Everything you need to know about cultivating and harvesting medicinal plants. Learn about:- 1. Introduction to Medicinal Plants 2. Advantages of Cultivating Medicinal Plants 3. Factors Affecting Cultivation 4. Methods of Medicinal Plant Propagations 5. Collecting Barks 6. Harvesting 7. Drying 8. Packing 9. Storage.
Contents:
- Introduction to Medicinal Plants
- Advantages of Cultivating Medicinal Plants
- Factors Affecting Cultivation of Medicinal Plants
- Methods of Medicinal Plant Propagations
- Collecting Barks of Medicinal Plants
- Harvesting of Medicinal Plants
- Drying of Medicinal Plants
- Packing of Medicinal Plants
- Storage of Medicinal Plants
1. Introduction to Medicinal Plants:
Though, several countries in the world have a rich heritage of herbal drugs, very few can put claim for their procurement only from cultivated species. It is recently, that some of these drugs have been subjected to systematic cultivation based on modern scientific information. Our reliance on wild form of crude drugs and the lack of information of sound cultivation technology have resulted in gradual depletion of raw material from wild sources.
Even though, cultivation of medicinal plants offers wide spectrum of advantages over their wild sources, it may be an uneconomical proposition for certain types of crude drugs which occur abundantly in their natural habitat e.g. nux-vomica, acacia, myrobalan, etc. On the other hand, crude drugs like cardamom, clove, Indian hemp, poppy latex, tea, cinchona, ginger, linseed, isapgol, ceylon, cinnamon, saffron, peppermint, fennel, etc. are obtained from cultivated plants.
The cultivation of vegetable drugs involves convergence of various factors from agricultural and pharmaceutical sphere, such as soil, climate, rainfall, irrigation, altitude, temperature, use of fertilizers and pesticides, genetic manipulation and biochemical aspects of natural drugs. When all such factors are precisely applied, the new approach to scientific cultivation technology emerges out.
2. Advantages of Cultivating Medicinal Plants:
The advantages of cultivation may be briefly summarized as follows:
1. It ensures quality and purity of medicinal plants. Crude drugs derive their utility from chemical contents in them. If uniformity is maintained in all operations during the process of cultivation, drugs of highest quality can be obtained. Cultivation of rhizomes demands an adequate quantity of fertilizers and proper irrigation.
Systematic cultivation results in raising a crop with maximum content of volatile oil and other constituents. The examples of ginger, turmeric and liquorice can be cited to illustrate this point. If the cultivated plants are kept free of weeds, the contamination of crude drugs can be conveniently avoided.
2. Collection of crude drugs from cultivated plants gives a better yield and therapeutic quality. However, it is a skilled operation and requires some professional excellence. If the collection of crude drugs for market is done from cultivated plants by skilled and well-experienced personnel, the high yield and therapeutic quality of drugs can be maintained.
For example, collection of latex from poppy capsules and oleo-resins from Pinus species, if done by experienced persons, can result in better yield of crude drugs. Preservation of green colour of senna leaves and minimising the deterioration of cardiac glycosides in freshly collected leaves of digitalis can be achieved only by highly skilled labour.
3. Cultivation ensures regular supply of a crude drug. In other words, cultivation is a method of crop-planning. Planning a crop cultivation regularizes its supply and as a result the industries depending upon crude drugs do not face problem of shortage of raw material.
4. The cultivation of medicinal and aromatic plants also leads to industrialisation to a greater extent. The cultivation of coffee and cocoa in Kerala has given rise to several cottage and small scale industries. The cultivation of cinchona in West Bengal has led to the establishment of the cinchona-alkaloid factory near Darjeeling. The government owned opium factory at Gaziabad is an eloquent testimony to the significance of well-planned cultivation of poppy.
5. Cultivation permits application of modern technological aspects such as mutation, polyploidy and hybridisation.
The high cost of cultivated drugs as compared to wild sources and the losses due to ecological imbalances such as storms, earthquakes, floods, droughts, etc. are major disadvantages of cultivation.
3. Factors Affecting Cultivation of Medicinal Plants:
Cultivation of medicinal and aromatic plants takes cognizance of plant habitats and climatic requirements for their favourable growth.
