PEPPERMINT
Mentha x piperita L. (M. aquatica x viridis. — M. viridis — aquatica F. Schultz)
This article was translated by Angela Iancu!
Mentă; Izmă; Fr.: Menthe poivree; G.: Pfefferminze; M.: Borsos menta; R.: Miata perecinaia
Identification elements: the plant: perennial species with rhizomes and stools, grows to 30-100 (120) cm, highly ramificated starting from the base, with aromatic characteristic smell; underground part: on the whole, superficial poorly developed radicular system; branched, brown-yellowish root, which disappears towards the end of the first year of vegetation, this being replaced by stringy adventives roots up to 40 cm long, that derive from the lower part of the aerial stem which lignifies; also from the basal part of the lignified stem develop underground, whitish stools, 0,5-0,8 cm thick, that grow at the nodes adventives roots and reduced leaves and also new aerial stems; aerial stem: square in cross section, green sometimes with shades of violet, without hairs or with short hairs on the angles; at the middle and upper nodes opposite ramifications are formed from the buds, at the base of the stem aerial stools are formed that grow adventives roots and small leaves; leaves: opposed, ovate-lanceolate with an acute apex, the upper side smooth, the down side with prominent veins; the young leaves are more densely haired, then the hairs remain only on the veins; flowers: produced in whorls at the axils of upper leaves, forming thick, blunt spikes, 4-10 cm long; the flowers are not bilabial, they have a cylindrical calyx with 5 teeth, a four-lobed violet corolla, 7 mm in length, from which it comes out the style with the bifurcated stigma; fruits: tiny nucula, shiny brown, approx. 1 mm, grouped in 4 and covered by the persistent calyx.
Flowering: VI – IX.
Observations: two types are used in cultivation:
- rubescens type – red-violet stems, dark green leaves, violet flowers; it is more resistant to disease and pests, less selective, more productive but with a lower quality oil (the most used in our country);
- palescens type – the aerial part pale green, white flowers, less resistant, with higher demands, smaller productions but higher quality oil.
Raw material: Folium Menthae piperitae – leaves with petiole 1 cm long, hairy on the lower part. The blade is oblong to lanceolate, acuminate, 3-8 cm long, 1,5-3 cm wide, unequally toothed on the sides, dark green on the upper side and lighter on the down side, sometimes with reddish hues. On both sides, the leaves have small, setiform hairs with numerous glands. The odor is delicate, acute, and specific and the flavor is aromatic, strong, leaving in the mouth a pleasant cool sensation.
To obtain the volatile oil for pharmaceutical or industrial purposes it is also harvested Herba Menthae or Herba Menthae recens, which have the characteristics presented at the plant description.
Ecology and distribution: The dormant plant is resistant to low temperatures during winter (the stools resist up to -10…-15° without snow and up to -30° with snow cover) but the open buds are destroyed at -6…-7°; the vegetative state starts at 3-5° and the optimum temperature for vegetation is moderate, up to 18-20°, the maxims being 22-25°. The temperature has a direct influence upon the qualitative traits because in the colder regions the quantity of volatile oil is reduced. Even within the same crop, the harvest in the warm months has a higher percentage of oil than the one in autumn, but with reduced menthol content.
The peppermint likes the sunlight and it needs to bathe into the light otherwise the leaves will fall prematurely and the quantity of essential oil will be reduced. This ecological requirement can be met by avoiding a large density and by controlling the weeds.
The humidity has to be high, the best results being obtained in areas with 600-1000 mm of annual rainfall or on fields that are irrigated (the spray irrigation is less indicated because it favors the ragweed attack). The biggest necessity for water appears in the first half of the vegetation period and during flowering this necessity drops. Another large quantity of water is required after the first harvest in order to produce the second harvest. The stagnant water is harmful; longer periods of stagnation will compromise the crop.
Humidity is determinant when planting the stools because in dry soil they lose water and from most of the buds will not spring stems. If the soil humidity is under 20%, the planting is compromise by the drying of most of the stools.
