Authors: Péter Radácsi and Zsuzsanna Pluhár

Features of the medicinal plants sector

In the medicinal plants sector, like in the other horticultural and agronomic sectors, the cultivation comes to an end by harvesting. It must be done very carefully because it is dominant step of the one or more years of cultivation process. The aim of the harvest is very similar to other cultures: to do the harvest with the least possible loss, during the shortest time and to provide the best quality. One particular characteristic of medicinal plants is that not all plant part contains biological active compounds or the plant parts accumulate them in the same amount. For this reason, at the time of harvest we must attempt to collect plant parts of higher level of active agents. We have to pay attention to the timing of the harvest because many times it does not coincide with the full biological ripening phase. As an example woundwort species show after blooming character, for this reason they have to be collected in bud-stage. In the case of majority of plants accumulating essential oil, the maximum amount of essential oil accumulates between the bud-stage and full blooming. The climatic conditions can decrease the short harvesting period (rainy weather). The available short period must be used as much effectively as possible. Thus we have to use the labour work and the machines with the highest efficacy.

Determination of time of harvest and its effect on drug quality

In the case of medicinal and aromatic plants the optimal harvesting time can be determined considering the following factors:

• the harvest is due when the target plant organ contains the active compounds in the highest possible level (%),
• the harvested organ reached the maximum size and specific maturity
• it is possible to obtain an adequately high yield (t/ha), when the calculated active substance yield (kg/ha) is at the maximum

Generally, a specific optimization procedure is needed at all the cultivated medicinal plants in every growing year, if the grower aims to find the best harvesting period. However, there are similarities at those crops where the harvested organ is the same or at plants species, which belong to the same family.

The optimal harvesting time is frequently differs from the complete biological maturity, thus the technological ripe phase has to be determined instead. The latter can be characterized by a specific developmental phase of the plant organ, which has already accumulated an appropriate high level of active principles.

Considerations on all the above mentioned criteria, together with the quality standards are very important during medicinal crop production. Specifications of the Pharmacopoeia (e.g. Ph.Hg. VIII., 2004) as well as national and international standards (e.g. ISO) comprise descriptions and limits for drugs including criteria of organoleptic and active compound properties. In order to fulfil the requirements involved in the quality standards, the circumstances of harvesting have to be properly planned to obtain dried drugs or essential oils of appropriate features. For example, concerning the standards of pharmacopoeia concerning Thymi herba min. 1.2 ml/100g essential oil and min. 40% for phenolic monoterpenes (thymol and carvacrol) are specified in the dried and crumbled aerial parts.

The grower has to take into account the active substance yield, which is the quantity of the active compounds expected from the unit area. It can be calculated by multiplying the biomass harvested (t/ha) with the level of active compounds (e.g. g/100 g or ml/100 g). For example, in the case of tarragon (Artemisia dracunculus), 25-30 kg/ha essential oil can be produced from approx. 15-20 t/ha fresh biomass of shoots.

Biological bases of the harvesting time optimization

In order to properly determine harvesting time, the grower has to know several specific properties of the medicinal plant cultivated. In addition to the characteristics of the variety, the species and the plant family, it is essential to be aware of the botanical features of plant organ harvested and of the ultra structure of active substance containing particles (secretory tissues, glands, ducts or cavities, etc.).

Moreover, the grower should determine the phase of technological maturity by detecting the appropriate size, shape, colouration or dry mater content and other features. Other specific characteristics influencing the success of the harvest should also be considered (e.g. tendency for fruit shedding, the height of wooden branches, developmental phases of the fruits, etc.).

It is indispensable to know the phases of ontogenesis, the effects of plant age and the seasonal changes. According to the life forms of medicinal plants, we can distinguish annuals with short season (e.g. mustard) or with long season (e.g. pot marigold), biennials (e.g. clary sage) as well as perennials. In the case of perennials it may occur that on the basis of the life form one cannot predict the exact duration of the culture: sometimes the valuable parts can be harvested within a shorter life cycle. Such a shorter, annual culture is sufficient for the development of valerian root; therefore the grower can collect it at the end of the first growing year.