The factors which are given special attention for cultivation are listed below:
1. Altitude, temperature and humidity
2. Rainfall or irrigation
3. Soil and soil fertility
4. Fertilizers
5. Pests and pest control.
1. Altitude, Temperature and Humidity:
Altitude is a very important factor in cultivation of medicinal plants. Tea, cinchona arid eucalyptus are cultivated favourably at an altitude of 1000-2000 metres. Cinnamon and cardamom are grown at a height of 500-1000 metres, while senna can be cultivated at sea level. The following are the examples of medicinal and aromatic plants indicating the altitude for their successful cultivation.
Temperature is another factor affecting the growth of a plant. Excessive temperature, as well as, frost also affects quality of medicinal plants adversely. The following are few examples of ranges of temperature necessary for luxuriant growth of certain medicinal plants.
Camphor and coffee cannot withstand frost, whereas saffron needs only cold climate and pyrethrum requires dry weather for cultivation.
2. Rainfall or Irrigation:
Except the xerophytic plants like aloe, acacia jojoba and few others, most of the plants need either proper arrangements for irrigation or sufficient rainfall for their favourable development. In few cases, well distributed rainfall throughout the year is desired.
4. Methods of Medicinal Plant Propagations:
Medicinal plants can be propagated by two usual methods as applicable to non-medicinal plants or crops. These methods are referred as sexual method and asexual method.
Each of these methods have certain advantages and also disadvantages:
1. Sexual Method (Seed Propagation):
In case of sexual method, the plants are raised from seeds and such plants are known as seedlings.
The sexual method of propagation enjoys following advantages:
i. Seedlings are long-lived (in case of perennial drugs) and bear more heavily (in case of fruits). Plants are more sturdy.
ii. Seedlings are comparatively cheaper and easy to raise.
iii. Propagation from seed has been responsible for production of some chance-seedlings of highly superior merits which may be of great importance to specific products, such as orange, papaya, etc.
iv. In case of plants where other vegetative methods cannot be utilised, propagation from seeds is the only method of choice.
Sexual method suffers from following limitations:
i. Generally, seedling-trees are not uniform in their growth and yielding capacity, as compared to grafted trees.
ii. They require more time to bear, as compared to grafted plants.
iii. The cost of harvesting, spraying of pesticides, etc. is more as compared to grafted trees.
iv. It is not possible to avail of modifying influence of root stocks on scion, as in case of vegetative propagated trees.
For propagation purpose, the seeds must be of good quality. They should be capable of high germination rate, free from diseases and insects and also free from other seeds, used seeds and extraneous material. The germination capacity of seeds is tested by rolled towel test, excised embryo test, etc.
The seeds are preconditioned with the help of scarification to make them permeable to water and gases. If the seeds are not to be germinated in near future, they should be stored in cool and dry place to maintain their germinating power. Long storage of seeds should be avoided.
Before germination, sometimes a chemical treatment is given with stimulants like gibberellins, cytokinins, ethylene, thiourea, potassium nitrate or sodium hypochlorite. Gibberellic acid (GA3) promotes germination of some type of dormant seeds and stimulates the seedling growth. Many freshly harvested dormant seeds germinate better after soaking in potassium nitrate solution. Thiourea is used for those seeds which do not germinate in dark or at high temperatures.
Methods of Sowing the Seeds:
Numerous methods of sowing the seeds of the medicinal plants are in practice.
Few of them using seeds for cultivation are described:
(a) Broadcasting:
If the seeds are extremely small the sowing is done by broadcasting method. In this method, the seeds are scattered freely in well prepared soil for cultivation. The seeds only need raking. If they are deeply sown or covered by soil, they may not get germinated. Necessary thinning of the seedlings is done by keeping a specific distance, e.g. Isapgol, linseed, Sesame.
(b) Dibbling:
When the seeds of average size and weight are available, they are sown by placing in holes. Number of seeds to be put in holes vary from 3 to 5, depending upon the vitality, sex of the plants needed for the purpose and the size of the plant coming out of the seeds.
