- Where does cork come from?
- Cork oak
- Where it grows
- Common uses
- Wildlife facts
- Useful links
- CANOPY BLOG
- Tree Spotlight: Cork Oak
- The once-in-a-decade harvest of cork requires blunt force and tender care in equal measure
- Cork Forests: Actually, Money Does Grow on Trees
- Cork Oak Trees for Sale
- Cork Oak Tree – New Seedlings grown from March ’19 Acorns
Where does cork come from?
Just about every tree has an outer layer of cork bark, but the cork oak (Quercus suber) is the primary source of most cork products in the world, including wine bottle stoppers. These trees primarily grow in countries that run along the coast of the Mediterranean Sea, where there’s plenty of sunshine, low rainfall and high humidity. The countries that produce the most cork include Portugal, Algeria, Spain, Morocco, France, Italy and Tunisia.
So, why does the cork oak have a thicker layer of cork bark than other trees? The tree evolved to protect itself from the harsh conditions of the forests near the Mediterranean. These forests experience frequent droughts, brush fires and temperature fluctuations. Cork is actually made of water-resistant cells that separate the outer bark from the delicate interior bark. It has a unique set of properties not found in any other naturally existing material. It is lightweight, rot resistant, fire resistant, termite resistant, impermeable to gas and liquid, soft and buoyant. It’s these properties that make it ideal for stopping wine bottles and tile flooring. Let’s take a look at how cork gets stripped from the tree and processed into consumer products.
- Stripping the bark — A cork oak must be at least 25 years old before its bark can be harvested. Its cork can then be stripped every 8 to 14 years after that for as long as the tree lives. The cork is stripped off during June, July and August using a long-handled hatchet to cut sections out of the bark. These sections are then pried away from the tree. Workers must be careful not to damage the inner layer of the bark, otherwise the bark won’t grow back.
- Washing the cork — The cork slabs that are cut away from the tree are boiled and the rough outer layer of the bark is stripped away. Boiling the cork also softens it, making it easier to work with.
- Punching Bottle Stoppers — From the slabs of cork, holes are punched out to make bottle stoppers. This leaves the slabs full of holes. These bottle stoppers are then sorted and shipped to various destinations. The stoppers can at this time be printed or branded with names or logos.
- Uses for Scrap Cork — Once the bottle stoppers have been punched out of the cork slabs, there is some leftover cork scrap. This scrap is ground up, molded into large blocks and baked in ovens to make other cork products, such as cork tile flooring and cork message boards.
Cork has been used as bottle stoppers for more than 400 years. It is possibly the best suited material to use as a bottle stopper because it contains a natural waxy substance, called suberin. This substance makes cork impermeable to liquids and gas, and prevents the cork from rotting.
Here are some interesting links:
- This is one of the few trees able to regenerate their bark. Cork is a kind of bark where the dead cells are waterproofed by a wax called suberin. Most trees produce some cork but the cork oak produces lots!
- One cubic centimetre of cork contains 40 million air cells. It is warm to the touch, durable, light, bouncy, chemically inert, and the suction-cup effect of the cut cells makes it stick to a bottle neck.
- Cork oak wood pastures are rich in plant and animal biodiversity. Buying cork products supports cork oak wood pastures and their biodiversity.
Where it grows
South-western Europe (France, Corsica, Italy, Sardinia, Sicily, Portugal, Spain) and northern Africa (Algeria, Morocco, Tunisia). The cork oak favours acidic soils, requires a hot dry summer season and a cold and moist winter, and can be found in open woodlands, on hills and lower slopes at 300–1000m altitude.
- Cork is one of the world’s most important renewable forest products. The cork bark is stripped off the tree in a thick cylindrical layer. Each tree is harvested every nine years.
- A single tree can cork 4,000 bottles. Fine wines can develop through the happy marriage between cork and a bottle made tall enough to lie on its side. The wine ‘breathes’ through the cork as it ages.
- Cork is a biodegradeable alternative to environmentally unfriendly PVC flooring. It is hard-wearing, very sound absorbent and agreeable to walk on due to reflection of warmth and its natural bounce. Cork is also used in insulation, floats, engine gaskets and even skirts, heels and handbags!
