Green Cover in Olive Groves: Boosting Biodiversity and Sustainability

Weeds: A Historical Overview

The Spanish Society of Malherbology defines weeds as "any plant or vegetation that interferes with the objectives or needs of men." This is a subjective definition because what for someone could be a weed, for others it may be a plant of their appreciation and interest. In other words, an herb will be good or bad depending on personal interest and, to a large extent, where it is. In fact, some plants grown and traded in one place are weeds in another. We could say, therefore, that a weed is one that, according to whom, should not be where it is and, therefore, as an improper term in general, it will at least be convenient to put quotation marks around "weeds".

In the olive grove, the farmer's relationship with the "weeds" has been a love-hate story that has shaped the agricultural landscape with varying intensity depending on the weapons at his disposal. First, until pre-industrial times, this relationship was conciliatory. The herbs of the olive groves were not bad, used as forage, edible, medicinal, and were an essential part of a multifunctional olive grove where the provision of the herbaceous cover was almost as important as that of olives, and firewood that the olive trees gave. Then the grass only got in the way of the olive grove, mainly because it made harvesting difficult.

Later, the olive grove began to specialize in those areas where it was possible to export its production and there its multifunctionality was not important for the growers. The grass competed with production and was already in the way, not only in around the trees, but also in the street between trees. In addition to pruning and fertilizing it, the olive grove had to be cultivated profusely to prepare the soil and, above all, to eliminate a herb that was no longer used. And so, with the blow of a hoe and by dint of hoisting and hoisting, first with teams of mules and then with tractors, the "weeds" were settled on the edges, roads, streams, and “herrizas”.

Later, in the late 1980s, with the EEC's productivist policies and the herbicide boom, a total war was declared on the olive grove to the herbs. Any plant that was not an olive tree was considered a weed, and its interest was exclusively associated with terms such as infestation, control, eradication or resistance. The herbs in the olive grove did not paint anything and their extermination was a clear target. It was part of a new rural culture, which it condemned as a bad farmer, a lazy man, who did not keep the soil of his olive grove free of herbs, "clean" as a paten. The grass was not only in the streets, but everywhere, also in unproductive areas. And the "weeds" were left without shelter, because now, where the tractor did not reach, the hose or the backpack with the herbicide arrived. If "weeds never die," many should not have been, because in a large part of the olive grove hundreds of species became extinct. This belligerence against the grass has continued without respite until a few years ago, when some olive growers became aware that the first environmental and agronomic problem of the olive grove, erosion, is the end product of that war without quarter and without meaning to the "weeds".

Now we are experiencing a change and reconciliation seems possible again. The manuals for the control of "weeds" coexist with those that deal with the management of herbaceous covers, they talk about their implementation and there are even companies that are dedicated to multiplying and marketing seeds of "weeds" so that the farmer can return them to the olive grove. In this new scenario, it is convenient to take a step beyond the quotation marks and call "weeds" as they should always have been called: weed plants. 

And, because they have been unfairly treated, we are going to speak well of them. Obviously, both from the agronomic and biodiversity point of view, there are more functional covers than others depending on their composition and, of course, the herbaceous cover must be managed so that it is as functional as possible and so that it does not enter in competition with the olive tree for water and nutrients. But, at present, what is clear and more than proven by science, are the benefits of herbaceous cover for the crop itself. With the available knowledge, cultivate the olive grove keeping the soil bare all year round abusing the use of herbicides or tillage it is an outdated olive growing model and unsustainable. 

Weed plants should already have a fundamental role in olive growing in general, and it is important to recover biodiversity and transform it into profitability.

Now we know that the herbaceous cover plays an essential role in recovering biodiversity. If what is sought is profitability in the medium and long term, ultimately sustainability, properly managed weed covers increase the biodiversity of the crop and with it, its ecosystem services: they protect and fertilize the soil, promote auxiliary insects and the natural control of pests and stop the spread of olive tree diseases. Furthermore, an olive grove with biodiversity is an agrosystem that is more resistant to environmental disturbances and even market fluctuations, because working in favor of nature is more profitable and safer than working against it. Because the value of the ecosystem services of biodiversity does not depend on the markets and frees the olive grower. 

