Topic: Using Subsoil

[Trenchboy]

The time is now upon me to refurbish the trenches around and across my plot. The problem is that the material coming out of the bottom of the trenches is a mix of sand and light(orange) clay, and a smattering of topsoil that fell in and drowned earlier in the year.

First use is to remake and level the perimeter and central paths on which I lay carpet or whatever else is to hand.

Is it a definite no-no to mix it with topsoil and then try to grow things in?

If anything would grow in a 50/50 mix of subsoil stuff and topsoil, what do you all reckon would do best?

[wardy]

I think it's a no no but if it's all you'e got but if you have a choice I wouldn't do it.  I love soil and I think it would be a shame to spoil it  ;D

[Ed^Chigliak]

Clay is not necessarily a bad thing. It hold moisture and the small particle sizes help make minerals available to the plants. Sand on the other hand opens the soil and increases the drainage. Subsoil is lifeless which isn't so good but mixed with plenty of compost or well rotted manure and spread out over a wide area I imagine it'll be OK. Sow a green manure crop and incorporate that into the soil in spring for futher soil improvement. Do you need to do all the trenches at once or can you spread it over a couple of years.

[jennym]

I have heavy orange clay on my plot, and had exactly the same situation when digging out ditches. What I did was to pile all the clods of clay in one place, near to where I have compost heaps. Then over time, the clay weathers and the top layer breaks down into finer sized pieces. At present, in high summer, I have about 4" fine, crumbly clay on top. At that stage, I incorporate limited amounts into the compost heap. This gives a good usable mixture. As Ed says, it's not all bad. Mosts clays are full of the mineral nutrients the plants need, and hold onto water. I hardly ever need to fertilize, and you should find this too.

[Trenchboy]

Thanks Ed and Jennym

I don't really have a choice about trenching, as the lower half of my plot was under 4" of water in February. One day my son will keep his promise and show me how to post the pictures taken when the flooding was depressing...

Whatever the subsoil is, it isn't what I have always thought of as clay - it crumbles easily when clouted with spade/fork/mattock.

Am going to throw some into the horse manure piles I have dotted around my plot, and use quite a bit of the rest to repair paths and form the (loose)bases of new raised beds.

You must be spot on about it being full of nutrients Jennym, as waterlogging must have leached goodness down into it. It makes sense to try and tease/cajole/wring it back out via compost/manure heaps.

[wardy]

We're using crappy soil for filling divots in the lotty paths.  I mix it with a bit of compost or better soil and it does a good job of levelling off.  Our lotty and path leading to it are all over the place and with having a bad back it's murder when you step into a pot hole or dip  :o

[amphibian]

I have a yellow sandy clay subsoil. We are in a narrow sandstone strip that forms the High Weald. My subsoil crumbles easily when hit, but is almost impossible to get a spade into. A few inches below the subsoil I hit green sandstone bedrock in some places. The bedrock crumbles to sand very easily too, you can turn it to sand by rubbing it hard with your fingers. If my subsoil is left on the surface it turns to rock hard clods which are hard to break even with a hammer.

I have a little subsoil mixed in my beds, I figured a bit of sand wouldn't harm a clayey soil.

[redimp]

I need to increase my soil depth - in places I cannot even sinlge dig, never mind double dig.  I am having to break up some stone and at the same time am bringing up some subsoil.  I am thinking that a little cannot do any harm mixed in with the top soil - it may even add some mineral as that is what comfrey is all about isn't it?

[jennym]

Gardening on clay is a pain - I too have a plot that used to flood. Building up the level of the topsoil takes some time - I've been at it 6 years and am now seeing some really good results. Have incorporated into the soil the following: Horse muck, all kitchen waste, all vegetable waste from allotment, grass cuttings from allotment and back garden, ash from burning lots and lots of wood (this has helped a lot) - I collect offcuts of untreated wood from building works, skips etc, duckweed, algae from ponds and allotment water tank, veg waste from local vegetarian cafes, and I've even asked neighbours for the green waste that they normally put out for the council, but only when I know they haven't got dogs and its mainly grass clippings. I don't always bother composting all of it separately, it's quicker sometimes to just lay it thinly on a spare bit of ground and pile some soil on it. Seems to work just as well.

[Trenchboy]

Jennym

Your scavenging makes you a cult figure to me!

The old boy two plots away from me is a pyromaniac and is forever setting small(and large) fires - and not on his allotment but all over the place. He'd love your ideas re scavenged wood, but I am trying not to encourage him.

I am going to make mounds of earth and subsoil mix out of the trenches I am digging and add manure and compost as and when, but plant things anyway.

Lettuces and overwintering brassicas, for a start. With the depth of water I saw earlier this year root veg wouldn't stand a chance, so it's going to be the top growth veg in the mounds.

I have made raised beds using railway sleepers. Method: dig out topsoil. Dig out another spade depth of subsoil. Fork over the rubbishy rocky stuff left in the bottom. Add more subsoil, the original subsoil, soil conditioners like peat and manure and mix up. Put back topsoil. Beds then 12-15" above main level of the ground.

[jennym]

Me, a cult figure!!! I get it from my ancient mother. When she moved out of her house 12 years ago, we had to remove a stack of bricks about 3 yards by 3 yards by 1 yard high from her back garden. She'd been collecting them in order to build herself a conservatory or lean-to or something on the back of the house, but hadn't quite got round to it yet.
You may have visions of a bespectacled granny in a pick-up truck, touring the skips and building sites, but no.
Mother collected them a few at a time and took them home in her shopping trolley.
But I am not knocking. Mother re-built the chimney breasts in her house all by herself from salvaged bricks.
Enough of my mum.
Youm plans sound good. My raised beds are now mounds in most places, with only sleepers at the back of the plot where it dips down a bit. I had planks for edging my raised beds, but took them away this year when firstly they rotted, and secondly the soil level had built up sufficiently for them to become redundant. But they lasted about 4 years.