- Author: Help Desk Team
Note: This was originally published in the Contra Costa Times.
Q: I know that acorns are the seeds of oak trees, but how do I plant them?
A: Oaks are an important part of the California landscape. If you are lucky enough to have oak trees on your property, or access to others' oak trees, you can collect the acorns and plant them. There are some simple things you can do to ensure a good start for your oaks.
Selecting the Site:
First of all, only plant a given oak species in areas where it naturally occurs or has grown in the past, and only use acorns from oaks growing in the same general environment as the planting site. Even within a species, there are genetic adaptations to different soils and climates. Use acorns from trees that grow as close to the planting site as possible.
Collecting Acorns:
Collect acorns in the early fall, when they are just starting to turn from green to brown and the first ones fall to the ground. Acorns collected from trees are generally healthier and more likely to germinate than those that have fallen to the ground. Pick them from the tree, twist off the caps (they should come off easily) and immediately put the acorns in the refrigerator to slow their metabolic activity.
If you collect them from the ground, discard any that are broken, cracked, very small, or lightweight, and soak them for a day in water, discarding any that float. Then dry them off and put them in plastic bags in the refrigerator.
Storing Acorns:
Although they can be planted right away, acorns that have been stored in the refrigerator for one month have higher germination rates than those planted right after collecting. Check them for mold, and if any mold develops, rinse it off, dry the acorns, and put them back in the refrigerator in plastic bags. Leaving part of the bag open at the end helps to reduce mold growth. If you see white tips emerging from the pointed end of the acorns during storage, it's best to plant them right away. That's the start of the root system emerging, and it can turn dark and mushy if left in storage.
Planting Your Acorns:
The best time to plant the acorns is from November after the first rain to early March. However, earlier is better to give them more time to grow before hot weather arrives.
Plant them in full sun. Keep the eventual height and canopy size of the tree in mind when you choose a location. Loose, well- drained soil is best, and the area should be fairly free of weeds.
Plant the acorns one half to one inch below the soil surface. Dig a hole several inches deep then partially backfill it. Place the acorns on their sides in the holes and cover with soil. If they've already started to germinate, plant them root down, being careful not to break the root tip. If you have a lot of nearby pocket gopher or ground squirrel activity, you can give the acorns a better chance by planting them two inches deep, but don't go any deeper than that or the acorns will rot.
You can also start the acorns in containers and plant the seedlings later. For information about this method, see the UC web page, How to Grow California Oaks (https://oaks.cnr.berkeley.edu/how-to-grow-california-oaks/).
Caring for Your Trees:
Weeds, especially grasses, will out-compete oak seedlings for sun, water and nutrients, so keep a two-to-three-foot radius around each seedling clear of weeds. Remove weeds by hand or with a hoe. Mulch suppresses weed growth and helps conserve soil moisture. Bark chips, straw, compost, or paper can be used.
Oaks develop vigorous and large root systems—that's how they survive drought. If the rains are very light, one or two deep supplemental waterings in late winter and early spring can help the seedlings survive through their first summer.
Acorns and oak seedlings are an important food source for rabbits, insects, mice and other animals. A variety of protective devices can be used to prevent their damage.
With some encouragement and protection, your seedlings will be well on their way to becoming oak trees. You may not live to see them mature, but future generations will enjoy these magnificent trees.
Help Desk of the UC Master Gardeners of Contra Costa County (EM)
- Author: Michael I Jones
From an entomologist's perspective, 2023 couldn't have been a more interesting year for oak pests!
But, what causes the wounds that introduce the bacteria to the acorns? Well, it can be many different things, including physical damage or things that feed on acorns. Perhaps the coolest of the things that eat acorns are the insects that rely on the acorn for their food and reproduction, acorn weevils (filbert weevil) and filbertworms.
The timing of these acorn drops makes it seem like the oaks are "using" fire to help control the pests of the seeds. Well, they are... in a sense. Oaks have co-existed with fire (both from lightning and Native Californians using fire as a tool) for thousands of years so holding on to healthy acorns until after fire season is one more fire-adapted strategy exhibited by the oaks.
While I was following acorn pests throughout the year, in early December I started to receive questions about coast live oak with leaf discoloration and loss in Sonoma County.
- Author: Denise Godbout-Avant
(From old proverb)
I love to stroll under the shade of majestic Valley oak trees in the oak woodland riparian habitat along the Stanislaus River at Caswell State Park in Ripon. I visualize Lakisamni Yokut women (the indigenous people who lived in Stanislaus County area for millennia) as they gathered acorns.
Vital Roles
Early humans built their homes, created tools, built shelters and ships from oak wood. Oak galls were used to make dyes, writing ink, and tan leather. Today we use its strong wood to construct furniture, flooring, cabinets, and wine barrels. If you like truffles, thank oak trees, since truffles have a close relation with the roots of oak trees. Truffles are almost impossible to grow. Instead, truffle farmers plant oak trees, hoping to create favorable conditions conducive to the growth of truffles.
California Oaks
- Valley oak (Quercus lobata) – One of California's iconic species, it is the largest oak tree found here, living up to 300 years. The Valley oak grows where there is a water table within reach of the roots, often near creeks and rivers. They grow quickly, reaching 20 feet in 5 years and up to 60 feet in 20 years. A deciduous tree, it's distinguished by deeply lobed shiny green leaves and long, narrow acorns.
- Interior live oak (Quercus wislizenii) – An evergreen tree, growing up to 25-80 feet tall, it is found in hilly or mountainous areas, near creeks and streams, living up to 200 years. It can produce two types of leaves at the same time, one with a serrated edge and the other with a smooth edge, and produces small, thin acorns.