But apart from for the cultivation itself and the olive grower, an olive grove with a well-managed herbaceous cover provides environmental services to society that should be rewarded by it. The control of erosion, the conservation of biodiversity or the fight against climate change (the soil of an olive grove with herbaceous cover sequesters twice as much CO2 as another with bare soil), are services that these olive groves provide and they should count in agricultural policies and in the appreciation of the added value of their oils by consumers. 

And if we talk about multifunctionality and cultural value, of added value, we have to see the olive grove as much more than a mere producer of olives, and weed plants play a fundamental role in this challenge. The herbaceous cover substantially improves the landscape of the olive grove, makes it more pleasant, livable and its cultural use opens up new possibilities for oleotourism. Can you imagine the seas of olive trees in Jaén with a green cover in spring?

The Grass Among the Olive Trees

What has been the management that the farmer has made of the grass throughout history? In the case of the olive grove, Arabs or Romans have already tried to reduce their presence in the soil around the olive tree. However, to make better use of the fields, the wide streets formed by the trees were used to grow cereals, vines or even herbs that were used as green manures, which protected the soil. 

To have hedges without vegetation. In short, the cover began to be removed somewhat more aggressively through the plow and even with crews of men and women dedicated solely to weeding the fields. However, when working with physical methods, the possibility of it was completely reduced and the affection to the environment limited. 

By means of plows drawn by mules or donkeys or with hoes it was difficult to finish all of it, even working countless days. And it is that, probably, when they finished on one side of the farm it would have already reappeared on the other. For all these reasons, tractors, but especially chemical methods (much easier to administer and effective for eradicating grass) were quickly embraced by many olive growers. 

With the entry of Spain into the EEC (the current EU), this productivist vision was consolidated and encouraged, the use of herbicides became widespread and bare soils appeared. All due to the easier access to the administration of said chemical products, together with the supposed idea of ‘weeds’ and the lack of knowledge of the benefits that the coverage had for the fields. What ended up finally resulting in the elimination not only of those located in the olive groves or the streets, but everywhere, since keeping the bare ground became part of the new culture that was being inherited.

Chemical methods that are still being used indiscriminately, although to the loss of the aforementioned advantages it must be added that it has been known for a long time that they are not harmless neither for the environment nor for human health. 

And, as it has been indicated, for the olive grower the grass had traditionally been negative, more than because of the competition it generated, because of the difficulty that concerned the work and now they had the option of ending it easily and relatively cheap. Thus, the presence of vegetation cover was quickly associated with poor agricultural practices and sloppiness at work. The belief was implanted that a good farmer was one who had his soil free of vegetation throughout the year. Even if there was no competition, even if it did not interfere in the correct performance of agricultural practices and although later on many people realized the benefits that it brought. But social pressure caused continue to eliminate, since keeping the bare ground became part of the new culture that was being inherited.

Beneficial Wild Plants

Although the inherited culture says otherwise, there are many benefits to maintaining and properly managing a green cover. One of them, probably the most direct, is the economic one, since with a good management of the cover it is possible to reduce the cost of inputs, such as herbicides or fertilizers, which will mean an improvement in the olive grove accounts. And the fact is that the elimination of the grass reduces the fertility of the soil, making the farmer totally depend on the contribution of fertilizers to achieve a nourished soil and that the olive trees produce. Something that is exemplified in the case of legumes, which fix atmospheric nitrogen and make it available to the crop. 

On the other hand, there is soil conservation against erosion. While the vegetation cover preserves it, tillage (especially in sloping areas) and the use of herbicides cause millions of tons of fertile land to be lost each year in olive groves. 

In short, fewer nutrients that end up resulting in the destruction of the soil due to the loss of organic matter, which favors its compaction. A crust is formed that not only makes the appearance of vegetation more difficult, but also makes it waterproof, preventing rainwater from penetrating, reducing its availability for trees and aggravating the erosive processes mentioned above. 

And it is that, a soil with vegetal cover accumulates more water, by facilitating its infiltration. On the one hand, because it slows down the speed at which it travels across the surface and, on the other, because it allows its penetration between the roots of the plants. To which is added that evaporation on well-managed covers is less than on bare soils. So, olive trees that grow on land with well-managed vegetation cover will have more water available than those that lack it completely.

