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DouGlA5 D. McCREARY, NAruRAL RBouR.as SPECIALJSf
UNMRSITY OF CAuroRNIA CooPBtAllVE f.xm.JsloN, 8279 Scorr FoR..Bf5 R.oAD, BR.oWNS V AI.l.EY, CA 95918
Native oaks are a vital and important component of the vegetation of California
They grow in a wide variety of
habitats and help provide a distinctive
character to the landscape. Not only
are they beautiful to look at, but they
also provide food and shelter for many
wildlife species, they stabilize soil,
and they help counteract the
"greenhouse effect" by taking up
carbon dioxide and producing oxygen.
It is estimated that one or more species
of oaks grow on over 20 percent of the
state's 100 million acres of land Un-
fortunately, there are also reports that
some native oaks may not be regener-
ating very well in some locations.
Poor natural regeneration raises
concerns about the long term fate of
these species. To assist Mother Nature
in establishing new oak trees, efforts
are underway to plant acorns and
small seedlings. Such regeneration
efforts will ensure that our magnifi-
cent oaks, which have graced
California valleys and foothills for
thousands of years, will be around for
future generations to enjoy also.
The following guidelines provide suc-
cessful techniques for growing oak
trees. While there are many ways to
get an oak tree started, the procedures
described have proved successful for a
variety of species and environments.
ACOR.NS OR. SEEDLINGS?
Oak trees can be started by either di-
rectly planting acorns or transplanting
small seedlings. However, since rela-
tively few native oak seedlings are
produced in the state, it may be
difficult to purchase them. Those that
are produced are generally grown in
containers ranging in size from a few
cubic inches to 5 or 15 gallons.
Seedlings grown in the smaller
containers should be no more than one
year old before transplanting since
they quickly outgrow small pots. Even
with large containers, it is important
that seedlings be transplanted within a
couple of years since oaks tend to pro-
duce massive root systems and can
easily become "pot-bound"
Some bareroot oak seedlings are also
available. For the past several years
the California Department of Forestry
Nursery at Magalia has been growing,
and making available to the public,
several species of oaks. The supply of
both container and bareroot oak
seedlings should increase in future
years as techniques for rearing them
are developed and perfected, and more
people express an interest in planting
native oaks.
The choice of whether to plant acorns
or seedlings depends on a whole host
of factors including availability of
planting material and conditions at the
planting site. Generally, acorns are
easier to plant, but the survival of
seedlings may be greater if they are
planted correctly at the right time of
the year. Another factor that may in-
fluence the choice is what kinds of
animals are present at the planting site.
If there are high populations of acorn-
eating rodents (ground squirrels or
deer mice), it may be easier to plant
seedlings than trying to protect the
acorns.
MAINrAIN Loe.AL SEED
SOURCES
Since most tree species have adapted
to the specific environments where
they grow, it is important to only plant
a given oak species in areas where it
naturally occurs or where it may have
grown in the past Even within a
species, you must be careful to only
plant acorns or seedlings that come
from a parent tree growing in the same
general environment. If you took an
acorn from a blue oak tree growing on
the coast and planted it in the foothills
of the Sierra Nevada, for instance, it
would probably grow poorly, or die,
even though blue oaks grow in both
locations. Since coastal trees are
genetically adapted to more temperate,
moister conditions, they would be
subject to injury from the colder, drier
conditions of the interior. If you
collect acorns yourself, you can be
sure where they come from, and know
that they are also handled and stored
properly. If you buy from a nursery,
make sure you find out the location
and elevation of the acorns collected,
and insist on seed sources from as near
your planting site as possible.
Co11ti11Ul!d 011 page 2
COU,ECTING ACORNS
Acorns can be collected either directly
from the trees or from the ground be-
neath. However, the healthiest acorns
are generally those picked from the
trees. Those that fall to the ground
often dry out and are damaged-
especially if they lie exposed for more
than a few days during hot and dry
weather. If you do collect acorns from
the ground, leave behind those that are
very small, cracked or feel light and
hollow. Acorns collected directly from
trees can be hand-picked or knocked
to the ground using long poles or
pieces of plastic pipe. It's easy to pick
them up if tarps are placed under the
trees first
The best time to collect acorns is
generally in the early fall, when they
are just starting to turn from green to
brown and some are falling to the
ground. It's probably too early to
collect them if they are all dark green
and it is difficult to remove their caps
(the cup covering the rounded end).
