How to Dig a Garden Trench Content from the guide to life, the universe and everything

How to Dig a Garden Trench

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A selection of tools for digging a trench.

A definition of ditch is: a trench made in the earth by digging.

It might just be that the definition of a trench is a ditch made in the earth by digging. But why worry about ditches? We'll go directly to a trench, of the common or garden variety, and, more specifically, how to dig one.

Before Starting

So what is the purpose of your trench? Is it to bury or retrieve an electric cable or a water pipe, or is it for drainage? Perhaps it's just to while away a week or so?

Whatever your trench is for, you should be as sure as you can be that there's nothing under the route that you'll be following that could cause problems. Even trenches down as little as a single spade's depth sometimes find things unexpected and unwanted. You may also find it necessary to remove things such as tree stumps or roots.

Do check the plans and surveys for any gas, electric or telecomms cables or water pipes. You could do a lot worse than borrow or hire a CAT (Cable Avoidance Tool) with instructions, to help you do this. During the work, keep an eye out for changes in the ground such as tiles that may be protecting something, marker tape, disturbed ground or gravel from previous diggings, or even planks that may not be just rubbish.

Are you trenching to bury a water pipe or electric cable? You'll need to refer to local regulations - especially for electrical installations - as to depth and other requirements such as materials, suitable protection and so on.

If it's for drainage then you'll need to work out your preferred fall and depth. The fall is the slope of the bottom that allows water to flow downhill the full length of it to the outflow, for disposal into a soakaway or your property's storm/surface water system - consult an expert if in doubt. A suitable fall would be at least 1 or 2 degrees. If your land is sloped, just follow that slope. However, if your land is flat, you'll need to ensure that you'll be able to dig deep enough at the outflow point.

The depth will depend on two things - how deep it needs to be for it to be out of the way of your normal cultivation and how deep it needs to be at the bottom of the slope (the point of outflow). Hopefully, it won't get too deep for you to manage otherwise you'll have to call for help. See Boning for the traditional method of measuring a fall. Nowadays it would be more appropriate to borrow or hire a laser level (and, of course, the instructions).

You would then, after making suitable arrangements for the outflow, be able to install the drainage - bury gravel covered by geotextile material and, if necessary, land drainage pipe within the gravel.

Your Basic Tool - the Spade

You may need no more than a standard garden spade. In the UK these items have a blade with the shaft suitably bent near the blade top to allow easy digging. The handle is a D or T shape. The blade is more-or-less straight and parallel vertically, slightly curved across (convex at the back and concave at the front), for strength and is usually about 11 ins long and 7 ins wide (280 x 180mm).

Elsewhere in the world the blade may be shaped more like a playing-card spade, having a longer shaft with a thicker end to provide purchase as a handle. Both types have to be robust, of course - but are not all that difficult to break. This tool is pretty well indispensable for gardeners.

Marking Out

Mark all the way along the line of your trench about an inch (25mm) outside at least one side of the actual digging line, using pegs and line or spray-on marker paint.


If all or part of your trench is to be in a lawn you'll need to strip the turf from the appropriate area. You'll probably be best marking lines on either side of the route you're taking, leaving about an inch (25mm) each side wider than your spade. There are powered sod cutters available to make neat, even sods but here we'll describe the manual method.

The cheapest way is to use your garden spade, which is quite satisfactory despite the curve of the blade - just line it up evenly. Otherwise you could obtain a lawn edging tool (edging iron). This is a half-moon shaped blade usually with a turn-over on the top straight edge to accommodate your boot and it has a long straight shaft, with handle.

Note that these are rarely robust, their name suggesting their intended use. They will usually take a moderate amount of wiggling side-to-side (along the blade) for loosening but very little front to back, so get a good one. Use it by lining it up near your marked line, hold it vertically, put your boot on the top of the blade and press down. Withdraw it vertically.

But first, mow your lawn (at least the appropriate part) as short as you reasonably can. The tool can be employed by lining it up with your marked lines and pressing down so that it cuts in to near its full depth, cutting each side so that the width of the sod where the turf will come out, is a little wider than your spade, say 1/2 inch (10-12mm) each side.

Now cut across, between the lines, at one end of the trench, then once again at about 6–8ins (150–200mm) from the end. Make sure those cuts are deep enough around the whole sod that you're preparing and that they extend a little beyond where you'll be removing the turf, to ensure the earth is cut ready for you to take a horizontal slice, keeping an inch (25mm) or so of earth, from the lawn. The lawn will quickly recover from those cuts - but not quite so quickly from scuffs and boot damage, so tread lightly.

