You have probably heard the story that grass is greener after a lightning storm, but is this really true?
How can lightning affect the color of your lawn? Lets shed some light on this story.
The Story – Greener Grass After Lightning
The story goes something like this. The air contains 78% nitrogen and during lightning some of this is converted to nitrogen dioxide, which dissolves in rain drops, and falls on your lawn. This extra nitrogen works just like a fertilizer; grass absorbs it and becomes greener.
Others say that the darker green color is created from wet grass sparkling in the sun. It’s all just an optical illusion.
Does Lightning Produce Nitrates?
We know that adding nitrate fertilizer to a lawn will make it greener and we know plants absorb nitrates. If lightning produces nitrates then it is quite possible the story is true.
The air does contain 78% nitrogen, and the energy of lightning is high enough to break apart the nitrogen gas creating reactive nitrogen molecules, which capture oxygen molecules to form nitrogen dioxide. This dissolves in rain droplets forming nitric acid, which is hydrogen nitrate.
The chemical part of the story is quite true.
How Green Does The Grass Get?
I had no problem finding lots of online posts about grass getting greener, but I did not find a single post that actually measured the color.
Without actual measurements, or some kind of controls, we don’t really have any data confirming greener grass.
If you find some data, add a link in the comments.
Rain Washes Nitrates Away
A lightning storm may add nitrates to soil, but the rain washes nitrates that already exist in the soil to deeper levels, reducing the amount of nitrate in soil. Extensive rain can reduce the nitrogen available to plants which would make grass less green.
Where Does The Rain Fall
This may seem like an odd question to ask, but meteorologists report that the rain falling during a lightning storm actually falls a great distance from the lightning itself.
So if there is lighting above you, the nitrogen produced does not fall on the grass below you, which means your grass does not get greener. For your grass to be affected, the lightning has to be far enough away so that by the time the rain reaches the ground it is in your backyard. This distance depends very much on the prevailing winds.
It is almost impossible for a gardener to know that the rain falling on their lawn passed through a lightning strike, so how can they accurately report on any color changes in their lawn and relate it back to lightning?
How Much Nitrogen Does Lightning Produce?
The science is clear, lighting produces nitrogen, but does it produce enough to make grass greener?
According to Dr. John Lauzon, an assistant professor in the Land Resource Science department at the University of Guelph, Ontario receives about 20kg of N per hectare per year from the atmosphere. “That number is made up of two components and roughly half of it is related to atmospheric losses of ammonia, with the other half related to the lightning strikes”.
Lighting is adding 10 Kg/hectare/year. Lets say there are 5 lightning storms a year – an educated guess, but I do live Ontario. That is 2 Kg/hectare (1.8 lb/acre), or 0.2 g/sq m (0.006 oz/sq yd) of nitrogen being produced from one lightning storm.
According to Fertilizer for Dummies, a single application of fertilizer for lawns should be 4.9 g/sq m (0.15 oz/sq yd), or 20 times what the lightning storm adds.
Would 1/20 of the normal fertilizer you add to lawns make it green enough so that you could spot the difference? Not likely.
The Journal of Geophysics Research reports, that lightning adds 100Tg/yr globally, which is 0.2 g/sq m/yr – the same as the above number (Earth surface area is 5 E8 sq Km).
NASA also calculated the amount of nitrogen produced by lightning and came up with 9Tg/yr. If anything, the 1/20 value is on the high side.
Does Lightning Make Grass Greener?
Lightning does add nitrogen to the soil but the amount is unlikely to show up as greener grass unless you live in an area with a very high number of lightning storms.
Why Do People Think The Grass is Greener?
It is quite possible that the grass is never greener. People just think it greens up because they have heard the story before. Knowing it gets greener convinces them it got greener.
It might look greener in full sunlight, after a rain?
The most likely scenario, assuming grass does green up, is that the water from the rain increases root activity, which in turn absorbs more nitrogen from the soil, causing greener leaves. If this were true, the grass would get greener after any heavy rain, even when lightning was not part of the storm. That is not what people report.
But lets not forget that there seems to be no data supporting the idea that the grass is actually greener after a lightning storm. The whole story is most likely a fabrication of peoples imagination.