 A whole series of advantages to which must be added another one that is really important for the future of the olive grove and the life of the entire planet, given that the plant cover is a great ally in mitigating climate change, as it is a sink carbon dioxide and reduce the concentration of this carbon dioxide greenhouse effect in the atmosphere. It can be said that if the traditional olive grove is an agrosystem that fixes a significant amount of CO2, in one that the grass is properly managed, its soil can absorb more than double.

But in addition, the presence of certain species has a clear impact on the health of the olive grove, since cruciferous species such as white mustard (Sinapis alba) or dandelion (Diplotaxis virgata) act as natural biofumigators of the Verticillium dahliae fungus, which so much damage is doing to the olive grove. 

Similarly, the auxiliary fauna is greater in those olive groves with a well-managed vegetation cover. In this regard, we can give the example of a parasitoid of the olive fly (Bactrocera oleae), whose cycle is closely related to the olive (Dittrichia viscosa), so that in farms where this plant is found, this insect is practically not located and its effect on olive and oil production is significantly eliminated. Two examples of the benefits of biodiversity on this crop that could be completed with others, some of which are probably not yet known. 

And finally, we also must add that the existence of plants diversifies and improves the olive landscape, having a positive impact on activities of socio-economic value such as birdwatching, nature tourism or oleotourism.

A Remedy Against Erosion

Soil is a non-renewable resource, since its formation takes thousands of years. Therefore, the very high rate of erosion that this crop supports is a serious problem. Every year, due to the removal of the vegetation cover, millions of tons of fertile soil are lost in the Andalusian olive grove, forming gullies that even divide the farms, making their proper management extremely difficult.

 In fact, in a study developed jointly by the Institute of Sustainable Agriculture (IAS-CSIC) and the Pablo de Olavide University (UPO) it was quantified that in olive groves in Granada, planted 250 years ago in sloping areas, soil loss caused by water erosion averaged between 29 and 47 tons per hectare per year. In graphic form, each year dozens of trucks would be entering the olive groves to leave filled with the most fertile soil on which the olive trees live. 

This same study has reached the conclusion that in 250 years a third of the existing soil has been lost, something already serious, but to which we must add that what has really happened is that it has been accelerating this trend as time has passed, due to the gradual removal of plant covers, the use of herbicides and an increasingly intensive agricultural management. 

A problem that could be solved in a relatively simple way, if proper management of the herbs that accompany olive trees were carried out. Furthermore, it must also be taken into account that erosion and plowing at great depths mean that, as already mentioned, it is essential to administer huge quantities of fertilizers - usually chemical - since organic matter is it goes along with the earth or it rusts. Some chemical fertilizers that, contrary to what happens with organic matter that is found naturally and that has been formed through the plant cover, are very soluble, so they are largely lost.

Biodiversity

To the previously mentioned advantages (slowing down erosion, increase in organic matter, more capacity to retain rainwater ...) we must add the benefits that plant cover has on biodiversity. 

Obviously, the number of plant species is much higher in those olive groves where it is managed properly, so they will have more insects, reptiles, amphibians, birds or mammals. And we must not forget the microscopic fauna, with a fundamental role in creating a living and fertile soil or in the resistance of olive trees against diseases.

The recovery of biodiversity should be one of the main objectives in the olive grove in addition to adequate management of the vegetation cover, restoring elements that have been systematically eliminated in recent decades, such as “majanos” or plants and shrubs of borders, banks, streams or wastelands, and introducing new ones such as nest boxes, ponds or insect nests.

The Vegetation Cover

To sum up, maintaining the vegetation cover in harmony with the needs of the crop will bring a series of advantages:

• Reduces spending on herbicides, insecticides or fertilizers, increasing the profitability of the olive grove.
• Reduces soil loss.
• Increases infiltration and water availability.
• Adds organic matter to the soil and increases the amount of available nutrients, reducing the need to administer fertilizers.
• Increases the number of species present in the field, improving biodiversity and providing ecosystem services.
• It allows obtaining another series of benefits from the farms, from those from areas such as oleotourism, to more traditional ones such as the collection of medicinal or culinary plants.
• Proper management of the herbaceous cover allows a long list of plants that traditionally were used and collected by people in the olive groves to reappear.

