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Options for new lawn on a clay subsoil

paulppaulp Posts: 8
in Problem solving
Hi,

Looking for advice on building a new lawn on top of heavy clay subsoil - ideally starting this year, so we have a usable lawn for spring.  The total area to be grassed is about 800m2, so need something economical.  Our initial priority is a 300m2 area.

We've just finished building and hard landscaping work, which have damaged the existing soil - compaction, mixing subsoil and topsoil etc.

We were originally planning to bring in certified topsoil enough for a 100mm cover and seed it.  But are concerned we'll have drainage issues underneath.  Also the specification for the medium grade BS standard topsoil states it can range from 5-35% clay.  it was paying for more clay made us stop and question this.  Here are the options we've come up with so far:

1.  100mm covering of certified topsoil (medium grade) and seed - I can get 20 tonnes  loads for £360, so would need 3 loads for the initial area with some left over.

2.  Rotovate in 100mm of PAS 1000 compost and seed - I can get a full load (40 cubic metres) for £480

3.  Rotovate in 100mm of fine bark chips/compost and seed - A full load of this (also 40 cubic metres) is £1500

4.  Turf laid on top of 50mm of sharp sand - I've been quoted £7000 by a reputable local landscaping company for this.

Option 2 is cheapest.  Option 4 is quickest.  But what will work and stay working?

I could also add sharp before or after to options 1, 2 and 3.  A 20 tonne load is about £400.  
With options 2 and 3 - while we wouldn't do it when it's raining, given the time of year, the existing soil will be wet or damp in places.  Is it sensible/OK to rotovate 100mm dry compost into 50-100mm of wet or damp clay soil?

I'll stop there!  Any guidance would be appreciated!?

Thanks,
Paul
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Posts

  • 1634 Racine1634 Racine Posts: 568
    Hey Paul.  I laid new turf onto my own hard compacted clay in spring this year.  The area was probably around the 300 square metre mark.  The issue you might get with rotovating is that you will need time to let the ground settle - ideally around 4-6 weeks, otherwise you will end up with lumps and bumps.  Given the time of year already I wouldn't then think it would be a good time to establish new turf, and definitely not seed.
  • paulppaulp Posts: 8
    Thanks for the reply Rancie.  Did you lay the turf on sharp sand or new topsoil?  Have you had any drainage issues if the clay subsoil is still compacted?  
  • 1634 Racine1634 Racine Posts: 568
    paulp said:
    Thanks for the reply Rancie.  Did you lay the turf on sharp sand or new topsoil?  Have you had any drainage issues if the clay subsoil is still compacted?  
    I dug over the whole plot to a spades depth, levelled and then raked in a layer of topsoil.  I didn't add any sharp sand but on reflection that would have been useful to add some extra drainage. The old lawn did get very damp but I try to stay off it in winter.
  • treehugger80treehugger80 Posts: 1,923
    I would rotavate (adding some grit or sharp sand if you can), then lay top soil over the top of that and not mix it in, and lay turf (or seed next spring) on top of that.
    if its really bad think about putting land drains in, just think about where they drain too otherwise you get flooding
  • paulppaulp Posts: 8
    Could I rotovate 100mm of dry compost into damp clay soil?  I know it's not ideal, but will I get away with it?  Also I was hoping to through seed down on it before the winter kicks in.  I can reseed in spring again if required.
  • Allotment BoyAllotment Boy Posts: 6,774
    It's getting a bit late for seed even if you are a mild area the lack of light will be a factor. Seed is obviously cheaper than turf but it depends on whether you can stand looking at patches of bare soil over winter.
    AB Still learning

  • paulppaulp Posts: 8
    edited November 2018
    Hello again!

    After posting back in October, we ran some experiments with combinations of turf and seed laid on various mixes of sharp sand, soil and compost mixes.   

    Our garden is on a hillside.  The results of turf and seed so far seem OK on the upper slopes and flat sections.  A bit early to say for sure, especially with the seed, but the grass is growing and that's even with some nights of ground frost - we're in Edinburgh.

    The problem we have is with the bottom area, which we call the basin!  Even tho there's a slight run on - it drops 300mm over 24m - it's waterlogged.  The turf strip i laid on 50mm of sharp sand /compost mix is now also water logged.  And the grass seeds haven't come up yet. 

    My test strips are only 1m2 each is this skewing the results i.e. these test areas are surrounded by 300m2 of waterlogged clay and are soaking up the water from it?  Alternatively, do you think 50mm of sharp sand and compost will still be insufficient when the entire area is covered?

    If it is likely to be insufficient,  I've been searching the web e.g. pitch care and flowerpot man.  And these sites seem to suggest that more substantial drainage course and/or root zone is required above the clay.  

    We installed land drains in the summer.  These were installed as interceptor style trenches at the bottom of each slope and cutting across the slopes.   However, the water isn't moving very well,at all in some places, either vertically or horizontally.

    Should I to try to improve the soil I've got by mixing in sharp sand and compost in at a greater depth e.g 150-200mm?

    Or should I build over i.e. cover the whole area with a 50-100mm bed of 10mm pea gravel as a drainage course followed by 100mm of new sandy topsoil?

    Sorry for the long post... but any further thoughts / guidance appreciated?

    Thanks,
    Paul


  • RubytooRubytoo Posts: 1,630
    Sorry it is stating the obvious with clay soil and compaction and a slope if you don't know what you are doing you can make matters worse.
    Sorry.
    Where do the drains drain to?
    Soakaways on clay can be difficult and don't work unless you can get to a lower level where the "soil" is permeable.

    I am not very good art getting my head around explanations. But anywhere you improve the soil on a surface like yours just means the water drains through to the clay layer and takes even longer to soak in or most often, runs off.
    You make a sump or run off area with nowhere for it to go but across the compacted layers, rather than drainage.
    Do you get what I am trying to say?

    I am not sure it helps, sorry if i have confused the issue, feel free to ignore me :) I may have misunderstood your drains.
    Good Luck.
  • RubytooRubytoo Posts: 1,630
    Also if it continues to be an issue look at rain gardens?
    An area within your garden designed to deal with garden water run off with planting to suit and enhance it.
  • paulppaulp Posts: 8
    Thanks for responses...

    French drains are  600mm to 1m deep.  It's twin wall pipes in 20mm gravel all wrapped in white geotextile Terram.  

    The pipes drain into a manhole and then pumped into the main rainwater drain for my house.

    The issue I think is the water isn't reaching the drains, rather than the drains not working.  I''ve got rodding eyes at 20m intervals so we could put a camera in to check.  But if I dig a small hole 50cm away from a  trench and fill it with water it takes days even longer to drain.  Hence I think it's small structure that's the issue?

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