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Chapter 16
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Thyme
TehreemaIftikhar, HammadMajeed, SyedaShehwarZahra,
MuhammadWaheed, MubashirNiaz, andNaheedBano
16.1 Introduction
Commonly known as garden thyme, Thymus vulgaris L. is a perennial owering
plant, member of the mint family Lamiaceae. This family comprises of 236 genera
and more than 6000 species. The members of family Lamiaceae are quite diverse
and cosmopolitan in distribution. Square stems, zygomorphic owers and distichous phyllotaxis are the distinguishing characteristics of this family. Lamiaceae
species are mostly aromatic and are a source of valuable essential oils [1]. Members
of this family are greatly used in self-care products, avoring, fragrance, scents,
pesticide, and medicine industries [2]. Globally Thymus vulgaris L. has several
common names. It is also known as Garden Thyme, French Thyme, rubbed Thyme,
red Thyme, folia Thyme depending upon their states in which they grow. In Romania
it is called as cimbru and avishan in Persian.
T. Iftikhar (*) · S. S. Zahra
Applied Botany Lab, Department of Botany, Government College University Lahore, Lahore,
Pakistan
H. Majeed (
Knowledge Unit of Science, University of Management and Technology, Sialkot, Pakistan
M. Waheed
Applied Botany Lab, Department of Botany, Government College University Lahore, Lahore,
Pakistan
Government Islamia Graduate College, Civil Lines, Lahore, Pakistan
M. Niaz
Atlas Environmental Laboratories, New York, NY, USA
N. Bano
Faculty of Veterinary and Animal Sciences, MNS-University of Agriculture, Multan, Pakistan
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2023
M. Zia-Ul-Haq etal. (eds.), Essentials of Medicinal and Aromatic Crops,
https://doi.org/10.1007/978-3-031-35403-8_16
*)
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16.2 Classication [3]
Kingdom: Plantae
Subkingdom: Tracheobionta
Super-division: Spermatophyta
Division: Magnoliophyta
Class: Magnoliopsida
Subclass: Asteridae
Order: Lamiales
Family: Lamiaceae
Genus: Thymus L.
Species: Thymus vulgaris L.
16.3 Crop Description
16.3.1 Origin andDistribution
Thyme is a common term used that encompasses all varieties of Thymus species
found globally. Thymus species are native plants of Europe and Asia. They are also
indigenous to the Mediterranean region, south-eastern Italy and northwest Africa
(Table16.1). Thymus zygis L. is native to Portugal and Spain whereas the serpyllum
species is indigenous to all European countries. Spain produces a total of 90% of
thyme oil of world trade, In Pakistan, Thyme is being cultivated in different agroecological zones of Baluchistan [4].
16.3.2 Plant Morphology
The genus Thymus is a member of Nepetoideae subfamily of the Lamiaceae family
that consists of approximately 215 species. Thymus vulgaris L. is a widely known
aromatic herb. Thyme is a tiny perennial shrub that seldom grows 40cm tall with
Table 16.1 Occurrence of various types of Thymus sp. [4]
Common name Countries Botanical name
Thyme (Common thyme)
(Garden thyme)
Spanish thyme Spain, Portugal, Morocco Thymus zygis
Wild thyme Europe and North Africa Thymus
Spain, Portugal, France, Germany, Italy, the UK,
North Africa, Canada, and the USA
Thymus
vulgaris
L.
serpyllum L.
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evergreen groundcover. With growing age, the stem becomes woody. Thymus vul-
garis L. leaves are extremely small and eshy, usually 2.5 to 5cm long with oval to
rectangular form. Thymus vulgaris L. have greyish-green leaves and purplish or pinkish owers in early summers. The leaves of Spanish thyme (T. zygis L.) are narrower
that are found clustered at the nodes. It possess an elongated inorescence with clusters of whitish owers spaced at regular intervals. Wild thyme (T. serpyllum L.) and
large thyme (T. pulegioides L.) are entirely different in appearance. Only at the base
they are woody. As a whole they are more herbaceous. They have ciliated sub-sessile
leaves with at, linear to elliptical lamina. Both these species of thyme have capitate
inorescence. Thyme prefers a dry, sunny and temperate environment for its growth.
Full exposure to the sun is essential for thyme to grow to its full potential. Excessive
moisture will lead to disease development in thyme. Thyme has extremely small and
round seeds that retain their germination capacity for around 3years [5].
