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Often Asked Questions About Olive Trees and Olives

The Q&A below is based on questions I am often asked by people who take a tour of Sandy Oaks Olive Orchard.  If you think of a question I did not answer, email me at saundra@sandyoaks.com and I will post the question with the answer. 

Question:  Does this variety of tree produce green or black olives?

Answer:      There is not a variety that produces just green or black olives.  Olives on all olive trees start out green, then ripen to rosy, and finally to black.  Unripe olives are green, partially ripe olives are reddish-purple (rosy), and ripe olives are black.  Pickled green and rosy olives are firmer than black olives, with a more pungent taste.  Black olives are softer and have a subtle, yet fuller taste.  Olive oil is pressed from a blend of unripe, partially ripe, and fully ripe olives. For a sweeter flavored oil, the mix is ¼ green, ½ partially ripe, ¼ black.  For a sharper flavored oil, use ½ green olives ¼ partially ripe olives and ¼ fully ripe olives in the mix.  This mixture will also have more polyphenols and hence a greater shelf life.

Question:  Can olive trees survive freezing temperatures?

Answer:     Olive trees can survive freezing lower temperatures down to the upper 20-degree F range.  Some varieties can survive temperatures in the upper teens.  (See the chart to determine the varieties in the Sandy Oaks Nursery that are cold hardy) 

                  Olive trees grow well in zones 8, 9 and 10.  The lowest temperature for zone 8, for example is 10 to 20 degrees.  It rarely drops to 10 degrees in zone 8 in Texas.   Cold hardy olive trees can survive 15 degrees, but not 10 degrees.  The upper temperature is not critical, as olive trees thrive in areas where the summer temperature reaches more than 100 degrees.  Each state has a zone map.  (Show the zone map for Texas).

                  Often people will try to grow olive trees in pots in zones that are colder in the winter.  They will put the tree in the garage for the winter and bring it out for the rest of the year.  Unless your garage gets full sun during the day, this is not a good practice.  If you have a greenhouse, that is a different matter, especially if you keep the temperature in the 40 degree-range to insure adequate chill hours.

Question:  Do olive trees lose their leaves in the winter time?

 Answer:     Olive trees are evergreen. 

Question:  How many chill hours do olive trees need in order to bear fruit?

Answer:     Olive trees need 200-300 chill hours (e.g., the number of hours below 45 degrees F) to produce fruit.  Once the tree has flowered, a temperature of 90 to 100 degrees F and above can burn the flowers.  This will limit your level of production.  However, if the olive tree has fruit on it already, the higher temperatures will not affect the fruit.

Question: Can I plant a tree in a pot?

 Answer:     Olive trees have a root structure that does not lend itself to remaining in a pot over time.  The roots of the olive tree are shallow and grow horizontally well beyond the drip line of the tree.  The important roots (i.e., the feeder roots) are located in the one-foot area below the top of the soil. The remaining roots reach down 4 feet.  When the roots are confined, as they will be in a pot, they will begin to wrap around the boundary of the pot and finally girdle the tree which will kill it.

 Trees planted in a very large pot will thrive until the drip line goes beyond the boundary of the pot.  When this occurs, either move the tree to a larger pot, or if that is not an option, trim the roots back and the top to match – similar to turning the tree into a bonsai, but on a larger scale.

Question:  Can olive trees be grown indoors?

 Answer:      Olive trees require full sun.  Most houses do not provide full sun, even in front of a window.  If you have a garden room or an atrium, then the tree will grow in the house. 

Question:  Does soil type matter for olive trees?

Answer:      Yes, but the pH is not nearly as important as soil drainage.  Olives can grow in almost any soil that is well-drained (water flows downward through soil, never standing in the soil for a long period of time).  Olives grow better in rocky or sandy soils because those soils are usually well-drained.  When growing in clay or other heavy soils, it may help to make use of slopes so excess water runs off.  Underground hardpans if less than five feet below the top may create poor drainage conditions and so it would be best not to plant there.

Question:  Does soil pH matter:

 Answer:     Olive trees can grow in soils with a pH between 5.0 (acidity level) to 8.5 (alkalinity level).  Additions of dolomitic limestone may be required in very acid soils so that trees receive enough calcium.

                            

Question:  How often should olive trees be watered?

 

Answer:      After planting, trees should be watered frequently enough so the roots are kept moist, but not soaking wet, until established.  Frequency of watering will depend on soil type, rainfall and temperature.  If soil holds water, it may not be necessary to water for a week or more should it rain ½ inch.  Sandy soils do not hold water, so ½ inch of rain buys you only a few days of not watering.

                  Usually, if the soil holds water, the best way to judge whether to water is to check to see if the soil is wet down to 12 inches.  If dry, water.  In sandy soil, the trees need to be watered more frequently, especially when hot.  My orchard is planted in sandy soil.  I need to water in the summertime, between two to three times a week.  Watering in soils that are primarily clay based is usually necessary only in really dry periods.

