- Early planting can help beat summer annual weeds.
- Avoid areas prone to saturated conditions.
- In-row density helps with weed control.
- Higher planting density is a cheap way to control weeds early.
- Narrow row spacing results in higher grain yields.
- Narrow row spacing results in shorter plants.
- Do not harvest too wet or too dry.
- Harvest before significant shattering occurs.
- Wet hemp threshes harder and the grain is more easily damaged.
- Wet hemp grain produces a dirtier sample that will require screening before drying.
- Wet hemp grain heats up and spoils quickly if left without aeration.
- Have adequate aeration and drying facilities ready to go after harvest. Do not let the combine outpace aeration/drying capacity.
- Avoid dual-rotor combines – New Holland and Claas/Lexion.
Where to Plant
Field selection is key to growing a successful hemp crop and cannot be overlooked.
Hemp does not tolerate wet feet! Avoid low, heavy, poorly drained fields. When hemp sits in saturated soil conditions stand losses can be very high and require replanting or cause weeds to out compete the hemp crop.
Know what herbicides were applied during the previous growing season and be sure you won’t fall within any rotation restrictions.
Understand the weed pressure your farm faces and place your hemp in fields with lower weed pressure. Following a sod-forming perennial like alfalfa can result in very clean hemp fields despite the lack of labeled herbicides. Planting hemp in a field with high weed pressure, just like planting into water logged soils is a recipe for failure but can be avoided completely.
When to Plant
Depending on your region, hemp seed can be sowed successfully from April to June on a range of row spacings using a traditional grain drill or planter. If soils are unlikely to become saturated, plant early to help combat summer annual weed pressure. Hemp can germinate and emerge at lower soil temperatures than summer annuals and this head start improves its competitiveness. However, if saturated soil conditions are likely, it is better to wait for favorable conditions for rapid emergence and growth. Plant into moisture or have irrigation available to establish a good stand.
How to Plant
With well timed planting and good weed management, most growers plant with a grain drill to maximize yield potential and harvestability. Recommended plant population and agronomic practices vary depending on which product is primary: Stalk, Grain, or CBD.
Customers have successfully planted hemp into full-tillage as well as no-till systems. Plant into a weed-free seedbed as soon after the last tillage or burndown herbicide application as possible. This gives your hemp crop the best competitive advantage against weeds. At this time, no herbicides are labeled for in-crop use. Other than burndown application that contains no residual herbicides, weeds must be controlled with cultivation and/or early establishment of crop canopy.
Row spacing considerations:
- Row spacing of 6″ to 15″ will produce thinner stalks, shorter overall plant height, improve harvestability and yield potential.
- Tighter row spacing requires:
- Excellent pre-plant weed control
- Inputs to maximize stand establishment to outcompete weeds
Note: Cultivation is not an option for tighter row spacing.
- Row spacing >20″ allows in-row cultivation for weed control.
- Generally plant at a depth of 0.75″ or less into a firm (>45° F) seedbed with good moisture.
- Some success has been reported from planting into moisture at 1″ depth or more during dry conditions, but this comes with risk.
- Deep planting followed by heavy rain guarantees a failed stand. Consider soil conditions and weather forecast when setting planter depth.
- Seeds require moisture until an adequate stand is established. It is possible for hemp to sprout and die. This is more likely later in the spring as temperatures warm.
Hemp is very sensitive to soil crusting! If you are planting in soils prone to crusting, take action to mitigate crust before stand losses occur.
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How Much Seed
Planting density should be determined based on the desired number of plants per acre as the number of seeds per pound vary by variety and lot.
Recommended seeding rates also depend on the row spacing of your equipment. Narrow row spacing usually results in higher grain and fiber yields and a shorter crop that is easier to harvest mechanically. Wider row spacing allows for cultivation.
General seed spacing recommendations for grain and dual-purpose crops (assumes 30,000 seeds/lb):
- 7.5″ rows: 1.1″ in-row seed spacing (~25 lbs/ac)
- 15″ rows: 0.9″ in-row seed spacing (~15 lbs/ac)
- 30″ rows: 0.75″ in-row seed spacing (~9 lbs/ac)
Effect of Row Spacing
Figure 1. Grain yield from a replicated small plot field trial averaged across NWG varieties in one location in one year.
Figure 2. Plant heights from a replicated small plot field trial averaged across NWG varieties in one location in one year.
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Planting for Fiber
Hemp stalks have two components: the inner woody core (xylem) called the hurd and the outer layer of fibers (phloem) called the bast. The bast is shown pulled away from the inner hurd in this photo.
Both bast and hurd have commercial applications and the quantity and quality produced can be managed by the grower adjusting planting density and harvest timing.
Planting density for fiber production:
- Hemp growth is plastic and total stalk biomass can be maximized at populations less than 200,000 plants per acre.
- Higher planting populations results in better weed control and thinner stalks with less branching.
- Thinner stalks have a larger surface area to volume ratio, meaning that while total tonnage is similar, a greater proportion of it is bast. There is evidence that very high populations yield less due to heavy competition between hemp plants.
- General planting density recommendations for hemp fiber production – planted with a grain drill:
- 25 lb/acre for bast + hurd production
- 35 lb/acre for bast production for textile fibers
The following graph is from data reported by Amaducci 2008, showing a fiber yield penalty, and increasing bast percentage with increasing density.
The following figures are from Amaduccci et al 2002 showing the effect of increasing plant density various traits, highlighting the plasticity of hemp and the importance of good agronomic management.
Hemp plant height decreases with increased planting density.
Surface area to volume ratio increases with density. More of the fiber produced is bast.