The duration of the culture at the arboreal perennials (e.g. thyme, sage or lavender) is not always identical with the whole lifespan of the species. Furthermore, the geographical site and the training system are also influencing factors for the maintenance of the plantation. The purpose of drug production (dried aerial parts or essential oil extraction) and the annual frequency of harvest also have effect on the economic utilization of a woody perennial field. The adequate level of nutrients and water supply may compensate the plantation for repeated harvest, however, the ageing and decline by exhaustion of the plants or the woodenness are unavoidable, either. A good example for the correlation between the growing purpose and the duration of the culture is the utilization of garden thyme for essential oil production. In this case, thyme plantation is harvested once a year for essential oil distillation, therefore the duation of the culture can be 8 years. However, if used for the production of dried and crumbled drug by cutting twice a year, the plantation can be economically maintained only for 4-5 years.

The above mentioned biological points of view, as influencing factors of harvest, are to be considered before establishing the fields of medicinal and aromatic plants.

Environmental factors influencing the optimal harvesting time

According to the geographical location of growing site, the optimal time for harvest can be different, affected by the regional macroclimatic and edaphic (soil, relief, exposure, etc.) factors. Furthermore, the grower has to pay attention to the weather conditions (e.g. precipitation, temperature, duration of sunshine, etc.) during harvesting period and the divergent effects of the growing year (e.g. weather anomalies, drought periods). All the mentioned factors may have influence on the development of plants and the success of harvest. The level of certain active compounds (e.g. poppy alkaloids) possibly decreases if cloudy and rainy days occur prior to harvest.

The daily rhythm of the active compound accumulation has already been described in the case of numerous medicinal plants, though, a more accurate timing of harvest is possible (e.g. the flowering shoots of clary sage contains the highest level of essential oil at dawn, 3 to 6 h).

In another situation the grower chooses the early morning period for harvest in order to avoid seed shedding (e.g. mustard species) as well as to increase the yields.

The growing conditions also have effect on the development, the ripening as well as on the yields. Fertilizers and irrigation applied after the first harvest increase the regeneration and sprouting of the plants in the case of the multicut herbs (e. g. mint, lemon balm, St. John’s Wort) and promote the second harvest.

When using pesticides, the attention paid for timing and waiting periods prior to harvest is essential, as the harvested plant parts must not contain harmful residues.

The harvest of medicinal plants

Harvesting of medicinal plants can be categorized by origin, in this case we differentiate between cultivated and wild-growing (collected from natural habitats) medicinal plants, furthermore distribution can be made by the level of mechanization as well. In this case we can talk about manual-harvesting, semi-mechanized-harvesting and mechanized-harvesting.

Manual harvesting

The row material harvested by skilled worker can be of great quality, there are some cases when because of the sensitivity of the plant material, the only feasible way is manual harvesting (for example the style of saffron must be taken one by one from the flower). In other cases for the harvesting of the plant there is not appropriate mechanization (for example: collecting of black pepper). It can be stated, that manual collecting is a process demanding heavy manual-labour that is why this kind of collection is rarely profitable both in developed and developing countries. As the different pickers collect in various ways, it goes without saying that employment of high number of workers result in a heterogeneous quality of the medicinal plant collected. In Hungary manual collection had been limited to wild-growing medicinal plants recently, primarily because of the increasing costs of labour.

Semi-mechanized harvesting

In this case we do not mechanize the process of harvesting, but we want to make it more comfortable. Several research and conception on semi-mechanized harvesting have been published yet, but only few of them have been introduced into practice. Wild-growing chamomile is collected by hands or by means of the so called”chamomile-comb”. It is a common practice that chamomile-comb is equipped with handgrip as well, making the work more ergonomical. For the semi-mechanized harvesting of chamomile flowers we can also use a little gathering-wagon applied in Argentina. The upper part of this machine reminds us to chamomile-comb, but it rolls on cart-wheels, this way gatherer only has to move the utility-wagon at appropriate speed among the population. The advantage of this method is that gathering can be carried out at equal level of plant height (but this is its drawback as well, because the high level of relief-variancy makes the gathering process more lumbering).

