Why doesn't the grass grow in half the garden?

[BowserTheTenth]

We redid the garden two years ago. Dug it over with a digger, imported top soil from a single source which was laid to about 150mm depth all over. Then seeded with a mix of rye and red fescue.
The fescue has taken everywhere, but the rye only grows in half the garden, with a very definite line. The line can't be explained by shade/sun as both sides are half in half out of sun. The topsoil is the same throughout. Underneath the topsoil is an unknown depth of normal stony mud.
Other plants like clover, daisies and buttercups grow over the whole garden.

We reseeded this year but the rye didn't grow again. Why does the rye grass hate half my garden?

Any large plants or trees down the non growing side that might be draining nutrients away ?

Following as I need to try and recover my grass so hopefully some good tips will follow!

No, no large plants anywhere in the garden.

Photo?

I can't take a photo of the demarcation line without outing myself! But here's a patch from each side.

Is there a layer of concrete beneath the soil ?

@Whataretalkingabout not a solid layer. There will be the odd bit of broken concrete I expect because we filled a hole with mixed topsoil, rubble and rocks. But it's at least a foot down and probably nearer two feet.

Have you tried treating for leatherjackets? They eat grass roots once the seedlings get to a certain size so you reseed fine and then patches just die. Apparently the crane flies always go to the same place- only 1/3 of my lawn was affected. A good dose of nematodes from green gardener seems to have sorted it

@CMOTDibbler that's interesting! I will definitely look for them (just read about a method with black polythene) and see if that's the problem. Thank you!

Definitely not the leatherjackets. Shame, as that looked like an easy fix!

Do you have a soak away on one side of the garden?

@SlipShodSue haha, the healthy half you mean? Nicely fertilised 🤣 Sadly no, that's not it as we're on mains.

Is it waterlogged in winter (though would still expect it to grow back in summer).

@Poynsettia no it actually drains really well. Also it wouldn't make sense for it to be only half the garden? It's literally a straight line right across as if drawn by a giant ruler.

Last suggestion is someone fed the lawn with something unsuited to it, did so much then ran out of stuff and used something else on the rest.

@Poynsettia unfortunately we laid the lawn ourselves with 'new' topsoil, two years ago, and haven't put anything on it except grass seed and water.
I really appreciate your problem solving though, thank you!

The way I'd try to find out is to dig a small hole 1ft ish diameter between 1 and 2ft deep, one in the good bit and one in the bad bit and try and see if there is any difference in soil below the stuff you added. Then whilst the soil is out, fill both with water and see if the bad side drains as fast as the good side.

@Shedmistress I'm not averse to digging holes but feel I wouldn't have a clue what to look for in the soil/under the soil. Do you have any idea what I'd be looking for?

Something under the topsoil. Was one half more compressed ? The diggers/ labourer’s more one side than the other? Might mean it’s struggling after cold winter and then no rain.

@Goingawayistricky yes, the poorer growth area probably is more compressed - it was harder to rake anyway. Could that be it? Can I soften/aerate it somehow?

I am afraid it will probably be your compressed soil or rubble and rock underneath that need clearing before you can ever hope to grow grass on that area. Maybe try planting different plants instead ? If it is highly compacted and poor draining that must be fixed for any results.

It does drain fine. Can we loosen the top layer? Scarifier?

I need to see a photo of the line I'm intrigued 😅 never seen anything like this

A difference.