Hemp Biomass: A Step-by-Step Guide to Harvesting
What is Hemp Biomass?
Hemp Biomass is the remaining organic material (stalks & leaves) after the flowers and/or seeds have been harvested from the plant.
Biomass can be regarded as “waste” in conventional farming, but this is not the case with hemp. There are two methods for collecting hemp biomass, and each are dependent on your end goals.
For collection of oils, leaves, or for use as fuel, hemp biomass should be dried as effectively as possible before further processing.
For fibre, cloth, or cord production hemp biomass should be “retted.” This insures the fibrous strands that make up the stalk can further separate to make further processing more efficient.
Hemp leaves and stalks can be used to produce a wide variety of goods. Having a successful hemp harvest is key to the quality of theses goods. There are a few factors that are imperative to know, to get the most from your crop.
What We’ll Need to Harvest Hemp Biomass:
For CBD Biomass: Flower, Oils, Leaves or Fuel
- Machete, scythe, or shears
- Transportation Vehicle
- Drying location
- Storage location
- Processing equipment (Oil press, container, etc.)
For Hemp Fibre Biomass
- Machete, scythe or shears
- Transportation Vehicle
- Retting Location
- Storage Location
- Decorticator (fiber extraction machine)
The Hemp Biomass Harvest
Depending on your geographical location, this stage needs to be planned well before you sow your first seeds in the ground.
In North America, hemp harvest typically takes place in late-summer/early-fall. Natural weather patterns lead to hurricanes on the Atlantic and prime wildfire season on the Pacific. Timing is very important.
The size of your crop is directly related to the size of your harving team or equipment. If the crop is too large for the team of harvesters to cut and transport during the time of harvest, not only is man power wasted, but the risk of loss in the quality of your crop due to mold, mildew, and bacteria increases drastically.
Crop size = Harvesting style
The size of your crop should be based on the method of which you plan to harvest.
Size: 1 acre or less
I recommend starting with one acre or less for the first season. This allows you the freedom to test a manageable harvest and drying period. Starting slowly will also help you to understand the needs for harvesting hemp biomass. You will soon understand if you have the proper facilities for production.
Size: 2-4 acres
A hemp harvest of 2 acres is a perfectly balanced size. This could be done with as little as 2-4 people, but also allows for proper crop rotation through the year. One acre can grow the production crop while the other is rejuvenated. I recommend rejuvenating soil with a cover crop such as legumes, buckwheat, or alfalfa.
Combines are very expensive to own and maintain, yet they cut harvesting time down to almost nothing. The mantantice cost, mechanical settings, and operation experience necessary for optimum harvest are a few factors to consider.
For larger applications, the additional expense may be worth the investment. Time is money, and harvesting hemp is no exception.
Once you have experience growing hemp at 2-4 acres, the combine is most effective way of growing your yield. Unless you are willing to hire a team of skilled, manual harvesters, a Combine is the only way to sucessfully harvest hemp in a short window of time.
If hemp is going to be cut with a combine then the correct conditions for cutting need to be assessed before hand.
The proper conditions to harvest hemp with a combine are:
- humidity (50% or less)
- temperatures (65-90°F)
- wind (light wind)
[BONUS TIP] Be sure to check the following days forecast and ensure there is no precipitation. This will allow the hemp to dry out properly before being baled.
Harvesting hemp plants should be on days where there is no precipitation in the forecast. Ensure there is adequate time to move the harvest into storage for the next stage of processing prior to any precipitation.
When harvesting, plants should be cut 2-3cm from the soil with a machete, scythe, or shears and stacked in piles for easy transport. Once the field is cut, there are two options for the next stage: Drying or Retting.
Drying Hemp Biomass
Drying hemp can be done in a variety of ways. From the inside of a sterile lab facility, to the rafters of an open air barn, the major factor here is space and adequate air flow.
The quickest way to reduce the quality of your crop is retaining moisture. While moisture is your friend during the growing period, as soon as the stalk is cut down rid as much moisture from the stalk as possible. Otherwise, mold and mildew can grow rapidly and reduce the quality of your harvest. This will effect the quality of your finished product as well.
Some choose to hang the entire plant upside down like traditional tobacco. However, this can allow for moisture build-up near the center of the plant. Hanging can also lead to mold and mildew growth making the plant less than desirable for production.
Snipping each branch from the plant and hanging them individually, allows for not only a quicker drying process and results in less product loss.