Cork oaks have been grown since the Middle Ages in Portugal and Spain in open woodlands grazed by sheep and cattle. High-value ham is obtained from the Iberian pigs that thrive on the fallen acorns. No fertilisers, herbicides or irrigation are used. This traditional farming supports a remarkable abundance and variety of rare and endangered wildlife, including the black vulture, booted eagle, Bonelli’s eagle and short-toed eagle, which make giant nests in cork-trees and eats snakes.
- Portuguese Cork Association
- Lobe: incomplete division in any plant organ (eg leaf).
- Scale: overlapping structure on cone or fruit.
Tree Spotlight: Cork Oak
By Galyna Vakulenko on October 22, 2018
Photo by Denisbin via Flickr.
Tree Spotlight Series: Follow along as we learn about the fascinating trees that live among us. This series is in partnership with Rhee Lab in the Plant Biology Department of the Carnegie Institution for Science.
Other posts in the series: ginkgo biloba, Douglas fir, giant sequoia, Chinese tallow, silver-dollar gum, Monterey pine, green dracaena, and coast live oak.
The unassuming cork oak
Gnarled bark of the cork oak, growing in Palo Alto. Photo by Galyna Vakulenko
Imagine having a fancy dinner with family, friends, or a loved one. You pop open a bottle of wine and untwist the cork from the wine opener—the cork is light and rubbery in your hand. If the occasion is special enough, you may save the cork as a memento of the evening. The cork stopper is unassuming and easily forgotten, thrown out or piling up in a box in our homes, but it is a vital part of the wine industry. All the cork used to make these stoppers is harvested from one species of tree—the cork oak.
The cork oak (Quercus suber) is a large evergreen oak tree native to Spain, Portugal, and the Mediterranean region. It has green spiny leaves, twisted branches, and deeply fissured bark. But beneath the top layer of bark is a thick spongy layer of cork.
A cork oak being harvested. Photo by Cazalla Montijano and Juan Carlos.
At the start of the seedling’s life, the cork oak mainly grows upwards, a process known as primary growth. Later on, the oak grows in thickness to support itself—this is called secondary growth. Cells become dense with a sturdy molecule called lignin and the brown wooden bark is made. Just underneath the bark, there is a ring of specialized cells around the trunk called the cork cambium. The cork cambium creates special cork cells and pushes them outwards.
Mature cork cells are actually dead and heavily packed with a large molecule called suberin. Suberin is a very stable molecule that resists both water and fire. This layer of cork forms a seal around the tree, protecting it from the outside world.
Cork from cork oak trees is constantly being produced and can be harvested every few years. Since the tree produces such a thick layer of it, and since the cork cells themselves are not living, harvesting cork does not actually harm the tree. This makes cork a truly reliable resource. As a material, cork is invaluable to the wine, flooring, and textile industries.
Structure of suberin.
A protected ecosystem
Additionally, wild cork oak groves are protected ecosystems. Cork oaks provide homes for a variety of endangered organisms including the Barbary ape and the Iberian lynx, the most critically endangered feline in the world. In fact, in Portugal, cork is such a valuable source of income and biodiversity that it is illegal to cut down any cork oak.
A recent shift away from using cork stoppers in wine bottles may pose a threat to the cork oak. If the economic value of the tree diminishes, they might be less protected, and that may threaten the ecosystems they uphold. But while wine corks are seeing a decrease, cork is still being used to make many other things, such as flooring, bags, shoes, jewelry. Our fascination with this incredible material is far from over, and cork oaks around the world continue to thrive.
Galyna Vakulenko was a 2018 summer intern at the Rhee Lab in the Plant Biology Department of the Carnegie Institution for Science at Stanford University. She is an undergraduate student majoring in plant physiology at Carleton University in Ottawa, Canada.
How cork is made
An illustrated guide to the cork production process
It all starts in the forest. Cork oaks are harvested every nine years, once they reach maturity. It doesn’t harm the tree, and the cork bark regrows. Most cork forests are in Portugal and Spain.
The year of harvest is marked on the trunk, so each tree isn’t harvested at the wrong time. Cork is a great insulating material, and gives these oaks a chance to survive the forest fires that occasionally happen in the hot Mediterranean summers.
Here’s a close-up of a tree that was harvested the year previously.
