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Mast years: why oaks, hickories and beech bear a huge crop one fall and almost none the next

By Blue Whale Trees · Published Sep 24, 2026 · 7 min read

Why oaks, hickories and beech crop heavily in some years, how red and white oaks keep separate calendars, what mast does to wildlife, and when to collect seed.

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What a mast year looks like Why trees bear in booms and busts Red oaks and white oaks keep different calendars What a mast year does to deer, squirrels and mice How long a seed-grown oak or hickory takes to bear Collecting seed in a mast year Common questions Sources

A mast year is a fall when the oaks, hickories or beeches of a region bear a heavy crop together, after years of little or none. Most oaks have one every three or four years. The leading explanation is predator satiation: lean years keep the seed eaters few, and a flood of seed then outruns them. Weather and pollen help decide which year it falls in. Red oaks take two summers to ripen an acorn, so their mast years keep a calendar of their own. For anyone growing oaks from seed, a mast year is the year to gather acorns: more of them are sound, and more trees contribute.

White oak acorns and their empty caps lying thick on bare soil among fallen oak leaves — White oak acorns on the ground in Duke Forest, Durham, North Carolina, on November 15, 2011. White oak bears a good crop only every 4 to 10 years. Photo: Dcrjsr, CC BY 3.0 (source)

What a mast year looks like

Mast is the seed crop a woodland feeds on, and masting is the habit of bearing it in pulses. The pattern is an abundant crop one year followed by a year or more of moderate or low ones. White oak yields in Illinois have ranged from about 3 to about 1,450 pounds of acorns per acre.

What turns one good tree into a mast year is synchrony. Seed crops can keep in step across populations more than 600 miles apart, and sometimes across species. Within a stand, white oaks tend to bear together while red oaks vary far more from tree to tree.

Individual trees keep their habits. Some trees bear good crops again and again while others stay poor, and genetics is likely the main reason. Even in a big year, only about 30 percent of large, healthy white oaks are heavy bearers. The table gives each tree’s earliest bearing age and its usual gap between good crops.

Tree	Group	Starts bearing, years	Good crop every, years
White oak	White	20	4–10
Swamp chestnut oak	White	20	3–5
Overcup oak	White	25	3–4
Dwarf chinquapin oak	White	3–5	1
Northern red oak	Red	25	2–5
Cherrybark oak	Red	25	1–2
Shagbark hickory	Hickory	About 40	1–3
American beech	Beech	About 50 for heavy crops	2–8

All eight are ours; white oak and northern red oak are the common natives.

Why trees bear in booms and busts

Four explanations lead, and they can work together.

Starving the seed eaters

Predator satiation has two halves: lean years starve the seed eaters down, and the next big crop is more than the survivors can eat. Pooling 48 studies of 60 plant species in 2022, Rafał Zwolak and colleagues found both halves at work, each strengthening the other, with one sharp limit:

“Masting satiated invertebrate but not vertebrate seed predators.” (Zwolak, Celebias and Bogdziewicz, Global patterns in the predator satiation effect of masting: A meta-analysis, 2022)

Only 13 of the studies measured vertebrate seed eaters, so that result rests on less data. The same analysis found the effect on invertebrates weakening from 1972 to 2018, probably because a warming climate has changed masting. Predator satiation is well supported, though it is not the whole story.

Pollen on the wind

Oaks are pollinated by wind. The pollination efficiency hypothesis holds that wind pollination works better when the trees flower heavily in the same year. Work in Missouri found that most of an oak’s potential crop is lost when female flowers abort between pollination and fertilization. The hypothesis is among those still being weighed.

Stored reserves

The resource budget model says a tree bears heavily only once its stored reserves pass a threshold, and that its need for pollen from neighbors keeps the trees in step. The model is widely invoked but largely untested, with experimental support so far in one perennial herb.

Weather that sets the year

Weather cuts crops short through late spring freezes, humid weather during pollination and summer drought. Weather may also be the signal that tells trees which year to bear. Valentin Journé and colleagues analyzed 746 populations of 331 species in 2025 and found temperature the main cue. In temperate and boreal species, the season most often tied to a big crop was the summer before. That weather can cut a crop is settled. Whether trees evolved to read it as a shared signal is still an open question.

Red oaks and white oaks keep different calendars

A white oak ripens its acorns the same year it flowers. A red oak takes two growing seasons, so its twigs carry two crops at once. Small acorns sit on the new growth and ripening ones on last year’s, the small ones being next fall’s crop. A look at the twigs in summer shows a red oak’s next crop a year early.