”Chamomile-comb” for gathering flowers of chamomile (Photo: Bernáth)

Drawing of little gathering-wagon for gathering chamomile (a-comb, b-travel direction) (According to Öztekin & Martinov, 2007)

Similarly this would be adaptable for other species giving flower drug as well. But we must take it into consideration that the collection is not selective, in other words it collects buds and overblown flowers as well. If we think of the collecting of styles of saffron, we can understand it easily that long-lasting bending and the uncomfortable working posture really outwears the picker’s physique. In this case it would be also possible to promote collecting by applying a more ergonomical posture. The cart rolling near the ground surface, in which the sitting collector can pursue picking, is not an unfeasible task. Similar application had been used for collecting asparagus, where cutting is made by the collector but while sitting in the cart. Furthermore it is worth mentioning the method of gathering of hautboy strawberry, where worker gather fruits in a reclining posture facing the ground.

„Picking-cart” made for gathering of asparagus (Source: http://www.british-asparagus.co.uk/blog/ )

”Picking-cart” applied for gathering of hautboy strawberry (Source: http://www.haygrove.co.uk)

When collecting wild-growing plants, one of the problems waiting to be solved is that how the raw plant material can be delivered to the collection-hub at the lowest energy-need. One possible example is that the collected plant material, with the help of an exhaust-fan, ends up at a collection-container located on the picker’s back. Another conception can be bound to the collecting of coffee, where beans are beaten down by a mechanical beater(-machine) to collect them on a foil laid down under the coffee-shrub. The beater(-machine) is driven by an engine and it is fastened to the collector’s back. This way bigger production can be achieved than by applying manual collecting or hand-beating.

8.5 Figure Beater(-machine) applied for gathering of coffee (beans) VIDEO (Source: http://www.efico.com/watch-how-it-works/semi-mechanical-harvesting ) ( gyógy_8.5..flv )

Mechanized harvesting

As it was previously discussed the mechanical harvesting is usually applied in the case of cultivated species. Mechanical harvest of plants can be realized only if the following conditions are fulfilled:

• ripening of the plants must be homogenous (one step harvest of the biennial caraway is not effective because of the high rate of fallen seeds)
• harvested plant organs must be homogeneous on the shape, size, ripening and plant height

Mechanized harvesting is economical only if the area is big enough. Otherwise the harvesting of the small, fragmented areas is not effective enough. The transportation of the equipments and the harvested raw material from one growing site to the other is expensive.

Root and bulb harvesting

Harvesting of root and bulb has two major aims: digging (lifting the plant organ from the soil) and separation of the plant material from the soil gains. If the aboveground parts are intact usually they are removed before the digging procedure. You must be aware of the differences between the different roots and bulbs. Celery has ball shaped root with thick but not strong side roots which are in the upper 10 cm part of the soil. The carrot intrudes deeply into the soil and the shape is cylindrical. The rhizomes of the horseradish intrude also deeply into the soil however they grow usually almost horizontally and there are many branches on it. The valerian has very branching root system. Roots intrude only 20 cm deep into the soil. Taproots of the dandelion are 15-20 cm long. Their shape is rather spindle shaped. It is easy to recognize that it is impossible to find one equipment which could fulfil the requirement for all of the mentioned root types.

Main steps of the root harvesting

1. removing of the aboveground plant organs
2. digging in the depth of the roots (or deeper)
3. lifting of the roots
4. separation of the soil grains

For harvesting the roots of the medicinal plants the same equipments are usually used, which were developed for vegetable or other crop harvesting. The modified potato and onion harvesters are mainly used but the simplest tool is the mouldboard plough. Two different harvesting methods are used: potato harvesters and ploughs are the so called diggers while the carrots are harvested usually in the pulling-lifting way. The schematic diagrams show the differences between the two systems. The lifting system based on a blade, which unstring the soil under the roots and two parallel rubber belts which grab the green tops of the carrot plant and lift them out from the soil. The removal of the aboveground part is done only after the lifting. Harvesters used in Europe are the EM-11, E-825 and ASA-LIFT. These machines are mainly used for carrot harvesting.