Hanging can be done a variety of ways. Hemp is commonly hung by wedging the stalk/branch through traditional drying wires or clamps. These wires/clamps allow it to hang with adequate air flow (from a fan or breeze) to dry for 3-5 days.
The times the plant need to dry are solely based on temperature, plant size, and air flow. Some plants may take a little longer than others.
Retting Hemp Biomass
If you intend on using your hemp biomass for fibre, retting can help make the process more effective. Retting uses micro-organisms and moisture to break down the stalk separating the individual fibres from the remainder of the stalk. This can be done two ways.
This is the most common type of retting and is done by soaking the stalks in water. Soaking them in water causes the cellular membrane to swell, and allows for easy separation of the fibre. There are two methods for using water retting
- Natural Water Retting
- A tried and true method, done for centuries around the globe. Natural water retting involves submerging hemp stalks in a naturally occurring water source such as a stream, river, or pond. When using a natural water source, be sure to secure the bundles of stalks under the water with a weight assuring that they do not float back to the surface. This process normally takes 8-14 days depending on the mineral content of the water.
- Tank Retting
- As the name suggests this method is done in controlled conditions, such as inside a container for 4-8 days. The process is faster and allows for another valuable post-harvest product, mineral dense water. This water can be poured back onto the field as liquid fertilizer, as long as no harsh chemicals were used on the crop during growth. If harsh chemicals were used then the water needs to be filtered before returning it to the soil.
With either form of water retting, the biomass then needs to be dried for a few days (1-3) to begin a curing process that will allow for easier processing in the next stage.
Dew retting is only appropriate for climates where water is sparse. After the hemp is cut, it is then laid flat on the ground, in rows allowing air flow around each stalk. The night will bring in moisture and then the day will bring warmth and light, promoting bacterial growth.
This creates a moisture rich microclimate within each stalk that allows for a similar breakdown in the biomass creating equal separation. Though, it does take a while longer (2-4 weeks) and the quality of “dew retting” biomass has been know to be lower than “water retting.”
Hemp Biomass Storage
There are a number of ways to store hemp biomass and each depend on harvesting methods and end goals.
With manual harvest methods dried hemp can be stored in everything from plastic garbage bags, plastic bins, or cotton/hemp sacks. Stored then in a covered low moisture barn or similar low moisture storage facility.
For the combine farmer, once the hemp is cut it will be also need to dry out for a few days. To promote faster drying, try raking with a hay rake or tedder to arrange into biomass into rows.
Once it is dry the hemp will be baled by an automatic baler and tractor. Hemp can be baled with any hay baler.
It can be baled using square or round bales based on the storage option for each unique situation. The biggest focus here is to do everything to insure low moisture content in each bale, 15% or less.
It is essential to reduce the moisture content. Not only for the prevention of rot and bacteria, but for another frightening reality. Bales can spontaneously combust due to the close proximity of the biological material and bacteria feeding within the bale.
This is not hard to test and there are warning signs that are “tells” that the bales may be getting too warm. The most visible, is steam emission.
If the ceiling or eaves of the barn/storage facility are showing signs of condensation, action will need to be taken. Call the fire department immediately. Bales should be tested and checked regularly with a probing thermometer.
Another simple way to test the internal temperature of the bales is to insert a iron rod as far into and as close to the center of the bale as possible. Remove the rod after two hours and feel the temperature of the metal.
If it is too hot to handle easily, then the temperatures have increased above 120°F and action should be taken. Although bale storage does require additional maintenance, it is manageable if hemp is cut under the right conditions and the moisture content is monitored throughout the process.
Hemp Biomass Processing
One of the most rewarding parts of the process is taking what you have grown for months and seeing the final product. With so many finished goods possibilities, each it unique in its own way.
Processing fibre can be done by hand with protective gloves and a club or baton.
Most processing of fibre is done using a “decorticator.” A decorticator is a machine used to strip the bark/skin off the hemp stalks.
They range from manual hand-crank to automatic fully-electric. When selecting a decorticator, confirm that it has settings to process hemp.
The dried biomass is run through the machine’s ridgid crank system breaking the hard outer shell/skin from the stalk and separating the fibres. Creating a workable product for production use.
From here the dried biomass is ready to be stored until enough of the biomass has been harvested to allow for viable oil production. Decorticator can be also used to “shuck” the dried biomass, making oil production more organized and efficient.
The dried leaves can now be removed from the stalk and stored for later tea use. The leaves can remain loose or tea filter bags can be purchased for individual servings.
Now the biomass is dry it is able to burn burned for fuel in fire places, cast iron stoves, or thermoelectric generators.
