What Is Pith in Wood? Where It Is and Why Boards Crack Around It

Pith is the soft, spongy core at the exact center of a tree, the oldest tissue in the trunk, and boards that enclose it are the ones most likely to split as they dry. The pith itself is tiny, so the real culprit is the ring of wood around it. This guide shows how to spot pith, why it cracks, and how to saw, buy or turn around it.

What Is Pith in Wood?

Pith is a small core of soft, thin-walled parenchyma cells at the center of every trunk and branch, the point where the tree began growing. It is usually only a few millimeters across, looks like a dark or off-color dot on the end grain, and has almost no strength. All the later growth is laid down around it in rings.

In botany, “pith” also means the spongy center of a young stem, and in the kitchen it means the white layer under citrus peel. In woodworking it always means the center of the log, and the first several growth rings around it make up juvenile wood, which behaves differently from the mature wood farther out.

The pith is rarely dead center in a real log. Trees that lean or grow on a slope put on wider rings on one side, so the pith drifts off-center. That matters when you saw: an off-center pith can land in the middle of a board even when you aimed to cut around it.

Pith vs Heartwood vs Sapwood

These three are constantly confused because they all sit inside the bark. Working from the center outward, the order is pith, heartwood, sapwood, then the thin cambium layer and bark. For a full breakdown of the last two, see our guide to heartwood versus sapwood. This table is the short version, with pith added.

Feature	Pith	Heartwood	Sapwood
Location	Exact center, a few millimeters	Inner rings around the pith	Outer rings under the bark
Cells	Soft, thin-walled parenchyma	Dead, often filled with extractives	Living, carries water
Strength	Almost none	Highest durability	Lower decay resistance
In a board	Starting point for heart checks	Stable, preferred for furniture	Often lighter in color

How to Find Pith on a Board

Look at the end grain first. Pith shows as a small dot, often darker or slightly hollow, at the exact center of the growth rings. If the rings run in complete circles around a single point inside the piece, the board is boxed heart. If the rings run in arcs or straight lines across the end, the pith is outside the piece or on its edge.

On the face or edge of a board, pith appears as a narrow dark line running the length of the piece. Do not confuse it with pith flecks, which are small tan or brown streaks in the grain of species such as maple, birch and cherry. Pith flecks are scars left in the living tree and cosmetic only, while a true pith line is the center of the log.

Sawing pattern	Where the pith is	Crack risk
Boxed heart	Fully enclosed in the middle of the piece	Highest: rings form a full circle around the pith
Split heart	On or near one edge or face	High: pith exposed on the surface, checks run from it
Free of heart center (FOHC)	Sawn out of the piece	Low: no ring circle around the center
Quartersawn	Outside the board	Lowest: rings run nearly straight across the face

Why Pith Cracks (and Why the Common Explanation Is Incomplete)

The usual explanation is that the pith is weak, so it splits. That is only half true. The pith is the place cracks start, but the stress comes from the rings around it. Wood shrinks far more along the growth rings (tangentially) than across them (radially), so each ring tries to get shorter while the radius shrinks much less. A complete ring cannot shorten without opening a gap, so the wood splits along a radius. That radial split is called a heart check.

Here are the shrinkage figures from green to oven-dry for five common species, taken from the table in the USDA Wood Handbook, with the tangential-to-radial ratio worked out from them:

Species	Radial shrinkage	Tangential shrinkage	Tangential / radial
Northern red oak	4.0%	8.6%	2.2
White oak	5.6%	10.5%	1.9
Sugar maple	4.8%	9.9%	2.1
Black cherry	3.7%	7.1%	1.9
Black walnut	5.5%	7.8%	1.4

Worked example (our arithmetic, not a measurement): take a 6-inch boxed-heart red oak post, so the outer ring sits 3 inches from the pith. At full oven-dry shrinkage the radius drops 4.0% to 2.88 inches, and a circle that size needs a circumference of about 18.1 inches. The ring itself shrinks 8.6%, from 18.85 inches to about 17.2 inches. That leaves roughly 0.87 inch of material that has nowhere to go, which is why it opens as cracks. Real boards stop drying at equilibrium moisture, so actual cracks are narrower, but the geometry is the same, and it explains why a dry-looking post can still check across its width.

Species with a high tangential-to-radial ratio, like oak and maple, are the ones most prone to heart checks. Source: USDA Forest Products Laboratory, Wood Handbook, Chapter 4

Juvenile wood adds a second problem. Unlike mature wood, which barely changes length as it dries, the juvenile core can shrink noticeably along the grain. That uneven pull between the center and the outer wood adds to twisting and splitting in boards cut near the pith. You can estimate your own piece with our wood shrinkage calculator.