Two green acorns in scaly brown caps on a red oak twig, with oak leaves blurred behind them — Red oak acorns still green in Ann M. Banchoff Park, Ewing Township, New Jersey, on August 30, 2023. A red oak acorn takes two growing seasons to ripen. Photo: Famartin, CC BY-SA 4.0 (source)

The acorns a red oak drops in a given fall were set the year before, so a freeze that kills this spring’s flowers cannot touch them:

“For this reason, sometimes red oak species have good acorn crops when white oak acorns are nonexistent due to a late freeze earlier in the year.” (Mississippi State University Extension, Managing Hardwood Stands for Acorn Production)

The red oak pays a year later, when the flowers it lost become the acorns it does not drop. In Missouri, good crops came every two years in black oak, three in white oak and four in northern red oak. Why oaks with one-year and two-year acorns live side by side is a puzzle Daniel Janzen raised in 1971, and it is still unresolved.

For a planter, the lesson is to plant both groups, as red oaks and white oaks sets out. An even split between them is a safeguard against a fall with no acorns at all.

What a mast year does to deer, squirrels and mice

For some of the animals that eat mast, a boom or bust shows up a year later:

Deer and turkeys. Oak, hickory and beech mast are among the important foods of both. A planting plan for deer and wild turkey gives the years each tree takes to bear.
Black bears. Mast crops can affect black bear reproduction the following year. In New England, bears raid farm crops most often in poor acorn and hickory nut years.
Squirrels and chipmunks. In a poor year, birds, mammals and insects can eat most of a shagbark’s crop. Squirrels and chipmunks are also its main carriers, far ahead of birds.
Mice and ticks. In 13 years of records from Dutchess County, New York, white-footed mice and eastern chipmunks tracked the acorn crop of the year before. Nymphal blacklegged ticks tracked the rodents a year after that.

The nymph is the tick stage behind most cases of Lyme disease, so a big acorn year raises the risk two years later. Swings of more than threefold in the deer indices made no difference to nymph numbers in that record.

How long a seed-grown oak or hickory takes to bear

Oaks in natural settings take 25 to 30 years to bear consistently. The earliest bearing age is 20 years for swamp chestnut oak and 25 for overcup oak and cherrybark oak. Shagbark hickory begins at about 40 years and bears best from 60 to 200.

Size and light matter too. Most oaks bear best from about 20 inches in trunk diameter. Peak crops come at 19 to 22 inches for red oaks and 24 to 30 for white oaks. Both favor a crown in full sun, clear of crowding neighbors. The growth estimator shows how thick a trunk each of our species should have at 20 or 50 years on a given site.

For acorns within a few years, plant a shrub oak: dwarf chinquapin oak bears within three to five years and crops every year rather than in booms and busts.

Collecting seed in a mast year

Collect in a mast year if you can, for two reasons. The first is soundness. Insects are the seed eaters a big crop satiates, and in light crop years a large share of acorns carry insect larvae. Acorn weevils, filbertworms and acorn moths are the main ones, and they do not spread to other acorns in storage.

Acorn in a scaly cap with a round exit hole, and a pale weevil larva lying beside it on a wooden table — An acorn weevil larva beside the acorn it left through a round hole, in Spain, on October 25, 2021. In light crop years a large share of acorns carry such larvae. Photo: Alfonex, CC BY-SA 4.0 (source)

The second is parentage. When a restoration on Santa Rosa Island, California, gathered its oak acorns in a poor year, the trees it raised for planting carried less genetic diversity. The suggested remedy is a longer collecting window, timed to the return of big crops.

Float the acorns on the day they are gathered, because sound acorns sink and the floaters are unsound. After dry weather some good acorns float until they have soaked overnight. After rain some bad ones sink until they have dried a few hours. Storing, chilling and sowing come next, in planting acorns, nuts and seed, and the seed sowing planner gives the dates to chill and sow each species.

At Blue Whale Trees we sell acorns and nuts collected from the same parent trees as our saplings, under acorns, nuts and seed.

Common questions

What is a mast year?

A mast year is a fall when many oaks, hickories or beeches across a region bear a heavy crop at once, after one or more lean years. Most oaks have one every three or four years.

Why are there so many acorns this year?