The harvested cork planks are stored before processing. Good cork companies will store them on concrete rather than bare earth, lowering the risk of contamination.
This is a close-up of a piece of bark. It’s quite thin, and won’t be used to produce high-quality natural cork. But now there are also technical corks, made up of small pieces of cork fused together, which means that more of the cork bark is suitable for producing wine bottle closures.
Before processing, the cork planks are put on pallets. Then they are ready for the first stage in the cork production process: boiling. The following pictures were taken at Amorim’s facility in Coruche, ion the south of Portugal.
The planks are boiled to soften them, and also to clean them. In the bad old days these would be boiled in murky pits without the water being changed very often. Now, to avoid cross-contamination, the water is cleaned, filtered and replenished regularly, with volatiles being removed on a continuous basis.
This batch is just going in.
The boiled planks are flatter and easier to work with
This is a nice-looking piece of cork.
Next the planks are graded and cut into workable pieces.
Some will be used for punching natural corks out of; others will be used to make technical corks. The pictures below were all taken at Amorim’s factory in the north of Portugal, south of Porto.
These workers are hand-punching corks from strips of bark: these will be high-end corks. Others are machine punched.
It is a skilled process: make the wrong decisions and the corks aren’t good enough, or cork is wasted.
What remains after the corks have been punched. This remaining cork can be ground up to make granules that can then be glued together to make agglomerate cork.
The corks are optically sorted: blasts of air are used to send the corks into the right grade bins.
Then the corks are sorted by eye.
Great care is taken sorting the top grade corks.
These corks will be really expensive: over a Euro each.
On to part two: making technical corks
Back to top
A person sees many countries on a European tour—and I don’t necessarily mean those divided by political boundaries and languages. I mean truffle country, sweet wine country, bear country, bike country, tax-free perfume country, cider country, salmon country and Basque country.
Further to the south, on the sweltering, blistering hot plains west and south of Madrid, the traveler finds the stately old monarchs of cork country. It’s not the grandest claim to fame for a landscape—its parched soils produce oak trees whose spongy bark will be cut up and plugged into wine bottles. But the corks of Spain and Portugal have played a key role in the making of wine for 200-plus years. The trees are beauties. They assume a huge girth over the centuries that they stand on these interior plains, and in a country where the summer sun all but sets the land on fire (I’m here now, and it’s 105 degrees in the sun, 80 in an air-conditioned hotel room), their shade is precious. Readers may know the story of Ferdinand, the great and gentle bull who lazed away the blazing Spanish days in the shade of his favorite cork tree.
The cork tree’s bark is a thick spongy hide that is stripped stripped away by workers using knives and axes once every nine years—the normal time it takes for the tree to recover. A number is often spray painted on the tree to indicate the year in which it was last harvested. The average specimen of Quercus suber produces about 100 pounds of cork in a stripping, while the very largest tree—named the Whistler Tree, 45 feet tall and a resident of Portugal’s Alentejo region—produced a ton of bark at its last harvest in 2009. It was enough for about 100,000 corks—enough to plug up the entire annual sweet wine production of Chateau d’Yquem.
A close-up view of the cork tree’s great gift—its spongy, pliable bark, freshly exposed by a cork harvester’s axe. (Photo courtesy of Flickr user Marco di Pisa)
The Whistler Tree is the oldest known cork tree. It sprouted from its acorn 20 years before Lewis and Clark described the Rocky Mountains and produced its first cork crop in 1820. But even the youngest trees of cork-producing age (they aren’t harvested until they’re about 25 years old, and the first two harvests are often unsuitable for use as bottle stoppers) date back to the years before the advent of the screwcap—which puts a, um, twist into this story. For that little aluminum artifice of convenience for the wine drinker has become enemy number one of the cork industry, which employs tens of thousands of people full time or seasonally. And things look bleaker than even the desert plains of La Mancha for the Mediterranean’s five million acres of cork country. A report from World Wildlife Fund in 2006 predicted that by 2015—just three years away—95 percent of all wine bottles would be sealed with screwcaps, plugged with synthetic corks or packed as “bag-in-box” wines. That report remains the official prophecy of the future of corks.
