Wouldn’t it be ideal if you could grown your own hemp and then use it to build your home? 1 or 2 hectares of hemp stalk is potentially all you need to harvest enough building materials to build a house. Imagine that – growing your own house! … but it isn’t a simple thing to do.
The hemp plant has four elements: seeds, leaves, fibers and a wooden core. The part you need for construction is the wooden core – also called the hurd or shiv. Separating it from the other elements of the plant requires effort. You need to grow the hemp, deffoliate it (remove the leaves) before harvesting, harvest or remove the seeds, harvest the stalk, let it ret (start decomposing so that the fibers can be separated from the hurd) and then decorticate it.
This finally step of decortication seems like the greatest obstacle – this is the process of separating the fiber and the wooden core. It can be done either through massive manual labor (of which I don’t yet have all the details – but it involves collecting the harvested stalks into small bales and then beating them to separate the fibers and wooden core) or in an industrial process. The indutrial process is usually designed to extract the fibers, the actual wooden shiv is simply a left over of that process.
It would be so much easier to grow your own construction hemp if decortication could be avoided – and this may be possible but my understanding is that it depends on the climate you live in. This research paper on Hemp-Concretes claims that it is possible to create hempcrete using both shives and fibers – BUT it is important to note that the research focuses on the structural aspects of the resulting hempcrete. It does not address the effect of fibers on insulation and breathability of the hempcrete.
Introduction of fiber to the hempcrete mix can cause humidity problems. When fibers are clumped together they tend to draw moisture and that is not something you want to happen in your wall. According to Steve Allin it is possible to add 5%-15% of fiber to the mix but not much more. This may be less of an issue in a hot and dry climate – but otherwise the risk seems unwarranted.
Maybe when the hemp industry matures it will be possible to cultivate stalks with very little fiber and a massive wooden core – which could then be used in whole? For now though it seems that self-grown hemp is not a feasibly reliable option for construction unless you have the means to decorticate it.
Following is a transcription of this article from November 1942 by A.H. Wright, published by the University of Wisconsin, Madison – College of Agriculture, which to date is the most informative, accessible, freely available online guide about growing hemp that I’ve encountered (I found it stashed away here). I liked it and thought to make is easier to access by transcribing it.
Wisconsin farmers are the leading hemp fiber producers in America. They are using methods based on thirty years of experience and experiment in growing and handling the crop. The American navy and army need hemp – vast amounts of it for rope, cordage and threads.
Four hemp mills are running in Wisconsin – at Markesan, Brandon, Beaver Dam and Juneau. Although other parts of Wisconsin have soil adapted to the crop, all the hemp in the state has larely been grown around these mills.
Hemp yields well under favorable conditions. On suitable soils in the state, hemp has rarely failed to produce a good crop. Yields have usually ranged from 700 to 1000 pounds of fibre for the acre. The average yield of dry stalks after dew retting as the farmer delivers them to the mill is from two and half to three tons an acre.
Hemp is seeded in solid in the spring; is harvested and spread out on the stubble in the early fall; the straw (stalks) is allowed to ret (partially rot) while still spread out; is picked up, bound and shocked after retting, then hauled to the processing mill where it is stacked.
What the Hemp Crop needs
Plenty of moisture
Rotation with other crops
Good seed bed
Dark prairie silt loam soils – uniform and fertile – are best for hemps. Reasonably level clay loams are good. A plentiful supply of organic matter is very important and thorough drainage is necessary. Not suitable are peat and other marsh lands, or sandy, gravelly and rocky soils, heavy clay soils and bottom lands.
Plenty of Moisture
Hemp will not withstand drought and so does best on soils that do not dry out quickly. Dry areas are decidedly unsatisfactory. The stunting of hemp by dry weather results in low yields and low quality fiber. Hemp needs much the same moisture as a good crop of corn.
Because hemp grows rank and luxuriant, it is often incorrectly thought that it is hard on the land, but experience shows that it has about the same effect as a good crop of corn. Hemp leaves the soil in excellent condition crop crops that follow.
Rotation with Other Crops
Hemp should not be grown continuously on the same field for the same reason that corn or grain should not be repeated on land. It does best after corn, alfalfa, clover or bluegrass pasture. It does not follow timothy satisfactorily, and often does not do well after small grains. The usually practice is to plant the hemp after corn, followed with a small grain seeded down to clover, then the clover is followed with corn. On very fertile soils, hemp may be grown two years in succession.
Barnyard manure is ordinarily the best fertilizer for hemp but commercial fertilizer can well be used to supplement six to eight loads of manure to the acre. On most soils a complete fertilizer – containing nitrogen, phosphorus, and potassium – is most likely to give the best results. Such standard commercial fertilizers as a 3-9-13, or 3-12-12 have been used to advantage. The usual amount is around 200 pounds an acre; the use of 300 to 400 pounds an acre of 20% super-phosphate alone has given good results on typical dark prairie soils in Wisconsin. Commercial fertilizer alone will not make up for lack of manure or lack of natural fertility. Lime, at three to four tons an acre, may well be applied on acid soils.