The best development is achieved on light, loose soils, rich in nutrients like the alluvial soils and peat soils on drained lands. The fields rich in humus are not indicated because the high content of nitrogen imprints on the essential oil an unpleasant odor and flavor. Heavy, clay soils without structure, impermeable and also sandy soils are not indicated.
Cultivation technology: It is recommended the crop rotation with other plants, autumn cereals or fodder legumes on soils free of weeds, deeply works and rich in nutrients. The peppermint can return to the same soil after 5-7 years. Maintaining the crop on the same land can expose the plants to ragweed attack and compromise the crop.
The land is ploughed at a depth of 27/30 cm and it is broken. Together with the plough are introduced around 20-30 t/ha of compost, 60-80 kg/ha of phosphor and 25 kg/ha of potassium. The use of these fertilizers enhances the peppermint harvest with 20-30%. It is not allowed to use fresh or slightly fermented farmyard manure because this will inhibit the growth of the stools and at the same time favors the development of ragweed. The nitrate fertilizer 50-60 kg/ha is introduced on both sides of the rows at the first hoeing, at a depth of 8-10 cm towards the middle of the interval and on the second hoeing at a depth of 10-12 cm. On acids soil, together with the fertilizers are introduces around 2-3 t/ha of powder chalk.
Until planting, the land is kept free of weeds through discing, as many times as it is necessary. Before the planting in autumn, the soil is loosened with the cultivator at the depth of 15-18 cm. If the soil is very hard-packed, then it has to be ploughed again 18-20 cm deep, applying also the harrowing or discing.
In case the stools could not be planted in autumn, the harrowing and loosening work will be performed again in early spring. The peppermint cultivation has a certain specific regarding the breeding, maintenance and harvesting. The plants reproduce through stools which are underground roots. The forming of the stools starts during June-July when the plants are in full vegetation and continues until October.
The rainwater during the months of June-July favors the growth of the stools. If the rainwater is insufficient during August and September, the peppermint crops have to be irrigated 2-3 times for the development of the stools and for obtaining a second harvest (300-350 cm water/ha each time).
The biggest quantity of qualitative stools is achieved from special crops, resembling the seed lots for other plants. The surface reserved or organized for obtaining the stools is worked under the best conditions, by applying the maintenance, irrigation and fertilizing works, without harvesting the peppermint grass off this surface. Only the high quality and first quality leaves can be harvested. The quantity of stools obtained from the special lots can mount to 8-10 t/ha, best quality product.
The harvest of the stools is done only when planting starts so as not to depreciate their quality through dehydration. As the stools are taken out, they are put in heaps covered by earth or straws and are watered until plantation.
If they are transported on a long distance, supplementary measures are taken to water the stools and to cover them with canvases or mats. For the railway transport open wagons are necessary, to avoid the stools getting warm. The transports between counties are difficult and also expensive and that’s way it’s good for each farmer to grow the necessary stools.
The planting is done in autumn, during September-October and only in exceptional and rare cases in early spring, in March or if the weather allows it in February. We underline that the autumn planting, every year on a different land, contributes to an increased production of peppermint leaves and grass, with a high content of essential oil.
The autumn planting favors the rooting of the stools and the emergence of the plant before the first frost. In this way, the plants will better endure the cold, will maintain the normal density of the crop, will start the vegetation very early and will develop quickly, thus obtaining a great harvest of extra quality and first quality leaves, as well as a big production of peppermint grass. This method has the highest economical efficiency.
In our climate in the cultivating areas the peppermint stools winter in the soil and endure relatively easily temperatures up to -25°C. The autumn planting of the peppermint rhizomes is convenient because it can be done in a longer optimal period, between September 20 and October 20 and even until October 31 (when the weather is good and sufficient humidity in the soil) compared to the spring season which is generally short and usually dry.
Both for the autumn and spring plantation the quantities used are 0,8-1 t of peppermint stools cleaned of stool shoots, free of disease and without earth. The depth for the plantation in the autumn period is of 12-15 cm, at an interval of 65-70 cm between rows and in spring the depth is 8-10 cm at the same interval.