Plants that were used in the kitchen, for curative purposes or to make utensils and that we have compiled in this publication, both for their ecological and ethnological value.

Management of the Vegetation Cover

For all the benefits it brings, maintaining a green cover is going to be positive. However, it will be necessary to manage it properly, to avoid that it ends up competing with the olive grove. Something that can be done through different methods:

• Tillage: This method eliminates the grass without the need to use toxic products, but it also increases evaporation - soil moisture is lost - and favors erosion, particularly if there is a slope. In the same way, it reduces the amount of organic matter in the soil and destroys it. Even so, its use favors the appearance of some species that need soil alteration to germinate.
• Chemical mowing: The eradication of the vegetation cover using herbicides, either pre-emergence (applied to the soil before it appears) or post-emergency (once it has emerged), is a simple method, but it has a whole series of inconveniences, such as soil contamination, deterioration of soil microorganisms, exposure of the soil to erosive processes, its compaction or the reduction in the penetration capacity of rainwater. In addition, it can cause the appearance of resistant and difficult-to-control species or animal pests. However, if it is used, it is preferable to do it in spring, once the grass has come out.
• Mechanical mowing: It involves cutting the grass with machinery, keeping the dead plant cover on the surface. A technique that reduces soil erosion and increases the nutrients in it. However, it should also be noted that it may require a bit more effort in terms of weed control than chemistry, as some plants can sprout again, usually the most creeping. A fact that does not have to be negative, since they will reduce the evaporation of the water from the soil and will increase its humidity, by helping to fix the morning dew.
• By “tooth”: It is perhaps the least widespread due to the logistical complexity it presents, but it is an option that has significant benefits.

 It is usually carried out by means of sheep or horses, since it does not harm the olive tree, just as goats and cows do. Through this method, the control of the grass is perhaps less, but in return the cattle contribute manure, which increases the nutrients in the olive grove.

Taking stock of the advantages and disadvantages of each management, we can conclude that the best option will be the establishment of a vegetative cover managed through clearing, together with specific crops that are developed in different areas of the farms to remove the seed bank.

When Grass is an Ally. Testimonials

These olive growers manage the vegetation cover without using herbicides. Some for a long time and others very recently, but in any case they value their presence positively due to the benefits it brings to the olive tree. These are some of their testimonials: 

Emilio Morcillo, manages and works the Ardachel farm, in Siles (Jaén) that is part of the collective project for the production of organic oil Oleaí. He uses the techniques of regenerative agriculture and permaculture. 

According to him, grass is not a problem, but rather an ally that generates multiple benefits if it is properly managed: “We have plant cover all year round on the whole of the farm, which is quite large (about 20 hectares), where we keep a herd with about 200 sheep for a month, between April and May. Later we usually cut the grass in the olive groves with brush cutters (between May and June)”. 

Apart from the interesting esthetic values and those related to biodiversity, Morcillo highlights other benefits of vegetation cover. “It retains many nutrients, which are incorporated into the soil in the form of fertilizers. When mowing it, has a cushioning effect, which makes it difficult for more grass to come out, retains moisture for longer and ends up becoming compost.

On the other hand, certain deep-rooted plants pump water from the subsoil to the surface and create mists, which together with the mulch create a watering effect that lasts well into noon. Furthermore, when plants die, the roots tend to remain as channels for aeration and infiltration of rainwater”.

Morcillo also highlights other benefits of the grass: “it avoids erosion, the loss of soil due to rain and reduces compaction, improving its structure with the roots. They are also allies in the biological fight against pests, since some serve as food for insects such as the lacewing, whose larvae are great eaters of prays (a moth that attacks the olive tree). Also, there are plants that appear on the edges or streams of the olive grove and that are also important to maintain, because they harbor certain insects that reduce the population of the olive fly”. 

However, he remembers that “with a green cover you have to interact more with your olive grove, study and observe, as there is no fixed formula, but over time you learn, control and enjoy”.

Tránsito Habas Sánchez, together with the rest of the family, runs the “Olivar de la Luna”, a farm and mill dedicated to the production of organic Extra Virgin Olive Oil from olives obtained in the mountainous lands of the Cordovan municipality of Pozoblanco. 