Seeding the Hemp Crop
Hemp Needs a Good Seed Bed
The seed bed must be well prepared. Although spring plowing will give fair results, fall plowing is best. The soil should be worked up thoroughly before planting but should also be firm. A corrugated roller used just before and just after will do much to put the seed bed in proper shape. on soils that are inclined to crust, broadcasting usually gives better results than drilling.
While hemp is one of the best smother crops know yet weed infested soils must be prepared so that the hemp will outgrow the weeds. Canada thistles and quack grass will choke out the hemp unless they are subdued before the hemp is planted. Any method which will put the soil in good shape and check the weeds is satisfactory. Hemp will not smother out weeds on unfertile or poorly drained soil.
On average hemp soils in the north central states, from four to six pecks of good seed to the acre seem to give best results. On very fertile soils, five to six pecks are advisable. On soils less fertile then average, four pecks are enough but less than four pecks is rarely advisable. Hemp seed weighs 44 pounds the bushel.
It is very important and necessary to leave an unplanted strip (turn way) all around the field. This turnway, 16 to 20 feet wide, should be left on both sides and both ends of the field. The hemp harvesting machine requires such space at the edges of the fields in order to make the first round. After the field is sown the turnways should be filled in by planting them to small grains, soybeans for hay, canning peas or a similar crop. Corn for silage, early potatoes or other early rowed crops may also be used, but thickly seeded crops, such as small grains are best because they usually prevent a rank growth of hemp around the edges of the field.
Kentucky Hemp Seed Best
All hemp seed recommended for the United States is grown in Kentucky. Hemp seed from foreign countries cannot be relied upon. Most of the hemp grown in this country is from seed from adapted selections and has proved decidedly superior to that from other countries.
Early Seeding is Best
Results vary in different seasons but in most years early seeding is best. While some plant hemp almost as early as oats, yet the usual practice is to sow just after oats are sown and before corn planting starts. Under emergency conditions hemp may be sown as late as the first week in June.
While good stands of hemp have followed the use of a broadcast seeder, yet a grain drill is decidedly better on soils not apt to crust. The seed should be sown not more than one inch deep.
Harvesting the Hemp Crop
Early Harvesting is Best
Hemp should be harvested when the pollen bearing (male) plants are in full or late bloom. At this stage, the lower leaves have mostly fallen and the upper leaves are yellowing. Generally, hemp harvested early has the best season for retting, consequently it is better to harvest a little on the early side rather than to wait until it is too mature. So far as the quality and yield of fiber are concerned, the crop may be harvested any time in the four weeks between blossoming and early seed forming. Over ripe hemp does not produce good quality fiber.
Hemp must be harvested with special machines. In very small fields, the self-rake reaper is used to advantage. Fields of five acres or more are cut with a special hemp harvester which is now standard equipment and is usually furnished on a rental basis by the processing mill. It harvests the hemp and spreads it in one operation. The hemp harvester operated by a tractor will harvest from 5 to 10 acres a day.
Proper Retting Important
Retting is the most important item in handling hemp for the kind of retting determines the quality and value of the fiber. The green stalks, after they are spread on the stubble by the harvesting machine, remain there until they rot enough so the fiber can be readily separated from the woody part of the stems.
The time varies with the weather. If the weather is warm and moist just after the crop is spread, retting may be complete in seven to ten days. If it is dry, retting may be delayed until late in the fall. Usually the early fall is moist and warm, so early harvesting is best. In unfavorable retting seasons, there is a tendency to life the hemp before it is retted. This should not be done. The hemp should be left spread out in the field until the outer layer of fiber can be taken off easily. Unless very quick retting occurs, the straw should be turned over in the field during the retting period so that an even ret is obtained.
Retted Straw is Bound and Shocked
As soon is straw is properly retted, it must be lifted and bound in bundles. This is done with a special hemp binder (picker) which is supplied on a rental basis by the hemp mill.
The bound bundles are placed in shocks a little larger then those used for corn. When the bundles are well cured they are hauled to the hemp mill and stacked. Great care should be taken in building stacks as too much invested in the retted straw to stack it carelessly. Each layer of bundles should have a pronounced pitch; and the center should always be kept high. In lapping, very little of the butts of each layer should be exposed to the weather, as such parts will decompose if left long in the stack. Hemp straw, properly stacked, will keep for many months with very little loss.
gives good yield on suitable soil
usually not damaged by insects or disease
is not “hard” on the land
helps to control weeds
Hail Causes most Damage
Hemp in the north central states is nearly free from insect damage and fungus disease but cut worms and white grubs have caused some damage. Grasshoppers will destroy hemp leaves around the edges of fields near freshly harvested small grains. Stem borers, including the European corn borer, have been known to attack hemp plants.