Hemp Biomass is the remaining material after the flowers and/or seeds have been harvested from the plant. There are two methods to harvest hemp biomass.
How to Harvest and Dry Hemp for CBD Production
There is a lot of interest in growing industrial hemp for CBD production, especially since hemp was legalized in the 2018 Farm Bill. Take a look at some of my previous articles regarding the potential risks and rewards in the CBD market as well as agronomic considerations for successful industrial hemp production.
Fresh cut hemp drying. Whole plants hung in this fashion during the drying phase may have humidity trapped in the center due to the ‘closed umbrella’ shape that an entire plant takes on. Breaking off and hanging individual branches is recommended. Photo by George Place.
CBD oil extraction process. Photo by George Place
Harvesting hemp is a critical stage for CBD production. The presence of molds and mildews will lower the value of hemp floral biomass so a timely harvest is essential. There are visual clues on the hemp bud that growers should monitor. When trichomes on the hemp bud shift from white to milky white it may be time to harvest.
Weekly testing of CBD content can inform the grower of when harvest should be initiated. This is in addition to the required THC test with the North Carolina Department of Agriculture. While some of the tests for CBD, cannabinoids, terpenes, pesticide residue, mold, and heavy metals can cost as much as $300 the return on investment can be significant. For example, if 1000 lbs of biomass will be harvested on one acre the difference between harvesting when the crop is at 6% CBD versus when the crop is at 7%CBD is equivalent to 10 pounds of CBD oil. Current prices for CBD oil are $5 per gram. With 454 grams per pound, a 1% discrepancy in CBD content on one acre can be a $20,000 crop value difference. Growers need to test frequently to make the right decision regarding harvest timing.
Weather will also be a key factor in determining when to pull the harvest trigger. Harvest time for hemp coincides with the hurricane season. Growers will have an easier time drying and curing their hemp floral biomass if they can bring it in before the arrival of a storm. This is the time when adequate labor is crucial. The vast majority of hemp growers for the CBD market are relying on labor to cut the stalk (the machete is the current tool of choice) and load the biomass. This takes a lot of time and physical exertion. I have heard reports of growers that had an excellent crop of hemp floral biomass but suffered massive losses because they could not harvest it in time (their two-person harvest team was not adequate). The importance of measuring the labor requirement is a big reason why we recommend that first-year hemp growers for the CBD market start with 1 acre or less. Growers need to keep track of the amount of man and woman hours that it takes to bring in the harvest. Maintaining sharp tools during the harvest process will also save time and effort.
Drying and Curing Hemp
Hemp biomass made from chipping the entire hemp plant. This biomass is low quality and will receive a reduced price. Photo by George Place
Once hemp is harvested growers should immediately move the floral biomass to the drying facility. This could be a simple structure like a barn. The facility should be under roof, out of direct sunlight, and well ventilated. Growers need to set up several fans and have them blowing continuously. Significant ventilation is crucial! Ideal temperatures for drying and curing are 60 to 70 degrees F at 60% humidity. Some processors say that hemp growers should not dry their floral biomass at the same temperatures as flu-cured tobacco. Those temps are too high and dry the hemp too quickly. A slow drying with high airflow will cure the hemp, produce a higher quality end product (better cannabinoid and terpene spectrum), and fetch a higher price.
It is difficult to estimate the square footage of drying space needed per plant. Using a flu-cured tobacco with 800 square feet a grower was able to dry 1 acre worth of plants (approximately 1350 plants) in 3 days. Another grower was able to dry approximately 1.5 acres worth of hemp (plant number not stated) in a 2500 square foot barn.
Hanging entire plants upside down on wires in the drying barn is a common practice. Unfortunately, as those plants dry the branches droop down in the formation of a closing umbrella. That closing umbrella shape results in less airflow to the center of that entire hemp plant. Thus more mold and mildew will grow in that center portion. We advise growers to break off the individual branches from the hemp plant and hang branches on the drying wire, not whole plants. This step is more labor intensive but will help minimize mold and mildew.
Dry and shucked (stem removed) hemp flower biomass. Photo by George Place
Dry hemp biomass still on the stem, referred to as unshucked. Photo by George Place
There is a lot of interest in growing industrial hemp for CBD production, especially since hemp was legalized in the 2018 Farm Bill. Take a look at some of my previous articles regarding the potential risks and rewards in the CBD market as well as agronomic considerations for successful industrial hemp production. Hemp Production – Keeping …