Lemon balm 393
should be well irrigated in arid and semi-arid regions for obtaining high green herb
yield. The average life of a plant is ten years, but economic life length is about five
years.
Lemon balm can be propagated from seeds, stem cuttings and root division. The
seeds (8–10 kg/ha) are very small, thus should be covered with a fine layer of soil in
the spring or early autumn. Seed germination is slow, taking between two or four
weeks. Therefore, probably, obtaining seedlings from seeds is preferable to direct
seeding in the field for successful propagation. In addition, the use of seedlings as a
propagation method produces a better herb yield compared to root division with a
single shoot (Saglam et al., 2004). For seedling production, 50–80 g seeds are sown
in 12–15 m^2 of a pre-prepared seedbed (Ilisulu, 1992). These produced seedlings will
be enough to transplant 0.1 ha area. Transplanting time of seedlings to the field is
autumn or spring. However, instead of propagation from seeds or seedling, vegetative
propagation such as stem cutting or root division could be an easier and faster
method to establish a lemon balm plantation (Davis, 1997). In another method for
expanding a lemon balm plantation, a long stem, which is still attached to the parent
plant, is buried in moist soil by allowing a few inches of the tip to remain above the
surface. In a few weeks, the buried stem develops new roots and the new plant can
be separated from its parent.
Although plant density changes depending growing conditions, both 30 ¥ 30 cm
and 40 ¥ 20 cm plant densities give satisfactory results (Ceylan et al., 1994; Saglam
et al., 2004). In the establishment year, application of a sufficient amount of phosphorus,
potassium and nitrogen is recommended according to soil analysis. For example,
Saglam et al., (2004) obtained a good result with side dressing application of 80 kg/
ha P 2 O 2 and 60 kg/ha N in the first year. In consecutive years, additional mineral
nitrogen may be applied after cuts. Recently, however, as organic production gains
more attention, organic manure or fertilisers may be preferred.
Weed control is one of the important cultural practices in lemon balm, as presence
of weeds in the fresh or dried herb will reduce quality. Herbicides for weed control
could be applied, but avoiding chemical residues on the plants because vegetative
parts of lemon balm can be directly used for medicinal and aromatic purposes (Zuin
and Vilegas, 2000). Therefore, organic control methods for weeds, diseases and
insects should be preferred if they are available.
Lemon balm as a perennial plant can be harvested twice or three times a season
just before blooming. Harvesting after complete flowering causes a reduction in
herba quality. Plants are cut at 8–10 cm above ground in the morning after the dew
has evaporated. The fresh herba is immediately dried in shade at 20–35 ∞C after
harvest; otherwise the drug herba colour turns to dark brownish. Moreover, bruising
the leaves during harvest should be avoided, because it causes the dry herb colour to
become also dark brownish and, consequently reduces quality. Harvested and dried
herba should be stored in dry places with good ventilation.
The fresh or dry herba yield varies depending upon genotype, growing conditions
and cultivation practices. After transplanting seedling to the field, the first year can
be considered as an establishment year; therefore high herba yield should not be
expected and the yield increases after first year. The second and third years are
production years, and between 5000 and 10,000 kg/ha dry herb yield can be obtained
in a season (Saglam et al., 2004).
Although it is difficult to determine the size of the world market for lemon balm,
as specific trade statistics are not available, most commercial production takes place