Wait a couple of weeks and check
them again.
If left unprotected, oak seedlings are vul-
nerable to attack from grasshoppers and
other animals.
2 ,. How to Grow California Oaks
STORING ACORNS
Prior to storage, the caps on all acorns
should be taken off. They should come
off easily when twisted. Acorns col-
lected directly from the trees should
be put in plastic bags and immediately
placed in a refrigerator. Refrigeration
slows the metabolic activity and helps
prevent them from heating up or
drying out - both of which can be
damaging. A recent study indicated
that storing acorns in a refrigerator for
a month or so before planting resulted
in faster and more complete
germination than planting acorns
immediately.
Acorns picked up off the ground
should be soaked for a day before they
are placed in cold storage. Those that
float should be discarded. "Floaters"
are generally acorns that have been
damaged by insects or have dried out
while they were on the ground.
"Sinkers" should be saved. Remove
the acorns from the water and place
them on cloth or paper towels for a
half hour to dry their surface. Then
place the acorns in plastic bags in the
refrigerator. Check them occasionally
for molds. If molds do develop, take
the acorns out and rinse them, and
then put them back in the refrigerator.
Leaving the plastic bag partially open
at the end seems to reduce the
tendency for molds to develop.
Another problem that can develop in
cold storage is premature germination.
Blue oak acorns are especially prone
to this. The white tip emerging from
the pointed end of the acorn is actually
the start of the new root system. Once
these roots have grown for a few
weeks, they can start to go bad and
tum dark brown or grey and mushy.
Therefore, if you see the acorns
starting to germinate in storage, it's
best to plant them as soon as possible.
ACORN AND SEEDLING
PLANTING
Acorns can be planted from early No- 1-
vember (after the first rains have
soaked the soil) until early March.
However, it's generally better to plant
acorns early in the season since the
earlier they are placed in the ground,
the earlier they start to grow. Early
planting also reduces the problems
associated with premature germination
during storage.
Plant the acorns one-half to one inch
below the soil surface. Dig a hole
using a hand trowel, hoe, or shovel.
It's best to dig the hole several inches
deeper than the acorn is actually
planted, and then partially fill the hole
back up with loose soil. This gives the
new root a chance to get a good start
in soft, easy to penetrate soil. If the
acorns have germinated, try not to
break the root tip, and position it in
such a way that the root is pointing
down. Even if the tip of the root has
begun to turn brown, the acorns
should still be okay as long as some of
the root is white and fleshy. Place
ungerminated acorns on their side in
the hole and cover with soil.
Planting seedlings requires a little
more care since there is greater risk of
transplant shock and root injury.
Seedlings should be planted between
December and February, when the soil
is wet but not frozen. When planting
potted seedlings, try to keep the soil
from falling off the roots when the
seedling is removed from the
container. Place the seedlings in the
ground such that the top of the soil
from the container is even with the
ground line. It is especially important
not to plant the seedlings so shallow
that the potting mix sticks up in the
air, since this can cause moisture to
"wick-out" and the seedlings to dry
up. If you are planting bareroot
seedlings, be sure not to "J-root" them
(planting in too shallow a hole so the
root bends up). Also, tamp the soil
down in the planting hole so that air
pockets are removed. If possible,
water the transplants when they are
planted. This settles the soil, ensures
there is adequate moisture, and helps
eliminate air pockets.
Recent studies have indicated that
augering holes 1-2 feet below planting
spots and backfilling with the broken-
up soil can promote deep root
development and stimulate vigorous
growth. This is especially beneficial if
you are planting in hard, compacted
ground. Deep root development pro-
vides seedlings with greater access to
moisture, thus reducing the ill effects
of summer drought Placing a fertilizer
tablet a few inches below and to the
side of the bottom of the root can also
help ensure that the developing
seedling will have plenty of nutrients
for its initial growth.
