Tag: bastard trenching

Cottage Garden Project Update: July 2016

With the weather holding reasonably dry at long last, I was (finally!) able to make a start on some rough measuring out and actual digging in our new back garden.

Having lifted and disposed of the old crazy paving patio we’d revealed an expanse of builders’ sand, and I was eager to get a spade in and see what state the soil was in underneath. The answer, based on an initial test-hole, was: what soil?

July 2016 Test Hole
Not looking promising so far: sand, sand and more sand…

Well, I reasoned to myself, maybe that’s because it’s the area near to the solid concrete base that the old garage was build on. Undeterred, I began excavations for our fig pit. This will house the Brown Turkey that we’ve ordered from Grow at Brogdale (along with three apples and a morello cherry) in what is the sunniest spot of the garden for the longest part of the day, and the tree will hopefully be trained espalier-style up and along the outside of the shed in years to come.

A fig pit – roughly two-feet deep, lined with concrete slabs (and old roof tiles by the time I’m done) and part-filled with rounded stones (to aid drainage without damaging the roots) – will restrain the roots of the fig, encourage fruiting and prevent the tree from becoming far too large for the space. The finished result looks okay, despite my stacking the far end and left-hand side slabs a bit wonky (but who’ll ever know once it’s back-filled, eh?)

July 2016 Fig Pit
Restricted root growth and a sunny aspect – ideal for figs.

The next section I decided to tackle was the top end of the planting bed that’s planned to extend out from the corner of the shed towards the house. Again, I was hoping to find soil under a top layer of sand and again I was disappointed. A couple of inches of builders’ sand, then between four and six of compacted silt (caused by years of run-off from the back of the house, I reckon), then more builders’ sand, down to a depth of about twelve inches or so. Then it’s hard-panned, compacted silt and clay all the way down, as far as I can tell. I found a few small traces of actual soil in and around the masses of tree roots from next door’s Prunus, but otherwise: nothing worth the name. Joy.

July 2016 - Soil Horizons
Barely a scrap of organic matter in sight…

This poses a number of problems, the main one being – as I learned on the RHS Level 2 course earlier this year – that although sand is good for drainage (until the water hits a solid sub-surface pan and starts backing up, of course), that’s about all you can say for it. It’s inert, so doesn’t hold on to mineral ions, and for that reason is pretty much infertile. And of course, excellent drainage means drastically reduced water holding capacity, which isn’t great either. There’s really not much you can do with it, except add an awful lot of organic matter in an attempt to bring both the nutrient levels and useful water levels back up again, so that’s what we’re going to have to do.

I’ve started the process with a spot of ‘bastard trenching’. This is a technique for recycling turf that I learned about at Ordsall Hall, during the RHS course. It involves digging a trench, putting the soil aside, then taking the top layer of turf from the next section to be dug and laying it upside-down in the bottom of the previous section of trench, before back-filling with the soil below. Repeat until you’ve dug over the entire target area, using the soil from the first section to fill in the last.

My version is a variation on the above: I started by digging out the rough shape of the planting area, piling the sand up to the side, picking out tree roots and stones (rounded ones into the fig pit, sharp ones set aside for a sump that I’ll be digging at the far end of the shed). Then I used the fork to break up the hard-pan underneath, to about a spit-depth, in an effort to sort out those potential drainage issues and give whatever we plant a fighting chance of getting its roots down deep enough to do some good:

July 2016 shed-side planting area
Hard going – double digging through compacted clay/slit is tough work.

Then I started slicing off the turf from the grassy patch (I can’t in all conscience call it a lawn) and inverting it into the dug area, and back-filling on top. I was hoping for a bit of decent soil underneath the turf, but close to the shed there’s not much at all; it’s pretty much sand all the way. (Although I did dig a 6′ trench where I’ll be siting a trellis over by the boundary fence furthest from the shed, and it seems there’s a decent amount of soil in that section – where the neighbours’ apple tree and Fuchsia have been contributing leaves over the years – so that’s a lot more promising.)

July 2016 - bastard trenching in action
Turf off, inverted and buried, giving a much-needed organic matter boost to poor soil.

Generally though, bastard trenching is a process I’m going to have to repeat for pretty much the whole garden. Except for the path sections, which I can just de-turf, coat with a layer of sand and level off before putting down weed membrane and gravel. It’s going to be a long, hard slog, and we’re going to have to invest in a lot of compost and composted bark to help the process along, but it will be worth it in the end.

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