Three Pith Myths Worth Dropping

• Myth: pith and heartwood are the same thing. They are not. Pith is a core a few millimeters wide, and heartwood is the wide band of mature wood around it.
• Myth: pith always makes wood crack. Cracking needs a full ring circle plus fast drying. A quartersawn board or a piece with the pith sawn out has no such circle, and big boxed-heart timbers are used in buildings, where heart checks are expected and treated as cosmetic.
• Myth: sealing the ends stops pith cracks. Sealing slows moisture loss through the ends, which helps, but it cannot change the shrinkage geometry. A sealed boxed-heart piece dried quickly can still split.

How to Saw, Buy or Season Around Pith

The most reliable fix is to keep the pith out of the finished piece. When you are buying lumber, look at both ends of each board and skip anything with a full ring circle if the part needs to stay flat. When you are milling a log, you have more options.

• Saw the pith into a waste slab. Take a thick center cut so the pith falls into the offcut, then cut your usable boards from either side. This gives you free-of-heart-center stock.
• Quartersaw if the log allows it. Boards cut radially have rings running nearly straight across, so they cup less and have no ring circle at the center. See what quartersawn oak is for how that cut looks.
• Split instead of sawing. Green logs split along the rays and straight through the pith. Spoon and bowl carvers split a log in half through the pith and cut the pith wedge away before it can check.
• Cut a relief kerf in large timbers. Timber framers saw a single groove along one face of a boxed-heart post toward the pith, which gives the wood a planned place to open instead of a random one.

If the piece must stay boxed heart, slow the drying down. Seal the ends right after cutting, stack the wood out of sun and wind, and give it time. Our guide to drying logs without cracking covers the full routine.

How to seal pith-bearing ends

1. Cut the end fresh, because sealer sticks best to damp, newly cut wood.
2. Brush a generous coat over the whole end grain, including the pith and the first few rings.
3. Let it dry, then add a second coat if the wood is a dense, fast-checking species such as oak.
4. Stack the piece off the ground in shade with airflow, and recoat any end you trim later.

Working With Pith in Turning, Carving and Furniture

Woodturners rough-turn green bowl blanks with the pith centered at the base of the blank, then cut the pith away as the foot is shaped, so the finished wall has no center in it. Turners also leave the pith out of hollow forms by coring, since the pith plus drying stress is the usual cause of a bowl cracking from the bottom.

For furniture and posts, ask for FOHC or quartersawn stock on parts that must stay straight. Square posts are a common trouble spot, because a boxed-heart 4×4 has the pith dead center. Our guide on keeping 4×4 posts from warping goes deeper on that case. For slabs, the center of a wide cut often contains the pith, which is why it is usually the first part to crack; preventing slab cracks covers what to do about it.

Frequently Asked Questions About Pith in Wood

What does pith mean in lumber?

In lumber, pith is the small soft core of the tree that can show up as a dark line or dot in a board. Boards that enclose it are called boxed heart. Lumber graded free of heart center (FOHC) has the pith sawn out or left in the waste.

What is the difference between pith and heartwood?

Pith is the tiny soft core at the exact center of the trunk, often only a few millimeters wide. Heartwood is the mature inner wood that surrounds it, made of dead cells and often darker. Heartwood is usually the strongest and most durable part of the tree, while pith is not.

What is the pith side of a board?

The pith side is the face of a board that was closer to the center of the tree. On a flatsawn board it is the face where the growth rings curve away from the bark. Boards tend to cup toward the bark side, so the pith side usually ends up the convex face.

Are the cells near the pith smaller?

In softwoods, the cells near the pith are generally shorter and have thinner walls than the cells that form farther out. This early wood is called juvenile wood. Cell size and length increase over the first years of growth before levelling off.

Does all wood crack at the pith?

No. Wood cracks at the pith when the growth rings fully enclose it and the piece dries too fast. A board sawn so the pith is outside the piece, or a quartersawn board, has no ring circle around the center, so it has far less reason to split there.

Should you remove the pith when sawing lumber?

Yes, when stability matters. Saw so the pith falls into a waste slab, or rip it out of the board. Furniture parts, spindles and bowl blanks are all safer without it. Large timbers are an exception, because boxed-heart beams are widely used and simply develop heart checks.

The Short Version

Pith is the tiny soft core at the center of a tree, and the problem is the rings around it, not the pith itself. Check the end grain, avoid full ring circles where stability matters, saw or split the center out when you can, and seal and slow-dry anything that must stay boxed heart.