This could mean the chainsaw for many of the trees, as their owners turn to more profitable uses of the land—and you can’t blame winemakers for seeking cork alternatives. Because cork taint, a condition that plagues even the greatest, most consistent wineries, makes as many as 15 bottles in 100 unpleasant, sometimes undrinkable. Cork taint is caused by “TCA” (or 2,4,6-trichloroanisole), a product of bacterial growth that occurs in the living bark of Quercus suber and which may be transferred to the wine if a cork is improperly sterilized. Screwcaps and other cork alternatives eliminate this risk. Many wine producers may never abandon the cork, which some say can positively affect the flavor of a wine and facilitate bottle maturation by allowing oxygen and other compounds to enter and exit through the porous cork. But some regional wine industries have have entirely shifted into the cork-free future. In New Zealand, when I visited the home of a friend in March, I picked up a bottle of a local Cabernet Sauvignon, harvested late in the Clinton era and plugged with a real cork. Today, virtually no wineries in New Zealand use corks, and when I showed my friend the bottle, she said, “But how are we going to open it?” Her household did not contain a corkscrew.
If the cork forests vanish, wildlife including lynx, red deer and pigs would lose their homes, and in Portugal alone more than 60,000 people might lose their jobs as the cork industry sink—like a rock. And instead of a sustainably harvested and biodegradable product, we would have synthetic replacements made of factory metal and plastic. Otherwise, most of us wouldn’t be affected, except that in fancy restaurants we wouldn’t get to feign scrutiny anymore when the waiter offers the wine cork to be smelled. And, of course, it would be a shame to lose the trees, whose shade in these parts, I assure you, is more precious than any wine.
Want to see a few cork trees and some real cork harvesting in action? In summertime, the highways through the Alentejo region of eastern Portugal and the bordering region of Extremadura in Spain are the places to be. Tourist services even offer guided bus trips deep into cork country, specifically to watch men and women stripping the trees, followed by a visit to a cork factory in Lisbon. Also to be expected are fine food and wine—probably not from screwcapped bottles, but watch closely. And a Portuguese cycle-touring company, Blue Coast Bikes, gears guests up for bike rides through the cork country, mostly to see castles and grapevines, but the cork trees are there, if for no purpose at all but to be enjoyed.
A harvester hauls away strips of bark from a Portuguese cork tree. The tree will stand for nine years before it is stripped again—if people are still harvesting cork by then. (Photo by Sebastian Rich and World Wildlife Fund)
The once-in-a-decade harvest of cork requires blunt force and tender care in equal measure
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We recently covered the (long) history of wine storage and transportation. As we discussed in that article, the glass bottles we’re so accustomed to today are only about 400 years old, despite the fact we’ve been drinking wine for 8,000 years. No glass bottle is complete without a stopper — to keep the wine inside and to keep oxygen and airborne bacteria out. After some brief experiments with other materials, cork emerged as the stopper of choice. It’s held that position for centuries, though recent innovations like screw-caps are threatening its long dominance.
So what is cork and where does it come from? A finished cork is made from the bark of a particular species of oak tree, Quercus Suber. You could say this species of oak tree is cousins with the types of oak trees that are used for barrel aging wine. Quercus Suber grows in a limited climate zone, and for various reasons (civil war in Spain and economic instability in Algeria) Portugal has come to dominate the modern production of cork. The country is home to about half the world’s commercial cork-producing oak trees, spread out over more than 1.6 million acres of forest.
In a 1.6 million acre forest of cork trees there’s bound to be some variation among the trees, but there’s one tree that really stands out, and its name is The Whistler Tree. To put The Whistler Tree in perspective, let’s take a look at a typical cork tree:
- A cork tree is typically harvested for the first time when it turns 25 years old.
- It can subsequently be harvested every 9 to 12 years (9 is the minimum under current Portuguese law).
- A cork tree’s average life expectancy is about 200 years.
- When a typical cork tree is harvested it will yield around 100 pounds of bark, enough corks for about 4,000 bottles. This number can vary quite a bit over a tree’s long life.
So How About The Whistler Tree?
The 1991 harvest is the most famous, and the largest on record:
- 2,645.55 pounds of bark were pulled from the tree.
- That record haul of bark yielded well over 100,000 individual corks.
