Round, sawn or split stakes – which to choose (sapwood and durability)

Ferdinand Terlinden

1 day ago

6 min read

Robinia series · Expert article

In this article, a stake is what is driven into the ground; a post is what carries a load. Choosing a robinia stake (Robinia pseudoacacia – also known as black locust, and often sold as acacia) is not just about the price on the label. In small sections, the way a stake is made can change its service life tenfold. The key comes down to one word: sapwood. A one-line reminder – only the core of the wood (the heartwood) is rot-resistant; the sapwood rots (see the guide “Robinia outdoors – the complete guide”).

Cross-section of 6-8 cm round robinia stakes showing the pale ring of sapwood around a small dark heartwood core — Cross-section of 6-8 cm round stakes: the pale ring is the sapwood (not durable); only the small dark core, the heartwood, resists rot.

The trap of the small-diameter round stake

A round stake 6-8 cm in diameter necessarily comes from a young tree. And a young tree is mostly young (still juvenile) wood of low resistance, surrounded by a thin ring of sapwood – the pale, non-durable part – that runs all the way round. The result: in a small round stake, the proportion of truly durable wood, mature heartwood, is tiny. Its service life in the ground suffers accordingly: in the order of only 3 to 10 years, far from the ~30 years you expect from a good robinia stake.

A sawn stake beats a small round one – and a 5×5 square stake does better still

First, a point that explains everything: the thickness of the sapwood is not fixed; it follows the tree’s growth rate. On a young, fast-grown robinia, the sapwood ring reaches 1.5 to 2 cm; on mature, slow-grown wood, it shrinks to half a centimetre. So two effects combine against the small stake: it comes from exactly the kind of tree where the sapwood is thickest, and it is also the stake in which that sapwood takes up the largest share of the cross-section. On a 7 cm round stake ringed with 1.5 cm of sapwood, two thirds of the cross-section is not durable – and what little heartwood remains is still juvenile wood. On a mature 30 cm post, the same sapwood is no more than a thin skin around a wide heartwood, and sanding removes it.

Beware of a common misconception: sawing stakes does not get rid of the sapwood. A sawn stake therefore keeps some of it, on one or two faces. Its advantage over a small round stake lies elsewhere, and it is twofold: the sapwood does not go all the way round – on a round stake, it wraps the whole stake – and, above all, the sawn stake comes from a mature log, whereas a 6-8 cm round stake is a young tree through and through. For the same cross-section, a sawn stake therefore holds up better than a round one of the same diameter – without being “sapwood removed” for all that.

In small sections, the right choice is the 5×5 square stake: sawn from mature, dense wood, it contains far more heartwood than a small round stake of the same size. Some customers come back to us with photos of 6-8 cm round stakes that rotted after 3 to 5 years – we encourage them to switch to the 5×5 square stake, even if the round shape still has its fans.

Scale diagram comparing a 7 cm robinia log with a mature 22 cm log, sapwood thickness and share of heartwood in a round stake and a sawn stake

Both logs are drawn to the same scale: the 7 cm round stake is the whole log of a young tree, whereas the 7 × 7 cm sawn stake comes from a mature 22 cm log. On the round stake, the sapwood goes all the way round and reaches 1.5 to 2 cm; on the mature log, it is only half a centimetre, and the sawn stake keeps some of it on one face only.

What about the price?

This is where it becomes counter-intuitive – the opposite of the received wisdom inherited from sweet chestnut:

The split stake is the most expensive: robinia, being very hard, splits poorly – the wedge of the log splitter follows the fibres and the loss of material is high. Allow about 50 % more than a sawn stake.
The round stake (simply debarked) is simple and economical to produce.
The sawn stake remains affordable: the saw kerf loses a little material, but this section is produced in very large volumes, at a keen price.

But up to a section of ~8 cm, a sawn stake is more durable than a round stake of the same section. It costs a little more, but lasts much longer: measured against its service life, it is often the most economical choice.

Our choice in small sections: the 5×5 square stake

For a small stake that is truly durable, we favour the 5×5 cm square stake, cut from old, dense wood. Cut from the core of mature wood, it contains almost nothing but rot-resistant heartwood – whereas a small round stake remains ringed with sapwood all the way round. This 5×5 section is also produced in very large volumes: it is commonly what vine stakes are cut from (two diagonal saw cuts give triangular vine stakes). High volumes, low prices – excellent value for money.

When a round stake is still the right choice

The round stake is not to be ruled out – quite the contrary, once you move up in diameter. A large round stake (from ~12-14 cm) comes from a fairly old tree: its heartwood core dominates, and the sapwood is no more than a thin skin. For corner, straining and vineyard end posts, the large round stake remains ideal and economical. The problem really only concerns small 6-8 cm round stakes.

Frequently asked questions

Why did my round stake rot within a few years?

Almost always because of the sapwood. On a small round stake cut from a young tree, the sapwood (the pale ring) makes up a large share of the wood – and it is not durable. A small stake may consist of nothing but sapwood and juvenile wood, with an insignificant heartwood core: in that case, it rots completely within a few years.

How do I recognise sapwood?

It is the pale zone just under the bark. The heartwood, in the centre, is darker (golden brown). The thicker the pale ring compared with the core, the shorter the stake’s life.

Round or sawn for my vineyard?

It depends on the training system. On a wire trellis: sawn line posts, round end posts – in thin sections a sawn stake lasts longer than a small round one, and at the end of the row, where the load is greatest, the large round stake is ideal. In a vineyard trained on individual vine stakes, a sawn stake is enough: at 1.8 m long and 15-20 cm in circumference, it supports the bunches of a Syrah vine, which twines around the stake. Full details in our article “Robinia vine stakes – trellising, vine stakes and end posts”.

Is a split stake durable?

Yes, if it is taken from heartwood – but the decisive variable is where the wood comes from: hard, dense robinia from dense forests with controlled growth will make a durable stake whatever the cut; softer wood that grew too fast will disappoint even when properly split. On price, however, it is not the economical option: because robinia splits poorly, a split stake costs about 50 % more than a sawn one.

My stake is cracking: is it serious?

Almost never. These surface cracks – surface checks (shrinkage checks) – are the normal behaviour of a very dense wood as it dries: the surface shrinks faster than the core and opens up. A check does not go right through the piece, stops developing once the wood has stabilised and takes nothing away from durability – the heartwood it exposes is just as rot-resistant as the rest. Only a through-split that makes the piece move needs replacing. To limit checking on posts, the sawmill offers end-grain wax and anti-split plates.