For example, in case of fennel 4 to 5 fruits of fennel are put in a single hole keeping suitable distance in between two holes. In case of castor, only 2 or 3 seeds are put. In case of papaya, the plants are uni-sexual and only female plants are desired for medicinal purposes. Hence, 5 to 6 seeds are put together and after the sex of the plants is confirmed, healthy female plant is allowed to grow while male plants and others are removed.
(c) Miscellaneous:
Many a times the seeds are sown in nursery beds. The seedlings thus produced are transplanted to farms for further growth, such as cinchona, cardamom, clove, digitalis, capsicum, etc.
Special Treatment to Seeds:
To enhance germination, special treatments to seeds may be given, such as soaking the seeds in water for a day. e.g., castor-seeds and other slow-germinating seeds. Sometimes, seeds are soaked in sulphuric acid, e.g. henbane seeds. Alternatively, testa is partially removed by grind-stone or by pounding seeds with coarse sand. e.g., Indian senna. Several plant hormones like gibberellins, auxins are also used.
2. Asexual Method:
In case of asexual method of vegetative propagation, the vegetative part of a plant, such as stem or root, is placed in such an environment that it develops into a new plant.
Asexual propagation enjoys following advantages:
1. There is no variation between the plant grown and plant from which it is grown. As such, the plants are uniform in growth and yielding capacity. In case of fruit trees, uniformity in fruit quality makes harvesting and marketing easy.
2. Seedless varieties of fruits can only be propagated vegetative e.g. grapes, pomegranates and lemon.
3. Plants start bearing earlier as compared to seedling trees.
4. Budding or grafting encourages disease-resistant varieties of plants.
5. Modifying influence of root-stocks on scion can be availed of.
6. Inferior or unsuitable varieties can be over-looked.
It suffers from following disadvantages:
1. In comparison to seedling trees, these are not vigorous in growth and are not long-lived.
2. No new varieties can be evolved by this method.
Asexual method of vegetative propagation consists of three types:
(a) Natural methods of vegetative propagation
(b) Artificial methods of vegetative propagation
(c) Aseptic methods of micro-propagation (Tissue-culture).
(a) Natural Methods of Vegetative Propagation:
It is done by sowing various parts of the plants in well prepared soil. The following are the examples of vegetative propagation.
1. Bulbs – Squill, garlic
2. Corms – Colchicum, saffron
3. Tubers – Jalap, aconite, potato
4. Rhizomes – Ginger, turmeric
5. Runners – Peppermint
6. Suckers – Mint, pineapple, chrysanthemum, banana
7. Offsets – Aloe, valerian
8. Stolons – Arrow-root, liquorice
Artificial Methods of Vegetative Propagation:
The method by which plant- lets or seedlings are produced from vegetative part of the plant by using some technique or process is known as artificial method of vegetative propagation.
These methods are classified as under:
1. Cuttings:
(i) Stem cuttings
(a) Soft wood cuttings: Berberry
(b) Semi hard wood cuttings: Citrus, camellia
(c) Hard wood cuttings: Orange, rose, bougainvillea
(ii) Root cuttings: Brahmi
(iii) Leaf cuttings: Bryophyllum
(iv) Leaf bud cuttings.
2. Layering:
(i) Simple layering: Guava, lemon
(ii) Serpentine layering: Jasmine, clematis
(iii) Air layering (Gootee): Ficus, mango, bougainvillea, cashew nut
(iv) Mount layering
(v) Trench layering
(vi) Tip layering
3. Grafting:
Graftings are further classified as:
(i) Whip grafting: Apple, rose
(ii) Tongue – grafting
(iii) Side grafting: Sapota, cashewnut
(iv) Approach grafting: Guava, Sapota
(v) Stone-grafting: Mango
Aseptic Methods of Micro-Propagation (Tissue Culture):
It is a novel method for propagation of medicinal plants. In micro-propagation, the plants are developed in an artificial medium under aseptic conditions from fine pieces of plants like single cells, callus, seeds, embryos, root tips, shoot tips, pollen grains, etc. They are also provided with nutritional and hormonal requirements.
Preparation and Types of Nursery Beds:
For various genuine reasons, seeds cannot be sown directly into soil i.e. very small size (Isapgol, tulsi) high cost, poor germination rate and long germination time (Cardamom, Coriander). Under such circumstances, seeds are grown into the nursery beds which not only are economical, but one can look after the diseases (if any) during germination period. Small size of beds can be irrigated conveniently along with fertilizers, as and when necessary.