In the digger system the roots and the soil get on the sifter where the soil grains are separated from the roots. In this system the leaves are removed before the digging.

Schematic diagram of the lifting root harvesters (a-paralell rubber belts, b-leaves removing blade, c-conveyor belt, d-ripper) (Radácsi)

Schematic method of the digger type carrot harvester (a-leaf remover, b-ripper/digger, c-conveyor belt with sieve) (Radácsi)

Harvesting of leaves and stalks

The aim of the leaves harvesting is quite simple: with a horizontal cut the beneficial plant organs have to be separated from the underground plant part. The height and the intensity of the cutting are always related to the different plant species. You have to distinguish the harvesting method depending on the desired plant organ to be harvested. If the plant material will be dried you have to treat the material gently. The gentle treatment is not so much important if the material will be distillated or other extraction procedure is planned right away after the harvest.

For the MAP harvest the equipments are usually used which were developed for other crops but the MAP often requires special demands. In some cases the prostrate brunches must be also cut (e.g. sage) but the conventional reciprocating mowers do not fulfil the requirements. The cut plant material must be treated gently but it is also important to decrease the damages. Some of the equipment developed for field crops does not fit for MAP harvesting because they are not gentle enough, the conventional reels are too fast and aggressive. They can cause serious damage in the case of low growing plants (e.g. thyme) and young plants with weak root system.

The area of the cultivated MAP is smaller than the other crops (cereals, vegetables) that is the reason why only a fey machine were developed for the MAP cultures. One good example is the Fendt Agrobil S which was developed in the 1970s. The Fendt Agrobils S does not have a reel. The self loading equipment is usually used as a forage harvester. Usually it is used in mint or lemon balm plantations. The weakness of the equipment is the precipitous elevator where the entanglement of the plant material is frequent. The Fendt Agrobil S does not have its own unloading system hence the unloading procedure requires manual work and quite long time period. The De Pietri self-loading wagon was also developed for forage harvesting. The machine has a well developed band elevator system and surpassingly good quality blades. The method of the unloading system is quite simple: the holder part can be raised to 4 meters. Unfortunately because of its high price, this machine could not spread in Hungary. The above mentioned machines are self-propelled. In the agricultural practice there are many trailed machines as well which require a prime mover or tractor. The trailed equipment is usually connected to the tractor with “three point linkage”. One of the trailed machines is the NB 2004 Evolution produced by the EUROPRIMA. The farmers have to consider whether the self-propelled or the trailed machine is suitable.

8.8. figure De Pietri forage harvester VIDEO (Soure: http://www.youtube.com/watch?v=4-DOiY46pxo ) (gyógy_8.8..mp4)

Working speed and capacity of self-loading wagon and self-propelled forage harvesters (NL 2003 alapján)

The self-propelled machines are usually more expensive than the trailed ones. The service cost is also higher but the setting possibilities are wider and that is why it is easier to adapt it to the special properties of the MAP. The self-propelled machines do not require additional tractors. They are able to transfer the cut plant material to the final destination. The two system types were compared from several aspects. It was established that the efficiency depends highly on the plantation density. The profitability depends on the area planned to be harvested.

The harvesting method of the plant material which will be distillated is different from the above mentioned systems. The fennel is harvested in France when the seeds are waxy. The plant material is harvested with 30-40 cm height stubble. During the harvest not only the cutting but also the grinding is realized. For this type of procedure those forage harvesters are suitable where 4 separated cutting wheels are working.

