History and uses of hemp - The Hempcrete Topic: Designing and Building with Hemp-lime - page 12

The gradual depletion of nutrients in the UK's soil through the last 60 years or so of ever-
more intensive and industrialized farming, and the 'replacement' of these nutrients with in-
creasing applications of chemical fertilizers, has resulted in a very poor soil quality across
much of the UK's farming land. Poor soil produces weak plants that are more susceptible
to pests and disease, which in turn are targeted with increased levels of chemical pesticides
and fungicides. These also indiscriminately kill beneficial insects - both soil-dwellers and
airborne pollinators, which are vital for the success of our food crops. Even if the contin-
ued use of such chemical fertilizers and pesticides were the best way forward (which it
isn't), the fact that many of these products are derived from fossil fuels means that they are
a non-sustainable resource.
The situation nationally at the beginning of the twenty-first century, apart from among
those farmers who are returning to smaller-scale, organic farming, is soil across the UK's
farms that is almost totally devoid of those insects and other organisms which convert de-
caying organic matter into the nutrients that plants need to grow. These tiny creatures also
provide a key source of nutrients at the bottom of the food chain, and their absence is a
significant factor in the huge loss of biodiversity in the UK that has occurred over recent
decades. The cultivation of a plant such as industrial hemp, which is not nutrient-greedy,
can be grown using only organic fertilizers and without chemical weedkillers and pesti-
cides, and breaks up the deep soil, has the potential to bring huge benefits in terms of soil
health, food production and the UK's ecosystem as a whole.
Industrial hemp is sown in the late spring, from early May to early June, at a density of
around 30-38kg of seed per hectare. The ideal conditions are a warming soil with plenty of
moisture present. Prevailing conditions are more important than exact timing when sow-
ing, since the seedlings are not frost hardy.
Seedlings emerge within five days, and grow rapidly, sometimes at a rate of 30cm a week.
The crop is harvested in August, having attained a height of 2-4m. As it is cut down, the
hemp plant is also cut into shorter lengths and is left on the ground for up to a month for
'retting': a biological process whereby the hemp straw becomes more workable and the
bast fibres begin to separate from the shiv. When the retting process is complete, and the
sun has dried the hemp, it is baled and stored under cover. The raw hemp straw is then
processed to separate it into saleable parts. The different markets for each part are shown
in the table below (see also table on page 19 ) .
Hemp can be grown for the straw alone, or allowed to grow on for a seed crop. It is possible
to grow a 'dual' crop, for fibre and seed, although this is much less common because the