The next step assumes you have enough room to work in – treading on your border if necessary. You'll be taking out one small sod at a time, cutting each side and the end for each. You can prepare more than one sod at a time, of course, but the slits can be easy to lose in the grass. You'll be working in a forward direction, cutting sods a little wider than your spade, of an easily manageable length along the trench route.

Holding your spade with the blade horizontal and one edge just outside one of the side lines, the other edge inside, push the spade forward an inch (25mm) or so, then do the same at the line on the other side. Repeat, going further in, first checking that the spade is horizontal, until you just pass the end cut.

Because you sliced slightly larger than the marked sod and your spade, you can slide the spade underneath it and should be able to lift it out cleanly. Repeat with cuts lengthwise and crosswise as you progress.

The sods won't be an even thickness across because of the spade's curve - that much unevenness is quite acceptable. Along the trench will not be so good - ideally it will be evenly thick but will probably be wedge shaped. Don't worry too much, you'll improve, so keep the sods short as suggested because you'll naturally tend to cut deeper as you enter further into the slice, making the job less easy when it comes to replacing it.

Place the sods grass down to store them, either on the lawn or elsewhere, on a tarpaulin if appropriate and well clear of your work area. If you lay sod on sod to save space, then lay them grass-to-grass, soil-to-soil for cleaner, easier picking for replacement. The grass under and within the pile will quite quickly turn yellow due to lack of light, but will last a week perhaps two, stacked like that, and will quickly recover. In hot, dry weather put them in the shade and keep them watered.

At the end of the job you'll need to replace the earth. Level it approximately, tread it, level it, tread it... until it's a suitable depth below the existing grass then replace the sods in reverse order.

The preferred state of finish is a slight dip rather than a hump (far better would be all dead level, of course, but that's... well, that's just a little unlikely). A hump will not be easy to repair, whereas a dip can be filled in, bit-by-bit, week-by-week, by scattering riddled soil (sieved using a metal garden riddle) and using the back of a rake to move the excess around, filling dips. At first, don't make the scattered soil more than about 1/8 inch (3mm) deep, on small areas (about the size your sods were). Lightly rub the back of a rake (or something with a straight edge 8-12ins (200-300mm long) along and across the repair - that will even out the soil and expose blades of grass to the light.

The wounds will heal fairly quickly but the lawn may take some time to recover to a seamless state. You won't have any patches damaged enough to need reseeding, will you?

Shallow Trenching in Moderately Easy Ground

You'll be working backwards, with your back to the yet undug part. If you're on the flat or a slight slope it probably won't matter which way you work but if your slope is noticeable, start at the high end, so that loosened earth will tend to fall back towards your spade rather than rolling down the slope away from you.

Push the spade, vertically, into the ground at the end of your trench, to at least the appropriate depth, as an aid to a clean start. You can start somewhere in the middle of course, but if your trench must be straight you'll need to take extra care to ensure lining up at the join.

As you work, use your spade to cut a short vertical slit (a spade's width or less) along each side of your trench, one side 1/2 inch (12mm) or so inside your line and say quarter to half depth, making the slits slightly wider apart than your spade width. This will reduce the amount of earth loosened by the spade work.

Don't bite off too much at a time, as you would have more earth falling in from the sides, making more work and tiring you more quickly (unless you're also using the work as part of your exercise routine - even so, you'd be better to pace yourself).

The optimum bite will probably be about an inch (25mm), except in more difficult ground where 1/2inch or less will be better - so experiment.

Starting - the First Nibbles, the First Bite And Onwards

Push the spade into the ground at a slant of about 45 degrees, to a depth of an inch or so (25–50mm) to almost meet your cut end then pull the handle back and down so that the blade toe moves up, with the back of the blade resting on the newly cut edge as a fulcrum (too deep, too much force and the shaft is at risk). Lift the clump of earth out and lay it to one side, well clear. You'll have a small V-shaped cut, vertical at your first, end-cut.

Move the spade back just a little, take another, slightly deeper, nibble, then another and another, until you've reached the required depth. Work backwards, by the same method, until you have, say, 8-12ins (200-300mm) of trench bottom, then clean up.

From there, you can continue to completion, working backwards, a full-depth bite at a time, occasionally clearing the bottom. Note here that a comfortable angle for pushing the spade in is probably about 20 degrees or so but that means a noticeable loss of depth. If you need to go to a full spade's depth, ensure the spade blade is vertical as you push it in.

