Soil Improvement For New Beds Previously Under Concrete.

Hello,



thanks for the link. I cannot find the name of the other plants in the border pic.

Also i'd like to ask, did you use a weed membrane there? Also how long did it take for the plants to reach that height?

 

Also Peter S, you mentioned at you used sharp sand to break up the clay. Most of the concrete I've dug out has a thin layer of sand underneath. Would it be safe to mix this into the clay or should I skim it off?

I would but I'm finding it difficult to persuade other half to pee into a jar for me. :th_scifD36:

 

What's the jar for? When I "activate" my compost heap I just wait til nobody's looking and let it all out.

 

We now live in the 21st century, you could at least stretch to a bucket :D

 

Jungle Jane

There are two main types of sand. Sharp sand, which is very angular and rough on the fingers. Its often used in concreting. This is the sort of sand to use, because it is so sharp the sand grains don't fit well together and its this lack of fit that makes for good drainage. I add this to my borders, and also mix it with compost for sowing seeds or potting up plants to help drainage.

The other type is soft sand, often called builders sand because it is used to make mortar for bricklaying. This is the sort of sand you find on the beach at the seaside. where the action of the waves has knocked all the sharp edges off and consequently its rounded and soft to the touch. Its often a more golden colour too. Next time you are at a garden cente or builders merchant, compare the two - you will soon see the difference. This soft sand is no good for the garden. Because the particles are rounded they fit well together and doen't allow for good drainage. I suspect your sand layer might be this.

Whilst I understand the debate, if it was my garden I would add all the sawdust to the soil as well - I hate waste. You would need to dig it in well so that it didn't just sit as one lump. It may take some nitrogen away in the short term, but I would regard it as an investment, you gain more in the long run. When I was doing my front garden I added in loads of stuff that was hardly composted at all. I mentioned this to one of the RHS gardeners as Harlow Carr a couple of miles from me and they agreed it was the right thing to do.

Garden learner

I am quoting from the thread I mentioned :-

This picture, taken today, shows two 'good plants'. They are the red Centranthus and the pink mound of hardy geranium 'Patricia'. I got the name Patricia from Bob Brown's site. It has been voted the best Geranium along with 'Rozanne' another superb one in blue by an American specialist geranium forum and both will flower from now until September or even October. The blue one at the front is Campanula poscharskyana, another very long flowering plant. At the back, in the middle, is a catmint Nepeta transcaucasica 'Blue Infinity' also very long flowering. The joy of this one is that it doesn't flop like most catmints. You can just see some white campanula perscifolia and Allium 'Mt Everest'.

The picture was taken in the second year. You can't really use weed supressant fabric on a border. There are just too many plants. And you can't stop all weeds, but by having plants close they run into each other and give the weeds below little chance to grow.

 

I had a dig about today and found that the sand is indeed builders sand. But there's are also a large amount of grit mixed in with it. The grit measures on average roughly 5mm. Would this help with the drainage at all?

Also found that the clay soil is black. Ive never come across this before. Should I be worried?

 

JJ - I suspect that builders (soft) sand won't really do any harm, it just won't do as much good as sharp sand. The advantage of clay is that it has a lot of nutrients in it. But clay particles are about 1/1000 of the size of sand particles, and the downside is that this tiny particle size makes it more difficult for air to get at the roots and for water to drain. Even the addition of soft sand will probably help as its still increasing the average particle size - its just that sharp sand would have been even better. Any grit will help.

I really don't know about black clay. I suspect that it has particles of something else in it as well. I found the following paragraph on this site, which is worth reading. http://www.vegetable-gardening-gnomes.com/clay_soil.html

Clay soil comes in black, red, brown, grey or yellow, depending on the type of minerals that they contain. What they all have in common is particle size. That’s what makes them clay.

 

I think its black because it hasn't had any air. The clay under an old tennis court we removed was vile - sounds similar to what you describe.

 

Update.

Ive tried almost everything to try and dig this soil over but I just can't get through the sub soil, its so dense. Ive tried pick axes, trench spades nothing will dig through it.

Just come across this gypsum clay breaker stuff and was wondering if anyone could tell me if this stuff would help make the soil sub a little easier to work with.

I'm not expecting perfect soil over night, just something I can get my fork into.

 

I think on average I can get down to about a third of a spades depth. I seem to already have the crunchy top layer problem already. Not really sure what to do with all this horrible dry top soil either tbh.

 

Are you sure its just clay subsoil, and not the remains of a hardcore foundation for the concrete floor you removed?

 

Nope I dug all that up and it seems to be hard to break through in areas that didn't have on concrete on them too, just lots of foot traffic.

What I mean is the soil is very dense. I can't push my spade or trench spade through it. I think adding water to it seems to soften it up a bit, but its still a struggle. Is this normal for clay? I moved into a new area recently and before was used to sandy clay.

Heres a picture of a hold I managed to dig out after giving it a good soaking with the watering can.