There are four types of nursery beds:
1. Flatbed method
2. Raised bed method
3. Ridges and furrow method
4. Ring and basin method
Taking into consideration the amount of water and type of soil required for a particular seed one should select the type.
Methods of Irrigation:
Water is essential for any type of cultivation. After studying the availability and requirement of water for a specific crop, one has to design his own irrigation system at the reasonable cost.
Following methods of irrigation are known traditionally in India. The cultivation has an option after giving due consideration to the merits and demerits of each.
1. Hand watering- Economical and easy to operate
2. Flood watering- Easy to operate, results in wastage of water
3. Boom watering- Easy to operate, but restricted utility
4. Drip irrigation- Scientific, systematic and easy to operate, costly.
5. Sprinkler irrigation- Costly, gives good results.
After collection of the crude drugs, they are required to be processed prior to marketing. The reasons for preparation of drugs are to stabilize them in transport and storage and to ensure the absence of foreign organic matter and substitutes. Market preparation of crude drugs also takes care of pharmaceutical elegance. While preparing drug for commerce, several methods are adopted to meet the standard pharmacopoeia requirements.
Generally, these methods include proper methods of collection and harvesting, drying and garbling. Sometimes, coating and bleaching are also necessary for converting the drug into suitable form for the market. While doing so, it should be observed that neither the action of the drug is lowered down, nor it is changed, due to the additives used in the process.
5. Collecting Barks of Medicinal Plants:
Irrespective of the type of crude drug and area of collection, there cannot be two opinions that the drugs are collected suitably when they contain maximum concentration of active constituents. The advantage of existing environmental conditions is also taken into consideration while collecting the crude drugs.
The drugs which constitute leaf and the flowering tops of plants are collected just before they reach their flowering stage (maturity); e.g., senna, digitalis, vinca, belladonna, etc., while the leaves of aloe are collected when they are sufficiently thick. Flowers need to be collected just before pollination or, many a times, before their full expansion, e.g. saffron, clove buds, chamomile, arnica, etc.
They are collected in dry weather and preferably during morning hours. Barks are generally collected in spring or early summer when cambium is active, as it is easy to detach them from the stem. Sometimes, they are collected in autumn (wild cherry) or in rainy season (cinnamon).
Three different methods for collecting barks are:
(i) Felling,
(ii) Uprooting and
(iii) Coppicing.
In felling method, the tree is cut at base and bark is peeled out. In uprooting technique, the roots are dug out and bark is stripped off from roots and branches. In coppicing method, the plant is allowed to grow for a definite period and then it is cut off at specific distance from soil. The stumps which remain in ground are allowed to send shoots, which develop further independently yielding aerial parts.
These new parts are cut off and bark is collected from shoots. As compared to other methods of collection of bark, this technique is more economical and less time-consuming. It is, therefore, the method of choice for collecting barks commercially. Cascara and cinnamon are collected by this method.
The fruits are collected depending upon the part of fruits is used. They are collected either ripe or half ripe, but fully grown. For example, cardamom fruits are collected just before their dehiscence; bael and tamarind, after their full maturity, while caraway, fennel and coriander are collected, when they are fully ripe.
The roots are collected in spring, before the vegetative process stops. Usually, the roots are sliced transversely or longitudinally to facilitate drying. Rhizomes are collected, when they store ample of reserve food material and also contain maximum content of chemical constituents.
The unorganised drugs such as resins, gums, latices are collected, as soon as, they ooze out of the plant. Acacia gum is collected 2-3 weeks after making incisions on the bark of the tree and when it is sufficiently hard. Opium and papaya latices are collected after coagulation of latex. Turpentine oleo-resin and balsam of peru are collected when the plant is about 8-10 years old.
6. Harvesting of Medicinal Plants:
Harvesting is an important operation in cultivation technology, as it reflects upon economic aspects of the crude drugs. An important point which needs attention over here is the type of drug to be harvested and the pharmacopoeia standards which it needs to achieve. Harvesting can be done efficiently in every respect by the skilled workers. Selectivity is of advantage in that the drugs other than genuine, but similar in appearance can be rejected at the site of collection.