16.3.3 Agronomy
Thymus grows well in lightweight, well-drained and aerated soil. Soil with a pH
ranging from 5.0 to 8.0 is best for thyme cultivation. Coarse and rough soils that
would be unsuitable for any other plant, supports thyme growth. Although calcareous, stony and dry soils are preferable for thyme growth yet they can also be grown
in heavy wet soils but it reduces their aroma. It should be planted in permeable soil.
Different Thymus species require different substrata for their growth [6]. Thyme
grows well in a sunny, warm and dry climate. Full exposure to sunlight is essential
for its best production. Thyme cannot grow under shade. It requires 68–86°F
(20–30°C) temperature for best growth (Fig.16.1). Excessive moisture leads to the
development of rot disease in the thyme. The annual rainfall in the Mediterranean
region, where thyme is mostly cultivated, is 500–1000mm. They can survive in
extreme climatic conditions [7].
Fig. 16.1 Agronomy of Thymus vulgaris L.Source [8]
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16.4 Cultivation Practices
16.4.1 Soil Preparation
As discussed earlier, thyme needs shallow soil for its growth. Such soil is not suitable for any other plant. Soil pH should also be in the given range. Before sowing if
the pH of soil is below 5.5 it is recommended to add agricultural lime to the soil.
Once established thyme can tolerate drought.
16.4.2 Using Vermicompost
Research has shown that using 50% vermicompost enhances the plant yield. It
effects both the fresh and dry weight of thyme, its chlorophyll and carotenoids content along with its essential oil production. Increased percentage of vermicompost
also suppresses pathogens such as Fusarium oxysporum and Phytophthora infestans.
16.4.3 Planting
It is advisable to keep a distance of 15–30cm between the rows of plants, with a row
width of 60cm. In beds, the spacing should be 20–30cm. In a research conducted it
was found that the maximum yield of oil and thymol was obtained when spacing was
of 15cm. Maximum percentage of thymol was found at blooming stage with spacing
of 45cm. Distance of 15cm between plants and their harvesting at beginning of
blooming season was found to be best approach for gaining high yield of dry matter,
thyme oil and thymol [9]. Moreover, during the rst growing season spacing doesn’t
create much difference. But in second harvesting season spacing between the plants
signicantly affects its height, diameter of canopy, fresh and dry weight of its foliage
and the number of leaves. Seeds can also be planted in a nursery in plant trays which
can later be transplanted when ready. The season for sowing seeds and transplant
cuttings is the spring season. Sometimes sowing is carried out before winter. Small
seedlings can be more frost resistant than mature plants of thyme. The quality of
thyme can be determined by the number of leaves present in the herb, as the glands
secreting essential oil are present numerously in leaves and scarcely in stem [10].
16.4.4 Propagation
Propagation of thyme is done via cuttings, seedlings and layering. Dividing the
plant at its root can increase thyme plantation. Seeds are sowed in spring at a depth
of 6mm or less. Direct sowing of seeds is often troublesome therefore seedlings are
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often prepared in greenhouses. Germination takes place in around 2weeks. However,
if seeds are planted in seed trays then it will take 6–8 weeks for germination.
Germination rate of thyme seeds is relatively low therefore it is recommendable to
use vegetative propagation. It is advisable to use cuttings for homogenous thyme
plants. Cuttings of 5 to 6cm are useful for this purpose. The vegetation period of
thyme is 200–210days. Under suitable conditions, it germinates after 4–5 days.
Flowering in thyme takes place after 40–50days. As soon as seeds are formed,
thyme is harvested. Thymus plants are capable of surviving 2 or 3years but in cold
regions like Canada and Eastern Europe, the plants freeze thereby in these countries
the thyme is treated as 1year culture [11]. Thyme used for culinary purposes needs
to be propagated after every 2–3years as they become woody with time. Agriculture
practices and environmental conditions greatly inuence the yield of the Thymus.
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16.4.5 Fertilization
Over fertilization leads to tall, spindly and weak growth of thyme. Based on annual
soil analysis results, fertilizers containing nitrogen, phosphorous, potassium and
sulfur should be applied. Applying nitrogen fertilizer after harvesting promotes
shoot growth in thyme during the growing season. However excessive nitrogen may
affect the quality of oil produced. Globally, the organic cultivation of thyme is a
common practice [12].
16.4.6 Irrigation
For irrigation of thyme, drip or trickle irrigation is mostly done. This irrigation system helps to place water directly into the root zone to minimize water loss via
evaporation. Another method used is overhead irrigation. It is similar to a lawn
sprinkler [13]. This method is used to irrigate a larger area of land. It should be
taken care that the soil doesn’t dries out.
16.4.7 Harvesting
Thyme is harvested annually for obtaining oil. Generally, thyme is most aromatic
during blooming period therefore it is considered as best time for harvesting.
