Help identifying lawn problem patches

Hi

We have these patches in our lawn that have appeared in the last couple of years. Initially the patches are dark green and damp, but over time they turn a lighter green and eventually turn black, crusty and dry up. I can scrape them off, but I'd really like to know what they are and if there's a specific treatment for them.

It's cut regularly, spiked, scarified and fed in the spring. We used to have moss patches in the past, but they cleared up. We also acquired two dogs in the last couple of years, a male and female, so I wondered if it could be a urine problem, but it doesn't look like any examples of related problems I've found on-line.

 

It could be dog urine, it kills the grass and if they keep going on the same spot the grass will not get a chance to recover.

 

Is it just this one spot or does the damage extend?

do you see the dogs there to do their you know what?

is there hedge or trees near this patch?

what type of soil do you have ie Sandy or clay content?

 

My immediate thought when I saw the picture was poor drainage. Look at the way the soil is cracked. Either it's low in organic matter, or it's severely compacted forming a crust or 'pan', which is virtually impenetrable to water, and roots.

The dark green is likely algae, sitting on a damp surface. As it eventually dries, the algae dies off and goes pale.

That's my assessment, but I could be wrong.

 

It's in patches all over the lawn.

The dogs do their thing in different places all over the garden.

Clay rather than sandy.

No hedges nearby, but there are a couple of trees.

 

I think you're correct, it probably is some sort of algae. We had a similar problem last year, but not so widespread. We scraped the algae off and re-seeded the affected areas which recovered quite well, but we're back to the same problem this year.

It drains reasonably well, except a couple of low places in very heavy rain, but even those dry out within an hour or so after the rain stops. The soil itself doesn't usually get to the point where it cracks, the cracking you can see is where the algae has dried out and formed a crust on the surface.

We have a gardening service in from time to time and they've been in to spike it, scarify it and feed it in the last couple of months.

It's frustrating because the summer when we moved in, the house had been empty for some time and the grass was over a foot high. We got it into decent shape and although there are clearly a few different varieties of grass, we had good cover across the whole garden. It's only gradually deteriorated over the last 3 or 4 years. I've done image searches to try to identify the algae, but haven't seen anything that looks even remotely similar.

 

I'd spike it, then top dress with sharp sand. You mention it doesn't stay wet for long, but is that like a puddle dries after rain through evaporation, or is it actually soaking freely into the ground?

If drainage is good, you shouldn't be getting standing water except in the heaviest of downpours.

 

It’s always a job when facing these problems. The cracks for example are an issue if say you want to apply a fertiliser as it would allow the feed ie granular pellet/dust to enter the ground which would be an issue if a risk assessment is carried out so as it stands you need to find out what’s going on.
Personally my first reaction would be a soil test as it could be an issue with some type of contamination if it’s all over the lawn as it’s an unusual problem. If there is contamination ie a drain or some water structure is leaking for example then spiking or dressing will not solve the issue.
It could be for example contamination from something under the ground ie. The site was back filled years back with rubbish that contained material that is harmful and is breaking down.
Normally you associate cracks with dryness yet we have not had the warm weather to create this so there is something going on that we need to find out before correction work can be carried out.
That’s my first step, I would want to know what’s in that soil before proceeding.

 

I just think the grass got killed by dog pee last summer during the drought and has struggled to come back, the winter and recent rains has caused the area to puddle for short periods and allowed algae to form, hence the green scum.

I'd just buy a few turves and dig it out, if the same spot dies again you could have a soil problem, (keep an eye on the dogs), but I'm convinced its a doggy thing.