Olive trees (Olea europaea) are one of the oldest cultivated plants. They originated in the Mediterranean region and are now grown on every continent except Antarctica. Olives have been an important food source and a symbol of peace for centuries.
Commercially grown olive trees make up the large majority of trees grown in the world but they can also be used for landscaping and as houseplants. They are relatively easy to care for and don’t need any special care. There are hundreds of cultivars available each with its own unique characteristics and uses.
In this article, we’ll tell you everything you need to know about olives and how to grow them yourself! Let’s start with a brief history and its many symbolic uses. We’ll wrap up by going over their present-day benefits and uses.
History of Olives
Olive trees have been around for millions of years and fossil records show that humans used them over 100,000 years ago in Africa. They are one of the oldest cultivated plants and were planted for human use in the Mediterranean Basin 7,000 years ago. Their commercial uses date back 3,000 years to Crete.
Olives were brought to the new world by the Spanish in the 1500s and planted in South America. They did not make it to North America until the 1700s in present-day California. It took until the 1900s before olive trees made it to Japan where they are still grown commercially.
Olive trees are long-lived and can easily reach an age of 500 years old. The oldest known olive tree lives in Crete, Greece, and has been named the “Olive tree of Vouves”. The exact age of the tree is not known, but it is estimated to be between 2000 and 4000 years old!
Olive Symbolism
Olive trees, particularly the olive branch, have served as a symbol of abundance, glory, fertility, peace, power, purity, and wisdom. They have been an important symbol in both religion and politics.
In ancient Greece, olive trees were an integral part of life and their branches were used to create a crown for victors of the Olympic games. They have still been used for this purpose as recently as the 2008 Olympic games.
Olive trees have been tied to many religions including Judaism, Christianity, and Islam. It is referenced in the Old Testament of the Bible when a dove brings back an olive branch to Noah’s Arc to show that the flood waters were finally receding. The New Testament of the Bible also references olive trees, olive branches, and the Mount of Olives several times.
Jewish law mandates that the me’eyn shalosh must be recited after olives are consumed. Olives are mentioned several times in the Quran as a ‘precious fruit’ and are acceptable to be eaten by Muslims during Ramadan fasting.
In politics, the olive branch is used on the flags of the United Nations. It is also incorporated into the Great Seal of the United States of America.
Olive Tree Care
Olive trees are relatively easy to grow, provided temperatures are above freezing and summers are hot and dry. They are drought-tolerant and can grow in almost any well-drained soil. You typically don’t even have to water olive trees unless a drought persists.
Fruit production requires a little extra effort. Trees must get full sunlight and humidity must be below 80 percent. Pruning helps increase fruit yield by encouraging new growth. New growth is important since flowers are only produced on new growth each year.
Soil
The best soil for growing olive trees is high in calcium carbonate (CaCO3) which is typically found in areas with limestone. However, olive trees will grow in any well-drained soil and will even grow in poor-quality soils with little nutrients.
Watering
Olive trees are drought tolerant once they reach an age of 5 to 7 years old and are well established. Water young trees every other week if rainfall is limited. Water them thoroughly, soaking the soil to a depth of at least 2 feet.
Depending on where you live and the amount of precipitation you get, you may not need to supplement rainfall by watering mature trees at all. During a dry, hot summer, you may need to provide a deep, thorough watering once per month. Overwatering can lead to disease issues and cause the tree to grow excessive amounts of foliage which will need more pruning.
Lighting
Olive trees need full sun to grow well. They should get at least 8 hours of direct sunlight per day during spring and summer.
Humidity & Temperature
Since olive trees are native to the Mediterranean, they prefer dry, hot summers which increase fruit production. They handle low humidity well and generally won’t yield as many olives when the humidity goes above 65%. Humidity above 80% during the flowering stage greatly decreases fruit yield. It will cause the flowers to fall off prematurely.
Winter temperatures are important for fruit production. Olive trees must go dormant for at least two months during winter to produce fruit the following season. They will go dormant when temperatures are below 50 degrees Fahrenheit. Temperatures below 20 degrees Fahrenheit can damage or kill your olive trees.
Fertilizing
Olive trees are light nutrient feeders and grow slowly. Thus, mature trees often don’t need any fertilizer or extra nutrients. Too much fertilizer may actually harm olive trees and decrease fruit production and quality.
You can fertilize young trees with a high nitrogen fertilizer such as urea (46-0-0) or blood meal (12-0-0). Mature trees planted in poor nutrient soil may need fertilizer. Use Leaf tissue analysis to determine if and at what rate you need to apply fertilizer.
Diseases & Pests
Diseases that can impact olive trees include:
- Botryosphaeria blight (Botryosphaeria dothidea)
- Crown rot (Phytophthora spp.)
- Mycocentrospora cladosporioides
- Olive anthracnose (Colletotrichum acutatum)
- Olive knot (Pseudomonas savastanoi pv.savastanoi)
- Peacock spot (Cycloconium oleaginum)
- Root rot (Armillaria and Phytophthora)
- Verticillium wilt (Verticillium dahliae)
Planting disease-resistant cultivars is the best way to prevent olive knot, peacock spot, and verticillium wilt.
Insect pests of olives include borers, mites, scales, olive fruit flies, and thrips. Olive fruit flies are the most damaging insect pest since they feed directly on ripe olives making them inedible. Management of olive fruit flies with chemicals is generally only warranted in commercial olive groves.
Hardiness Zone
Olive trees can grow in USDA Hardiness Zones 8 through 11. There are a few cultivars that are slightly more cold hardy and can survive in zone 7.
Propagating
The best way to propagate olive trees is by taking a stem cutting. Stem cuttings ensure that your new tree will be the same as the parent tree genetically and have the same growth and fruiting qualities. You should propagate them indoors or in a greenhouse.
