Hi All,

I did say I wasn’t going to post this week but I’ve managed to lever some time for a quick update on where I think we are and perhaps more importantly what I think is coming weather-wise. It’s a fact that April 2017 is rapidly turning out to be a hard growing month in some areas of the U.K and Ireland.


General Weather Situation 

A blocking Atlantic high pressure….

The issue we have currently during April is the presence of a blocking high pressure in The Atlantic (shown above) that is causing a number of weather processes to occur ;

Firstly, the path of rainfall is over us and down into Europe so we continue to be dry because if you remember my myriad of posts last autumn we had a similar blocking high pressure in situ during October and December 2016, Now cold and dry as I pointed out last week is a really poor combination to manage in terms of Poa annua because if it’s not temperature that is growth-limiting, it is moisture or indeed a combination of the two.

Secondly, the prevailing wind direction is northerly when you have a high pressure sitting out in The Atlantic because high pressure systems rotate clockwise so imagine the right side of that red high pressure circle shown above, it’s pulling down cold air from the north as it rotates in this direction. That means cool days but more importantly cold nights and these as we all know act as a hand brake to consistent growth.


The graphic above highlights the effect on growth of a cold night vs. a milder night with a near 60% reduction in growth despite the fact that the day temperature is the same.

Lastly, with north winds and a lower likelihood of rainfall we increase the chance of clearer skies, particularly at night and this means a higher risk of ground frost. So far in April 2017, up until and including this morning, we have had 10 ground frosts in some locations so 50% of the days have been scenario 1 in the schematic above. Milder night temperatures tend to result from a westerly or southerly wind direction in the spring and for only 5 days of the last 19 has the wind been from this direction.

So if we take all of that into account and look at how it has affected growth at our usual Thame location, this is how it has panned out so far this month up until April 18th.


So a very up and down growth scenario with the odd day of good growth quickly followed by a ground frost and a sharp decline in growth potential. If I continued this graph through to today, the 19th of April, it would be dropping back again because of the last two cold nights with -4°C recorded overnight in Suffolk.

Plus / Minus

As my good friend Bernie says in Switzerland it’s plus / minus 🙂

I have listed the negatives of the current weather and the fact that if you are currently needing growth to get recovery, produce consistent surfaces on sportsfields maybe where you’ve made the transition from winter sports to cricket over Easter, it can be a tricky time to achieve this. That said, higher height of cut grass tends to be less affected by this type of growth scenario than greens height Poa annua.

There are some positives though because growth is manageable in outfield areas, we haven’t come back after Easter to grass round our ankles and clippings lying everywhere and consistent dry weather means playability in terms of un-interupted revenue is potentially good. It’s just the grass and some of us that don’t like the current weather 🙁

Using the windows…

It’s going to be fact that in 2017 the best growth periods of the spring were from mid-February to the end of March and up until then we were pilling on the GDD and way ahead of last year. April has so far put the brakes on that trend and once again we will rock right up to the point Poa annua wants to produce seed and then we’ll stop. The continued dry weather will however put Poa annua more and more in the way of seeding so you can rest assured when this weather pattern does finally break we will see alot of seedhead very quickly. Last April we had a ground frost on the last day of April and the 1st day of May, but 3 days later we were warm at night and during the day and we experienced a huge growth and seedhead flush.

It also means that if you are sitting reading this with good surfaces and everything where you want it to be, you likely used the above growth period to the best of its potential. Yet again it points the finger squarely at getting work done earlier ‘provided’ and it is I accept a big ‘provided’, ground conditions and resources on your site dictate that it is possible.

You can see this week that we have a couple of milder days coming up on Thursday and Friday with better GDD / Growth Potential (because the nights will be milder) but it drops back down again at the weekend as the wind swings round to the north and the night temperature drops 🙁


How are we looking going forward ?

Weather-wise we have this stable high pressure over the rest of this week but with a slightly warmer feel as the wind will indeed temporarily shift to the west so you’ll see an increase in growth / uptake at the end of this week. It won’t last long though because by Monday it’s all change as we are set to see the winds ramp up from the north and that’ll push some unsettled weather down for the nest 2-3 days accompanied by strong northerly winds. So that means cooler with some rain (though not shedloads I think at this stage) before the high pressure re-establishes itself at the end of next week and we settle back down into the same pattern as described above.

Any light at the end of the tunnel ? Maybe, just maybe a change in early May but I’ll know more by next Monday…


Cool and dry isn’t a great combination for applying nutrition and with limited growth potential you can’t expect to see much from it either. Wednesday, Thursday and Friday this week are good application days because we look to hold better day and night temperatures so a foliar application made then will likely give a good effect. As usual you want low temperature-available nutrient forms so that’s potassium nitrate, ammonium sulphate and ammonium nitrate (though be careful with the latter). There’s no point in applying much above 6kg / N / hectare at present, more important than rate is frequency, ‘little, but often’ is the name of the current game and always mix a light rate of iron in when it is cool to maintain colour.

Sand cools down quicker than soil

One last important point, particularly if you’re dealign qith a mixture of rootoznes on your site (and let’s face it most people are..)

Sand rootzones tend to have a higher air-filled porosity than soil-dominated ones and this means they can hold more air (provided of course the particular size is coarse, medium-dominated). It also means that they are more ‘reactive’ because air being a gas will heat up quicker but also cool down faster than say water. So a dry, sand-dominated rootzone will heat up faster in the day but cool down faster at night whereas a soil-dominated rootzone will be slower to heat up and slower to cool down, in other words, less ‘reactive’ to temperature change…


Ok, I’m past my 9 a.m. deadline for this mini-update :(, back to normal (whatever that is) next Monday. If you’d like to send your April to date GDD / G.P spreadsheets in at the end of the week so I can do a bit of a month-so-far comparison in next Monday’s blog, please feel free to do so.

All the best.

Mark Hunt