In these 200-year-old olive groves, they manage the vegetation cover in two different and complementary ways: “On our farm we have two types of cover, one spontaneous and the other that we plant with selected species, usually vetch and underground clover. The latter, we usually distribute it on a rotating basis in a quarter of the farm".

"In any case, - adds Habas - the control of the herbaceous cover is carried out by grazing sheep and horses, from March to May, depending on the rainfall”.

In “Olivar de la Luna” have decided to use the grass in their favor, due to the benefits that it brings and that Transit details one by one: "The soil is the main support that keeps the olive groves alive, so it must always be cared for and protected. Much more if it is about steep slopes, such as those that can be found in the Sierra de Los Pedroches, where our farm is located, given that the vegetation cover is our main ally against the risk of erosion, as well as favoring water infiltration and improving the soil structure".

Also, as indicated, with cover planting it is possible to fertilize the soil -due to the ability of legumes to fix atmospheric nitrogen- and to obtain the added benefit provided by the livestock use of the farm. Both the spontaneous cover and the sown cover favor the presence of auxiliary fauna and increase biodiversity in the whole olive grove. A whole series of benefits to which is added the landscape improvement of the area, another resource of great importance. 

“I really believe that with these actions we are achieving an olive grove with a great diversity of life, within which our own life is included”, concludes Tránsito.

Good Practices for the Vegetation Cover

Leave a vegetation cover during the rainy season, preferably from November to May, when they still do not compete with the olive tree for nutrients and water, is a good practice for the olive grove.

In rainy years, some patches will be left on the streets throughout the farm to increase and improve the farm's seed bank.

The best methods to eliminate vegetation cover are physical, since with them a greater amount of organic matter will be incorporated into the soil and the contamination that chemicals generate will be avoided.

In case you want to select certain species, you can leave stands with them without eliminating, so that their seeds can spread.

The combination of different herbaceous cover management methods that alternate in different areas of the farm over several years will serve to increase its biodiversity.

Lastly, and in any case, vegetation will always be left on the edges of rivers and streams, banks and boundaries, as well as in the possible gullies that appear. In this way, soil erosion will be avoided, work on farms will be facilitated, olive trees will be protected and biodiversity will be improved.

The Traditional Uses of the Plant Cover of the Olive Grove

Antonio López (1945) is not surprised when I tell him that now wild plants have become fashionable in haute cuisine: I have spinach planted in my garden and I still look for wild ones. They are much finer, tastier.

Antonio was born in a farmhouse in the municipality of Martos (Jaén), and there he spent his childhood and his youth until he married. They were difficult years, more in the villages than in the countryside: In the farmhouse, we did not go hungry. We had a vegetable garden, cattle, and the countryside also gave you game and wild plants. Then he would eat almost everything.

Antonio tells us about the plants that were most consumed in the countryside: The «black jamargo» was eaten, the «cardilla», the «tetillón», the «cow's nipple», the field spinach, “collejas”, “cardo borriquero”, artichokes, fennel. What I like the most are field spinach and "cardilla." All that has been lost, and on top of that, since it is not raining now, it is very difficult to find them and also trust in them when you finally can find any of them.

Along with Antonio is his friend Manuel Ocaña, four years younger than him and also from Martos. He subscribes to Antonio regarding the difficulty of finding them and also warns of the care that must be taken when picking wild plants nowadays. Today a «jamargo» comes out and we are waiting for it.

Antonio Exposito, 86 years old, from Castro del Río, in the Cordoba countryside, mentions many of the above plants, although some with different names: Collejas, cardillos, cardillas, thistles, hinojos, artichokes, cardos borriqueros… He also agrees that it is already very difficult to find these plants and that interest in them has been totally lost: all of it has been lost. Before you would find these plants in any stream, in the gutters.

In the olive-growing countryside, weed plants have disappeared from village kitchens. It is difficult to find them and also there is no interest in it. The generation that knew them, collected them and fed on them is on the way to extinction.

