New build lawn - compaction, clay soil, poor drainage

[garmcqui]

Hi all,

We have a newish-build house (built 2014) with a plain lawn at rear. The soil is quite heavy clay, badly compacted and I'm sure the developers put the minimum amount of topsoil down below the turf.

It's in pretty bad condition after this winter, so I have descarified it (not much moss, but filled a wheelie bin with thatch) and aerated it with a rolling aerator and garden fork. However I may hire a hollow tine aerator and do it properly before top dressing.

However, there is one corner of the lawn which seems to have sunk somewhat and needs raising up slightly, it's always damp and boggy. You can just about make it out in the top left of this photo http://imgbox.com/o3TaVUOs http://imgbox.com/H9LnDRTh

I intend to build that corner up a bit with good quality sandy topsoil (just so it is level with the rest of the lawn) and sow some shade resistant seed. Before building it up, I may also dig a "sump" in the middle of the corner, as deep as I can and fill it with stones/gravel in an effort to improve drainage in that corner - would this help?

Regarding top dressing, I read so much conflicting advice online for clay soil such as this. Some say sharp sand, others say not to use sharp sand as it contains lime and/or salt. Others say you need to add organic material like compost, whilst others say add horticultural grit.

So I can get a dumpy bag of sharp sand from the local builders merchant for about £45, or I can get proper topsoil/sand top dressing for about £90, or horticultural grit for about the same price. Which of these would you go for?

http://www.compostdirect.com/topsoil-lawn-dressing/p72 (80% sand)

http://www.compostdirect.com/horticultural-grit/p22

Any advice appreciated!

Gareth

 

[garmcqui]

Grass seems to be reviving slightly even just with the scarifying and aeration carried out last week:

http://imgbox.com/UY38Da9q

But is still quite poor in that particular corner:

http://imgbox.com/snxeM8Iw

http://imgbox.com/kKEcT7yx

 

[r896neo]

With new builds its sometimes a case of managing expectations versus cost. You dont want to spend a lot of time and effort and then in 2 years time dig it all up to realise that there was a layer of sub base or something crazy buried 6 inches down.

Without going major on it and digging it up hollow core aeration is the best thing you can do. Use grit or coarse sand to fill the core holes. As for top dressing if its to bring up low spots then i use a 60/40 Sand to topsoil mix. If its for simply filling in core holes use just grit or coarse sand.

Sharp sand is just a term, everyone has different names for sand types and your sharp sand could be my plastering sand etc etc. Get the coarest sand you can get. Ideally a washed sand but that is regional and not available in some places. Screed sand or concreting sand can work but some of them can be full of clay.

Forget compost, its for fast draining lawns where you need to add water holding ability to a lawn. Putting it on a poor draining lawn is bad news.

In my book you can deal with nutrients, ph, weeds etc all very easily after a lawn is laid with treatments. The one thing you cant change after laying a lawn is soil structure thats why relieving compaction and adding free draining material is so important at the time of preparing.

The best thing you can do without ripping it up is hollow coring. This process along with brushing in grit is as close as you can get to improving the soil structure.

 

[garmcqui]

Thanks for your reply. So, would you go for the horticultural grit I linked to (2nd link)?

Only thing is, I was planning to top dress and overseed to improve thickness, which probably won't work too well with grit?

Also, for either choice, I have no idea how much I would need - garden is 88m2, so would an 850kg dumpy bag be massive overkill?

Cheers

 

[r896neo]

The top dressing would be good as I just saw it says its 80% sand. The grit will not provide a good seed bed at all.

You'd be surprised at how much a lawn will thicken from really hard scarifying and good feeding. Unless your after a really thick ornamental lawn using a fine fescue type of mix I wouldn't bother overseeding. Save your money and buy an extra bag of a good feed like scotts rennovator pro or clean run pro.

If you do want to topdress you will have no trouble losing 850kg on 88sqm. You may need a bit more than that to do it really well. I'm sure the supplier would advise.

 

[sky_bum]

If you have heavy clay soil, you'll likely struggle in the garden. I would doubt a hollow tine aerator would work - at least it didn't work for mine - and I think the amount of sand you'd need to use is staggering (see RHS link below).

I have done a combination of:
- sloping for plant beds;
- land drainage (currently installing this) for beds where sloping does not work - there is a version for lawns that works in a fishbone pattern as long as you can drain it somewhere;
- currently trying gypsum to break up the clay on turf but it can take up to 3 years apparently.

Have a read here https://www.rhs.org.uk/advice/profile?PID=620

My neighbour had an aerator fork which seemed quite good at opening up the clay, but he mentioned if you walk on it it will compact again. Oh and one of my other neighbours mentioned - while we were both moaning about the heavy clay - that when he moved in he bought 20 tons of topsoil and covered the whole garden.