After another scorching weekend, things are due to settle down a bit heat-wise as we see a slow breakdown in the weather. Some areas saw their first rain on Friday evening for 7-8 weeks with torrential downpours across London depositing 50mm in just 2 hours. Elsewhere we have seen rain across Ireland, the north-west of England and Scotland with a vertical band of rain slowly moving across the west side of the country this morning. (It looks like St David’s, Pembrokeshire is getting a proper hammering as I type this at 09.42)
Central and eastern areas though remain parched.
The big question for many will be “Will I see any rain this week ?” and the answer of course will depend on your location. The areas most likely to receive rain this week will be in the north and west and so the south and especially The Midlands may see little more than the odd shower I am afraid. That said the end of the week probably holds the best chance of some sneaky un-forecastable rain for the south of England.
We will see a lot more cloud than of late across the U.K and that’ll help the job temperature-wise with some cooler nights to boot but the breakdown will be slower than first thought because the low pressure is staying up north.
Not every plant dislikes the current weather though, I’ve walked through this Maize crop every week since it was late-planted in the spring and can’t believe how fast it is growing…
General Weather Situation
So we start Monday we that band of rain (/) moving across country and currently affecting the west side of the U.K stretching up from Cornwall through West Wales, up to the north-west of England and east of Scotland. It is a narrow band though and that means it is likely to fizzle out before reaching central and eastern areas which is a pity. As that rain tries to move east it’ll push some cloud up before it and that cloud will keep the temperatures 4-5°C lower than yesterday for The Midlands. Ireland will also see those showers cross-country through the day after a similar day yesterday and much cooler temperatures, down in the high teens. Further south away from the effects of that rain front we will see another hot day I’m afraid with temperatures pushing up into the high twenties. Winds will be light and westerly / north-westerly.
Onto Tuesday and that departing rain front will leave some thicker cloud across the east coast of England and in general we will see a cloudier, cooler day with temperatures down in the low twenties due to the wind aspect and cloud cover. There’s a risk of some showers across the north-west and north-east of England and may be a snap one further south. Ireland looks to have a similar day with any showers confined to Donegal and the north-west. So cooler than of late with Ireland and Scotland in the high teens and low twenties further south courtesy of that north-west wind.
Wednesday sees that north-westerly wind drop and swing more westerly so temperatures will rise again towards the mid-twenties in the south of England. Still plenty of cloud around, some of it quite thick again across the east of the country with Wales and the west coast perhaps seeing the best chance of the sun. Ireland looks to stay cloudy all day but dry. Similar temperatures for Ireland and Scotland in the high teens through to mid-twenties for central and southern areas.
Thursday sees the wind do a full 180° swing down south to blow lightly from the south-east and that’s one of the reasons why any rain later in the week will struggle to affect the south of England. Up north we will see that north-westerly wind push back in, light to moderate and that’ll swing cloud cover across the U.K and Ireland with temperatures dropping a degree or so across Scotland and Ireland as a result. So warmer where you get that wind direction change across central and southern England with temperatures once more in the mid-twenties, cooler further west where you keep that north-westerly air stream.
Closing out the week on Friday we see a rain front push into north-west Ireland / south-west Scotland overnight and this will move in south-easterly direction across Ireland pushing thick cloud before it. Now currently the odds are that this rain front will not make much progress into Wales and the north of England but it’s been changing on a daily basis so we’ll see. Ireland and Scotland look to be dull with plenty of rain for Ireland but further south it’ll be hotter because the wind will push from the south, so a hot dry day with temperatures in the mid to high twenties to finish off the week across the south of England.
So what’s the outlook for next weekend ?
Well a lot depends on where the winds coming from but currently the odds are that the wind will swing round to the west / north-west across all areas and that’ll push in a cooler, fresher air stream across all areas dropping the temperature significantly on Saturday with high teens likely across all areas. A real north / west / south divide on Saturday with Ireland, Scotland, the north-west and north-east still sitting under that thick cloud so cool and dull here vs. hazy sunshine and cloud further south. Sunday sees warmer air from that close-by, Atlantic high pressure push in over Ireland and the west raising temperatures up to the low twenties for Ireland and Scotland and mid-twenties further south.
So next week looks to start warm enough after a hot Sunday but if we are to see a real breakdown of this continued dry spell for many, next week will be the clincher. That’s because we have a deep low pressure sitting north-west of the U.K that through next week is projected to sink down and introduce cooler and more unsettled conditions through the week, starting with the north and west on Monday / Tuesday and then extending south to all parts later in the week. This transition is key because if it occurs it’ll introduce a westerly air stream which will end the blocking action of the Atlantic high and allow low pressure systems to feed in.
Now I know when we are going through this process it is a bit like waiting for a delayed train, every time you look at the timing board it’s delayed a little bit more so you wonder whether it will ever turn up.
Honestly-speaking, this could be the case here, we could have a re-run of this week with the low pressure staying further north and only bringing cooler weather / rain to the north and west, whilst the south and east bakes. Part of the problem is that we are sitting here in the middle of July so we still have heat potential to come, whereas in 1976, this process occurred in late August. I could counter that by saying the run of August weather we have had of late would point towards a greater likelihood of unsettled conditions than heat. Time will tell.
So in some areas we are into week 8 now without appreciable rain and the effects of continual E.T stress are plain to see.