But hail is the most serious enemy of growing hemp. While the total loss has been very little, yet there have been serious local losses. Wherever a hail stone strikes a growing hemp plant, a weak spot occurs, thus damaging the fiber. Hail insurance is commonly used.
Hemp Straw Must be Milled
At the hemp mill the retted straw is dried, crushed and the broken material is cleaned by brushing and combing with a hemp scutcher. The fiber comes from this machine in two forms. The long straight fiber is line and that is by far the most valuable. The short, tangled, snarled fiber is known as tow. This fiber has much less value. Hemp grown on good hemp land will generally produce around 55% line fiber and 45% tow. Hemp grown on poor hemp soil may produce nearly all tow and very little line. This is one reason why the selection of proper soils for hemp culture is extremely important.
I am currently living with an inspiring notion that we will (1) be able to grow the hemp needed to build our future home and (2) that we will have enough land to grow a houses-worth of hemp every year so that someone else will be able to do the same.
Though I have to say that the more I explore the world of Hemp the more doubts about this being a feasible goal. At the end of this post you will find some links and PDF’s I read and that led to my current understanding.
Hemp seems to be a relatively easy crop to grow. It’s strong, it doesn’t require pesticides, it grows pretty fast (~4 months) and it even renews the land in which it is grown. The more substantial challenge is harvesting and processing it.
Three Parts of Hemp
There are three parts to the hemp plant – each with it’s own uses:
The seeds can be used for all kinds of food products, oils and other medicinal by-products.
The fibers have all kinds of industrial uses (from clothes to cars) – they are the middle layers of the stalk covered by a thin protective layer.
The hurd – the wooden core that is left over after the fibers have been extracted – which is the part popularly used (together with lime) for construction (although I have come across information that indicates that it is possible to use the fibers and curd together for construction – which means that they don’t need to be separated).
Some Hemp Harvesting Facts
Seeds and stalk don’t mature together – they are (or at least should be) harvested at different times. Both the seeds and the fibers have (different) optimal times for harvesting – beyond which both lose some of the potency and qualities.
The seeds don’t mature all at once – they tend to mature in two cycles. Harvesting time is when you think you can harvest the most mature crop (when some of the seeds may have decayed or lost their potency and others still not quite matured).
Hemp is a tough plant – so you need resilient and strong harvesting tools. The strength of the fiber means it’s hard to cut down and the length of the stalk means it will catch on to and jam any moving part it finds (for example – combine machinery) – which means that you either need powerful harvesting machines – or that harvesting may be slow and tedious.
Hemp is a tall plant (much taller then wheat or barley) – which means you need harvesting equipment that can reach up high.
When the stalk is cut, it is useful to do it in such a way that it is then easy to collect into bales – if I understood correctly what this means is that the harvester needs to leave the cut stalks uniformly oriented on the ground.
The stalks should be cut as long as possible – long fibers are generally better and more useful then shorter ones.
It is possible to harvest both seed and stalk. Seeds go first (duh!) – but then you not only need tall harvesting equipment but it also needs to be sharp and fast spinning – so that the stalk is cut cleanly – leaving long fibers in tact.
The primary processing for seeds is removing them from their shells – I still don’t have information on how that is done.
The primary processing for stalk is separating the fibers from the wooden sheathe (this is called “decortication”- whichI am guessing comes from the idea of removing the core and, apparently, originates from a medical surgical process of separation). There are numerous methods for this – but generally they seem to be divided in two: industrial processes and organic/natural processes. I am less interested in the industrial aspect so I focused a bit more on the natural processes. Apparently the idea is to use water to cause decomposition of a kind of “glue” that keeps the fiber and curd attached. Usually natural dampness like dew will do the trick. You need to keep an eye out on the crop until separation begins – then you need to let it dry for a few days. I am not yet clear on all the details of this process.
All these facts seem to eminate from an industrial/financial view point. They are focused on creating optimal yields and financial returns. If harvesting and processing hemp can only be done using heavy and expensive machinery – that means that growing just a few acres or a hectare of hemp isn’t feasible. I was somewhat discouraged by this. But …
Since hemp has been grown for hundreds of years (if not thousands) I am sure there is much knowledge on how to do it on a smaller scale – for home needs but I haven’t been able to find any information on this yet. It may require more manual labour but I am confident it is possible. Our needs are humble – maybe to build another small structure for meditation, enough seeds for eating, making oils … the needs of a small family.
I’ll continue to look for more home-oriented information on this – I promise to share it here when I do find it.