TITLE:
The Effect of Air Temperature on Growth of Eight Herb Species
AUTHORS:
Leiv M. Mortensen
KEYWORDS:
Air Temperature, Basil, Cilantro, Growth, Lemon Balm, Oregano, Rocket, Rosemary, Sage, Thyme
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.5 No.11,
May
16,
2014
ABSTRACT: The effect
of different constant air temperatures (18°C, 21°C, 24°C and 27°C) and variable
temperatures (24°C/18°C and 27°C/15°C in 12 h/12 h periods) on basil, sage,
thyme, lemon balm, cilantro, rosemary, oregano and rocket was studied.
Supplementary lighting was given 16 h·day-1 at a photon flux density
(PFD) of 150 μmol·m-2·s-1 (corresponding to 8.6 mol·m-2·day-1 photosynthetic active radiation [PAR]). Including daylight the PAR was 29.6 ± 6.9
mol·m-2·day-1 as a mean during the experimental period.
Increasing the temperature from 18°C to 27°C increased the fresh weight in
basil (106%), sage (95%), rosemary (126%) and rocket (62%), while an increase
from 18°C to 24°C increased the weight in lemon balm (78%), cilantro (41%),
oregano (40%) and thyme (58%). For the last four species the fresh weight was
unaffected by a further increase to 27°C. No significant difference was found between the 24°C/18°C and 27°C/15°C treatments. These treatments gave a mean temperature of about 21°C, and
no significant differences were found between these treatments and the constant
21°C treatment. The plant height generally increased in the same proportion as
the fresh weight increased in the different species. No differences were
visually observed between the treatments after two weeks under indoor
conditions. All species remained green except cilantro and rocket, for which
some leaf yellowing took place. A simple test indicated that the flavour
increased with increasing temperature (from 18°C to 27°C) in all species except
cilantro.