                  Just looking at the tree to see if it needs watering is not a good way to judge if a tree needs more water.  An olive tree looks wilted when it does not have enough water and when it is overwatered.  The best way to judge is by testing the soil to see if it is dry 12 inches below the top of the soil.

                  Warning:  Do not overwater olive trees, they do not like wet feet!

Question:  Is Irrigation really necessary, after all they do grow in the desert?

 

                  Although olive trees are drought tolerant, an irrigation system is really necessary for several reasons:

  1. To insure consistent production. Though trees are not irrigated in some parts of the world, they do not produce on a commercial basis.  The production varies from year to year depending on the amount of rainfall per year.
  2. To preserve the fruit on the tree. When the trees are laden with fruit, trees that dry out will go into self-preservation mode.  They will drop the fruit first and then begin to defoliate.
  3. To protect the tree during a cold front. In the winter, when a cold front is predicted, the best way to protect the trees from damage is to irrigate them thoroughly before the cold front moves in.  You might still have tip burn on the limbs of the tree, but the roots will survive and the tree as well.

Question:  Can you diminish production by overwatering the last two months before harvest?

 

 

Answer:     The meat of the olive is composed of water and oil.  In some parts of the world, farmers will cut back on watering a few months before the harvest to increase the amount of oil in the olive.  We cannot do that in Texas, because our summers are very hot and often very dry.  Therefore, in order to preserve the fruit, we water until harvest.

Question:  How often should trees be fertilized?

 

Answer:     Olive trees do not require heavy fertilization compared to other fruit trees.  Trees grown in sandy soils require more fertilizer than those grown in soils with more clay in them.  Fertilizer labels usually have three hyphenated numbers (e.g., 4-3-3).  These numbers represent the level of the macronutrients N (nitrogen), P (phosphorous), K (potassium) in the fertilizer.  Nitrogen is required for leaf and stem growth and is needed in greater quantity for young trees in the first few years to help them establish.  Phosphorous and potassium are essential for flowering and fruiting.  The macronutrients, as well as micronutrients and trace minerals are required for the olive tree.  At Sandy Oaks, we use organic fertilizers that provide nutrients in liquid and solid form.  Our go to fertilizer is a combination of liquid seaweed and fish emulsion. We use the following list of fertilizers depending on the needs of the tree: 

  • Fish emulsion is a fast-acting organic fertilizer that is rich in nitrogen, phosphorus and potassium, plus micronutrients and trace elements such as calcium, magnesium, sulfur, chorine, and sodium.
  • Liquid Seaweed contains the three major nutrients, but it also contains a vast array of trace minerals. It improves the productivity and overall health of the olive tree.
  • Bat Guano or Chicken Litter are good sources of nitrogen, especially bat guano
  • Chicken Litter returns nutrients and fertility to the soil. It contains all of the macronutrients plus calcium, magnesium, sulfur, and many micronutrients.
  • Alfalfa Tea contains many macro and micronutrients, but more importantly it feeds beneficial soil organisms as well. It also contains a growth hormone, tricontanol.  It can increase the tolerance for cold.
  • Azomite is used to improve depleted soils. It is a natural source of micronutrients and trace elements.
  • Worm Castings help plants absorb the nutrients in the soil. They contain humic acid which stimulates plant growth.
  • Humic Acid is a plant stimulator because it helps trees absorb more nutrients. It like seaweed encourages strong root development.
  • Boron is necessary for fruit production in deficient soils. We apply it as a foliar spray once at the end of January and again at the end of February before flowering.

Question:  Do olive trees need another tree to be pollinated?

 

Answer:     Many olive trees are self-fertile, i.e., they fruit by planting only one tree.  However, there are some trees that are self-sterile or partially self-fertile.  In this case another variety is needed to produce fruit. Orchards benefit from planting at least three varieties to improve cross-pollination.  This can improve production by at least 10%.

Question:  How does pollination occur?

 

Answer:     Olive tree pollen is carried by the wind.  Bees are not necessary to insure pollination.  The pollination period lasts for about two weeks.

Question:  What is the season in Texas for olive production?

 

Answer:     The season begins in late February or early March when fruiting shoots, inflorescences, occur.  These occur at the axil of the leaf.  An inflorescence can contain 15 to 30 flowers.  The inflorescences after about 10 days to two weeks become flowers.  After the pollination period of 10 days to 2 weeks, the flowers drop and behind about ¼  of the flowers there will be a small olive.  The olive will grow on the tree for about 6 months until harvest time.  (Show picture of Stages)

From the end of February through the middle of March, the olives trees begin to bud. 

Flowers emerge from the buds and are on the tree for about 10 days. The trees are wind pollinated. Flowers drop and a small olive is formed.

Olives continue to grow for five to six months changing from green to rosy to black.

In Texas, the harvest season is from late August through October.

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Question:  What are shot berries?

 

Answer:     Sometimes olive trees will produce tiny fruit that isn’t pollinated, called shot berries. 

 

  • This can occur when they did not receive enough water.
  • Another reason is that they do not have a pollinator.
  • Weather can affect the pollination. If it rains too much when the trees are being pollinated the pollen might be trapped in the flower.
  • There may be a deficiency of boron in the soil. Boron helps the fruit to set.

