Olive trees are propagated in California several different ways, including budding or grafting onto seedling rootstocks, leafy semi-hardwood stem cuttings, and hardwood cuttings. Less commonly used techniques locally, but somewhat more common world wide include truncheons, removing rooted suckers from the crown of the tree, and ovuli. (much content courtesy Glenn T. McGourty Plant Science Advisor and County Director UCCE Mendocino County)
Many cultivated olives will grow from the seed or pit of the olive under the right conditions. We have been asked if the pit of an olive in a jar of brined olives can be grown. The answer is no; the pit has been killed by the brine. Growing an olive from fresh olives is usually a frustrating experience as very few germinate but a tree dropping thousands of olives over hundreds of years will produce seedlings. Trees grown from seeds have some interesting characteristics. The tap root goes straight down so the tree is very drought resistant. That also means that it cannot take advantage of surface irrigation so typically grows slowly and produces fruit much later than trees grown by other means. It can also attain great height depending on the variety. That is a bad trait in trees grown in orchards where dwarf trees are preferred for easy picking. Oddly, the tree and fruit which grow from the seed will not always resemble the tree it came from. Olive pollen can drift for hundreds of miles and olives easily hybridize with other varieties. To get an exact replica of an olive tree, you must use cuttings or truncheons.
Mist propagation of cuttings is one of the best ways to propagate many olive cultivars. Being a subtropical, the roots and shoots of olive trees grow rapidly during late spring and early summer when soil moisture is relatively high, soil temperatures are warm (above 70° F), and air temperatures are not excessively hot (between 85° and 95° F.) Towards the end of this rapid growth is the prime time to take cuttings, during the months of late June and early July. Wood should be collected from vigorously growing trees, and kept cool until propagated. Pre-trim and place in plastic bags with moist sawdust, and process the material as cuttings as soon as possible. It is possible to keep the wood for several days under refrigeration without any problems. Semi-hardwood cuttings are selected from healthy branches, cutting pieces about 1/4 to 1/2 inch in diameter, and 4 to 6 inches long, with the lower leaves removed, and 2 to 4 sets of leaves remaining. Some propagationists will "wound" the lower portion of the stem, making slight cuts with a sharp object, and then use either a hormone powder or concentrated dip to help induce rooting. In my experience, quick dips of 3,000 ppm indole butyric acid (IBA) have worked well for many of the olive oil cultivars, such as 'Lucca,' 'Frantoio,' 'Moralolo,' 'Mission,' and 'Picual.' Hormone powders for hard to propagate species should be chosen, such as Root Tone #40. 1 have also gotten tip cuttings to root, but I only propagate those when material is very limited and precious, as often, the wood is not mature enough to root. Some cultivars are just difficult to root, such as 'Sevillano.' A successful rooting rate of 20% would be high for this cultivar, while many of the others are as high as 90%. Sterile rooting media should be used in standard nursery flats. A common propagation mix is 90% perlite and 10% peat moss. Standard nursery flats can often hold up to 70 cuttings without much difficulty. Some propagationists like to place cuttings in trays that keep root systems separate, as they find that subsequent transplanting is easier and less transplant shock means these trees grow more rapidly when placed in one gallon containers. Intermittent mist and bottom heat are critical for success in rooting olive tree cuttings. The "artificial leaf" controller for a pressurized misting system is very effective. The controller consists of a rectangular piece of fine metal mesh on a counterbalanced metallic lever that rises as it dries, activating a mercury switch that energizes an electric solenoid to turn on the misting system valve. When wetted, the screen becomes heavy, traveling down, causing the mercury switch to shut off, closing the solenoid, stopping the mist. The entire cycle usually lasts about 5 seconds, occurring as frequently as every 3 minutes under hot conditions, or as infrequently as once every few hours during cooler conditions. Many propagationists believe this to be the best system available. For small systems electric heating cables buried beneath a thin (one inch) layer of gravel controlled by an adjustable thermostat is quite effective. Bottom heat of 75. F is usually very helpful in getting the cuttings to root rapidly. The cuttings should be placed in a shaded area in a greenhouse or propagating structure, and not exposed to direct intense sunlight, as this often causes desiccation. Air temperature up to 9O° F is acceptable. Temperatures below 7O° F often result in slow or poor rooting. If you don't have a mist system keep the bed covered with plastic film, as close to the cuttings as possible to reduce air circulation and water loss. Under normal conditions, rooting becomes obvious after about 45 days, but may continue for up to six months or longer (since olive trees can live for hundreds of years, they are in no hurry!) When several healthy white roots are present, you can transplant into bigger containers. If the young rootings are going to be kept in a greenhouse, some growers will transplant into smaller containers such as rose pots (about 2 inches square,) and move into one gallon containers when the weather is better the following spring. Young trees need to be protected from heavy frosts, and dry, cold weather.
For cultivars that don't root easily, grafting or budding onto seedlings is used. Seeds collected and cleaned from 'Redding Picholine' have been used in California. This small fruited cultivar seems to have a fairly high percentage of seeds that germinate, although once again, germination occurs over a long period of time (up to two years!) Sowing with lots of seed is a common strategy to insure that adequate material is available. Seedlings are grown on for one to two years, and then either t-budded, whip grafted, and side tongue grafted. Bark grafting is also used in Europe. Once successfully top worked, trees are grown on in the nursery for an additional year before delivery, in most cases. Sevillano is commonly grafted onto another cultivar in California. For a nice discussion of bud grafting on mature hardwood, go to Grafting Olive Trees - by Matt Starczak - pictures below are from his website. or go to the UC document showing how to limb graft.
Hardwood cuttings can be made from 2 or three year old wood about an inch in diameter, and 8 to 12 inches long just prior to warm spring weather. All leaves are removed. Soaking the ends of the cuttings in hormone solutions, followed by storage in moist sawdust at 7O~ F for a month to help induce callus formation is often used. Cuttings are then placed in the nursery to root, often being lined out in well worked, friable soil. The cuttings should be mostly buried, and kept moist but not wet. Rooting will occur over several months. Trees are then dug bare root and containerized or planted into the orchard.
The truncheon system is also used as a low-tech
system for olive tree propagation. Limbs 3 or 4 inches in diameter are
removed from trees and cut into 12 inch pieces, and then planted horizontally
in soft, well tilled friable soil. Usually several shoots with an
accompanying root system will grow. They can be separated, and grown for
another year before being planted in the orchard.
Swellings found on the trunk of the olive tree, known as "ovuli", can be cut off and planted in early spring. These structures contain both adventitious root initials and dormant buds so that new root and shoot systems can develop. This practice is damaging to the parent tree, and is not used very often in the US, but is used in other parts of the world.
Finally, suckers with a small piece of root can be removed from the trunk of the tree in the spring and grown in the nursery for a year before planting into the orchard. SOURCE FOR SPECIALIZED PROPAGATION EQUIPMENT: M C Developers, located in Ceres, Ca, telephone # 1-800-511-6151. |