- Blue oak (Quercus douglasii) – A deciduous tree found in the hot, dry foothills, it grows to be 20-60 feet tall with blue-green leaves which vary in size and shape. With a lifespan of 200-500 years, their acorns are fat and stubby.
Oaks tolerate fire due to their thick, furrowed bark and tough leathery leaves. During wildfires, the larger oaks in areas cleared of fuel may scorch, but rarely burn completely. Damaged trees will resprout from the root crown.
Acorns
An oak tree can produce millions of acorns during its lifetime, but only one in 10,000 acorns grows up to be an oak tree. Acorns are highly nutritious, carbohydrate-rich, and were a diet staple of the Californian indigenous people. Mammals and birds who eat acorns include the Acorn woodpecker, Yellow-billed magpie, California ground squirrel, and Mule deer. However, acorns are toxic to dogs and horses.
The indigenous people called the California scrub jay the “gardener bird” because of its propensity for caching thousands of acorns and not eating all of them, which helped replenish and expand oak forests.
Oak Galls
A favorite oak gall of mine is “jumping galls,” the size of poppy seeds, round with a dot in the center. Some years large numbers of them drop and litter the ground and sidewalks. The galls “jump” each time the larva moves inside. You can see this in action in this YouTube video: https://www.youtube.com/watch?v=0VI7USm4J5I
Oak Challenges
Today, oak trees face many challenges. Disease, drought, and fire can all destroy oak seedlings. Young oaks are stepped on by grazing animals or run over by machinery. Full grown oaks are often damaged or killed when new homes, roads, stores, or businesses are built. Sudden Oak Death is a disease caused by the pathogen Phytophthora ramorum,discovered in Mill Valley in 1995. Causing a rapid color change from green leaves to brown in infected oaks, it has killed thousands of live oak, black oak, tanoak, and Shreve oak in 14 California counties. Climate change is also putting pressure on oak trees.
To maintain a forest or woodland, each oak tree needs to produce just one replacement tree in its lifetime. You can help regenerate California oak habitat by caring for an acorn seedling and protecting it from harm while it grows into a mighty oak.
All photos by Denise Godbout-Avant unless otherwise noted.
/h3>/h3>/h3>/h3>/h3>- Posted By: Richard B Standiford
- Written by: Rick Standiford, Forestry Specialist, UC Berkeley; Ralph Phillips, UCCE Livestock Advisor Emeritus; Neil McDougald, UCCE Natural Resource Advisor
Two thinning studies in the southern Sierra Nevada resulted in enhanced acorn production. A thinning experiment evaluating three levels of stocking for blue oak (Quercus douglasii Hook. & Arn.) was initiated in 1994 near California Hot Springs, California in Tulare County. The goal of the thinning was to evaluate how oak canopy overstory levels affected individual and stand tree growth, forage production, grassland diversity, and oak regeneration. The control level for the unthinned stand was close to 100 square feet per acre with a tree canopy level of 55 percent. The stands were thinned to 1/3 and 2/3 of the existing basal area level. In the first year after thinning, in addition to tree and grassland measurements, there was a measurement of acorn production by rating each tree using the four-class system developed by the Department of Fish and Game (see below).
Acorn Class |
Class Description |
Production (lbs./10 sq. ft. of canopy) |
1 |
No acorns visible on tree |
0.0 |
2 |
Acorns visible only after close examination. Maybe 1 or 2 acorns are observed |
0.1 |
3 |
Acorns are readily visible, but do not cover entire tree |
0.7 |
4 |
Acorns are readily visible, cover entire tree. Limbs appear to sag from weight of acorns. |
2.3 |
Figure 1 shows the impacts of the thinning on blue oak acorn production. For ease of presentation, we show the proportion of trees with no acorns (Acorn Class 1), to the proportion of trees with any acorns (Acorns Class 2, 3 or 4). This shows that for 5 of the 7 years we surveyed acorn production, the thinning treatments had a significant impact in increasing the proportion of blue oak trees with acorns. The two years with non-significance due to the thinning (1997 and 2002) were generally poor acorn years for the region.
Figure 1. Blue oak acorn production by thinning levels.
A second thinning study was carried out on interior live oak (Quercus wislizenii A. DC.) near North Fork, California in Madera County. This was a dense (close to 100 percent canopy cover) that developed after a wildfire 40 years previously. The same three thinning treatment levels were carried out, namely control/unthinned (75 square feet per acre), and a 1/3 and 2/3 thinning. In addition to tree growth, regeneration, and forage production data, acorn yields were also evaluated using the same procedure described above. Figure 2 shows the results of three years of observations on interior live oak acorn production. Thinning resulted in a significantly higher proportion of trees with acorns in all three years surveyed.
Figure 2. Interior live oak acorn production by thinning levels.
Discussion
We evaluated the fire history of the blue oak thinning area using fire scars, and found the fire return interval from 1851 to 1966 was 12.8 years (+2.3 years), with no fires on the site since 1966. We might speculate that the historical density of blue oak stands was much lower during the period of regular fires, and the thinning created more open conditions that mimic the effects of a period of frequent, low intensity fires. The live oak stands were quite dense, following 40 years of fire exclusion. The more open stand conditions created by the thinning for both species in these studies resulted in a higher probability that a tree would produce acorns. Blue oak produces acorns that mature in the fall of the first year after spring flowering, while interior live oaks produce acorns that mature in the fall of the second year after flowering. Despite the differences in the physiological processes guiding acorn formation between these two species, these two studies show that thinning may play a key role in the yield of acorns from our oak woodlands.