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putting new topsoil onto clay
davect
Posts: 2
Hi there. Fairly new to the garden! Need information on how to turf a fairly large area of garden. Recently had a contractor remove a few tons of stone and rubble at the side of an existing raised lawn(that is well drained and dry) and wanting to extend the lawn. I have unfortunately started the work with no real knowledge of what to do! have had 9 bags of topsoil delivered and laid it over the area in question which was nearly all clay and after all the recent rain the whole area is now like a large container of soil soup. Comments from you all would be very welcome. I am a reasonably fit 70 year old and want to do the work myself.
0
Posts
Where to start- You do not say how big an area you have so it's hard to picture. Unfortunately just putting a thin layer of soil onto compacted clay will not work. Should have got contractor to dig or rotavate, after clearing. you would need a depth of at least 4 inches of the topsoil to stand any chance. Try RHS website rhs.org.uk or Lawnsmith website they have information on all lawn related things including ground preparation.
This could be a bit of a problem. I'm not quite clear about what you mean: is the raised lawn now above the cleared ground? How much depth of ground do you need to add to level it or will there be steps between the old and new lawn? What happened to water landing on the cleared area, did it pool there?
Clay is difficult to drain. The first question to resolve is where you want the water to drain TO. For example, will it run down towards your house? Is there a channel below the new lawn along which it can run off harmlessly? Are you hoping the water will just soak away into the ground as it falls? Is the old lawn well drained because all the water runs onto the part you have just cleared?
If water is running off your lawn onto the cleared area, you may need professional advice about making drainage, it's engineering rather than gardening. If you just want to improve the clay because the garden drains well then you really need to dig your clay, breaking it up, preferably to about 12 or 18 inches. I would want to dig grit into the top 6 inches and then add topsoil. It will be hard work I fear.
You need to improve the drainage. Loads of manure and grit dug into the clay before you add any soil. Adding compost as well will help - it depends just how heavy the clay is. You can't really add too much of those three things.
Mix well into the clay to get a better medium before adding topsoil.
I live in west central Scotland - not where that photo is...
Thanks for the reply! Realise might need pro help, will keep posting info based on replies, thanks again!
I have a site over 6000m2 where the top soil has been removed as part of the development and we are looking to build back up to a lawn from now from a base of London Clay.
Ideally we would like to keep the depth of the new top layer as shallow as possible to avoid removing more clay from the site (the levels are fixed from the approved landscape plan and we will have excess material to remove from site which is expensive).
We have now started a discussion with the ground workers about what level of top soil we should be accounting and planning for.
My research across various websites has indicated that probably 10cm is the minimum top soil I can get away with particularly as we will be looking to seed the grass instead of turf, again to save on costs due to the large areas.
Further research has indicated to me that there may be a benefit in creating a 10cm second layer (above the clay and below the topsoil) with a mixture of clay, horticultural grit and mulch.
Does this sound like a good strategy that balances the aim to have a high quality lawn with an affordable cost considering the large areas. I would be interested in any advice you have on how you would do this and what products you would use/recommend for this situation.
Thanks!
If you can lay the lawns to a fall with a well constructed land drain at the lowest point, you may be OK with just the topsoil laid onto the clay. Soil handling and avoiding compaction is critical on clay soil, this is useful guidance: Construction Code of Practice for the Sustainable Use of Soils on Construction Sites (publishing.service.gov.uk)