The site where you choose to plant
acorns or seedlings may also be
critical for their success. Choose a
sunny spot that has loose, well-drained
soil and is fairly free of weeds. Also,
avoid areas where there are lots of
pocket gopher mounds or ground
squirrel activity. If you do feel that the
acorns may be threatened by rodents
such as squirrels or mice, plant them a
little deeper-say, two inches below
the surface. If they are planted deeper,
. it will be harder for these animals to
dig them up. However, if they are
planted too deep, they may rot or not
be able to grow up to the soil surface.
PLANTING LAYOUT
The number of acorns or seedlings to
plant in a given area will depend on
how many oaks you eventually want
to grow there. Unfortunately, it is very
difficult to predict how many trees
will be produced from plantings, since
a whole host of uncertain factors
including weather, animals and
competing vegetation can influence
this. When laying out the planting
area, consider spacing seedlings or
acorns in a naturalistic manner, rather
than in straight rows, using surround-
ing oak trees as a model. On open
rangeland, it is recommended that
trees be established in small clumps or
clusters, with the goal of about 40
planting spots per acre. This comes
out to an average of one cluster every
30-40 feet Within each cluster, plant
3-4 seedlings. In restoration projects
Tree shelters protect oak seedlings from
animals and stimulate growth.
in riparian zones, a greater density is
usually desirable, so have the clusters
closer together-say 15-20 feet apart.
SEEDLING
MAINTENANCE AND
PROTECTION
Another critical factor affecting young
oak seedlings is competing vegetation.
Adjacent plants----especially grasses-
can use up so much of the available
soil moisture that little is left for the
seedlings. It is therefore recommended
that a 2-3 foot radius circle around the
planting spots be cleared of other
vegetation. This can be done by hand
weeding, hoeing, scalping, or by
spraying a contact herbicide. How-
ever, with any of these methods, be
sure to check back in the spring and
early summer to remove any addi-
tional weeds that may have come up.
It is generally best to keep the weeds
away for at least 2 years after planting.
Another way of reducing weeds near
seedlings is to place some type of
mulch around the planting spots. Bark
chips, straw, compost, mulching
paper, or even black plastic can be
used. Mulches have an added benefit
in that they also help conserve
moisture by reducing evaporation
from the soil surface. In areas where
water is accessible, several deep irri-
gations (2 gallons per seedling) during
the late spring and early summer can
also help ensure that the seedlings are
not damaged by drought
Since acorns are an important food
source for a whole host of animals,
there is always a risk some of them
will be dug up and eaten. As the
seedlings start to grow in the spring,
there is a also a chance that their
tender young shoots will be eaten by
livestock, rabbits, grasshoppers, or
other animals. The risk of such injury
to both acorns and seedlings can be
reduced by placing protective cages
around the planting spots. One type of
cage that has worked well in research
plots consists of an 18x18-inch
aluminum screen that is formed into a
5-inch diameter cylinder and stapled
to a lx2x24-inch wooden stake. The
cylinder is folded closed at the top.
The stake is driven into the ground so
that the screen cage covers the spot
where the acorn or seedling is planted.
This cage will keep out rodents,
insects, and browsing animals.
A new type of protector is a rigid
translucent tube. These "tree shelters"
vary in height from one to six f eeL
These shelters not only keep away
insects and browsers, but appear to
stimulate height growth as well.
Recent research indicates that tree
shelters secured with metal fence posts
can even protect seedlings from cattle
and sheep. These protectors also
facilitate chemical weed control
around planting spots.
Another cage protector consists of a
screen cylinder placed around a I-
quart yogurt or cottage cheese
container that is open at both ends.
Place the quart container in the soil so
that the top is at the soil surface. This
protective cage will not only prevent
shoot damage, but will also help keep
away burrowing animals such as
gophers which can damage roots.
When the seedlings grow to the top of
the screen cages, open the cages up so
the seedlings can continue to grow.
You're now well on your way to es-
tablishing an oak tree!
(continued on next page)
How to Grow California Oaks .i. 3
Publication of the Integrated Hardwood Range management Program
Printing Provided Through Renewable Resources Extension ActHow To Grow California Oaks
Nurseries Producing
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