For the stools harvest, the land is ploughed at a depth of 15-18 cm with a plough without moldboard and the stools are extracted with the fork. The harvesting of the stools can be done also with a potato harvesting machine. Until plantation, they are covered with humid earth, straws and they are watered. If the autumn is dry and the water resources in the soil are low, then the extraction and plantation of the stools must wait until the weather conditions allow it. Before plantation ditches are made by furrowing the earth with the plough. For an increased economical efficiency when making the ditches, the butting plough can be replaced with the knives of a mechanical cultivator. The cleaned stools are arranged on the bottom of the ditch, end to end, in a continuous row. Regarding the size, the fragments of the stools must have at least 12 cm. The ditches must be made as the plantation progresses, so as to keep in the soil the humidity necessary for the crop growing.
After the stools are laid, next follows the covering of the rows using a hoe, then rolling and harrowing the soil so that the stools stick to the earth and to prevent the formation of a crust. The rows have to be straight so that mechanical works can take place.
In early spring, before emergence, as soon as the weather allows it, the lands planted in autumn are harrowed across the rows using a light harrow. This work applies to the surfaces planted in spring, when the soil forms a crust. When the crust is too hard and the emergence is difficult and the rows are not visible, then it is used a wooden roller which has coiled barb wire from 10 to 10 cm. This work can also be done with roller with nails or with star shaped roller.
Genarally, the maintenance works of the peppermint crops consist of keeping the soil loose and free of weeds, additional fertilization and disease and pest control. After the peppermint emerges it is recommended to make the first aeration of the soil between the rows intervals using a cultivator at a depth of 8-10 cm. This operation is usually followed by a harrowing in diagonal or across the rows. To avoid the plant deterioration, the harrowing has to be done at noon when the peppermint is less fragile, it does not brake and only when reaches a height of 7-8 cm. Together with the first aeration of the intervals, all the weeds that appear on the rows are removed. At this stage, the hoeing on the row is not executed so as not to cut the plant under the crust.
As the plants are growing, in summer have to be applied 4-5 hoeing so the crops are free of weeds. In order to provide the best conditions for the stools development, the second work with the cultivator or the hoeing machine must be executed at a depth of 10-12 cm.
Before the ramification of the peppermint plants, in the intervals of the rows it has to be introduced 5 t of decomposed farmyard manure together with 10 kg /ha of nitrogen 8-10 cm deep or – if the manure is missing – 15 kg/ha of nitrogen at the first hoeing and another 15 kg/ha of nitrogen at the second hoeing. As the plants are more and more branched and the stools reach 10 cm, the width of the protection zone enlarges and the aeration is done at 6-8 cm deep.
The deep aeration must end after the plants from the rows are merged to avoid hurting the stools and even the stems. The irrigation of the peppermint crops enhances the production of leaves and aerial parts with 100% in arid years or in the years with little rain; in the vegetation period, the peppermint crops should be irrigated twice a month (300-350 cm/ha each time). The irrigation is recommended after 5 p.m. because the excessive heat during the day damages the plants.
For obtaining the second harvest of raw material (Herba Menthae) it is absolutely necessary to irrigate the crop during the month of July, after gathering the first crop, and with this occasion a hoeing is done. In the following months, if the rains are missing, the irrigation is done on a monthly basis to ensure the storage of 80-100 l of water / m². During the month of September, between 10-15, the second crop is gathered. After harvesting, the crop is watered again for the growth and development of the stools for their future planting.
The evaluation of the peppermint leaves production is done before flowering, taking into consideration the usual elements like: average number of plants on m², average number of leaves on a plant, the weight of a 1000 fresh leaves, the dehydration ratio which is of 5 kg of fresh leaves for 1 kg of dehydrated leaves.
It is also taken into consideration that until flowering and up to the first flowers appears, the production grows with 40%; from the appearance of the first flowers and until 50% of the plants flower, the growth of the production is of 100% (for the safety of evaluation it is considered only 80%).
Let’s suppose that the estimated production is of 350 g/m² of fresh leaves before flowering. It results that the dry leaves production is of 70g/m² (350g : 5= 70g) and in a hectare the production is: 70g x 1000 m²/1000g= 700kg.