However, depending upon the different geographical conditions in which thyme
exists their vegetation and blooming period vary. For example, in Spain, the major
producer of thyme, there the harvesting takes place from February to August during
the blooming season. Whereas in Morocco collection of plant material for oil extraction takes place at the beginning of April. And if we talk about France there
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harvesting is carried out twice a year, once in May and then again in September.
Thus in various parts of the world harvesting period differs. The quality of thyme
depends largely upon geographical location and climatic conditions. Moreover,
light greatly inuences the production of essential oil within thyme. Herbs growing
in full sunlight showed highest production of thymol and myrcene within them.
Weather conditions also matters a lot. Harvesting of thyme should be carried in
morning on sunny days when there is no dew. Dew and moisture deteriorates the
herb much faster by destroying its color and benecial properties. Harvesting begins
during late summer when owering begins. The low growing habitat of thyme
makes it mechanical harvesting quite difcult. Therefore, thyme plants are picked
by hand. For obtaining a dried yield, the entire plant i.e. 10–15cm above the ground
is harvested [14]. For fresh yield, only tips of branches are being cut. Harvesting
should be done carefully because if the crop is left too long or is cut too low, plant
death can occur. Heavy cuttings should be avoided. Therefore, sharp tools should be
used to prevent the splitting of stems.
T. Iftikhar etal.
16.4.8 Effect ofHarvesting Time onComposition andContent
ofEssential Oil
The most important feature of aromatic herbs is their yield and composition of
essential oil. The composition of thyme essential oil varies throughout the year. This
has been proved through various researches. For example it was found that in May
percentage of p-cymene was highest in Thymus vulgaris L. while the amount of
thymol was lowest at the same time. Later it increased gradually and was stable at
the time of vegetation. It was also found that the concentration of α-terpinene was
rather low in June and in the beginning of July. However in the end of June and
beginning of August its concentration increased considerably when the percentage
of thymol reduced. So this shows that harvesting period signicantly impacts the
composition of essential oil. It is therefore possible to optimize the amount and
quality of thyme essential oil by selecting right stage of development for harvesting
the plant.
16.4.9 Post-harvest Treatment
Temperature is the most critical factor in maintaining the quality of post-harvest
thyme crop. An optimum temperature of 0°C provides a shelf life of 3–4weeks.
Temperature of 5°C keeps the plant alive for 2–3weeks. Thus an optimum period
of cooling is required to extend the shelf-life of thyme. In post-harvest treatment
rstly, the leaves should be removed from dried stems and then sieved to remove
dirt and get the uniform product. There are several methods for drying plant
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material. The simplest way of drying is to keep thyme for some time and wait for it
to dry naturally. However natural drying can be problematic as the leaves of thyme
dries instantly whereas its stem takes time to dry. Thyme can also be dried by keeping it in sun. This solar drying maintains the green color of thyme thus making it
attractive. To maintain the avor and green color of thyme, it should be dried by hot
air drying below 40°C.The dried material should be again sieved to remove all dirt.
Hot air drying is cost effective approach. However it has a major disadvantage; it
results in loss of volatiles. Contrarily, freeze drying although it maintains the color
and quality of thyme but it is quite expensive.
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16.4.10 Grading
According to International standards, a least of 0.5% of essential oil should be present in thyme leaves, which is equal to 5ml/kg dried herb. Likewise, ground thyme
should contain 0.2% essential oil [15]. For essential oil production, there are six
chemotypes present. The most frequent constituent that is found in thyme is thymol
and carvacrol. Thymol has powerful disinfectant properties.
16.4.11 Packaging
The main objective of packing is to protect thyme from both external and internal
conditions. Generally, dried thyme is stored in cool and dry conditions. Storing
dried thyme at 5–7°C keeps it stable for 12months. Room temperature decreases
the stability of product. Ideally plants should be stored in air-tight boxes so that it
doesn’t oxidize. Because of their volatile nature, essential oils need to be handled
carefully. They are packed in small quantities as well as in bulk quantity. Storage at
−20°C for a period of 12months is best for maintaining the composition of essen-
tial oil. Oil should be packaged carefully because moisture, heat, oxygen and light
destroys the oil. The glass of dark color should be used for packaging [16]. Fresh
thyme is packaged either in crates or in cellophane packets. Multi-layered paper
sacs can also be used for this purpose.
16.4.12 Storage
An essential oil should be stored in cool and dry areas. Airtight glass bottles should
be used. Oil should not be exposed to heat and heavy metals (Fig.16.2).
