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Dig fence post holes in clay

Updated: October 2026

You have a short run of garden fence or a gate, the posts are in the shed, and the soil is the heavy clay much of lowland Britain actually gives you. The question is how deep, how wide, and which tool starts the hole. For a typical garden fence around 1.8 m, fencing publishers use about 600 mm of depth and a hole clearly wider than the post. Clay does not change that depth so much as the tool: start with a narrow blade or a bar, and lift with a clamshell only after the ground is loose. The tools are on the [hole spade comparison](/hub/digging-tools/hole-spade). These figures are publisher rules of thumb, not a by-law. If the boundary or a buried service is unclear, you stop first. Peter F. compared the listings and public UK sources in October 2026. There was no lab test. A qualifying purchase can earn a commission at no extra cost to you.

You have a short run of garden fence or a gate, the posts are in the shed, and the soil is the heavy clay much of lowland Britain actually gives you. The question is how deep, how wide, and which tool starts the hole.

Our top picks

Spear & Jackson Spear & Jackson 2154HK draining shovel

Best overall

Spear & Jackson Spear & Jackson 2154HK draining shovel
9.4/10about £16.20
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Roughneck Roughneck drainage and post hole shovel

Rank 2

Roughneck Roughneck drainage and post hole shovel
9.4/10about £21.54
View offer
Roughneck Roughneck ROU68250 post hole digger

Rank 3

Roughneck Roughneck ROU68250 post hole digger
9.4/10about £39.99
View offer
On this page
  1. 1.Depth and width, as published rules of thumb
  2. 2.Clay and stones
  3. 3.A short run versus a long one
  4. 4.What goes in the bottom of the hole

Depth and width, as published rules of thumb

Jacksons Fencing treats about 600 mm as the usual hole depth. One worked example is a post about 1.83 m above ground, a hole about 230 mm wide and 600 mm deep for a narrower post, plus about three times the post width as a width pattern. DIY Doctor uses one third of the above-ground height: a 100 mm post with 1.8 m above ground, a hole about 300 mm by 600 mm, on a chart tied to their premix. Path and Patio repeat one third and about 600 mm for a typical 1.8 m fence. The three do not agree on width, and none of them is a statute. Read them as a band. A slim intermediate might sit nearer 230 mm across if the post and the fill both fit. A 100 mm post on that DIY Doctor chart is drawn nearer 300 mm. Three times the post width is a check, not a trench. Conservation-handbook practice says not to make a hole you can stand in. Their note of about 400 mm is for a straining post, which is a different job from a slim garden intermediate. None of the 600 mm figures replaces a services check. Plans, a locator, and in Great Britain the electricity-network line 105 come before the string line. The motion of the tools is on the how to use a post hole digger page.

Clay and stones

Dry or stony clay wrecks the plan of just using the post-hole digger. The clamshell lifts. In handbook practice it does not make the hole, except in soft soil, sand or peat. PHD-WH reviewers say it is poor at cutting unbroken ground. Roughneck 68-250 reviewers still want a bar or a drainage shovel for rocks and hard clay, then use the 5.2 kg clamshell for holes about 40–90 cm deep. The OLLIDOT sample includes bending or breaking on early holes. That is a weak lifter, not every clamshell. Start with a narrow blade. UK reviews of the Roughneck drainage shovel and the Spear & Jackson 2154HK both describe fence-post holes in clay. The Roughneck is the lighter fibreglass shovel, with treads, and reviewers mention holes about 600 mm deep. The 2154HK is the forged drainer, with a stated 711 mm handle and no foot tread in the spec. A bar takes the stone the blade will not shift. The clamshell comes third, once the hole is deeper than the spade cleans easily. Keep to the publisher band for your post. If the Neilsen is your lifter, do not rotate it on a stone. Reviews say it twists if you do. The pair, in the abstract, is on the drain spade versus post-hole digger page.
Spear & Jackson Spear & Jackson 2154HK draining shovel

Testsieger

Spear & Jackson Spear & Jackson 2154HK draining shovel
9.4/10about £16.20
View offer

A short run versus a long one

A short run in clay you can loosen is a weekend with hand tools. A gate and six panels is still one narrow blade, a bar if the ground is mean, and a clamshell if the holes will pass about 600 mm. A long run in compacted ground or rubble is when an auger hire makes sense. Hire for that compacted run, rather than a third day levering a clamshell. An auger is not a hole spade, and it still will not find a cable. Locate services first. Stop when you do not know where the services are, when the boundary or the fence height may need advice this page will not invent, when water appears that you cannot explain, or when the blade or the clamshell starts to bend. A failure on hole one means change the method, not finish the line with a bent hinge. A 1.8 m fence at about 600 mm is a rule of thumb you can explain to a neighbour. It is not a guarantee if the hole is a bowl, the concrete holds water against the timber, or the post is the wrong length for the leaf it carries.

