Seed source and provenance: why where the parent tree grew decides how yours will do

Where a tree’s seed was collected, its provenance, decides how well the tree fits the seasons where it is planted. Populations of one species inherit differences in when they leaf out, when they shut down for winter, how fast they grow and how much drought they take. Seed carried too far, in distance or in elevation, falls out of step with the seasons, and frost catches it in spring or fall. Trees tend to grow best in their local climate or one slightly warmer, so seed from somewhat to the south often grows fastest. For most eastern species, current guidelines treat a move of about 200 miles north as safe.

What provenance means for a tree

A species with a wide range is a set of local populations, each shaped over generations by its own winters, summers and soils. The differences among them are inherited, so they travel with the seed. A seedling raised far from its parent keeps the parent’s calendar, which is one reason two oaks of one species can break bud weeks apart.

The evidence comes from provenance trials, also called common gardens. Seed gathered across a species’ range is raised side by side on one or more test sites. A difference that lasts when the trees share one site is inherited, while a difference seen only in the wild may have been the site’s doing. Decades of such trials lie behind the transfer limits below.

How one species differs from place to place

Timing is where a long move most often goes wrong. A tree out of step leafs out too early in spring or fails to go dormant before winter. Trials of eastern trees have found inherited differences in six kinds of trait, and the first two are the timing:

• Spring. The direction differs by species. Sugar maples from northern seed leaf out first, while black walnut from southern seed starts growing three days before walnut from northern seed.
• Fall. In black walnut the end of growth differs more between sources than leaf-out does, and southern seed keeps growing two weeks longer. Sugar maples from northern seed color and drop their leaves first.
• Growth. Seed from south of a site often grows fastest there, as in black cherry, black walnut and eastern white pine. In northern red oak, the offspring of single trees differed more in first-year growth than provenances did.
• Cold. Loblolly pine from northern sources is more cold resistant than loblolly from the south, and black walnut’s cold tolerance rises with the latitude of its source.
• Drought. Loblolly pine from the Lost Pines of Texas is more drought resistant than loblolly from farther east. Sugar maples from dry climates resist drought better than those from cool, moist ones.
• Disease. Loblolly pine from western sources resists fusiform rust better than loblolly from the east.

The damage can show at once, or decades later as poor growth. Most trials were planted near the middle of a species’ range, so the edges are the least tested.

Seed zones, and how far seed can move

The federal seed policy of 1939 asked for seed collected within 100 miles north or south of the planting site and within 1,000 feet of its elevation. Seed zones map the same idea: areas of similar climate, within which seed can move with little risk. In 2014 forest geneticists drew 64 provisional seed zones for the lower 48 states, as a starting point for any plant species. Each zone pairs a band of winter cold 5 degrees Fahrenheit wide, the width of a half zone on the hardiness map, with a class of dryness.

Current guidelines give each major eastern species its own limit, and most run to about 200 miles north of the seed’s source:

Of the trees in the table, we grow black walnut and longleaf pine. The ZIP code to hardiness zone tool gives the half zone for any address, so a half-zone move can be read off the map. A move south has its own cost. Northern black walnut moved two hardiness zones south may get too little winter chill to break bud properly. A range map shows where a species grows, not which of its populations suits your ground.

Moving seed uphill is moving it north

Elevation works on a tree the way latitude does. By an old rule of thumb, spring comes about four days later for every 400 feet of climb, the same as for every degree of latitude north.

Seed from a valley planted on a ridge meets that later spring, and black cherry shows the cost:

“Seedlings from southern sources and lower elevations break dormancy sooner and suffer more severe frost damage than seedlings from northern sources and higher elevations when planted in the North or at higher elevations.” (USDA Forest Service, Silvics of North America, Black Cherry)

Moving seed ahead of a warming climate

Assisted migration is moving seed on purpose from warmer places to cooler ones, ahead of a changing climate. It comes in three scales: within a species’ range, just past its edge, or far beyond it. The case for it is that the climate may be changing faster than trees can adapt in place or spread by seed.

Sources disagree on how far to push it. Julie Etterson and colleagues at the University of Minnesota Duluth planted northern red oak seedlings from the state’s southern and northern seed zones at 16 sites in the north. Over three years the southern seedlings survived better and grew faster. The authors drew a plain conclusion:

“Collectively, these results suggest that state seed sourcing guidelines should be reexamined to permit plantings across seed zones, a form of assisted migration.” (Etterson, Cornett, White and Kavajecz, Assisted migration across fixed seed zones detects adaptation lags in two major North American tree species, 2020)

A summary from the USDA climate hubs is warier. It notes that such moves can clash with the precautionary principle and with established seed transfer zones, though in some cases doing nothing is the greater risk. For our part, we favor species with wide natural tolerance of heat, drought and flooding. We also collect seed from parent trees that have thrived at the warm or dry edge of their range.

Why a grafted cultivar is a different thing

Seed combines the genes of two parents, so each seedling differs from both, and a batch of seedlings keeps the genetic variation that helps a species adapt. Grafting, budding, cuttings and tissue culture copy a plant instead, and the copies are genetically identical to it. Most fruit and nut trees are grafted or budded, often onto seedling rootstocks. Every copy of a grafted cultivar therefore carries the genes of one tree, and the provenance of that tree.