Some quick math will tell you that this harvest alone was responsible for more corks than some trees produce in their entire 200-year lives. The Whistler Tree’s harvest was a bit more modest in 2000, but seeing as the tree’s been harvested regularly since 1820, it’s estimated that by the time its bark is removed for the last time it will have yielded the raw material that went into more than 1 million corks.
The Whistler Tree, located in Portugal’s Alentejo region is the world’s largest, oldest cork tree!
If you’re wondering how bark turns into the typical cork with which you’re familiar we suggest you check out these two great resources:
- Watch this video to see how you harvest a cork tree (hint – axes are involved).
- To learn how the harvested bark is turned into an actual cork check out The Wine Anorak’s great guide (with photos!).
Header image via .com
Posted on March 2, 2011 – by admin
Cork Forests: Actually, Money Does Grow on Trees
Think about the last bottle of wine you drank. Was it sealed with a natural cork? A synthetic plastic closure? A screw top cap? Where does cork come from, and what’s with all the buzz about cork trees being endangered? To investigate, we ventured off to Alentejo, a rural region in south-central Portugal, and one of the world’s largest sources of cork oaks. All told, Portugal produces about 75% of the world’s cork, and about 75% of this goes into wine bottle stoppers. About 33% of all cork trees grow in Portugal, and 95% of these are in the Alentejo region.
At Herdade da Maroteira, Philip Mollet guided us on a tour of his 540 hectare farm. Much of the land is forested, with approximately 2/3 covered by cork forest, 1/3 covered by stone oaks, and some cleared land for vineyards and livestock. Mollet is a 5th generation farmer, whose family originally hailed from Britain. As the story goes, in the beginning there were two brothers who were on their way to Australia. They stopped in Porto to make repairs on their boat and look for cork stopper resources. The brothers ended up traveling to Alentejo, where they found this particular cork farm. One brother continued on to Australia, while the other stayed in Portugal. Later on, the brothers arranged for a cultural swap, with one brother sending eucalyptus to Portugal and the other brother sending cork acorns to Australia. However, the acorns that were sent were sterilized—nothing like a little sibling rivalry to help foment family feuds!
A cork oak has two layers of bark—the cork, which is the outer layer, and the inner bark. After the cork has grown to sufficient thickness, you can strip it by hand using an ax with a curved blade. To date, no mechanical harvesting method has been developed, and it requires skill and experience to harvest cork without damaging the tree. Workers must be able to gauge the cork sheet’s thickness, and not cut too deeply into the tree, or they will cause irreversible damage. Done properly though, cork is a renewable resource, and a healthy tree will produce cork almost indefinitely, or until its life expectancy of 600 years is up.
Cork can first be harvested at about 25 years of age, but this virgin cork is considered low-quality and is worth about the price of the stripping. Thereafter, cork is usually harvested every 9-10 years. To keep track of the last harvest, each tree is marked with a number to indicate the last year it was stripped. For instance, a “6” means the tree was last stripped in 2006.
When do you harvest cork? As it turns out, the cork layer usually sticks to the tree like glue, but there is a narrow 3-week window each year when you can strip cork. As the weather moves out of cold temperatures into warm ones, the trees “sweat” and it is possible to separate the cork from the inner bark. The timing of this window varies from region to region, and depends on humidity as well.
At Herdade da Maroteira, cork harvesting takes place for about ten days in June, and is done primarily by a team of 12 men with axes. Any more than that, and it becomes difficult to supervise workers and make sure they are doing the job properly, said Mollet. They are supported by a back-up team of employees who drive the tractors, paint numbers on the trees, and stack the cork sheets.
The quality of cork depends on the thickness and density of the cork sheets—the greater the better. Cork is traded in units called arroba, which is equivalent to 11.5 kg in Spain and 15 kg in Portugal. Top-notch cork, with high density and thickness, is sold for €40-50/arroba, while lower quality cork might be sold for as little as €8/arroba. Mollet’s cork is middle of the range, with high density but average thickness, and sells for about €18/arroba.
What about all the rumors of a worldwide cork shortage? According to Mollet, cork production is fully sustainable and there is no truth to these claims. “The problem is the wineries,” he said. “Everyone’s looking at cost.” He explained that natural corks cost 28¢ each, while lower-grade 1+1 conglomerate corks and powdered corks cost 8¢, and a 100% conglomerate cork costs 4-5¢. Meanwhile, plastic corks cost 3-4¢ each. Mollet lamented the rise of synthetic closures and said, “Look, this cork is ecological, biological and natural. If we lived in the US or the UK, we’d be marketing this product heavily. But the Portuguese government has their hands in their pockets. So, winemakers are moving to plastics to cut costs, not watching quality and not knowing what goes into the wine.”