When the first flowers appear the production will be of 980kg/ha of dry leaves. From this quantity, around 200 kg are extra quality, 300kg are first quality and 480kg are second quality.
The evaluation of the plant production is performed with 3-4 days in advance. Supposing that out of 5 different lots of a peppermint parcel, 1m² each, it was harvest 6 fresh kg, meaning 1,2 kg/m², at the end results that the average dry peppermint production per hectare will be of 2400 kg.
The best harvesting moment is chosen depending on the raw material that is to be obtained – the entire plant for the oil extract or the dry leave. The harvesting is done on dry weather, without dew or mist. Depending on the type of product, the harvesting methods are different in order to preserve the quality of the product.
The peppermint leaves are harvested in several stages according to quality that is to be achieved (extra quality, first and second quality).
In the first phase, as the leaves grow to have 6 cm in length, they are collected straight from the field, leave by leave, from the entire cultivated area. They are put in hampers and they are transported immediately to the drying place. This first phase lasts for 15 days and in the next phase – that lasts for 10 days – the extra quality leaves are harvested separately at the same time with the first quality leaves that need to be 5 cm long. Also, in this phase the harvesting is done leave by leave, staring from the base of the plant and working to the top.
In the third phase, when the plants are flowered 15-20%, the plants are harvested by cutting to obtain the second quality leaves. The fresh plants are harvested if they can be quickly splintered because any delay makes the plants fade and the splintering becomes difficult and inefficient.
The plants are cut 7-8 cm above the ground so as to facilitate the growing of the second harvest of leaves or grass.
The splintering is done with the left hand holding the top of the plant and with the right hand pulling the leaves and the branches. The leaves are separated from the branches and are put to dry. The branches with leaves are dealt with the same as the stems. The aerial parts for the dry raw material are harvested when plants are flowered 15-20% and are transported to dry in baskets or in bulk in the same day. When the fresh raw material is used for extracting the volatile oil, the harvesting is done when the plants have flowered more than 25% and only what can be processed during one day. In this case, the harvesting can be done mechanically with mowing machine.
In all situations, the harvested products should not be rained.
Diseases, pests and ways of control: The peppermint is attacked by ragweed, which is controlled with the following measures:
- treating the stools before planting with a copper sulphate solution 0,5% (this method has a limited action);
- planting only the stools that come from a healthy crop;
- planting the peppermint after 5-7 years on the same land that has been planted before;
- planting the peppermint as far as possible from the water;
- planting in rows, at a distance of 65-70 cm;
- using phosphate and potassium fertilizers that enhance the plant resistance;
- avoiding using too much nitrogen or only this fertilizer;
- using the well discomposed farmyard manure for the advance crop;
- destroying the wild peppermint species from the crop and from the neighboring area;
- harvesting the stools from the plants that resisted the ragweed attack for the future crops;
A rare disease found in the peppermint crops in our country is the fading of the leaves. To control this disease, a strict quarantine is required on a period of 10-15 years. This is doubled by following the crop rotation. In the crop rotation, the following scheme is used: one year peppermint, one year onion, one year carrot and then peppermint again.
Preparing the product for conditioning: The peppermint leaves are dried on white paper, mats, sackcloth or frames, spread in a thin layer (one layer of leaves) in rooms, barns, attics or in the sun. In an interval of 5-6 hours, between 10 a.m. – 5 p.m., the peppermint leaves are completely dried in the sun. In dry rooms, it lasts 5-6 days if there is good ventilation. When drying in the shade, the leaves are turned 2-3 times in the first day and once in the following three days. The entire quantity of leaves dried in the sun it is stored in the evening in a thin layer in the room on frames, mats, white paper and sackcloth where it is left to dry for one or two days.
The peppermint leaves dried in this way maintain their green color and their active principles. The drying in the sun is very effective because the cultivator does not have to use many workers, many frames or large rooms to dry the leaves in the shade.