However, the panorama in the “sierra” olive groves is different, although much less than before, there are people, almost all of a certain age, who still continue collecting wild plants for the kitchen. In the mountains, the use of these plants was an important resource and, it is still remembered how in the years of famine, they saved many people from the countryside from starvation. This is how Carmelo González, who was born in Torres de Albanchez, in the Sierra de Segura, in the province of Jaén in 1937, tells it: What if we ate wild plants! In the year of hunger, if it is not for these plants, we all die. In the year 46, in the Olivar de los Jacintillos the Lord blessed the vegetables. The olive trees were paired with grass because they worked them very late. People went there for vegetables and half the town was saved.

Then we ate it all, there were people who ate even the "anapoles" and got sick. I have never eaten that, but cardillos, tongues, ponds, borage, collejas.

Aurelia García, eight years younger than him, has been with Carmelo for more than 50 years. She remembers that those were difficult times, that she worked hard and got paid little. But she has good memories of her childhood: In the farmhouse, hunger did not exist. We had a vegetable garden, goats, chickens. We were much better than in town. 

Aurelia says she doesn't like field herbs. She continues to think that they are food for the poor, although she then begins to make exceptions: Well, cardillos are great for stews. The flavor that she gives it is unique. Well, and the cabbages give a point to the beans. They are cooked, rolled into a ball, and stored in the fridge, thus preserving them for when you need them.

From its habitual use in traditional rural cooking to its banishment on the table, from food for the poor to culinary treasures, time has put the so-called and abused “weeds” in their place. Who was going to tell Aurelia that perhaps her children or her grandchildren would pay good money to enjoy a plate of «Borriquero Cardo en toast buckwheat and bearnaise» in a renowned restaurant.

The prominence of these plants on the menu at Noma in Copenhagen, or initiatives such as that of the Basque Culinary Center to incorporate them into professional cuisine, are examples of their claim as quality food. Today, the Michelin Stars have discovered in the "weeds", those that we strive to exterminate, a culinary treasure.

Plants with Medicinal and Culinary Uses

There are numerous plants associated with the olive grove that have traditionally been collected and used for medicinal purposes. Used as remedies or relief of diseases by folk medicine. The following list compiles some of the most common.

• Fine chamomile or winter chamomile (Chamaemelon fuscatum): It is probably one of the best known. It has been used since ancient times to alleviate digestive problems. However, to this must be added its antiseptic and anti-inflammatory properties. In the same way, it used to be used to dye fabrics, to which it gave a characteristic yellow color.
  
  
• Poppy (Papaver rhoeas): The red poppy fields are one of the most iconic agricultural images in spring. However, beyond this valuable aesthetic value, the poppy also has various uses, among which the medicinal and culinary ones stand out. The presence of alkaloids in its petals has made it traditionally consumed to combat insomnia or reduce nervousness. However, they must always be taken with caution. Regarding its gastronomic value, the petals and tender shoots are tasty in salads and stews, as well as their seeds being incorporated into some breads.

• Ash (Chenopodium album): Although it is probably best known as the origin of certain allergies, this summer plant has traditionally been used for laxative or diuretic purposes. Similarly, it serves to protect the liver from toxicity derived, for example, from paracetamol or even to eliminate intestinal parasites. All this, of course, through an infusion of its leaves.
  
  
  
  
• Morning Glory (Convolvulus arvensis and Convolvulus althaeoides): Recognizable for its beautiful flowers and its creeping bearing, the bindweed is another of those plants that have traditionally inhabited olive groves and are currently scarce due to the intensive use of agrochemicals. It can be used as a purgative, so its infusion can solve constipation problems.
  
  
• Horsetail (Equisetum arvensis): It is a plant highly used in phytotherapy and with recognized cleansing properties, which is why it is usually used for diuretic purposes. But to this we must add remineralizing and astringent attributes, helping to control bleeding. In organic farming its decoctions are used as fungicide.
  
  
• Dandelion (Taraxacum spp.): Well known for the way its seeds are dispersed: a round corolla surrounded by vilanos that rise into the air with a simple puff. It serves to maintain the proper functioning of the liver, fights acne and eczema, improves eye health and helps to lose weight. All this, of course, through its consumption as a herbal tea, although the young leaves can also be eaten.
  
  
• Fennel (Foeniculum vulgare): Tall and woody, this plant is often used to flavor meals or in tortillas, but it is also known for its medicinal attributes as a digestive plant. Its flavor is reminiscent of anise, and can be used as an infusion. Olive growers also use its stems to dress table olives or pickled aubergines. They can be found easily on banks, gutters and unplowed areas between olive groves.
  
