Growing White Oak from Seed
The White oak family is a large and diverse group of trees. White oak (Quercus alba), Swamp White oak (Q. bicolor), Overcup oak (Q. lyrata), Bur oak (Q. macrocarpa), Swamp chestnut oak ( Q. michauxii), Chinkapin oak (Q. muehlenbergii), Dwarf Chinkapin oak(Q. prinoides), Chestnut oak (Q. prinus), Post oak (Q. stellata) are all members of the same family and have similar botanical characteristics. Each of these species have large natural ranges but may be locally common or uncommon in New York State and in your specific locality.
White oak (Q. alba) is the most wide spread and common oak in this group found growing throughout New York State and most of the eastern United States. All of the information in this article for germinating and growing oak trees is specifically referring to this species but can be applied to the other species as well.
The acorns of White oak are produced in one growing season, unlike the acorns from Red oaks (Quercus rubra) whose acorns develop over a two year period. Oak flowers are wind pollinated and are dependant on favorable weather conditions for successful pollination. Unseasonal wet cold weather may interfere with pollination reducing acorn production or even causing a total crop failure. Oak flowers are small, inconspicuous and open in the spring at the base of the new leaves on twigs from the previous seasons growth. Pollen is released form the male flowers (catkins) to pollinate the female flowers. If the female flowers are successfully pollinated the acorn begins to develop. The acorn remains as a small immature acorn for most of the summer months. If extreme dry hot conditions persist over the summer these embryonic acorns may abort causing the loss of that years crop. About late summer/ mid August the acorn begins to rapidly enlarge to reach its maximum size in just a few short weeks. There is great variability in size and shape of white oak acorns between individual trees depending on their specific genetics and local growing conditions.
Oaks are a masting species, meaning that they produce large crops of seed once every few years. All the trees of an oak species may go from a couple to several years without producing any acorns or very few and then in one particular yearall of the trees will produce a large crop of acorns. Amazingly all of the trees over a large geographic area are synchronized in this cyclical reproduction event. The mechanism for this synchronization still remains a mystery.
The acorn undergoes a physiological change as it reaches maturity. Like the umbilical cord of a baby being severed at birth the connection to the living tree is shut off between the acorn and the cap. A permanent round mark is visible on the end of the nut called the cap scar, where the acorn and the cap are connected. The acorn changes from a bright green color to a dark chocolate brown color and the acorn begins to dry and shrink slightly. Shortly after the acorn changes color they begin to loosen from their caps and fall to the ground.
In late August and early September when the acorns mature they can be collected from the tree or picked up off the ground. When collecting from a tree the acorns should easily separate from the cap or the acorn is probably not viable. Acorns that fall to the ground begin to germinate immediately. A white root radical emerges from the growing tip of the acorn, the end opposite from the cap scar. The emerging root will root into the ground if in contact with the soil, otherwise the root will gradually shrivel, desiccate and die.
The window of opportunity for collecting acorns is very short lasting about 2 weeks. Wildlife of all types seek out White oak acorns at this time of the year and can eat every single one, to the very last acorn. Wildlife relish the acorns because they are low in bitter tannins which makes them a preferred food. The White oak has no need to produce tannins to protect its acorns because the acorn germinates immediately upon falling from the tree and quickly converts its stored energy into new roots. The acorn quickly loses its nutritional value, which is changed to living plant tissue.
Acorns that germinate underneath the parent tree seldom grow to any size in the shade of the parent tree. Acorns are heavy and cannot be wind dispersed as is common with most other tree seed. An oak requires a mechanism to disperse the seed away from the parent tree. As the majority of common wildlife species such as Deer mice, chipmunks, squirrels, turkey and deer feed heavily on acorns and destroy them, how will an acorn be transported and survive?
Blue jays and grey squirrels both depend heavily on acorns for the majority of their diet, but they both are species that cache food for the winter. Jays and squirrels have developed a symbiotic relationship with oak trees. These two species play a key role in acorn dispersal for oaks. Both species cache or store acorns for a food supply during the long winter months. Their method of caching acorns is key to the reproduction of oaks. Jays and squirrels transport acorns away from the parent tree and seek out individual locations to bury the acorn in contact with the soil. Each acorn is placed in its own location and placed in the soil in a way that is ideal for survival and germination.
Blue jays have an extraordinary ability to remember the exact location of hundreds of individually cached acorns and retrieve them by creating a spatial map of the exact location. Research has shown that jays use triangulation between large permanent objects in their environment to relocate the exact cache site to within a few inches or a few feet. Squirrels tend to use their extraordinary sense of smell to relocate acorns buried in the ground. Fortunately for the oaks not all of the acorns are retrieved and when a jay or squirrel falls prey to a predator or dies, its acorns are likely to remain unclaimed and are in a perfect condition for germination.
For people interested in propagating and establishing White oak from seed the process is as simple as mimicking what squirrels and jays do in nature.
Acorns are collected in late August and September when they mature. Float the acorns in a pail of water to test for viability, sound seeds will sink to the bottom, unsound seed or weevil infested acorns will float to the surface or only partially sink. Discard the floaters. The easiest method of handling is to plant the acorn immediately in soil 1 to 2inches deep. Place the long dimension of the acorn horizontal to the soil surface. If in doubt as to which end is which, place the acorn on a flat surface, plant the acorn the way it naturally rests. Nature will do the rest, but many acorns will be discovered and eaten by animals during the long winter months or fail to germinate for various reasons.
To store and grow acorns under controlled conditions, collect acorns and place them immediately in moist potting mix, soil or peat moss to maintain the correct seed moisture level and protect the emerging root radical. As the root emerges form the acorn plant the acorn in deep flats or individual pots with the root pointing down. The deeper the pot the better to allow the root room to grow with out interference. A pot 6 or more inches deep is required.
Acorns cannot be stored for longer than the few months until spring.
To stimulate the shoot to emerge in the springtime the acorn must go through a chilling period. Outside temperatures normally satisfy this requirement, or subject the acorns to temperatures just above freezing for approximately one to two months time by placing the acorns in a refrigerator. Do not put acorns in the freezer as this will kill them.
White oak seedlings are shade intolerant and will not survive for long in too much shade. White oak seedlings will grow in full sunlight to slight shade. They grow in a range of soil types but require well drained deep soils for best growth and long term survival. Wet poorly drained soil is lethal to seedlings. White oak seedlings grow slowly the first few years. They invest most of their energy and growth into establishing a deep root system, but once establish, growth picks up and becomes fairly rapid during the adolescent years.
Oak seedlings are best adapted to sites that are in transition from grassland or old field to shrubland and young forest. These sites provide suitable sun exposure and habitat where the herbaceous vegetation has thinned and there are gaps in the vegetation for seedlings to get established.
White oak is long lived but slow growing compared to other tree species. It holds an important place in our forest community and provides valuable wildlife benefits for hundreds of years. Peoples biases towards faster growing oak species and its difficulty in transplanting using bareroot seedlings has limited its widespread planting. The process of growing oaks from seed is simple, easy and cost effective. This knowledge should encourage more widespread planting of White oak,. Hopefully our present and future landscapes will be graced with many more of this majestic tree.
this page updated February 20, 2009