It is, however, a laborious job and may not be economical. In certain cases, it cannot be replaced by any mechanical means, e.g. digitalis, tea, vinca and senna leaves. The underground drugs like roots, rhizomes, tubers, etc. are harvested by mechanical devices, such as diggers or lifters. The tubers or roots are thoroughly washed in water to get rid of earthy-matter. Drugs which constitute all aerial parts are harvested by binders for economic reasons.
Many a times, flowers, seeds and small fruits are harvested by a special device known as seed stripper. The technique of beating plant with bamboos is used in case of cloves. The cochineal insects are collected from branches of cacti by brushing. The seaweeds producing agar are harvested by long handled forks.
Peppermint and spearmint are harvested by normal method with mowers, whereas fennel, coriander and caraway plants are uprooted and dried. After drying, either they are thrashed or beaten or the fruits are separated by winnowing. Sometimes, reaping machines are also used for their harvesting.
7. Drying of Medicinal Plants:
Before marketing a crude drug, it is necessary to process it properly, so as to preserve it for a longer time and also to acquire better pharmaceutical elegance. This processing includes several operations or treatments, depending upon the source of the crude drug (animal or plant) and its chemical nature. Drying consists of removal of sufficient moisture content of crude drug, so as to improve its quality and make it resistant to the growth of microorganisms. Drying inhibits partially enzymatic reactions.
Drying also facilitates pulverizing or grinding of a crude drug. In certain drugs, some special methods are required to be followed to attain specific standards, e.g. fermentation in case of Cinnamomum zeylanicum bark and gentian roots.
The slicing and cutting into smaller pieces is done to enhance drying, as in case of glycyrrhiza, squill and calumba. The flowers are dried in shade so as to retain their colour and volatile oil content. Depending upon the type of chemical constituents, a method of drying can be used for a crude drug.
Drying can be of two types:
(1) Natural (sun drying);
(2) Artificial.
1. Natural Drying (Sun-Drying):
In case of natural drying, it may be either direct sun-drying or in the shed. If the natural colour of the drug (digitalis, clove, senna) and the volatile principles of the drug (peppermint) are to be retained, drying in shed is preferred. If the contents of the drugs are quite stable to the temperature and sunlight, the drugs can be dried directly in sunshine (gum acacia, seeds and fruits).
2. Artificial Drying:
Drying by artificial means includes drying the drugs in:
(a) An oven; i.e. tray-dryers;
(b) Vacuum dryers, and
(c) Spray dryers.
(a) Tray Dryers:
The drugs which do not contain volatile oils and are quite stable to heat or which need deactivation of enzymes are dried in tray dryers. In this process, hot air of the desired temperature is circulated through the dryers and this facilitates the removal of water content of the drugs (belladonna roots, cinchona bark, tea and raspberry leaves and gums are dried by this method).
(b) Vacuum Dryers:
The drugs which are sensitive to higher temperature are dried by this process, e.g. tannic acid and digitalis leaves.
(c) Spray Dryers:
Few drugs which are highly sensitive to atmospheric conditions and also to temperature of vacuum-drying are dried by spray-drying method. The technique is followed for quick drying of economically important plant or animal constituents, rather than the crude drugs. Examples of spray drying are papaya latex, pectin, tannins, etc.
Garbling (Dressing):
The next step in preparation of crude drug for market after drying is garbling. This process is desired when sand, dirt and foreign organic parts of the same plant, not constituting drug are required to be removed.
This foreign organic matter (extraneous matter) is removed by several ways and means available and practicable at the site of the preparation of the drugs. If the extraneous matter is permitted in crude drugs, the quality of drug suffers and at times, it doesn’t pass pharmacopoeia limits.
Excessive stems in case of lobelia and stramonium need to be removed, while the stalks, in case of cloves are to be deleted. Drugs constituting rhizomes need to be separated carefully from roots and rootlets and also stem bases. Pieces of iron must be removed with the magnet in case of castor seeds before crushing and by shifting in case of vinca and senna leaves. Pieces of bark should be removed by peeling as in gum acacia.
