The deepest-rooted native trees: how deep oak, hickory, walnut and pine roots really go

The deepest roots measured on native trees of the East reach past 27 feet in Osage-orange, 20 to 25 feet in black locust, and 10 to 20 feet in bur oak, hackberry and honeylocust. Longleaf pine’s taproot can explore 15.7 feet down, and the hickories, pecan, black walnut, post oak and white oak all start from a strong taproot. The soil decides more than the species: a water table, a hardpan or shallow, rocky soil holds roots near the surface, while deep, sandy or loamy soil lets the same tree go down. Even these trees keep most of their roots shallow and wide, in the top 18 inches. Deep-rooted means a taproot or sinker roots reaching below that layer.

Which eastern natives root deepest

The table ranks the deepest roots measured in each species, with the ground where they were found. Honeylocust and Osage-orange are trees we do not grow.

The same species roots far shallower on tighter ground. A 43-year-old bur oak on North Dakota clay had a taproot just over 8 feet long, half the depth reached in loess. Even the deepest of these keep their side roots high. Most of Osage-orange’s lay in the top foot of that silt loam, and white oak’s main roots stayed within 21 inches of the surface.

How deep pine and spruce roots go

A pine roots as deep as its soil allows. Of the pines and spruces named here, we grow only longleaf pine and red spruce.

The same pine changes shape with the ground under it. On heavy clay, loblolly’s taproot stays stout and short, and over a high water table or a hardpan its side roots spread near the surface. In much of shortleaf pine’s range no taproot forms at all, because the soils are shallow and rocky. Pitch pine bends the rule: where the water table lay less than a foot down, its roots still reached 3 to 5 feet in sand, growing below the water.

Eastern white pine roots wide by nature. It stands on three to five large roots angled outward and downward, with only a vestige of a taproot, and grows sinker roots mostly in deep, coarse soils. White spruce is called shallow-rooted mainly because it grows where the soil limits how deep roots can go.

What becomes of a taproot

Most trees lose their taproot as they grow, since side roots usually hold a grown tree up and oxygen and nutrients thin out deeper in the soil. Which trees keep one is where sources split. An extension page on root myths counts the oaks among the trees that keep one:

“Oaks, hickories, and other nut-producing species are generally deciduous trees that have tap root structures later in life.” (University of Illinois Extension, Clearing misconceptions around tree roots)

The Forest Service’s own account of white oak says that oak loses its taproot:

“White oak seedlings produce a conspicuous, well-developed taproot but this gradually disappears with age and is replaced by a fibrous root system with well-developed, tapered laterals.” (USDA Forest Service, Silvics of North America, White Oak)

Each is right for some oaks. A 65-year-old bur oak dug from deep Nebraska loam still had a taproot 14 feet deep. Chestnut oak goes the way of white oak: its seedling taproot gives way to 6 to 10 main side roots, none deeper than 36 inches. Hickories keep theirs. Shagbark hickory has a deep taproot, a grown mockernut hickory’s reaches about 4 feet, and grown pecan and bitternut hickory keep one too.

Do deep roots help in a drought or a storm?

Day to day, even a deep-rooted tree drinks near the surface, where it keeps most of its absorbing roots in the top 6 to 18 inches. The deep roots pay off in a drought, and only where deep soil holds water below. A walnut on deep, fine-textured soil draws its water mostly from the shallow layers and relies on the deeper ones to survive a drought. Bur oak’s taproot reaches 4.5 feet in its first season, one reason it can pioneer on droughty prairie ground.

Depth is not the only defense. Post oak seedlings proved the most drought-resistant of four Missouri oaks, mainly because the cells of their leaves and roots tolerate drought. On shallow, rocky soil a taproot may never form, so a deep-rooted kind has nothing below to reach.

In wind, the plate of thick roots around the trunk anchors a tree, and that zone matters even in a tree with a deep taproot. Depth adds to it. Shagbark and bitternut hickory, both taprooted, are rated windfirm, and pitch pine, which roots deeply, proved much less prone to windthrow than shallow-rooted Virginia pine. Longleaf pine, the most wind-resistant southern pine, owes that partly to its large taproot. Loblolly pines blow over most on shallow, coarse soils, and a hardpan close to the surface leaves even longleaf less windfirm.

What a deep-rooted tree costs, and how to plant one

The first cost is time above ground. A shagbark hickory seedling’s taproot reached 2.6 feet by age three, while its top grew to 7.8 inches. A bitternut hickory’s taproot goes 1 to 3 feet down in its first year, and at 10 years its top is only about four times as tall as the taproot is deep. Longleaf pine spends 2 to 15 years in a grass stage, a tuft of needles at ground level while the taproot grows. Black walnut grows fast at both ends: its first-year taproot can pass 4 feet, and its height growth generally beats the oaks.

The second cost is that a taprooted tree moves badly once the root is down. White oak is difficult to transplant, and pignut hickory is seldom sold because its taproot makes it hard to move. Shagbark hickory resents transplanting once its taproot is set. Common hackberry, with no strong taproot, moves easily, and bitternut hickory transplants better than any other hickory. Plant the rest young and plant them once, the case made for small saplings over big transplants. Dig for the taproot:

1. Make the hole deep enough for the taproot to hang straight down, and wide enough for the side roots.
2. Never bend, ball or twist the taproot to fit.
3. Set the root collar at the soil line and put the native soil back in.
4. Water every week or two through the first summer, then only in a long drought.

Deep-rooted trees we grow

Blue Whale Trees grows each of these from seed. Choose by the ground you have:

• Black walnut, for deep, fertile soil that drains. Zones 4 to 9, 70 to 100 feet.
• Bur oak, for almost any soil, sand to heavy clay. Zones 3 to 8, 60 to 80 feet.
• Common hackberry, for dry or city ground. Zones 3 to 9, 40 to 60 feet.
• Longleaf pine, for dry, sandy ground. Zones 7 to 10, 60 to 120 feet.
• Mockernut hickory, for deep, fertile ground. Zones 4 to 9, 60 to 80 feet.
• Pecan, for bottomland or any deep soil. Zones 5 to 9, 70 to 100 feet.
• Post oak, for dry ridges, never wet ground. Zones 5 to 9, 35 to 50 feet.
• Shagbark hickory, for any well-drained soil, and patience. Zones 4 to 8, 60 to 90 feet.
• White oak, for clay, loam, sand or rocky ground, never wet. Zones 3 to 9, 50 to 80 feet.

The site check grades any of them at your own distance from the house, starting from a bur oak 40 feet from a wall. For a large tree on dry ground, the tree finder lists the ones we grow.

Common questions

How deep do pine tree roots go?

As deep as the soil lets them: longleaf pine’s taproot has reached 15.7 feet, with 8 to 12 feet usual in grown trees, and loblolly’s goes 5 to 6.5 feet in deep sand or loam. Over a hardpan, a high water table or shallow, rocky soil, the same pines keep their roots near the surface.

How deep are spruce tree roots?

Shallow: red spruce rooted 13 inches deep on average in Maine, and white spruce keeps 85 percent of its root mass in the top foot. Where the soil allows, white spruce can still send taproots and sinker roots to 10 feet.

How deep do palm tree roots go?

Cabbage palmetto, the most northerly native tree palm, stands on a dense mass of roots 4 to 5 feet across and 5 to 6 feet deep, with roots reaching 15 to 20 feet from it. We do not grow palms.

Are deep-rooted trees safer near a house?

Not because of their depth, since most of their roots still spread through the top 18 inches. Give bur oak and white oak 40 feet from a wall, post oak 25 and black walnut 50.