Why a small sapling catches up with a big transplanted tree, and often passes it

A big tree dug from a nursery field leaves most of its roots behind and grows slowly until it regrows them. That takes a year or more per inch of trunk in a cold climate, less in a warm one. A small sapling has little root to regrow, so it soon grows at its own pace and often draws level with the big tree or passes it. The trials disagree on how often. A larger tree still pays its way where mowers, deer or vandals would kill a small one, or where a screen is wanted now.

What a big tree leaves in the ground

Tree roots spread well past the branch tips, and the fine roots that take up water lie mostly in the top foot of soil. A root ball is cut about a foot across for each inch of trunk, so it keeps only the roots near the stem. In a model of a nursery tree 4 inches thick, the spade ball held 2 percent of the soil its roots had drawn on:

“Tree spades, commonly used to transplant nursery trees, reduce the root system by up to 98 percent.” (Watson and Himelick, Root Distribution of Nursery Trees and its Relationship to Transplanting Success, 1982)

How long a moved tree takes to root in

A tree is established when its roots have spread into the soil around it and its shoots grow as fast as before. Roots regrow from the ball about 18 inches a year in good soil, as fast on a large tree as on a small one. The time therefore runs by the inch of trunk, and it is shortest where the growing season is long:

A tree kept short of water grows roots more slowly and takes longer still. The watering calculator gives the gallons for each watering by trunk size.

Why the small tree catches up

With roots regrowing at one pace, the tree with less spread to rebuild recovers first:

“The larger tree grows very slowly for many years, while the smaller tree resumes a normal rate after only a few years.” (Gary Watson, Tree Size Affects Root Regeneration And Top Growth After Transplanting, 1985)

In that model a tree moved at 4 inches regains its old root spread in under five years. One moved at 10 inches needs 13 or more, and by then the smaller tree can be the larger. In a trial in Texas and Mississippi, bald cypress and red maple from small containers grew faster for their size in their first season than the same species from large ones. Live oaks from small containers lost far fewer leaves in a drought in their second year than bigger ones.

A seedling has the least to rebuild, and one grown in a pot loses none of its roots to a spade. An acorn or seed sown where the tree is to grow loses none at all. Blue Whale Trees grows every tree it sells from seed, and its saplings ship bare-root or potted while they are dormant.

Species that drive a taproot down early are best planted small. Shagbark hickory has a taproot 2 to 3 feet deep by its third year. Black oak and black gum are hard to move once theirs is down.

When a bigger tree is the better buy

Not every trial agrees. In a red oak trial published in 2000 by Daniel Struve and colleagues, trees moved at 1.4 inches grew 31 inches taller in their first season. Trees moved at 3.3 inches grew 4. Yet the large trees that lived kept their lead through the four-year trial. Seven of the 12 had died, from planting too deep and from roots never pruned while they grew. Root pruning in the nursery and planting at the right depth should improve a big tree’s odds.

Size also buys protection a seedling lacks:

• Mowers and trimmers. A seedling in grass is hard to see and easily cut.
• Deer. Deer browse up to about 5 feet, and a crown above that escapes them.
• Vandals. Larger stock stands up better on public ground.
• A screen now. A big tree gives height and shade the day it is planted.

A small tree needs protection from deer instead, in a tube 4 feet tall or a wire cage. A ring of mulch and the tube also keep the mower away.

Cost per surviving tree

Forest plantings count on half their seedlings dying, and bare-root seedlings still come out the most cost-effective stock. The Forest Service’s 2006 planting guide priced a bare-root tree at 30 cents to $40 and a balled-and-burlapped one at $35 to $400, plus $18 to $50 to plant it. The big tree costs ten to more than a hundred times as much, and it is the one that grows slowest for years. In the red oak trial, each large tree that lived cost the price of 2.4 trees. Our saplings, acorns and seed are the small end of that range.

Common questions

Do small trees grow faster than big trees after planting?

Usually, because a small tree has less root spread to rebuild and resumes normal growth sooner. A tree moved at 4 inches or more can stall for several years.

How long does a transplanted tree take to get established?

About a year per inch of trunk in zone 5, six months in zones 7 and 8, and three to four in Florida. A 3-inch tree in zone 5 needs about three years of watering.

Is a bigger tree worth the extra cost?

It can be, where mowers, deer or vandals would kill a seedling, or where you need height this year. Elsewhere a small tree costs far less per surviving tree and often matches the big one within several years.

Why is my newly planted tree not growing?

It is growing roots first, and a large tree can show little new top growth for years while it rebuilds them. Keep it watered through the establishment period, until its twigs lengthen again.

Sources

• Root Distribution of Nursery Trees and its Relationship to Transplanting Success: G.W. Watson and E.B. Himelick, Journal of Arboriculture 8 (1982): the cut of up to 98 percent by tree spades, the 4-inch tree whose spade ball held 2 percent of its soil, and fine roots crowded near the surface.
• Tree Size Affects Root Regeneration And Top Growth After Transplanting: Gary Watson, Journal of Arboriculture 11 (1985): roots regrowing about 18 inches a year at the same pace on large and small trees, the model of a 4-inch and a 10-inch tree, fine roots in the top foot, trees over 4 inches stalled for years, and big trees planted for their immediate effect.
• Survival and Growth of Transplanted Large- and Small-Caliper Red Oaks: D.K. Struve, L. Burchfield and C. Maupin, Journal of Arboriculture 26 (2000): half-sibling red oaks moved at 1.4 and 3.3 inches, their first-season growth, 7 of 12 large trees dead and why, the survivors’ lead, root pruning, and about a year of establishment per inch in zone 5.
• Differential Environments Influence Initial Transplant Establishment Among Tree Species Produced in Five Container Sizes: L.M. Garcia-Chance, M.A. Arnold, G.C. Denny, S.T. Carver and A.R. King, Arboriculture and Urban Forestry 42 (2016): bald cypress, red maple and chaste tree from five container sizes, faster first-season growth from small containers, and the reasons buyers choose big trees.
• Effect of Tree Size, Root Pruning, and Production Method on Establishment of Quercus virginiana: E.F. Gilman, C. Harchick and M. Paz, Arboriculture and Urban Forestry 36 (2010): smaller live oaks less stressed and less defoliated in a drought 14 months after planting.
• Watering newly planted trees and shrubs: University of Minnesota Extension: a year and a half of establishment per inch of trunk and roots growing about 18 inches a year.
• Chapter 9: Tree Health Care and Pruning: Virginia Tech, Tree Steward Manual: six months of establishment per inch of trunk in zones 7 and 8, slower roots on under-watered trees, and roots beyond the drip line.
• Irrigating Landscape Plants During Establishment: UF/IFAS Extension (Edward F. Gilman, ENH857, 2002): establishment as the return of the old growth rate, faster establishment in warm climates, and 3 to 4 months per inch of trunk in Florida.
• Urban Watershed Forestry Manual Part 3: Urban Tree Planting Guide: USDA Forest Service Northeastern Area and Center for Watershed Protection (Cappiella, Schueler, Tomlinson and Wright, 2006): bare-root seedlings as the most cost-effective stock and the most exposed to mowers, planning for half of seedlings to survive, 2006 prices, the 5-foot browse line, 4-foot tubes, mulch and tubes against mowers, and large stock against deer and vandals.
• Transplanting Trees and Shrubs: Iowa State University Extension and Outreach: root ball widths by trunk size and machinery for balls over 24 inches.