Above is a pic from the north-west of England, an area normally associated with anything but a shortage of rainfall. This course got 15mm of rain late last week and I think I’m right in saying it is raining there now. It will however be a while before the grass comes out of dormancy and begins to respond to the change in moisture status and fresher conditions. Brown grass like this is at its very simplistic, exhibiting nitrogen deficiency, because with extremely low levels of soil moisture the grass plant is unable to uptake nitrogen and so sacrifices its leaves to protect the part of the plant that ultimately determines its fate, the crown.
The crown is where it all goes on in the grass plant because it is here where cells divide into root or shoot cells and during spells of prolonged drought this is the area that the grass plant prioritises. So when you are looking at an area of turf like the one above an obvious question springs to mind “Is this turf dead or is it dormant ?”
The survival of the grass plant crown is not only a function of moisture availability, its place within the turf canopy is key and that’s where things like surplus organic matter come in to play. Areas of turf that contain excessive organic matter will cause the crown to be elevated above the soil layer and resident within the surface organic matter layer. This in itself drastically lowers the ability of the plant to survive. Firstly organic matter heats up far quicker than soil and so areas of thatch will literally bake off, dehydrating the crown and killing the plant. An elevated crown is also prone to damage by wear and tear being situated above the soil layer so turf that is dormant with an elevated crown will show more wear damage and soon take on a black appearance as the grass begins to degrade.
More of a golf green scenario for many but the level of topdressing integrated within the profile will also dictate the grass plants ability to withstand this type of prolonged heat and ultimately survive. I’ve used this picture before but you can clearly see how the crown of the grass plants (in this case Poa but it applies to any species really) on the right are sitting down in the rootzone and so protected from the worst of the summer heat and wear and tear to boot. The plants on the left taken from an area which has received little topdressing are elevated and right in the firing line unfortunately.
So one thing you may notice is that your thatchiest areas on the golf course / sports pitch, etc won’t recover once rainfall re-commences and this is because the crown has died and is starting to degrade. The images above show a healthy white grass plant crown above compared to a tan-coloured crown that is starting to degrade. (in fact you can see fungal hyphae on the crown)
So should you apply fertiliser to drought-stressed turf ?
It may seem a daft question but in some instances (domestic lawn care for example) this one comes up a lot. It really depends on the type of fertiliser because depending on how much rain falls when the drought breaks, you could make the situation worse my desiccating the plant further as moisture is drawn out of the plant towards the fertiliser.
The amount of desiccation is dependent on the osmolarity of the applied fertiliser (whether it be liquid or granule) and this is a function of the salt index of the fertiliser. (the lower the salt index, the lower the osmotic draw from the plant)
If we have plenty of rain then this won’t be an issue but the smart money is on waiting for moisture levels in the rootzone to re-establish and the grass plant to begin growing again before applying fertiliser.
E.T Stress – Where are we now ?
At the end of June I put together two graphics comparing 2018 y.t.d with 2017 in terms of rainfall, Demand E.T and soil moisture deficit.
Two weeks on I thought I’d re-visit this to see how we are doing…
So in the above graph from 2017 you can see we had a period during June for about 16 days when no rainfall was forthcoming, we then got rainfall on the 27th. It went hot and dry again and E.T ramped up but on the 12th July we got rain again, that’s a gap of 14 days. So in terms of crown hydration the grass plant kept getting a little water every fortnight to keep it healthy and viable.
Overall the theoretical moisture deficit from June 1st, 2017 to July 15th, 2017 was -116.1mm
Compare that with the scenario below for this year ;
Quite a different shaped graph with no rainfall since June 1st and consequently an ever-increasing theoretical soil moisture deficit, now at 177.4mm up until the 15th July, 2018, that’s over 7″ in old money.
As mentioned before this cumulative plant stress is likely to result in some plants in less than optimal conditions checking out depending on their crown and of course root status.
Coming back to the beginning of this blog, the reason that maize is still looking good is because it has a very deep root system and so finds it easier to maintain plant moisture status. The same is true of grass plants but of course the functionality of the root system is dependent upon so many other factors aside from just plant species.
I once saw an autumn over-sown Fescue / Rye fairway go under drought stress the following summer and I expected to see the Fescue survive and the Ryegrass check out. When I visited the course, the exact opposite was true, the Fescue was dead and the rye alive.
Upon examination the previous autumn sown rye had got its roots down through an organic matter layer present in the rootzone and into the clay beneath and so had survived whereas the less vigorous Fescue had not penetrated through the organic matter layer and its roots had dehydrated to a point where the whole plant died. Not what you’d normally expect species-wise but an illustration that the local environment (rootzone characteristics, organic matter content, root depth) has a big say in what happens to a grass plant in a severe drought scenario.
Humidity = Disease
One last point is that ‘if and when’ your site does finally receive some welcome rain it may not all be good news. The increase in humidity is sure to kick off some of the more stress-related turf diseases like Dollar Spot and Anthracnose. Be on your guard.
Ok, that’s me for this week, I am on my travels next week but I’ll still be taking time to put the blog together as I know next week is critical from a weather perspective. In a little under a months time I’ll be off to the Alaskan Wilderness once again and taking a sabbatical from the blog till late August as mercifully Upper Camp on the Kanetok River has no WiFi, no phone reception, well nothing really except Tundra, Salmon, Dolly Varden, Trout, Bears and lots of Mozzies 🙂
All the best…