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Fig. 16.2 Cultivation
process of Thyme
16.4.13 Maintaining theQuality ofThyme Plant
T. Iftikhar etal.
In this regard two factors are important i.e. (a) the quantity of leaves and stem, and
(b) the content of essential oil. For getting higher quantity of leaves it is advisable
to harvest before blooming. Leaves present high quality. Essential oil yield is dependent upon the climatic conditions of the region. In dry places, care should be taken
during drying of leaves and it shouldn’t be exposed to sunlight. For this purpose
plants are placed in ventilated beds that are supplied with warm air. The temperature
is maintained at 30–45°C.Plant material dries in 2–3days. Resultantly, 10–12% of
moisture is left behind. The cost of thyme cultivated in mountains is expensive
because there it is impossible to provide such conditions.
16.4.14 Maintaining theQuality ofThyme Essential Oil
Different processes used for thyme oil extraction affects the quality of oil produced.
Therefore, much care should be taken. Fresh thyme has a different taste. Researches
showed that Thymus vulgaris L. dried by hot air or microwave ovens results in the
loss of important constituents. It was found that the percentage of thymol content in
thyme essential oil decreased on processing by microwave oven. Different methods
used for thyme oil extraction are mentioned below [10].
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16.4.15 Steam Distillation
It is widely used method for extraction of thyme oil. This method is advantageous
because it results in lesser instability of compounds at higher temperature. Simple
steam distillation and Clevenger system are two methods used for this purpose.
16.4.16 Solvent Extraction
For extraction of phenolics from the thyme leaves solvent extraction is performed.
In this process soluble compounds are being separated from solid to liquid matrix.
It is used to obtain antioxidants from raw material [17].
16.4.17 Supercritical Fluid Extraction
To get good yield of antioxidants this technique is used. For extraction of polyphenols from thyme, this extraction process is used. It has low extraction time and
results in minimum degradation. It is the most widely used process [11].
16.4.18 Pressurized Liquid Extraction (PLE)
It is the recent solvent technique used to minimize damage. It uses solvents above
normal boiling points and pressure, thus keeping the uid in liquid state during the
whole process. Resultantly, high yields are obtained from this process.
16.4.19 Extraction atAtmospheric Pressure
For this purpose raw material is prepared which is then exposed to the extraction
solvent. After extraction, miscella is removed from the extracted material. And
nally the solvent is removed. For this process, it is essential to have optimal particle size. The particle size shouldn’t be so small that it doesn’t allows the penetration
of solvent. Penetration of solvent is accomplished in three stages i.e. penetration of
solvent in dry mass, achieving equilibrium and nally replacing the solute with new
solvent. This process can be done by making batches [18].
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16.4.20 Weed Control
It is necessary to keep the nal product weed-free. For this purpose, organic mulches
and hand weeding is used. Mulching is an effective approach for controlling weed
growth. It enhances plant growth and its diameter. In case of thyme crop it is advisable to utilize organic mulch. Plastic mulch is also used to prevent weed growth. It
is also an effective technique to grow a dense stand of pasture crops followed by
fallowing of land before planting thyme crop. Both these steps will signicantly
reduce the weed.
16.4.21 Pest Control
Thyme contains volatile oils that have insect repellant properties. But still, spiders,
mites and whitey may infest thyme plants. To control pests, a pest management
program should be followed. Crops should also be scouted regularly. Thyme is
being attacked by aphids as well. T. vulgaris L. also gets infected by Botrytis cine-
rea that causes gray mold of thyme. Rhizoctonia also causes root rot in thyme [19].
Correct identication of these pests is also essential for their control. It is preferable
that instead of chemical control, biological control should be used to eliminate
pests. Moreover, plant extracts can also be used to control pests. Certain insect
repellant herbs can also be used for pest control.
16.4.22 Disease Control
Wetter environment and imperfect soil drainage result in disease development in
thyme plants. Rhizoctonia root rot, Botrytis blight, Alternaria and rust are some of
the diseases that develop in thyme if not provided with a suitable environment. To
prevent the diseases uncontaminated seeds and plant material should be used.
Regular scouting should be followed. The earlier the disease is diagnosed, crops
could be saved from large scale damage. Moreover, mulching thyme with limestone
gravel layer is a common practice of suppressing unnecessary weeds and retaining
moisture [20].
16.4.23 Diseases ofThyme
Thyme is susceptible to a number of plant diseases such as botrytis rot, Rhizoctonia,
Alternaria blight etc. In disease caused by fungus Alternaria small round, black or
yellow spots form on the leaves surface resulting in lesions and holes. This fungus
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