Much like the stone of an avocado, olive pits require a little assistance to grow into trees. The shell is tough and conditions in the U.S. generally don't suit olive germination and growth. However, growing an olive from the pit is possible. But, planting your pit isn't the most effective way to produce trees bulging with juicy olive fruit.
Commercial olive growers rarely grow their trees directly from olive pits. Growing in this manner doesn't guarantee trees with the same fruit characteristics as the parent tree. In many cases, the tree produces smaller fruit, similar to wild olives. Olive growers tend to use grafting or cuttings to propagate new plants. This creates a plant that produces similar fruit to the grafted species. Pits take between one and six months to germinate, with some species' germination rates no more than 5 per cent, according to the "Olive Production Manual" by G. Steven Sibbett and Louise Ferguson.
Olive pits are extremely hard -- as you know if you've bitten into a stray olive stone. This makes germination difficult. Gardeners usually give olive pits a helping hand by either soaking them in sulphuric acid for a day or by cracking the external shell with a hammer. In the case of acid bathing, the seed must be rinsed in fresh water before planting to get rid of all the corrosive liquid. Both of these methods help with scarification -- a process of damaging the seed to aid germination.
Olive trees grow when temperatures reach and stay above 21.1 degrees Celsius. Under that temperature, olives stay in the dormant phase. When temperatures warm up, the seed germinates and starts to grow. However, a late frost can interfere with growth and limit fruiting. Olives also require mild winter temperatures. Anything below -8.33 degrees C causes tree damage, while conditions lower than -12.2 degrees C usually kill the plant or prevent growth entirely that year.
Though very vulnerable to low temperatures, olive trees tolerate lots of different soil conditions, including relatively shallow soil beds. Planting a prepared olive pit in soil with a pH between 5.5 and 8.5 will likely produce a tree in the right climate. Soil texture can range from sticky clay to light sand, though well-draining soil works best. The tree grows at a slow pace. It could be over five years before you have a sizeable olive tree grown from your pit.