Commercially Producing Live Oaks From Seed
Texas Live Oak at the Alamo
Image courtesy of Wikipedia
Live oaks have been grown commercially in Texas since the early 1900's. They are excellent landscape trees that contribute to property values in all parts of the state. Many Texas live oaks are surrounded by historical circumstances and are held in high esteem. There are several Texas species commonly known as "live oak", each of which is native to a particular area of the state, yet only two are commonly grown commercially (Quercus virginiana, native to East Texas and along the Gulf Coast, and Q. fusiformis, Edwards Plateau, Rio Grande Plains, Blackland and Grand Prairies, West Cross Timbers to the Red River).
Propagators could benefit by selecting acorns from the most desirable trees native to that particular area of the state. Characteristics worth noting when choosing a mature tree as a seed source are desirability of leaf color and shape, drought tolerancae, absence of galls, trunk form, vigor and umbrella-shaped canopies. Growers should understand, however, that oaks are wind pollinated. The undetermined pollen source in the formation of the acorn may dilute the desirable characteristics sought. Trees standing side by side in the nursery row may exhibit separate, distinct characteristics and variations, despite having been selected as acorns from the same "mother tree."
Acorns are collected in the autumn months, from October to December. It is not uncommon for acorns to geminate while on the trees. Ripe acorns can be picked before they fall; often it is wise to do so in order to escape weevils (Curculio spp.) which attack those that fall to the ground. Acorns that are brown in color are physiologically mature; those which are yellowish are not ripe. As a rule of thumb, a mature acorn will snap cleanly from its cup without leaving a tiesue residue.
Discard acorns that float in water along with those that show pin-sized weevil exit holes. Live oak seeds frequently contain weevil larvae that prevent germination. Larvae in sound acorns ("sinkers") can be killed by immersion in 120°F water for 30 minutes. (Warning: Higher temperatures may kill the seed.)
Acorn viability is adversely affected by dry storage. If acorns lose as little as 15% of their initial moisture, percent germination may be reduced by one-third; 20% moisture loss may reduce viabiity by 96%. This is why acorns that have been lying on the ground for 2 days may not germinate. If stored in damp peat moss, acorns will germinate and may remain healthy for a short period of time. After 4 or more weeks storage in wet peat they will begin to rot.
Ideally, acorns should be planted immediately after collection. No scarification or stratification is required; but any remaining cups should be removed.
One of the two trees considered to be "Texas live oaks"
Image courtesy of Image Archive of Central Texas Plants
Acorns initially may be sown in flats in the greenhouse to be planted later, sown outside in nursery seedbeds, or seeded directly in nursery rows. A well-drained growing medium is preferred for germination in flats. Flats should be at least 6 inches deep. Covering the bottom of the flat with copper wire mesh promotes an extensive, well-developed root system. Seedling tap roots are killed when they touch the mesh, and lateral branching is encouraged. This type of root system is deal for continued frowth in 1- and 3-gallon containers. Seedlings may be moved to containers during the spring following fall germination.
Acorns may be sown in outdoor beds. Organic matter and fertilizer can be incorporated into the seedbed soil at planting time if required. Weed control is essential. Pre-plant fumigations and pre-emergence and post-emergence herbicides may be required to control weeds. Manufacturers label directions should be followed explicitly.
Seed may be broadcast or drilled into rows 8-12 inches aparts. Generally, sowing 4.5 pounds of acorns per 100 square feet will provide a seedling density of 10 per square foot. This rate allows for an anticipated 30% loss in seedling number due to environmental conditions and culling. Acorns should be planted 1-2 inches deep. An organic mulch applied to the seedbed will conserve moisture, protect against soil rusting and cold temperatures, and help control weeds. Covering the mulched seedbed with hardware cloth will protect acorns from birds and rodents. Remove the screen before seedlings touch the metal.
Seedlings generally remain in the seedbed one year. They may then be transplanted to nursery rows for additional growth.
In some areas, direct seeding of nursery rows is practiced. Acorns are sown 4-6 inches apart and 3 inches deep in rows 4-6 feet apart. These dimensions may require modification with soil type, maintenance practices and digging equipment selected.
If the nursery is located on soil containing some clay, trees can be balled and burlapped when sold; the procedure is more difficult on sandy soils, and trees may have to be boxed. Soils should be well-drained and of moderate to good fertility for optimum growth.
Source and quality of irrigation water must be considered. Fertility rates will depend upon soils. County agricultural extension agents can provide soil and water analysis procedures.