8.10. figure Forage harvester in fennel plantation VIDEO (Pluhár Zs., 2012) (gyógy_8.10..jpg)

Flower harvesting

It is the speciality of the MAP cultivation that the final product can be the flower as well. In the case of other crops you can find only a few examples (cauliflower, artichoke). The flower type, shape, size and the plant family of the cultivated MAP is diverse. For some of the species the mechanical harvesting system already exists (chamomile) while the others are harvested manually (mullein). We have to stress that the flowers are more sensitive than the other harvested plant organs so higher attention is recommended during the transportation and storage. The prime aim of the flower harvesting is to separate the flower head from the stem. The secondary aim is to reach the stage which is written in the pharmacopoeias. For flower harvesting the horizontal reciprocating mowers are used however the usage of different combs are also frequent. Some prototypes are constructed where two parallel rubber wheels are rotating against each other. The rotating drums are picking the flower head. The weakness of the method is that the rotating drums press the flowers and high pressure damage might be caused.

Picking type flower harvester with two rotating drums (a-travel direction, b-drum rotation direction, c-rubbered drum)

Mechanized harvesting of chamomile and lavender

Henceforth the mechanized harvesting of two different plant species the chamomile and the lavender will be discussed. The inflorescence types, the morphology of the two species are different. The flowers of the chamomile are usually harvested with different combs. The principle of the picking combs is that the stem slides between the fingers of the comb and while the comb holds the flower head the machine goes forward so the stem is going to be broken away. In the case of the manual chamomile combs the same principle is used. Diverse types of combs were developed for the chamomile harvesting during the last decades. Based on the direction of the movement we can separate combs with linear movement, rotating combs and the picking system is also known.

Schematic figures of the different chamomile harvesters (Source: Brabandt and Ehlert, 2011)

(A – linear comb; B – Rotating picking combs with central discharge of flowers; C – Rotating picking combs with outside discharge of flowers; D – Picking rotor with a rotating pin drum; - E – Picking rotor with a rotating brush pair)

For harvesting the lavender flowers only a horizontal, linear cutting is used where the base of the machine is a reciprocating mower. The main reason is that the flowering stem is long, can be separated easily from the other organs of the plant. The main principle of the lavender harvesting is that all of the flowers must be cut from the hemisphere shaped bush also from the low limb level branches too. To reach this aim before the mower two lifting “torpedoes” are used which can lift the low level branches. After the lifting with a simple horizontal cutting the flowers can be harvested. In small scale areas the lavender flowers might be harvested manually. The speed of work might be accelerated if we lay down a tilt between the rows and the flowers are cut with a hedge trimmer. In bigger scale fields the above mentioned solution is not suitable so mechanized harvesters for lavender flowers must be used (MKL2,3).

Harvesting of lavender flowers with and without „torpedoes” (Radácsi)

8.14. figure Harvesting of lavender bushes with hedge trimmer VIDEO (Source: http://www.youtube.com ) ( gyógy_8.14.wmv )

8.15. figure MKL2 type lavender harvester VIDEO (Source: http://www.bizon-ins.com/productdetailseng.aspx?id=74 ) (gyógy_8.15.mp4)

Harvesting of fruits and seeds

The harvesting of the fruits is usually done manually. The weakness of the manual harvesting is that the quality of the harvested material is heterogeneous and its effectiveness is low. One individual harvester can approximately harvest maximum 5kg of fruits. Majority of the harvested fruits used as MAP came from wild growing populations. To increase the ratio of the cultivated fruits some plantations were planted but the mechanized harvesting of this population is still not solved. For the harvest of the rosehip plantation the SAMSON and JOANA 3 harvesters were developed. These harvesters use precision beater bars. This beater method is theoretically usable for almost all of the fruits but in the practice we have to recognize that the holding force of the different plant species can be quite diverse. In some cases we had to give so much energy to break the pedicle that the damage on the plant would be disproportionately high.

Two methods were developed for the fruit harvesting. On of them is the earlier mentioned beating bar system the other is the shaking. Our aim is the same in both of the methods: we have to accelerate the fruits until the pedicles will be broken. The mechanized fruit harvesting is soluble only if the plantation was created for mechanized harvesters. The distance between the plants and rows must be fit for the machines. Efforts should be made to use a cultivar where the binding force of the fruit is not too high and the ripening of the fruits is homogenous.

