than this with more sunshine but we are talking 5-7°C day time temperatures.

Closing out the week on Friday and that sharp wind chill will remain, especially along eastern coasts but it'll be bright, sunny and dry on Friday, just about everywhere with a sharp frost starting the day. So a dry, bright and cold day to round off the week with temperatures nudging up to 6-8°C, still a long way down on the start of the week, with that ever-present north easterly wind in situ. This will mean it'll feel ever-so-slightly warmer and be brighter across the west and it'll be duller and cooler across the east with the threat of wintry showers pushing in off The Wash for the later part of Friday afternoon anywhere south of The Humber.

So how does the forthcoming weekend look ?

Well the projected GIF from suggests that the cool air will retreat a little as high pressure builds off the coast of Co. Kerry so that means we will lose those really cold winds that will be such a feature of the second half of this week.

So the weekend outlook is mainly settled and mainly dry with overnight frost into Saturday and Sunday and similar day time temperatures to the end of the week at 7-9°C, despite plenty of sunshine. Lighter winds as already mentioned. It won't be completely dry though as rain will edge in from The Humber and The Wash later on Saturday and we will also see some showers across the west and south west of Scotland, consolidating into longer spells of rain across the north of Ireland later on Saturday. Sunday looks the driest day of the weekend with fine, bright and cold weather hanging on through Sunday but less risk of showers across eastern coasts. Another overnight frost though on Sunday morning with maybe the west and Ireland just missing out.

Weather Outlook

As you can see from the GIF above, the projection for the start of next week shows that colder front retreating to the east but I'd still highlight there's plenty of cold air around on this schematic so we won't be heading back to factor 30 territory anytime soon 😎

We will though move into a westerly airstream and to me that means we are less likely to see night frosts even though the temperatures are likely to be nothing to shout about. This is because a northerly low pressure system is set to edge southwards pretty much from the start of the week and this will introduce unsettled and colder air, first into Scotland and then further south over all parts of the U.K & Ireland as we progress through the week. As we get past mid-week, next week, the low pressure will push eastwards and that'll mean we pick up the trailing edge of the low and the wind will swing northerly from late Wednesday / Thursday onwards. We will keep that wind through to the weekend when again high pressure will settle the wind down and temperatures will pick up a tad.

With low pressure dominating the weather, next week is likely to be wet and unsettled with rain fronts pushing through from the start of the week and plenty of rain and wintry showers leading through till Thursday when it starts to settle down again.

If I do a little 'Mystic Megging', I can see a big Atlantic low pressure due to present itself at the end of next weekend (10-04-22 I am talking about), which will return us to the more familiar sunshine and showers weather. Between now and then, we have a chilly and unsettled interlude, especially next week.

Agronomic Notes

April is often one of the worst months for growing grass I think in the U.K & Ireland, so often it is characterised in my mind by dry and cold weather so I thought I'd take a look back at the data to see if this picture in my mind was true. I presented some of this data at BTME.

So let's look at the GDD and rainfall data for April. I've used Sean's data from The Oxfordshire because it's representative of a number of locations but obviously I don't have access to other daily data going back to 2005, nor the time to collate it :P

So how does temperature and growth look for April's past and can this give us some pointers as to what we should expect ?

So if you look at the GDD totals from 2005 through to 2021 we can make the following deductions ;

GDD (6°C base) Rainfall (in mm)

Average 95 32

Minimum 26 2.4

Maximum 175 115.2

So an average GDD of 95 for April works out at around 3 ish GDD on a daily basis which would translate to a low growth rate for Spring. I'd look at anything around 6 GDD as being good growth for reference purposes. So first up we can see April isn't likely to be a good growth month based on the law of averages.

And an average rainfall of 32 mm for this location would obviously put it as a dry month so my gut feeling that April is a hard growing month due to the combination of dry cold would seem to be backed up by logic.

Then we throw in the in-built variability of the jet stream and that's where predictive becomes tricky. Just look at the last 2 years on the graph above. 2020 we had exceptionally warm weather, with high GDD, but it was also dry. 2021 was one of our coldest April's on record, if not the coldest in some places and again it was really dry.

