The Brew Cabin

I have heard the term 'coring' in draining a lawn. I presume this is my make deep holes into the lawn with an instrucment, and filling the hole with good drainage material like gravel.Is this correct/ And what tools would I need/hire to fo the job? Is it effective?

Also, my soil type is heavy clay. Even though there are no visible signs of standing water, it is pretty squishy to stand on. Would this help, as by land draining it wouldn;t be feasible as there is no access to a drain point, unless I drain the water into the back alley!!!!!!
What options are available?

Coring is just another term for what we call 'sand drains'. These are, as you surmised, tubes of free-draining material that allow surface and ground water escape to a lower, permeable strata. They can be formed using a narrow auger or a corer, which is like a steel tube that is 'screwed' into the ground and then withdrawn carefully, removing the core of earth as it comes. Geologists and Geo-Survey companies have these tools or, if you're a bit handy with the metalwork, they're pretty easy to knock up in a workshop.

However, the core has to reach down to a permeable layer otherwise it is just a hole. If there's nowhere for the water to escape, then the 'hole' will fill up and just sit there, doing nowt and going nowhere. Do you know what lies beneath your clay?

Knowing the structure of the soil beneath your garden can help determine the most effective drainage strategy. I don't know your plot, so I can't say what would be best without further information.

I did the old 'school' test of the soil and the mik bottle. You know the one, fill 1/3 soil 2/3 water and shake. And leave to settle. Well my soil is roughly 50% clay from what I can see. Pretty standard through out the garden.

Also, where can I buy Gypsum to add to my clay, soil beds to break up the clay. My garden centre hasn;t hear of it!!!! Could I buy it from builders yards? B&Q? And how much roughly is it.
As an enginner, yes I would say I am handy in the metal work department. Could you give me a rough idea on how to make a deep corer?? Cheers Dave

(Edited by charlieb at 1:11 pm on Mar. 4, 2003)

The 'Milk Bottle" test for soil analysis is described in a FAQ wot I writted for the uk.rec.gardening newsgroup and is on the u.r.g website, but this only determines the rough composition of the topsoil. For a sand drain to work, you need to know what's down in the sub-soil and beyond, which is best done, as stated before, with a core sampler or a trial pit.

To make your own corer - well, it's probably possible depth of up to 2m, but beyond that, I think you might struggle. My Dad made one that was 3m in length (depth) and we used the JCB to drive it in. He used 100mm dia steel tubing with a top collar to absorb the force of the JCB bucket without deforming the tube itself. It was fine for clays, but nay use at all for anything that could put up a fight.

Most of the geo-tech boys use a percussion mechanism to progressively 'hammer' the professional corers into the earth, and then use a winch to withdraw the yoke once they have reached the required depth. The core tubes are specially manufactured to link together so greater and greater depths can be chased.

In a garden setting, you might be better off digging a trial pit.

Gypsum - it's basically 'plaster', so you can get it at more or less any BM for around 4 quid a bag. Garden Centres give it a pretentious name like 'Claybreaker' and sell it in fancy little boxes, with 2kg costing around 3 quid. Have a read of the FAQ mentioned above - I think you'll find it interesting. :)

I have dug a pit 0.4mx0.4m x0.4m deep and the rain came. The water is still up to the brim of the hole 4 days later. To me that sounds a problem, is this normal? Do I have to go deeper ro penetrate below that. Where I dug the hole, I found I could not go deeper because it was solid. Should I dig somewhere else, at the bottom of the slope perhaps? The soil is so sticky, it clogs to your hands, boots etc. In my borders where I have plants, I plan to mix sharp sand, lime, and spent mushroom compost into the beds. And dig grass clippings into it when the growing season starts. Will this help the beds drain a little better and and make the ground a little less claggy?

A pit? 400x400x400? That's not a pit! That's a nole. My eejit son Tom gets more than that on his spade!! ;)

You need to get down at least 1 metre, preferably more. 400mm is not even deep enough to give protective cover to any pipework.

And why dig at the top of a hill? Water always flows downhill, so, if you're planning on using sand drains and/or a soakaway, you need to be in the lower part of the garden, not on top of a slope!

The sharp/grit sand and mushie compost will be a beneficial addition to the soil, but grass clippings need composting before digging in, or they strip the soil of nutrients to aid their decomposition, rather than releasing nutrients and improving the fertility of the soil. Adding lime might most likely affect the pH of your soil, so, if you're growing owt of an ericaceous bent, such as Rhodies, Azaleas, Camellias, etc, then best to leave it out.