Agriculture Reference
In-Depth Information
of hemp is known to possess sensitivity to
photoperiod.
grown to 30-60 cm high and will have three
pairs of leaves.
Active growth
3.5.2 Vegetative cycle and growth
This period stretches from the time of implan-
tation to the start of flowering. It is during this
phase of growth that the yield in hurds and
fibre is generated and that the water and min-
eral requirements are greatest and must be
met. Providing all these needs are met, growth
can attain 1 t of dry matter every 120°C days.
This corresponds to a growth rate of 1 t of dry
matter/week in an area with a climate similar
to that in northern France.
The vegetative cycle of hemp is relatively sim-
ple to describe, occurring in a few steps, with
each step being highly dependent on a number
of specific environmental factors.
The vegetative cycle (Fig. 3.16) consists of
the following.
Emergence
Emergence can be expected to occur approxi-
mately 100°C days, or 4-10 days, after sow-
ing, depending on the soil conditions. This is
the most vulnerable phase of cultivation, dur-
ing which it is possible to lose large numbers of
plants, either because they have received too
little or, more commonly, too much water.
Flowering
The appearance of the first flowers in a hemp
crop is dependent on the sum of the tempera-
tures experienced since sowing and by the
photoperiodic sensitivity of the variety. During
this period, needs are maximal and the seed
yield starts to be determined.
Implantation (3 weeks after
emerging from the ground)
Full flowering
This phase of growth is the slowest part of
the cultivation process and corresponds to
the extension of ground cover. During this
time, the root system is developed and
preparations are made to explore the
ground further: 3 weeks (25°C days after
emergence) are needed for this to take place
and for the correct density to be established.
By the end of this stage, the plant will have
This stage corresponds to the opening of the
last female flowers and is under the strict influ-
ence of the photoperiod. For any given variety
grown, cultivated in any given location, with
the exception of very late crops, this stage will
be attained at a fixed date regardless of the
date of sowing and independently of annual
differences.
3 m
Height
of crop
fibres maturity
end of flowering
end of growth
HARVEST
2 m
FLOWERING
fibres and
of seeds maturity
1 m
SOWING
EMERGENCE
beginning of phase of active growth
September
May
June
July
August
Fig. 3.16.
Vegetative cycle of hemp.