My gut feel for this April is that it will be a cold one because we have more cold air in the northern hemisphere than I would expect to see for a warm start to the month, so first half certainly would be cool / cold in my books and wetter than usual. Let's see if I am right in a few weeks time :)

Growth regulation and Poa annua seedhead flush

So I when I saw the Danish Sea Scurvy in flower on the roadside salt splash area recently, I immediately began to think about Poa annua. I also get a lot of questions about PGR usage at this time of year and of course the companies are pushing / advocating early PGR usage.

So first up, where are we are in 2022 GDD-wise ?

Here is the chart of cumulative GDD from 3 locations (Sevenoaks, Northampton, Glasgow) where I can access data from their Davis Vantage Pro 2 weather stations (with the kind consent of the owners of course). If you want some Welsh and Irish data on here, then I need the same please :)

An interesting graph I think when you look at say January as an example.

The Scottish location had the highest GDD total and The Midlands location, the lowest. Go figure. That's the way it was though because I installed a weather station and sensors in the first week of January up in Scotland and it was super-mild. It got colder as I came south. Here in The Midlands we had lots of ground frost, in my location, we had 16 frosts in January, in Sevenoaks, 13 and in Glasgow, 5.

My observation on the flowering of Danish Sea Scurvy coinciding with the annual biotype of Poa annua starting to seed on greens looks accurate as well bearing in mind the two English locations hit 100GDD cumulative around the 24th of March, so hey you don't need to record GDD, just look at the verges on your way home from work :)

Now although March has been a kind month in terms of letting us dry out and we have had plenty of PAR light, the cold night temperatures have held back greens growth somewhat and I think when we finish March, we will probably be around 60 GDD for the month, which isn't great and again affirms my hunch at the beginning of March that it wasn't going to be a high GDD one.

So where does this put us when we think about PGR usage ?

Of course we now have two very different A.I's on the market and the new kid on the block is quite a different proposition to the old fella. I am of course talking about Prohexadione-calcium as the new incumbent and Trinexapac-ethyl as the old stager.

I think it is fair to say we are still learning about the new kid despite the fact that it has been sold for 2 years in this market. We know it isn't a straight-forward tank mixer, you have to get the right pH to split the calcium from the PGR part of the formulation. We know it works very quickly and we know I think that it's more Poa annua specific in terms of the grass species it affects / regulates the most. The last point has yet to be proved conclusively in terms of exactly how it affects Poa annua.

Now that's when I think we have to just take a step back and consider because Poa annua as a species is a broad church. Lot's of biotypes, annuals and perennials and as I have talked about before when we apply a PGR (any PGR), we apply a selection pressure to our surfaces. The more regulated plant species grows less and the less regulated grows better. Simple logic. Over time the less regulated out-competes the more regulated and so you see a waning of your PGR effect. That's what I believe happens and has happened here in the U.K and Ireland already and in the States.

If I had a dollar for every GCSAA PGR seminar I've sat in and a superintendent puts his hand up and asks "Why doesn't my PGR work the same as it used to ?", I'd be a rich man. I believe PGR and sward selection pressure is the answer.

Back to seedheads and that's where I think the lines are getting blurred. Does PR-Ca (I can't be bothered to write the full name all the time) affect seedhead production ?

Well if you look across the water at the evidence, they would say not because in the U.S they tankmix PR-Ca with Proxy (Ethephon as we know it) in order to suppress seedhead production. Now we can't do that because we don't have Proxy available.

Now I asked a specific question there. "Does it affect seedhead production ?"

There's another I could ask, which is "Does it affect the visibility of seedheads in a mixed grass sward ?".

The latter is a very different question and I think that's maybe where the lines are getting blurred. If you apply it early before the main seedhead flush and hold back the Poa, does that mean that we see less seedheads produced during the seedhead flush as a result ?

My honest answer is I don't know but I think it's an interesting question and I'll certainly be monitoring this on the courses I work with on the weather analytics side of things.

That we have another A.I to me is a plus. That it may help us make the transition to a more bent-dominant sward is also a plus but as with anything in this world, you have to take a step back and consider it before jumping in both feet first. As you can see from the graph above, we have 3 very different cumulative GDD curves from 3 different locations, so my advice is build your own experience based on your site and your GDD and don't be influenced by someone else in a totally different growing environment and with a profound love of self-promotion on social media. This goes for a lot of things not just PGR usage I have to say.

Happy to have feedback on this either way so please drop an email to me on and we can discuss and consider :)

All the best for the coming week, time to put the shorts away and dig out those winter thermals and buffs !

Mark Hunt

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