Seed-grown flowering dogwood from wild stands carries far more genetic diversity than the few grafted cultivars in garden centers. That diversity matters against anthracnose and powdery mildew. Seed-grown eastern redbud from northern sources is hardier than the southern-sourced stock common in the trade. Our northern pecan is a northern-adapted strain that ripens its nuts in seasons too short for southern varieties.

What to ask a nursery about seed source

Four questions settle most of it:

1. Where was the seed collected? A state or county is enough for most species. For a mountain species, ask for the elevation too.
2. How far is that from you, and in which direction? Seed from your own area, or from up to about 200 miles south, suits most eastern species.
3. Did it come from one tree or many? A named parent tells you exactly where the seed grew. Seed mixed from many trees and stands carries more of the population’s diversity.
4. Is it seed-grown, or grafted or rooted from cuttings? For a cultivar, ask where the original tree grew.

Blue Whale Trees grows every tree it sells from seed, not grafted, so each seedling is genetically distinct and a planting of ten carries real diversity. When we can, we collect from named individual trees, chosen for size, form, vigor, health and hardiness. Where a line comes from one such tree, we say so: our cherrybark oak comes from one parent tree at the northern edge of the species, chosen in part for its hardiness there.

Our acorns and nuts come from the same parent trees as our saplings and are listed under acorns, nuts and seed. How to store and sow them is the subject of planting acorns, nuts and seed. The heights and zones we give are typical ranges for the species, and local conditions and seed source shift them.

Common questions

Does seed source matter for native trees?

Yes, because populations of one species inherit differences in leaf-out, dormancy, growth and drought tolerance. A tree from far away can fall out of step with your seasons and take frost damage in spring or fall.

How far north can tree seed be moved?

For most eastern hardwoods and pines, current guidelines treat a move of about 200 miles north of the seed’s source as safe. Seed of the southern pines can move about one half hardiness zone colder, for faster growth.

Is local seed always best?

Not always: trees tend to grow best in their local climate or one slightly warmer, and seed from somewhat south often outgrows local seed. At the northern edge of a range, local seed is often the best choice, as it is for black walnut.

Is a grafted tree different from a seed-grown one?

Yes: a grafted cultivar is a copy of one selected tree, so every copy shares that tree’s genes and its limits. A seed-grown tree carries genes from two parents and differs from both, so a planting of seedlings holds diversity that a planting of one cultivar lacks.

Sources

• Black Cherry: USDA Forest Service, Silvics of North America: seedlings from southern and low-elevation seed breaking dormancy sooner and taking more frost damage in the North and higher up, and better growth from southern and low-elevation seed.
• Loblolly Pine: USDA Forest Service, Silvics of North America: differences by seed source in survival, growth, disease, drought and cold, with the Lost Pines more drought resistant than eastern seed, northern sources more cold resistant and western ones more resistant to rust.
• Seed-Transfer Guidelines for Important Tree Species in the Eastern United States: USDA Forest Service, Agriculture Handbook 801 (C.C. Pike and D.L. Haase, editors, 2024): the transfer distances in the table, mismatches in spring and fall, local or slightly warmer climates, trials placed in the middle of ranges, the sugar maple, black walnut, northern red oak and white pine findings, mixed seed lots and the definition of assisted migration.
• Generalized provisional seed zones for native plants: A.D. Bower, J.B. St. Clair and V. Erickson, Ecological Applications 24 (2014): the 64 provisional seed zones, and winter cold in bands of 5 degrees matched to the hardiness map and paired with a class of aridity.
• California Tree Seed Zones: USDA Forest Service and California Division of Forestry (J.M. Buck and others, 1970): the forest seed policy of 1939, with seed from within 100 miles north or south and less than 1,000 feet of elevation.
• Estimating Alabama Bloom Times Using Hopkins’ Bioclimatic Law: Alabama Cooperative Extension System (Lynn Dickinson and Becky Barlow): seasons shifting about four days for each degree of latitude and each 400 feet of altitude.
• Assisted Migration (forests): USDA Northern Forests Climate Hub: the three scales of assisted migration, a climate changing faster than trees can adapt or spread, and the conflict with the precautionary principle and seed transfer zones.
• Assisted migration across fixed seed zones detects adaptation lags in two major North American tree species: J.R. Etterson, M.W. Cornett, M.A. White and L.C. Kavajecz, Ecological Applications 30 (2020): northern red oak from southern Minnesota outsurviving and outgrowing northern seed at 16 northern sites, differences that do not persist in a common garden, and the call to let seed cross zones.
• Extension Gardener Handbook, 13. Propagation: NC State Extension: seed combining two parents’ genes and keeping genetic variation, grafting, budding, cuttings and tissue culture giving identical copies, and grafted fruit and nut trees on seedling rootstocks.
• Life After Wildfire: Texas Parks and Wildlife Department: the replanting of Bastrop State Park from January 2013 with the drought-hardy loblolly pines genetically unique to the region.