# Why acorns fall early, green or small: the early-summer drop, drought, weevils and this year's crop

> Why oaks drop green acorns before fall, how weevils, drought and squirrels each leave their own sign, what that says about the crop, and what is worth sowing.

Published 2026-10-11. Tags: Oaks, How trees work. By Blue Whale Trees, a native tree nursery in the United States. Web version: https://bluewhaletrees.com/articles/why-acorns-fall-early/

An oak starts far more acorns than it can ripen, so some fall green every summer. An early fall has four usual causes, and the fallen acorn shows which. Tiny acorns in late June and early July are the tree's own thinning, and undersized ones in a dry summer point to drought. A round hole or a grub inside means weevils, and a leafy twig tip cut on a slant means a squirrel. The full-sized acorns still on the branches in September are the year's crop.

![A hand holding a white oak twig with one green acorn in its cap among rounded-lobed leaves](https://bluewhaletrees.com/img/articles/why-acorns-fall-early-1-1000.jpg?v=09f00e43 "A white oak acorn still green in its cap on September 28, 2022. A white oak acorn is ripe once its shell turns light brown, so one this green in late September has not got there yet.")
*Photo: Blue Whale Trees*

## The early-summer drop

Most of an oak's would-be acorns fall before midsummer, a drop researchers call premature abscission. Forest Service researchers in central Missouri followed the flowers of [white oak](https://bluewhaletrees.com/plants/white-oak/index.html.md) and [black oak](https://bluewhaletrees.com/plants/black-oak/index.html.md) from 1990 to 1997:

> "About 7% of the white oak flowers matured into acorns: most flowers aborted by early July just after fertilization." (Cecich and Sullivan, *Influence of weather at time of pollination on acorn production of Quercus alba and Quercus velutina*, 1999)

About 12 percent of the black oak flowers became acorns, and some black oaks almost never ripened one. In an earlier Missouri study, poor years brought a heavy fall of young acorns in late June and early July, the weeks when fertilization takes place.

Weather around flowering makes that drop heavier or lighter. Heat and hail during pollination cut the Missouri crops, and a freeze after the flowers open kills them outright, as one did to many of Kentucky's oaks in the spring of 2007.

## Drought: acorns that stop filling

In a severe drought, acorns stop short of full size and fall early. An eight-year study of white oak, [northern red oak](https://bluewhaletrees.com/plants/northern-red-oak/index.html.md) and black oak in east-central Missouri found smaller crops in drier summers in all three. For the tree itself, the case to watch is a dry summer after a spring freeze. Several stresses in one year can weaken an oak until ordinary insects and diseases kill it.

## Weevils: the hole and the grub

Acorn weevils did about two thirds of the damage to acorns in a Tennessee seedling orchard of northern red oak. In midsummer the female, a brown beetle with a long, thin snout, chews a small hole in a developing acorn on the tree. She lays her eggs in it and plugs the hole, and the grubs feed inside until fall.

Infested acorns can drop early. In parts of one Wisconsin county, a large share of the northern red oak acorns fell early, and most of them held weevils:

> "Even though the acorns looked perfect when they dropped, the insects had already been at work on them." (Wisconsin Department of Natural Resources, *Acorn weevils*)

![An acorn split lengthwise on a leaf, its pale kernel hollowed out and packed with brown crumbly droppings](https://bluewhaletrees.com/img/articles/why-acorns-fall-early-2-1000.jpg?v=6e46761a "A holm oak acorn cut open on December 5, 2014, after the weevil grub inside had fed and left. Acorns full of weevil grubs can look whole when they fall.")
*Photo: jacilluch, [CC BY-SA 2.0](https://creativecommons.org/licenses/by-sa/2.0) ([source](https://commons.wikimedia.org/wiki/File%3AInterior_de_una_bellota_(21969372925).jpg))*

Once the acorn is down, the grown grub chews a round hole about an eighth of an inch wide, in the side or at the edge of the cap. It then burrows into the soil for the winter. In the Tennessee orchard, acorns that fell in September were weeviled more often than those that fell in October and November. Weevils and the larvae of two moths ruin many white oak acorns, in some years half the crop, and light crops suffer most.

## Squirrels, and oaks that drop early anyway

Some green acorns on the lawn were cut, not dropped. Gray squirrels [nip off twig tips](https://bluewhaletrees.com/articles/why-trees-drop-twigs/index.html.md) with green leaves and acorns on them, mostly in late summer and early fall, with a clean cut on a slant that matches their teeth.

[Chestnut oak](https://bluewhaletrees.com/plants/chestnut-oak/index.html.md) drops early by nature, shedding its ripe acorns from early September to early October, 2 to 5 weeks ahead of other upland oaks.

## This year's crop, and which acorns to sow

A heavy early-summer drop is common and follows the weather at flowering. Weevil grubs eat the acorn, not the tree, and squirrel cuts do little real damage. To judge this year's crop, count the acorns in the crown with binoculars in late summer or early fall, before insects and wildlife thin them. Why one fall is heavy and the next nearly empty is the subject of [mast years](https://bluewhaletrees.com/articles/mast-years/index.html.md).

A white oak acorn is ripe enough to sprout once its shell turns from green to light brown, about 120 days after pollination. Green acorns that fall early have not reached that point, and the earliest fallers are the most often weeviled, so wait for the main fall. Sort what you gather with a [float test](https://bluewhaletrees.com/articles/glossary/index.html.md) the same day. In the Tennessee orchard, floating overstated the damage by 36 percent against cutting the acorns open, so cut a few floaters before you throw out a small crop.