Deeper Trenching

For this work you have three options:

Option 1: Use a trenching tool (or trenching spade, or spit1) Perhaps not so readily available but not difficult to find, this is normally a professional-grade tool. it's rather more robust (but can still be broken by misuse) and usually has a D-shaped handle.

The blade is thicker, narrower, longer, more tightly curved and tapers down relatively sharply. It is usually about 15-16ins (400mm) long, tapering from about 6ins (150mm) at the top down to 4 inches (100mm) at the toe.

Usually, the top of the blade has a 1 x 1 inch (25mm x 25mm) extension, which has two purposes: to give a better purchase for your boot and to make a shallow, slightly wider shoulder on your trench, hopefully reducing the amount of crumbled edge falling in.

The method is the same but the work less easy, so remember to take small bites. In addition, if you can, dig an inch (25mm) or two deeper than you need, as clearing out will then be that much easier - the (tapered) tool being not so tight within the trench.

Option 2: This will take at least four times the work, so be warned. Dig a wider trench first, say three spade widths or so, to allow yourself firm footing while going to depth along the middle. Put the removed ground from the first, wide, trench to one side of your marker line (or barrow it away), leaving the other side for the subsoil you'll be removing from the middle. You will then be able to replace the subsoil first, leaving topsoil uppermost.

Option 3: There is this final option, but there's no challenge in using a powered trencher, is there?

But seriously, digging by hand, anything deeper than you can reasonably manage with a trenching tool really does deserve serious consideration of a powered machine, preferably with an experienced driver as he will know how to cope with the awkward bits.

Meanwhile, you sit back sipping at something interesting in a glass while marvelling at the micro excavator you hired that just fitted through your 2 foot (600mm) opening down the side of the house - or even in through your front entrance and hallway (after the operator double-checked the tracks for cleanliness).

More Difficult Ground - the Mattock (or Grubber)

Used to loosen ground prior to the actual digging, a mattock is not too dissimilar to the pickaxe. This tool comes in more than one weight and more than one style. One, the pick mattock, has a point (pick) on one side of the head and an adze2 blade on the other, 4 inch (100mm) wide, or thereabouts. Another type has an axe type blade (for cutting tree roots) and the adze3 Choose your mattock with some care, it may have some hard work to do. The better ones will have fibre-glass handles, which are lighter and stronger than wood.

The mattock is best used by starting off with your grip similar to that on your golf club but the other hand higher. If you're right-handed then right hand at or near the shaft end. Lifting (with the left hand close to the head) to about shoulder height then letting it fall. Don't force it down, let the tool do the work.

Practise and experiment. If you need to swing it, go steady, as it's tiring work - again, raise it, with a hand near the head, then allow that hand to slide back to your other during the swing. After some practice, you'll be able to use it as a woodsman uses his axe and, with wrist work, get considerable force behind it (but - only if you need to!).

Keep (the point and) edges reasonably sharp using a hand, or a power, file. Sharpen over the edge, not against it, for a smooth stroke or to avoid shredding the abrasive belt. Be especially gentle with the power version until you have its measure, it'd take your fingernails to the second knuckle before you could release the switch.

The Man Tool

So called because, in the days of the navigators digging canals, it was said to be worth an extra man in a team. Why? Well, your tools and boots are heavy enough without great lumps of sticky clay clinging to them - every man had one to scrape off clingy earth.

It's simple, it's wooden and it's home-made. It will need to be suitably shaped to scrape back and front of the spade and the soles of your boots – a sort of elongated H with the legs shaped would do the job. A hard wood such as oak will (of course) last better than a soft wood.

Finally, a Word of Caution.

Unless you've been a particularly good boy or girl all your life, you will come across stones, nests of stones and/or stone farms.

What are stone farms? After years of research, it has been determined, beyond possibile argument, that the palaeolithic inhabitants of your land had techniques for breeding stones and they (the stones, that is) have been quietly growing and multiplying ever since.

What's more, those folk had proven predictive techniques that put Nostradamus to shame. They knew to the century, usually the decade and often to the year, when and where you – yes, you – would be digging a trench through their land. They did not like that idea and made preparations to discourage you (but then they didn't have trenching or man tools, did they?).

Enjoy your trenching.

1The depth of a spade.2Rather like a crossways axe.3A woodworking tool used for smoothing rough-cut wood.

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