  
• Wild asparagus (Asparagus acutifolius): Vegetable widely consumed by olive growers and anyone who goes out to the field, sought after in early spring in the asparagus that grow next to the trunk of the olive trees. It is usually consumed in various ways, usually stewed or in an omelette, and its flavor is more intense and tasty than the cultivated one. It is also very useful in weight loss diets due to its diuretic properties.
  
  
• Borage (Borrago officinalis): Although its consumption has traditionally been closely linked to rural areas, at present it is difficult to observe it inside olive groves and it is more common for them to take refuge on the edges. Borage is a vegetable with a very low energy value, but with very interesting nutritional characteristics. It can be consumed raw, steamed or even as a dessert, frying the most tender leaves and later sweetening them with sugar.
  
  
• White mustard (Sinapis alba): This cruciferous is very common in olive groves, although it can be confused with other plants with a fairly similar flower, such as those of the Diplotaxis or Brassica genera. As its name suggests, mustard is obtained from it, one of the most widely used condiments in today's gastronomy around the world. To do this, the plant is cut and dried, until the seeds fall, from which it obtains both mustard and an essential oil, since it has a large amount of lipids.

• Wild carrot (Daucus carota): Although the carrots we are used to eating are orange and have a large, fleshy root, their wild relatives are purple in color, smaller in size, and taste considerably less sweet. They can be eaten when they are still tender, although care must be taken not to confuse the aerial plant with hemlock, which is very toxic.
  
  
• Sarsaparilla (Smilax aspera): It is a vine that can reach up to 15 meters in length. Its thorny branches cling to and thrive on the branches of trees or thrive in shrubby layers. Its infusion (along with carbonated water, honey or sugar) was the forerunner of cola soft drinks and used to be common in the salons of the West, at least in the cinema. An infusion that is also a purifying remedy to alleviate skin problems and kidney problems.
  
  
• Colleja (Silene vulgaris): It is one of the most consumed weed plants. It usually lives in the shade of olive trees or on the edges of the roads. Although it can be eaten raw, it is more commonly cooked and tortillas are prepared with it, added to stews or scrambled eggs. However, for this, you will first have to select the most tender leaves and blanch them for a few minutes.
  
  
• Wild caterpillar (Diplotaxis erucoides): This small plant can be found not only among olive trees, but also in vineyards, for example. In the event that we use it for gastronomic purposes, the part that will most interest us will be the flower, which has a bitter taste, similar to mustard. With the dried seeds, ground and with a drizzle of oil you can prepare a great vinaigrette to dress salads.

• Wild chard (Beta vulgaris): In addition to its juice being used to combat liver diseases, the most prominent use of this plant is in food. In fact, it is usually consumed, especially when its leaves are still tender, since as time goes by its flavor begins to become increasingly bitter and its texture more robust.
  
  
• Nettle (Urtica dioica): Nettle tends to thrive in the shadiest areas of olive groves, normally troughs with a high concentration of nitrogen. It may seem a lie that a plant so irritating to the skin can be edible, since, while a simple scratch produces strong itching and skin irritations, cooked or sautéed with a good extra virgin olive oil is a delight for the palate. In addition, in infusions it is a great ally of blood circulation.
  
  
• Alcaucil (Cynara cardunculus): This type of wild artichoke, whose plant is a kind of thistle, is typical of dry environments. For this reason, it has often appeared on the edge of olive groves. Its shoots (the part that is eaten) are much smaller and harder than those offered by its cultivated relative. However, they also have much more flavor and aroma, being sold today in many stores as delicatessen products.
  
  
• Cardillos (Scolymus hispanicus): This other species of thistle is the origin of one of the most traditional dishes on the tables of olive growers and field workers. The lowest and most tender leaves are usually eaten, once the thorns have been removed, in the form of stews, scrambled eggs, omelettes…

Forage Plants

Traditionally used to feed livestock.

• Bagbreaker or bastard wheat (Aegylops geniculata): Hairless, hairless, annual, tufted grass, with many straight stems and abruptly twisted at the base, about 30 cm, very hard and persistent. It is used as a fodder for rabbits and poultry.
  