The leaves are well dried when they lose the elasticity and when the main nerve snaps if broken. The fresh grass is transported and laid out in a thin layer of 5-8 cm directly in the sun, on mats, frames etc. The drying lasts for 1-2 days (after 7 p.m., the frames with the grass are sheltered from the dew and exposed in the sun the following day), in the meantime they dry in percentage of 70-75. Next, the drying is done in attics, in layers of 10-15 cm, where the product is left for 3-4 days. During the direct dry in the sun, the layer of herbs will be turned 2-3 times a day for an equal drying. In attics or in other rooms this thing is not done so as not to shake the leaves.
Besides the mix drying, which quickens the end of the operation, the cultivators can dry the peppermint grass only in attics, in a thin layer of 5 cm. The drying in the attics can last 8-12 days, time during which the product will be turned once a day in the first 5 days. This can take longer if the weather is cold or cloudy. Generally, after September 15, the drying period lengthens with 50-100% and the product should be carefully watched so as not to turn black.
Both leaves and peppermint plants can be artificially dried at a temperature of 35°C.
The peppermint leaves are packed in special boxes. Herba Menthae is packed in mattresses for delivery. During the packing of the leaves are removed parts of the plant, the black or dotted leaves and other foreign bodies. From the raw material (Herba Menthae) are removed weeds, straws etc.
The drying efficiency for leaves and for the aerial parts is of 4-6/1.
The technical conditions for reception require the following – for leaves (Folia Menthae) – depending on the leaves size and the content of impurities, three qualities can be obtained:
| Property | Extra quality. | First quality |
Second quality |
| -minimal length | 5 | 4 | under 4 |
| -impurities, max. | 1,5 | 2,5 | 5 |
| -brown, discolored leaves, max.% |
1,5 | 5 | 10 |
| -organic foreign matter, max.% | 1 | 2 | 4 |
| -mineral foreign matter, max. % | 0,5 | 1 | 2 |
| -humidity, max.% | 14 | 14 | 14 |
For the fresh aerial part (Herba Menthae recens), harvested for the oil, the product will not contain stocks (stems longer than 10 cm before the last ramification) and the foreign matter is deducted from the total quantity (the parts of the plant attacked by ragweed are not considered foreign matter). Regarding the dry aerial part (Herba Menthae) it is not admitted branches and stems without leaves, the impurities will not exceed max. 5% of brown leaves and max. 3% of stems thicker than 2 cm, organic foreign matter – max. 2% and mineral – max. 1%, humidity – max. 13%.
Chemical structure: The aerial part collected during the flowering contain 0,3-0,5% volatile oil and the leaves contain 1-2% volatile oil with different chemical structure depending on the origin. The main component of the peppermint volatile oil is menthol (up to 70%) and also menthones, menthofuran, a-pinene, felandrene, limonene, cadinene, cineole, acetic aldehyde, amyl and isoamyl alcohols, tymol, carvacrol, sesquiterpenic alcohols, cariophilen etc. The leaves contain significant amounts of tanins (up to 12% in the guise of caffeic acid), organic acids, vitamin C, mineral salts, antibiotic substances etc.
Pharmaceutical actions – therapeutic uses: The peppermint’s pharmaceutical action is given by the composition of the volatile oil and of the other substances in the plant. It has a tonic-eupeptic action, slightly analgesic and carminative. In small quantities, the oil has especially an excitant action upon the thermic sensitive nervous endings within the skin and mucouses. At the beginning the excitation period produces a cold sensation, then an accentuated local warm sensation. Also, it has an antispastic action upon the recti muscles. It is used in dyspepsia, nausea, pyloric spasms, gallbladder and gastro-intestinal dyskinesia.
There were signals of intoxications with products that contain large quantities of menthol, with symptoms like abdominal pain, nausea, throw-ups, ataxia, muscular rigidity for several days, bradypnea, asphyxiation and death. The products containing peppermint oil have a pretty selective antibacterial range, especially on Brucella species.
It is a part of several medicinal teas: anti-asthmatic, anti-cramps, anti diarrheic, dietetic, gastric, hepatic etc. The volatile oil is used in different pharmaceutical products (Carbocif, Colebil, Boldocolin etc.), is used to correct the taste of same medicines, in rubbing, inhalations etc.
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