My pretty lawn is lumpy

[MisterBoy]

I built a brand-new lawn a couple of years back - tons of top-soil all nice and level, it's about 4x5m.

I noticed last summer it had gone really hard and bumpy, so sitting or kneeling was quite uncomfortable.
Right now, it is even more bumpy but very soft from all the rain. Not sure if it's frost-heave, or worm casts or animals. I know people don't advise rolling a lawn but with it being so soft, how else can I get it flat?
I don't mind the surface being very hard, as long as it's smooth.

 

[blup]

Seeded or turfed?

Blup

 

[MisterBoy]

Turfed, though it's been overseeded a bit since. It was initially pretty level until the first winter.

 

[blup]

Was the top soil laid on made up ground, bricks or rubble? Can you post a picture?

Blup

 

[MisterBoy]

A current photo won't show much, the bumps are small so hidden by the grass I have some photos of the laying process somewhere if that's helpful?

It has been long-term garden, then covered in stone until I cleared all that. It was firm and reasonably flat, then I added several tons of topsoil and raked/rolled to get it very smooth (I put a lot of effort in with levels and string-lines) before laying turf.

 

[blup]

Difficult to say, maybe worm casts.

Blup

 

[Old Salt]

Walking on the grass when its wet or soft will cause depressions. Remedied by cutting and top dressing filling in the low spots and reseeding where necessary. Bit too early to do it yet as the soil needs to warm up a bit more.

 

[Bullet-Proof_Biscuit]

I was about to suggest nice old Victorian cast iron rollers go cheap on the usual used stuff sites..

 

[ellal]

I was about to suggest nice old Victorian cast iron rollers go cheap on the usual used stuff sites..

Beat me too it...

About this time every year our lawn needs a bit of 'smoothing' whilst the ground is still malleable, although it doesn't do a perfect job.

 

[Robotmannick]

How big are the lumpy bits? I get bumps in my lawn that tend to be 9" or so across and anything from half inch to 2" high. It's ants nesting under ground. Don't know if you have the same problem.

Sometimes the lumps are soft and squish down level under foot pressure, others are rock hard. I try to dig out cubes, sprinkle ant powder directly into the next, remove some of the soil to make it level then replace the turf on top. It needs watering and the inevitable cracks will close up within a couple of weeks.