Take an 8-inch stem cutting during summer from a stem with new growth that has just begun to harden. Make the cut using sharp scissors to avoid crushing the stem and cut just below a leaf node. Remove the leaves from the lower half of the cutting leaving 4 to 6 leaves at the tip.
Fill an 8-inch diameter pot that has plenty of drainage holes with a rooting soil mix consisting of 1 part sand and 1 part milled peat. Wet the soil mix thoroughly and allow it to drain.
Dip the base of your stem cutting in a rooting hormone to help roots form quicker. Using your finger, make a 4-inch deep hole in the center of the pot and insert your stem cutting. Gently press down the soil around the cutting.
Keep your new plant in a location that gets ample sunlight. You should keep the soil moist and mist your cutting once or twice a day to ensure it doesn’t dry out.
After approximately 3 months, your olive should be rooted and you can reduce watering to once a week. Do not move your new tree outside until the following spring.
In spring, after the risk of freezing temperatures has passed, move your new tree outdoors so it can begin to acclimate to the weather. You can safely transplant it into the ground in the fall.
Harvesting
Olives will be ready to harvest in the fall beginning in the trees’ fourth or fifth year of life. Most olive trees are alternate bearing and will only produce a significant crop every other year. A single olive tree may produce as much as 40 pounds of olives and it can be time-consuming to pull them off the tree.
Depending on how ripe olives are when they’re harvested, there are three different groups of table olives: green, semi-ripe, and black. Green olives are fully grown but unripe, semi-ripe olives are beginning to turn color and ripen on the outside, and black olives are fully ripened. You can harvest both green olives and fully ripe olives to produce olive oil.
You must cure and ferment olives in order to remove some of the bitter phenolic compounds to make them palatable for consumption. There are many different ways to cure and ferment olives including using water, brine, dry salts, or lye. Some olives are better suited for certain curing methods than others.
After curing and fermenting olives, you can eat them or preserve them for later consumption. You can freeze, dry, pressure can, or store olives in a very strong brine solution to preserve them.
Growing an Olive Tree Indoors
Olive trees grown indoors typically won’t produce fruit but can still be used as an attractive houseplant. Choosing a dwarf variety is essential to growing an indoor olive tree. The most popular indoor cultivar is Little Ollie.
Make sure you plant your indoor olive tree in well-draining soil like a cactus mix and use a pot with plenty of drainage holes. Place it near a window where it will get at least 6 hours of bright sunlight daily. Only water your tree when the top few inches of soil are dry.
You can fertilize your olive tree once in the spring and once in the middle of summer with a complete, slow-release fertilizer. Prune your olive tree in late spring to help it maintain good shape. If you’d like, you can move your tree outside in the summer once the risk of freezing temperatures has passed.
Types of Olive Trees
There are hundreds of olive tree types available. Each cultivar has unique characteristics from fruit quality to disease resistance. It is important to consider the desired end-use of the fruit when choosing your tree. Also, consider if the tree is cold hardy enough for where you live.
Another important consideration is whether the tree can self-fertilize. Trees that cannot self-fertilize will need a second cultivar planted nearby. This allows the flowers to be pollinated and produce fruit.
Below are some of the most popular cultivars available and some of their characteristics.
| Cultivar | Uses | Cold Resistance | Self-fertilizing |
| Arbequina | Olive oil | High | No |
| Frantoio | Olive oil | Low | Yes |
| Koroneiki | Olive oil | Low | Yes |
| Manzanillo | Table olive | Low | No |
| Mission | Olive oil & table olive | High | Yes |
| Picholine | Olive oil & table olive | Medium | No |
| Picual | Olive oil | High | No |
| Sevillano | Table olive | High | Yes |
Olive Benefits
There are many health benefits associated with consuming olives and olive oil. The vitamin E contained in olives promotes healthy skin and also has been shown to improve the immune system[1]. Olives also contain antioxidants that reduce free radicals in the body. Free radicals are associated with cancers and heart disease[1].
Olives contain a compound called oleocanthal. Oleocanthal has been studied extensively and shown to reduce the risk of Alzheimer’s disease and cancer[1]. Consuming olives has also been correlated with a reduction in osteoporosis, heart disease, and diabetes[1].
Olive Uses
Olive trees have recently become more popular as landscape trees in some regions. Their uniquely shaped trunks and silvery-green foliage create a nice feature in the landscape. Since they are slow growers, they make great landscape trees for smaller yards and are also grown indoors.
Wood from the olive tree is very strong and has a unique grain pattern which makes it desirable for woodworking. It can be used to create all kinds of wooden items but it is generally expensive due to how slow the trees grow.
The majority of olive trees are used as crops for their edible fruits. The olives can be processed to eat whole or used to make olive oil. 9 out of 10 olives are used to make olive oil while the rest are eaten whole and are referred to as table olives.
There are three different types of oil that can be produced from olives. Extra virgin olive oil is the best-tasting and highest-quality oil. Refined olive oil is typically used as a cooking oil. Pomace oil is low quality and typically mixed with higher quality oils for use externally rather than consumption.
Olive oil has been used in religious rituals such as anointments for centuries. It is used for therapy such as messages as well.
Olives that are eaten whole are referred to as ‘table olives’. Most are too bitter to be eaten directly off the tree due to the various phenolic compounds they produce. They must undergo two processes (curing and fermentation) before being eaten whole.
What do Olives taste like?
Fresh olives have a bitter taste due to the phenolic compounds they contain which is why they are cured and fermented before being consumed. Depending on how they are cured and fermented, they can have a range of flavors including salty, buttery, sweet, and mild.
References:
[1] WebMD Editorial Contributors. (2020). Health Benefits of Olives. Nourish By Web MD.