What goes in the bottom of the hole

Fencing guidance puts gravel or ballast under a timber post so water can leave the end grain. Concrete or a post-fixing mix then holds the post, and the top of that fill should slope so rain sheds off. Follow the bag for ratios. This page does not invent a mix. A concrete post still sits in a hole you opened with the blade first.

Common questions

How deep is a normal garden fence post hole?
Jacksons, DIY Doctor and Path and Patio cluster around 600 mm for a fence about 1.8 m above ground, or about one third of that height. Jacksons’ example near 1.83 m uses 600 mm. A shorter stake needs less, and a gate or straining post may need the more generous reading. It is not a legal minimum on this page, and clay does not automatically add depth. Follow the post maker if their figure is deeper.
How wide should it be?
Wide enough for the post and the fill, and no wider. Jacksons describe about 230 mm for a narrower post and also about three times the post width. DIY Doctor’s chart, tied to their premix, shows about 300 mm for a 100 mm post with 1.8 m above ground. A hole you can stand in is too wide for a slim intermediate. About 400 mm in the fencing handbook belongs to a straining post, not to every panel.
Which tool starts the hole in clay?
A narrow drain or grafting spade, or a bar, starts it. Reviewers use the Roughneck drainage shovel and the Spear & Jackson 2154HK for fence posts in clay. The clamshell lifts after the soil is broken. Starting with the jaws in dry clay is how lighter diggers bend and how heavier ones get used as crowbars.
Do I still need a post-hole digger?
For a hole around 600 mm, yes if you want to lift spoil once the spade cannot clean the bottom. PHD-WH reviews talk about 600–900 mm once the ground is loose, and the Roughneck clamshell about 40–90 cm. You can skip the clamshell on a shallow slot the blade still empties. In soft soil, sand or peat the lifter can do more of the hole. That is the handbook exception, not the clay case.
What goes in the bottom of the hole?
Fencing guidance puts gravel or ballast under a timber post so water can leave the end grain. Concrete or a post-fixing mix then holds the post, and the top of that fill should slope so rain sheds off. Follow the bag for ratios. This page does not invent a mix. A concrete post still sits in a hole you opened with the blade first.
When is a manual kit the wrong plan?
When the run is long and the ground is compacted, rubble-filled or already too hard for the blade and bar, hire an auger or get help. Also stop if services, the boundary or planning are unclear. A bent tool on the first hole means change the method. Six ordinary panels in clay you can loosen remain a hand job.
Does clay change the 600 mm figure?
Not by itself. The publisher figures follow the fence height and the post, not how sticky the spoil is. Clay changes which tool starts the hole and how hard the lift feels. Very wet ground, a slope or a taller fence can change the depth, and then the fence specification leads. Do not shorten the hole because the clay is heavy. That saves an hour and leaves the panel under-set.

Related pages

Best drain spade UK

Hole spade

Drain spade buying guide: blade, clamshell or neither

How to use a post hole digger: cut first, then lift

Drain spade vs post hole digger: which cuts, which lifts

Sources

Public UK sources from the research digest. Prices, stars and review counts are the amazon.co.uk listing lines used in this comparison. We did not run a lab test.

  1. HSE — excavation and underground services (retrieved October 2026)
  2. HSE HSG47 — avoiding danger from underground services (retrieved October 2026)
  3. HSE CIS65 — excavating near underground services (retrieved October 2026)
  4. Energy Networks Association — Think before you dig (retrieved October 2026)
  5. BSI BS 3388:2004 — forks, shovels and spades (retrieved October 2026)
  6. Conservation Handbooks — hole digging for a post and wire fence (retrieved October 2026)
  7. Jacksons Fencing — how deep to dig fence posts (retrieved October 2026)
  8. Consumer Rights Act 2015 (retrieved October 2026)