The harvest of the buckthorn is easy in the northern part of Europe because the fruits are frozen and due to shaking the separation of the fruits from the pedicles is easy. In Hungary the harvest of buckthorn is more difficult. When the first frost arrives the fruits are over-ripened. In Hungary the branches of the buckthorn are cut with the fruits. The branches are transported to refrigerator house and after the freezing the fruits are shaken off. During this method the plants are injured and the transportation require extra cost so we can not call the method up-to-date.

8.16. figure SAMSON type rosehip harvester VIDEO (Source: http://www.youtube.com/watch?v=2K4iLm05FNU )(gyógy_8.16.mp4)

Fruit harvester with beating bars (Source: http://aroniaharvest.com/berry_harvesting.html?module=product_info_page&id=4&cat_id=5)

Shaking machines are used for the olive tree (Olea europea L.) harvesting. Similar equipments were developed for the peach trees. The arm of the machine grabs the trunk of the trees and shakes them with the frequency of 25-30 Hz. The amplitude is approximately 15 mm. As the effect of the shaking the fruits fall on the tilt hung out under the tree. The average working speed of the machine is 2-300m/h or 2500 m²/hour.

Shaker type olive tree harvester (Source: http://www.fitstyler.com.au/blog/2011/06/27/traditional-olive-picking-more-energy-expenditure-than-modern-tree-shaking-techniques/ )

For harvesting the seeds, grains the common cereals combines are usually used. The harvesting of the poppy, as one important industrial crop, was done before manually. The Alkaloida Pharmaceutical Factory in Tiszavasvári started the development of the poppy harvesting adapters. The machines produced did not work properly. That was the reason why the industry started to use the modified cereal combines. Special attention is required for the setting of the cereal combine. The header must be set that the poppy capsules with 10-15 cm long stem are to be harvested. The harvesting can be started only if the capsules are in the full ripening stage. The working speed and the drum speed always depend on the plant density and the relief of the area. It is also important that the sieve system of the combine must be set according to the requirement of the poppy. The capsules and the poppy seeds are collected together in the combine while the too long stem parts are removed.

8.19. figure Harvesting of poppy with combine VIDEO (Video: Bernáth) ( gyógy_8.19..m2ts )

Several modifications would be necessary on the common cereal combines to reach the ideal harvester for MAP seeds and fruits.

Several factors can influence the success of the harvesting:

• Binding force of the grain
• Size and shape of the grain
• Uniformity of maturation
• Moisture content of the grain
• Height and the moisture content of the stem
• Grain location on the plant
• Harvesting time

Ignoring the above mentioned factors might cause serious losses. In the case of fennel the too high moisture content of the straw and fruit caused more than 60% loss while in the case of milk thistle the blocking of the sieve system caused the problem. Despite the mentioned problems the seed and fruit harvesting of the MAP is solved compared to the other organs.

Harvesting of the pumpkin seeds

Harvesting of the pumpkin seeds belongs both to the category of fruit and seeds harvesting. However, because the size, the shape and the cultivation technology it is worth to discuss it separately. The primary aim is to separate the seeds from the pumpkin flesh. If we measure the ratio of the seeds we have to recognize that only a few percentages of the whole fruit is the profitable part. Due to this fact transporting the “useless” flesh is too expensive. That is the reason why the seeds are usually separated from the flesh on the field. Time of the pumpkin harvest is fall when the pedicles and leaves are dried. The pumpkin fruits are organized in rows with a tractor mounted scraper or manually. The fruits are harvested with a spiny drum which grabs and elevates the pumpkins. Inside of the harvester the pumpkins are destroyed and due to a sieve system the flesh is separated from the seeds. The flesh falls down to the ground where it will be ploughed in the soil as a green fertilizer. The flesh is also usable as an animal feeding material.

8.20. figure Pumpkin seed harvester VIDEÓ (Source : http://www.youtube.com/watch?v=zsbEO-_7CEw) (gyógy_8.20..mp4)

Control questions

Right answers