I noticed we are having what looks
to be a bumper crop of acorns here in central Pennsylvania. The red oaks
are loaded and I even saw a white oak in my yard that appears to have a good
acorn crop. I wanted to provide a few pointers about how to grow an oak from
seed. It is easy and you can begin collecting acorns now, before the
birds, squirrels, insects, and deer get them all. The number of acorns
produced by both oak groups varies greatly from year to year. Scientists have
been studying this for years but are unable to explain it. More than likely it has to do with the weather
conditions, nutrient availability, and acorn-feeding insects.
There are lots of reasons to grow
your own oak seedlings. Oak is one species that has a difficult time
regenerating in the forest. Not only will deer and other wildlife species
eat the acorns but deer also browse heavily on the twigs, leaves, and buds year
round as it is one of the most preferred species. Once an acorn germinates
in the forest it spends a lot of time and energy growing roots rather than stems. This
means it may sit in the understory for years, maybe even decades growing
roots. This gives oak a great advantage when the forest is disturbed by
logging or fire. But, if there are no well-established oak seedlings, called
advanced oak regeneration, present in the forest understory when a disturbance
happens then species like black birch and red maple are quick to take over the
site. These species will quickly outgrow an oak that is just starting from an
acorn. Enrichment plantings are used to re-introduce oak in a forest that
was recently logged or disturbed in another way, such as gypsy moth defoliation.
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| White Oak Leaf | |
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It is important to be able to tell
the difference between
red and
white oaks,
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| Red Oak Leaf |
which are the two broad categories
of oaks. They can easily be distinguished by examining the leaves. The
lobes, which are the projections along the edge of the leaves, of white oak
leaves are rounded without bristle-tips; red oaks typically have
bristle-tips on the lobes. Another important difference is that white oak
acorns take just one year to develop on the tree and will germinate in the fall
soon after hitting the ground. While red oak acorns take two years to
develop on the tree and will not germinate until spring.
Guidelines for Successful Acorn Collection and Planting:
·
Time your acorn collection until the majority of
acorns are falling. Ripening dates vary from year to year and from state to
state by as much as three to four weeks, making it difficult to use actual
dates to determine maturity. The acorn is perfect when green, plump, and the
cap is easily removed.
·
Lawns, woods roads, field edges, or paved areas
help in collecting acorns. Be sure to identify the species of tree and mark the
bag or bucket so you know the species collected.
·
Collect two to three times as many acorns as the
number of seedlings you want to plant.
This will allow you to remove bad ones and still ensure enough seedlings
even with low germination rates.
·
Discard acorns that show any rot, mold, or small
holes that may indicate insect damage.
·
It is critical that acorns are not allowed to
dry out or heat up. They can lose their
ability to germinate very quickly. Keep
acorns shaded and spray with water to avoid moisture loss. If not planting them right away place them in
polyethylene plastic bags with damp peat moss or sawdust and put them in the
refrigerator. Do not freeze acorns.
·
After collecting the acorns drop them into a
bucket of water. If the acorn floats it is no good, as this is an indication
that the embryo has not fully developed or is damaged and the seed is hollow. Soaking
also provides moisture to any acorns that may have dried out some during
collection.
Seed Dormancy and Stratification
Because of differences in seed
dormancy between red and white oaks, the process of storage and sowing differs.
White oaks germinate in the fall, and red oaks germinate in the spring.
Red Oak Acorns
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| Red oak, Treetopics.com |
Red oak acorns must go through a process known as
stratification before they will germinate in the spring. Stratification breaks
down the heavy seed coat allowing the acorn to sprout. Red oak acorns need about 4-8 weeks of cold stratification.
When storing, place moist acorns in plastic bags (4 to 10 mil
thickness), which can either be sealed or partially left open, and put in a
refrigerator. Do not place in airtight bags as that can kill acorns. Keep the
acorns moist by adding peat moss or sawdust. Every 2 to 3 weeks visually
examine acorns for fungus or mold growth and dry by opening the bag, which will
also release any gas buildup. Because of the risk of seed predation it is not
recommended to sow red oak acorns outdoors until spring, March or April.
White Oak Group Acorns
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| White oak, Ecoaddendum.org |
White oak acorns have no seed dormancy.
As a result, white oak acorns can be seen on the ground in the fall with the
root protruding from the seed. They can be planted immediately or stored and
planted in the spring. If sowing in the spring, they need to be stored by
placing them in refrigeration at 34–40°F in moist sand. Do not store white oak
acorns for more than 3 or 4 months.
Planting Acorns
Both white oak and red oak acorns
can be planted outside in a seedbed, in containers/pots, or in the forest
protected in tree shelters. An outdoor seedbed will produce large numbers of
seedlings at once. Prepare the seedbed as you would a garden. Acorns can be
planted at a density of 5 acorns per square foot and about an inch deep with
the acorn on its side. Once emerged, remove the suppressed seedlings to allow
more room for the other seedlings to grow and develop. Be sure to water and
remove grass and other weed competition as needed. Seedlings should be left in
beds until the following spring when they can be dug and planted when dormant
as bare root seedlings. It may be necessary to place wire cages or fences over seedlings
to protect them from deer browsing.
Acorns can also be planted in pots
that are at least a foot deep (1 gallon size or deeper) to accommodate the tap
root. Fill the container with a mixture of potting soil and top soil. Multiple
acorns can be placed in each pot. Again, plant acorns an inch deep and oriented
lengthwise. Once germination occurs weed out the smaller weaker seedlings leaving
one tree in each pot. Place pots off ground in a sunny location and water as
needed. By placing pots off the ground roots that emerge from drainage holes
will be air pruned. Seedlings should be transplanted as soon as the first
leaves open and become firm but before extensive root development occurs. Be sure to protect from deer browsing with wire
cages or fences.
Acorns can be planted directly in
the forest but must be protected from small mammals and deer. Plastic tree shelters or tubes are effective
at protecting the acorn while allowing seedling growth. Lay an acorn on its side
an inch deep in the forest soil where you intend to plant it. Place a tree shelter over
the acorn and gently tap it down until it sits approximately and inch or two in
the soil. Stake the shelter in place. If deer browse pressure is not a concern
then short tubes (16-18 inches) are sufficient. However, if browsing is a concern
a shelter 4-5 feet will be necessary to protect growing seedling.
Different species of oaks grow at
different rates. Growth is dependent on a number of factors including soils,
water, nutrient availability, and the amount of sunlight. Once established it is not uncommon to see
height growth of 1-2 feet per year or more. If you are growing oaks for wildlife and
acorn production then planting them wide apart is preferred. A more open grown
tree will begin to produce acorns at an earlier age. This can mean planting
trees as much as 20-30 feet apart. For timber production plant trees closer
together to force trees to self-prune lower limbs and grow straight and tall.
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