  
• Bromine (Bromus madritensis): It is a large forage, although coarse. It appears between winter and spring, when other species are scarce, allowing animals to feed on this grass.
  
  
• Vallico (Lolium rigidum): It is a spontaneous forage grass, known as cereal weed for its colonizing and competing capacity with them. It is considered a good quality forage, with a high content of crude protein that can range around 25% when the plant is in the leafy state and 14% when it is covered. It is used for both grazing and mowing.
  
  
• Alpistillo or Roman grass (Phalaris minor): It is one of the most common herbs, very similar to the Canary birdseed (Phalaris canariensis), whose seeds are also fundamental food for many singing birds, in particular canaries.

• Vetch (Vicia spp.): Interesting not only for fodder purposes, since it can be fed largely to livestock, but also for the olive groves themselves, since it is an important nitrogen fixer. In this way, it favors the fertility of the land and the productivity of the trees.

The Real Weeds in the Olive Grove

Although plants, both herbaceous and shrub, offer many advantages and services to olive growers, the truth is that some do need to be eliminated. They are the "exotic" or "invasive" species, which have been introduced by humans from other ecosystems, growing, becoming patent in quite a few olive groves and endangering the survival of beneficial autochthonous plants, such as those indicated below. throughout this publication, that so many eco-systemic services provide the olive grower. Brought for ornamental or gastronomic purposes, they alter the habitat, prevent the growth of the species typical of olive groves and reduce the benefits provided by the vegetation cover.

• Ailanthus (Ailanthus altissima): If we had to select a species that represented these exotic or invasive plants, we would probably choose this one. Coming from Asia, it was brought for ornamental purposes, to beautify certain structures such as roads or railways. However, from those places it has been spreading, especially along the roads and river and stream beds, and they are already visible in some olive groves, displacing the native plants by having a massive growth and producing chemical substances called "allelopathic", toxic to other plants. Added to this is the difficulty of controlling it, since it has a very high regrowth capacity, even after fires.
  
  
• Sour or Cruet (Oxalis pescaprae): A herbaceous plant from Namibia with a pretty flower. However, its rapid growth and vigor inhibits other species from growing, by making it impossible for light to reach them and germinate their seeds. In this way, only a monospecific cover usually appears around it, which also reduces the fauna present.
  
  
• Bledo (Amaranthus spp): The biggest problems with this family of herbaceous plants (in the demonstration olive groves we have found, above all, Amaranthus retroflexus) are going to occur on annual crops (cereals or orchards), by invading the land and reducing both their profitability and the yield of the harvests.
  
  
• Cañota (Sorghum halepense): Another herbaceous plant that is common to see on the edges of olive groves or on the banks of streams and that seriously damages the biodiversity of the area, due to its rapid growth and the enormous amount of biomass it creates.
  
  
• Cane (Arundo donax): A common species in many olive groves and to which we have become accustomed to seeing, so we do not usually notice that it is exotic. However, it is considered one of the 10 most dangerous invasive species on the entire planet, both because of the speed with which it grows and because it makes the presence of other plants impossible in the areas where it moves. Introduced some time ago in this region by humans from Asia, it closes spaces, creates large biomass and even modifies the structure of rivers and streams, by retaining sediments. Likewise, it reduces the space for native plants, displaces the fauna associated with them, consumes great water and is highly flammable.

Conclusions

The main advantages of maintaining the ecosystem of the vegetable cover are:

• Soil improvement:
  • Brake to erosion.
  • Greater amount of organic matter and better soil structure.
  • Greater availability of water Increased infiltration of rainwater.
  • Reduction in evaporation.
  • Increased humidity from morning dew.
• Presence of traditionally used species:
  • Groceries
  • Medicinal
  • Foragers
• Control of pests and diseases:
  • Olive tree verticillosis
  • Olive fly
  • Less presence of other pests, such as prays.
• Presence of animal species with economic value: Greater number of game species.
• Increase in economic profitability:
  • More nitrogen fixing species
  • Greater amount of organic matter
  • Pest control.
• Savings: less need for input
  
  

Source: Olivares Vivos. “Buenas malas hierbas del Olivar”