In recent years, the demand for cork and value of the raw product has fallen sharply. At the market’s peak about ten years ago, Mollet was grossing about €120,000 for each cork harvest, but that figure has fallen to €42,000 today. Simultaneously, stripping costs total €30,000. And that does not even account for the year-round costs of maintaining the cork forest and fighting the coraebus undatus beetle that infects cork trees. It is a poor time indeed to be in the cork-growing business.
To verify Mollet’s claims, I did some research on the sustainability of Portugal’s cork forests on my own. The cork oak is indeed listed on the World Wildlife Fund website as a priority species, but not for overharvesting. As stated by the WWF, “Harvesting of cork for use in wine stoppers is entirely sustainable,” but “increased market share for alternative wine stoppers could reduce the value of cork oak areas, leading to their conversion or abandonment.” In other words, not using cork stoppers will hurt the continued preservation of the trees.
Mollet realized long ago that it was risky to be dependent on the vagaries of the cork market, and decided to diversify his farm into other lines of business. Today, the farm also raises pigs, produces wine, olives, olive oil, honey and has two agrotourism guesthouses for visitors. The pigs are actually owned by Spanish livestock farmers, and are sent to Mollet’s farm in the fall to gain weight. These prized Iberian pigs arrive in October weighing approximately 80 kg, and leave in March at 180 kg. Mollet is paid based on the amount gained by each pig, which comes to about €120 per pig. “I make sure that they are happy and comfortable,” he said. “We keep them as calm as possible, in a stress-free environment.” The pigs are rotated from section to section of the forest, as they feast on acorns dropped by the oaks. They will later be processed into prized jamon iberico and other meat products, for a total value of around €3,000 per animal.
Why harvest the cork if it is a money-losing prospect? Mollet paused to reflect on the volatile prices and pests threatening Portugal’s cork oaks. “People used to say, ‘Money doesn’t grow on trees,’ and we would respond, ‘Actually, it does.’ But now I’m making just enough money to keep the tractor running. Fortunately, we diversified into wine, but the whole cork industry is in trouble, and if something doesn’t change, the forest will die.” Without protection, it is likely that the forest will be converted to other uses and the trees logged away.
Did your wine purchase for tonight’s dinner just get a little more complicated?
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This entry was posted on Wednesday, March 2nd, 2011 at 12:05 pm and is filed under FRESH Ideas. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.
Cork Oak Trees for Sale
Cork Oak Tree Seedlings
For Sale QLD NSW VIC ONLY
Cork Oak Tree – New Seedlings grown from March ’19 Acorns
Form: Evergreen. Tall and Erect to 20 metres. When acorns were put down in May, they had roots escaping from base of 200 mm long tube within 3-4 weeks. Cork Oak forests produce little leaf litter and so are considered “fire safe zones”.
Functions: These are our first seedlings to be propagated. So all plantings are experimental. Over time the evergreen nature of the Cork Oak makes it useful as a frost protector for other frost sensitive tree.
Frost and Hardiness: Grows around Canberra. Renowned for frost and heat resistance
Planting: Year-round with tree guard first 2 years recommended. In a sheltered location with regular water, you can get away with no tree guard. Direct summer heatwave sun first 2 years can rapidly kill an undeer watered seedling. Maintain periodic watering as needed. 20 litres per tree per tree per fortnight on average, more small waterings when small. SUPPLIED in EXTRA SUPER TUBES: Weight of a soil filled EXTRA Super Tube is 800 grams. These are longer than standard Super Tubes. 200 mm length. Individual seedlings were propagated in tubes, so they have never been transplanted. Gives better root development.
Source of Seed: Seed is from a Cork Forest near Canberra.
Growth Rate: Considered slow growing.
Natural Range and Soil Type: Spain and Portugal. From information obtained, we are planting in lighter sandy soil with a bio-char plug.
Predators: Seedlings we believe would be palatable to most mammals.