Blue Whale Trees offers [acorns](https://bluewhaletrees.com/shop/acorns-and-seed/index.html.md) from the same parent trees as its saplings, and [planting acorns, nuts and seed](https://bluewhaletrees.com/articles/planting-acorns-nuts-and-seed/index.html.md) covers storing and sowing. The [seed sowing planner](https://bluewhaletrees.com/tools/sowing/#species=northern-red-oak&method=fall) opens on northern red oak and gives the dates to sow your own oak's acorns this fall or to chill them for spring. If an oak drops its acorns early year after year, or a fallen acorn fits none of these signs, write through the [support page](https://bluewhaletrees.com/support/index.html.md#contact). A close-up of the acorn and a photo of the whole tree help.

## Common questions

### Why are my acorns falling in July?

Acorns that fall in July are young ones the oak sheds around fertilization, in late June and early July. Weevil grubs and drought add to the drop from late summer on.

### Do oak trees drop acorns every year?

Not in equal amounts: most oaks bear a good crop only every two to five years, and white oak every four to ten. [Dwarf chinquapin oak](https://bluewhaletrees.com/plants/dwarf-chinquapin-oak/index.html.md) and [willow oak](https://bluewhaletrees.com/plants/willow-oak/index.html.md) bear every year or nearly so.

### Why does my oak tree have no acorns?

A spring freeze may have killed the flowers, or the tree may be young, since open-grown white oaks bear from about 20 years and forest trees seldom before 50. Some oaks are poor bearers every year, and a red oak's empty fall can follow a bad spring a year earlier.

### Why are the acorns so small this year?

On a red oak, the small acorns on this year's twigs are next year's crop, and they reach full size only in their second summer. Small acorns that fall in a dry summer are drought's work.

## Sources

- [Influence of weather at time of pollination on acorn production of Quercus alba and Quercus velutina](https://research.fs.usda.gov/treesearch/12201): USDA Forest Service, Treesearch (R.A. Cecich and N.H. Sullivan, Northern Research Station, Canadian Journal of Forest Research 29, 1999): white and black oak flowers followed in central Missouri from 1990 to 1997, about 7 percent of white oak flowers and 12 percent of black oak flowers maturing into acorns, most abortion over by early July, black oaks that never or rarely ripened an acorn, heat and hail at pollination cutting the crop, and the quotation.
- [Ecology of mast-fruiting in three species of North American deciduous oaks](https://sorklab.eeb.ucla.edu/wp-content/uploads/sites/6/2018/01/1993Sorketal-Ecol.pdf): V.L. Sork, J. Bramble and O. Sexton, Ecology 74 (1993), the copy kept by the Sork lab at UCLA: eight years of white, northern red and black oak crops in east-central Missouri, a heavy fall of young acorns in late June and early July in poor years at the time of fertilization, and smaller crops after drier summers in all three.
- [Spring Freeze, Summer Drought and Our Woodlands' Future](https://kywoodlandsmagazine.ca.uky.edu/sites/kywoodlandsmagazine.ca.uky.edu/files/spring_freeze_p_1-3.pdf): University of Kentucky, Kentucky Woodlands Magazine (Jeff Stringer, 2007): the spring freeze that killed the flowers of many oaks, red oak acorns developing in their second summer, acorns that do not fully develop and fall early in severe drought, and oaks weakened by several stresses in one year.
- [White Oak](https://research.fs.usda.gov/silvics/white-oak): USDA Forest Service, Silvics of North America, with the chapters on chestnut oak and northern red oak: high rates of flower abscission tied to the weather at pollination, white oak acorns maturing about 120 days after pollination, the change from green to light brown at maturity, consistently poor and good bearers, bearing ages and crop intervals, and chestnut oak dropping 2 to 5 weeks before other upland oaks.
- [Acorn weevils](https://forestrynews.blogs.govdelivery.com/2017/10/27/acorn-weevils/): Wisconsin Department of Natural Resources, Forestry News (Linda Williams, 2017): weeviled northern red oak acorns dropping early in Oconto County while looking whole, the egg hole chewed and plugged, the exit hole at the edge of the cap, winter in the soil, and the quotation.
- [There are small, round holes in many of the acorns on the ground. What made the holes?](https://yardandgarden.extension.iastate.edu/faq/there-are-small-round-holes-many-acorns-ground-what-made-holes): Iowa State University Extension and Outreach, Yard and Garden (Richard Jauron, 2024): the adult acorn weevil as a brown beetle with a long, thin snout, eggs laid in developing acorns in midsummer, grubs feeding until fall, and the eighth-inch exit hole chewed after the acorn falls.
- [Acorn fall and weeviling in a northern red oak seedling orchard](https://research.fs.usda.gov/treesearch/9453): USDA Forest Service, Treesearch (D.R. Miller and S.E. Schlarbaum, Journal of Entomological Science 40, 2005): weevils as about two thirds of the damage in an eastern Tennessee orchard, more weeviling on trees with smaller crops, September fallers weeviled more often than later ones, and floating overestimating the damage by 36 percent against dissection.
- [Managing Hardwood Stands for Acorn Production](https://extension.msstate.edu/publications/managing-hardwood-stands-for-acorn-production): Mississippi State University Extension (Brady Self, Publication 2904, 2024): red oak acorns taking two growing seasons, the small acorns on a red oak's new growth as next year's crop, good crops every three or four years, and counting a tree's acorns with binoculars in late summer to early fall, before insects and wildlife thin them.
- [Tips on Oak Tips](https://bygl.osu.edu/node/1882): Ohio State University Extension, BYGL (Joe Boggs, 2021): gray squirrels nipping twig tips with green leaves and acorns, mostly in late summer and early fall, with a clean cut at the slant of their teeth, and little real damage to the tree.