8. Packing of Medicinal Plants:
The morphological and chemical nature of drug, its ultimate use and effects of climatic conditions during transportation and storage should be taken into consideration while packing the drugs. Aloe is packed in goat skin. Colophony and balsam of tolu are packed in kerosene tins, while asafoetida is stored in well closed containers to prevent loss of volatile oil.
Cod liver oil, being sensitive to sunlight, should be stored in such containers, which will not have effect of sunlight, whereas, the leaf drugs like senna, vinca and others are pressed and baled. The drugs which are very sensitive to moisture and also costly at the same time need special attention, e.g. digitalis, ergot and squill.
Squill becomes flexible, ergot becomes susceptible to the microbial growth, while digitalis loses its potency due to decomposition of glycosides, if brought in contact with excess of moisture during storage. Hence, the chemicals which absorb excessive moisture (desiccating agents) from the drug are incorporated in the containers. Colophony needs to be packed in big masses to control auto-oxidation.
Cinnamon bark, which is available in the form of quills, is packed one inside the other quill, so as to facilitate transport and to prevent volatilization of oil from the drug. The crude drugs like roots, seeds and others do not need special attention and are packed in gunny bags, while in some cases bags are coated with polythene internally. The weight of certain drugs in lots is also kept constant, e.g. Indian opium.
9. Storage of Medicinal Plants
:
Preservation of crude drugs needs sound knowledge of their physical and chemical properties. A good quality of the drugs can be maintained, if they are preserved properly. All drugs should be preserved in well closed and, possibly, in the filled containers. They should be stored in the premises which are waterproof, fire proof and rodent-proof. A number of drugs absorb moisture during their storage and become susceptible to the microbial growth.
Some drugs absorb moisture to the extent of 25% of their weight. The moisture, not only increases the bulk of the drug, but also causes impairment in the quality of crude drug. The excessive moisture facilitates enzymatic reactions resulting in decomposition of active constituents, e.g. digitalis leaves and wild cherry bark. Gentian and ergot receive mould infestation due to excessive moisture. Radiation due to direct sun-light also causes destruction of active chemical constituents, e.g. ergot, cod liver oil and digitalis.
Form or shape of the drug also plays very important role in preserving the crude drugs. Colophony in the entire form (big masses) is preserved nicely, but if stored in powdered form, it gets oxidized or loses its solubility in petroleum ether. Squill, when stored in powdered form becomes hygroscopic and forms rubbery mass on prolonged exposure to air. The fixed oil in the powdered ergot becomes rancid on storage.
In order to maintain a good quality of powdered ergot, it is required that the drug should be defatted with lipid solvent prior to storage. Lard, the purified internal fat of the abdomen of the hog, is to be preserved against rancidity by adding Siam benzoin. Atmospheric oxygen is also destructive to several drugs and hence, they are filled completely in well closed containers, or the air in the container is replaced by an inert gas like nitrogen; e.g. shark liver oil, papain, etc.
Apart from protection against adverse physical and chemical changes, the preservation against insect or mould attacks is also important. Different types of insects, nematodes, worms, moulds and mites infest the crude drugs during storage.
Some of the more important pests found in drugs are Coleoptera (Stegobium paniceum and Calandrum granarium), Lepidoptera (Ephestia knehniella and Tinea pellionella), and Archnida or mites (Tyroglyphus farinae and Glyophagus domesticus).
They can be prevented by drying the drug thoroughly before storage and also by giving treatment of fumigants. The common fumigants used for storage of crude drugs are methyl bromide, carbon disulphide and hydrocyanic acid.
At times, drugs are given special treatment, such as liming of the ginger and coating of nutmeg. Temperature is also very important factor in preservation of the drugs, as it accelerates several chemical reactions leading to decomposition of the constituents.
Hence, most of the drugs need to be preserved at a very low temperature. The costly phyto-pharmaceuticals are required to be preserved at refrigerated temperature in well closed containers. Small quantities of crude drugs could be readily stored in air-tight, moisture proof and light proof containers such as tin, cans, covered metal tins, or amber glass containers. Wooden boxes and paper bags should not be used for storage of crude drugs.