The oaks around you are in a mast year, bearing heavily together, usually after lean years that kept the acorn eaters few. A red oak’s acorns come from the previous year’s flowers, so its big year can differ from a white oak’s.

Are acorns from a mast year better for planting?

Usually, because acorn insects take a smaller share of a heavy crop and more trees contribute, which widens the seedlings’ genetic base. Float them either way, since sound acorns sink and unsound ones float.

Does a big acorn year mean more ticks?

In a 13-year New York study, yes, two years later: mice and chipmunks multiplied the year after a big crop, and nymphal blacklegged ticks rose the year after that. Deer numbers made no difference.

Tool

Sow it on the right dates

Pick a species and your ZIP code, and get the dates to sow outdoors this fall or to chill the seed for spring.

Open the sowing planner

Seasonal notes by email

Shipping windows, newly priced plants and new articles. Four to six emails a year, and nothing else.

Sources

Quercus L., oak: USDA Forest Service, Woody Plant Seed Manual, Agriculture Handbook 727 (F.T. Bonner, 2008): white oak acorns ripening the year they flower and red oak acorns the second year, good crops one year in three or four, the Missouri crop intervals of Sork and colleagues, freezes, humidity and drought cutting crops, flowers lost before fertilization, Illinois yields, the earliest bearing ages of five oaks and the crop intervals of four, insects in light crop years, and flotation.
Managing Hardwood Stands for Acorn Production: Mississippi State University Extension (Brady Self, Publication 2904, 2024): wind pollination in oaks, white oaks bearing in step and red oaks less so, heavy bearers at about 30 percent of large white oaks, two crops on a red oak’s twigs, red crops surviving a freeze that takes the white, 25 to 30 years to steady bearing, peak crops near 20 inches in diameter, crowns in full sun, and an even split of the two groups.
6.1 Mast, Good Forestry in the Granite State: University of New Hampshire Cooperative Extension: masting as an abundant crop followed by moderate or low years, genetics and consistently good or poor trees, full sun, red oak crop intervals and the peak diameters of red and white oaks, oak, hickory and beech mast as food for deer and turkeys, and beech bearing heavily from about 50 years at 2- to 8-year intervals.
Carya ovata, Fire Effects Information System: USDA Forest Service: shagbark hickory bearing from about 40 years and best from 60 to 200, good crops every 1 to 3 years, seed eaters taking most of a poor crop, squirrels and chipmunks as the main dispersers, and black bears after good and poor mast years.
Small Tree, Big Impact: Why the Dwarf Chinquapin Oak Deserves a Place in Your Landscape: University of Maryland Extension: dwarf chinquapin oak bearing within three to five years and cropping every year.
A brief history of masting research: W.D. Koenig, Philosophical Transactions of the Royal Society B 376 (2021): synchrony across more than 1,000 kilometers, the resource budget model and its limited testing, the standing of predator satiation and pollination efficiency, weather as veto and as possible cue, and Janzen’s unresolved puzzle of oaks with one-year and two-year acorns.
Global patterns in the predator satiation effect of masting: A meta-analysis: R. Zwolak, P. Celebias and M. Bogdziewicz, Proceedings of the National Academy of Sciences 119 (2022): 48 studies of 60 plant species, starvation and satiation reinforcing each other, invertebrate seed eaters satiated and vertebrates not, the weakening effect from 1972 to 2018, and the pollination efficiency hypothesis.
Weather drivers of reproductive variability in perennial plants and their implications for climate change risks: V. Journé and colleagues, Nature Communications 16 (2025): 746 populations of 331 species, temperature as the main cue, and the previous summer as the season most often tied to a big crop in temperate and boreal species.
Understanding mast seeding for conservation and land management: I.S. Pearse, A.P. Wion, A.D. Gonzalez and M.B. Pesendorfer, Philosophical Transactions of the Royal Society B 376 (2021): the Santa Rosa Island restoration that lost genetic diversity by gathering acorns in a poor year, and a longer collecting window timed to big crops.
Climate, Deer, Rodents, and Acorns as Determinants of Variation in Lyme-Disease Risk: R.S. Ostfeld, C.D. Canham, K. Oggenfuss, R.J. Winchcombe and F. Keesing, PLoS Biology 4 (2006): 13 years of records from Dutchess County, New York, mice and chipmunks tracking the prior year’s acorns and nymphal ticks tracking the rodents, the nymph as the stage behind most Lyme disease cases, and deer indices without predictive power.