Question:  What determines the size of the olive?

 

Answer:     The variety of the tree determines the size of the olive.  Olives range in size from extremely small to the size of a quail egg.  Size does not determine flavor.  Bigger in this case is not necessarily better.  

 

 

Range of sizes

Question:  When is the best time to prune olive trees?

 

Answer:      The best time to prune an olive tree to reshape it is in the spring, after there is no longer any danger of frost.  The olive tree at this time can be opened up so that it resembles a vase shape to allow the sun to reach all of the branches of the tree and to allow pollination to flow freely.  Some branches cross other branches as the tree grows.  You will need to select one branch that crosses the other branch and remove it as it will rub against the other branch as the tree grows. When shaping the tree, or hard pruning, as it is sometimes called, prune no more than 1/4th of the tree at a time.  This means that a tree may have to be pruned over several years if it needs significant shaping.                                           

 

You can prune suckers and dead branches from the tree at any time of the year.  If you buy your tree from Sandy Oaks Olive Nursery, it has been shaped for you and you will not need to prune it, except for suckers, for a few years.

 

Suckers grow at the base of the tree and will take over the tree, preventing nutrients from reaching the top of the tree if left on the tree.  Therefore, it is important to remove these low growing branches.  We prune our trees in the orchard so that the canopy starts about three to four feet above the ground. 

 

 

 

Question:  Are olives propagated from seed?

 

Answer:     Olive trees can be propagated from seed, but the resulting tree is characterized by a very long period before it begins to produce, i.e. a long period of juvenility.  Professional olive growers, propagate by using two and three-year old wood cuttings to produce new trees.  This achieves uniformity, quality and early production.

 

 

 

Question:  How tall do olive trees grow?

 

Answer:     About 15+ to 20+ feet, depending on the variety.  Trees can be topped to keep their growth within the desired height for picking.  If you see centuries old trees, the trunk will be huge, but the trees will often have a few branches and not be that tall.

                  This is because they have been topped over the centuries so that they can be easily harvested.

 

Question:  How fast do olive trees grow?

 

Answer:     Olive trees grow at varying rates depending on the variety, if they are watered and if they are fertilized.  All things being equal, they grow about 18 inches to 24 inches a year.  Production occurs in the last 12 to 24 inches of last year’s growth.

 

Question:  When is the best time to plant a tree?

 

Answer:     Spring is usually the best time to plant a tree.  But they can be planted in other months of the year, except for the winter months.  If you choose to plant in the summer, plant in the early morning before it becomes too hot.  Fill the hole with water, let it drain so the hole is muddy.  Plant the tree, water thoroughly.  Water every day for the next week and then begin to gradually level off so that you water only when the soil becomes dry.

 

Question: What pests do olive trees have in Texas and how are they treated?

 

Answer:     There are several insect pests that affect olives in Texas.   

 

  • Web Worms During February web worms will appear weaving webs that encase the tips of the tree. This can affect pollination.  The trees should be sprayed with BT (Bacillus Thuringiensis) which kills web worms.
  • Scale  Another pest is scale.  It resembles a black tick on the bark of the tree.  This usually occurs when circulation between trees is poor.  It thrives in warm dry climates.  One scale can reproduce 30,000 scales.  If left on the tree, it will develop black sooty mold.  We mix water, seaweed, olive oil, cloves and insecticidal soap in a spray bottle and spray the trees with this mixture.
  • Leaf Cutter Ants are prevalent in sandy soils. We have not found a pesticide that will kill them outright, so we just have to manage them.  We use a mixture of copper sulfide and boron.  We spray their main nest and auxiliary nests with this solution.  This seems to slow them down. 
  • Cotton Root Rot Some soils are infested with Cotton Root Rot. Trees will not thrive in soils infested with this fungus.
  • Verticillium Wilt is another soil born fungus that affects the olive tree. Verticillium wilt lives in the soil for years.  An infected tree will have whole branches of the tree die off.  It can be treated by watering regularly and fertilizing with a low-nitrogen, high-phosphorous fertilizer.
  • Anthracnose Nose is a fungal disease that affects olives. The fungus forms a large brown spot on the olive and renders it useless for oil or the table.  Spray the trees with copper about three times spread over 6 months when the olives are maturing on the tree, to control this fungus.

 

Question:  How many olives will an olive tree produce when mature?

 

Answer:     An olive tree will give mature production in about five years from when first production occurs.  On average a mature olive tree will produce between 35-45 pounds of olives.  This is about ½ to ¾ of a gallon of olive oil.  It takes about 57 to 70 pounds of olive to produce a gallon of olive oil.

 

Question:  Are some olive better for oil than others?

 

Answer:     The meat of the olive is comprised of oil and water.  Some olives contain a high oil content and these are preferred for oil, because it takes fewer olives to make oil than an olive that has a greater water content.  However, even though the oil content is high, these can still be brined to make table olives.  In this case, they are classified as dual-purpose olives.

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