Average stem diameter decreases with density.
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Center pivot irrigation on NWG hemp variety plot trial in Northern Colorado.
While hemp requires less water than some row crops, higher yields are achieved by sufficient precipitation or strategic irrigation. Use irrigation if available to maximize stand establishment.
Planting through emergence
- Sufficient moisture at planting supports stand uniformity and early vigor.
- Well-timed and managed irrigation can soften soil crusting and promote good establishment.
NOTE: Excessive moisture after planting can severely impact crop establishment. Saturated soil conditions must be avoided.
Flowering and grain-fill for grain crops
- Grain crops can tolerate some moisture stress during early vegetative stages and still yield well with sufficient moisture during reproductive stages.
Vegetative stages for fiber crops
- To maximize biomass, it is important for hemp to have enough moisture to fully elongate during vegetative growth
A minimum of 12″ moisture per season is generally required but high yielding grain or dual-purpose crops may use 18-20” of total water. A textile fiber crop cut at flowering will use significantly less. Water requirements are highly dependent on the transpiration demand (e.g. relative humidity) of the production environment.
Plan for weed control to maximize yield potential and quality. Weed pressure will decrease grain and fiber yields and contaminate fiber with foreign material. Field selection, planting timing, and a clean seedbed are the primary ways to achieve a vigorous stand of hemp that can canopy quickly and outcompete weeds.
Row-cultivation recommendations for wide rows:
- Cultivate at least 2x pre-canopy to control weeds.
- First – during early development (as early as possible), cultivate with shields.
- Additional passes – run at higher speed without shields to develop ridges at the base of the plants to cover weed seedlings.
- Hand weeding may be necessary to control areas of heavy weed pressure but is avoided with field selection
- Do not apply any herbicide unless it is labeled for hemp.
Hemp requires less fertilizer inputs than some row crops but should be fertilized similar to a winter wheat crop. It’s best to test your field’s soil fertility before applying fertilizer, as too much fertilizer can result in a crop that is too tall for mechanical harvest. Use caution with seed-placed fertilizer, hemp is sensitive to salt and stand loss can occur.
N: 60-150 lbs/ac of available N– take into account residual soil nitrogen, previous crop etc.
Less N for textile fiber & more for grain crops or dual-purpose crops in high-yield environments – 150 lb for 1500 lb/a yield goal.
P: 50 lbs/ac of available P (apply if less than “high” on soil test)
K: 50-60 lbs/ac (apply if less than “high” on soil test)
Topdress Fertilizer Applied to Hemp Seed Production Field in Wisconsin
For a multi-purpose hemp crop, prioritize harvest for your highest value product first.
Grain | Cannabinoids | Fiber
Most modern combines are well-equipped to harvest a hemp grain crop. Grain hemp is most often direct-harvested when the plant is slightly green to minimize stem fiber wrapping. It is important to cut as high as possible, just below the cola, to minimize the amount of stalk ingested by the combine. Hemp can be threshed anywhere from 10-20+% grain moisture but harvested grain should be dried to less than 10% moisture immediately. Reduce auger speeds, run augers full, and use larger diameter augers when moving hemp grain. Pneumatic or belt conveyors are preferred to augers. Hemp grain is relatively fragile and excessive mechanical damage can lead to rejected loads.
When to harvest
Hemp Seed Harvest NWG 2463
- The crop reaches maturity after 100-120 days.
- 70-80% of the seeds are ripe.
- Drying bracts and seed exposure are a good indicator that the crop is ready to harvest.
- Seed moisture is <20%
- Fall frosts assist in gradual drying, but a killing frost will initiate a rapid dry down. Combine within days of a killing frost.
- Direct-harvest is recommended, and a draper header is preferred over an auger header. Draper headers give more room for the hemp colas to lay down and feed evenly into the combine.
- Swathing or windrows are also an option in geographies which are favorable to field drying (i.e. Colorado).
Equipment for Hemp Grain Harvest: Combine
Most modern single rotor and conventional combines can effectively harvest hemp grain. Combine settings vary by model and harvest conditions but are generally similar to wheat or canola settings. Set the combine to thresh as gently as possible to minimize cracked seed. Adjust combine settings as conditions change but focus on minimizing stalk material entering the combine and thresh colas as gently as possible to remove the seed. This maximizes seed quality and minimizes the amount of green material entering the sieve area. Wetter colas are more difficult to thresh than dryer colas and the wetter chaff is more difficult to effectively separate from seed with fans and sieves to achieve a clean sample.
Twin rotor combines like New Holland and hybrid rotor combines like Class/Lexion are not recommended due to fiber wrapping on smaller diameter rotors.
Hemp seed is difficult to see on the ground compared to other crops. Spending time walking ahead of and behind the combine to understand and quantify sources of grain loss (pre-harvest shattering, header loss, separator loss and cleaning loss) are well worth the time.
General settings for first time hemp harvest:
- Rotor or cylinder 400-600 rpm
- Concave – small grain, medium wire and round bar concaves have been used successfully to harvest hemp.
- Concave clearance should be set as wide as possible while still threshing colas: 25-40 mm.
- Start open and tighten concaves until all seed is removed from colas but the straw left behind the combine is largely intact.
- DO NOT OVERTHRESH!
- Overthreshing results in grain damage, creates more fine material entering the cleaning system, uses more power and can decorticate stems, and increases the likelihood of wrapping.
- Sieves – Set similarly to wheat or canola as a starting point. A goal should be not to send too much material back through the tailings system, potentially doing damage to seed.
- Fan – hemp is less dense than other crops at 44 lbs/bushel, so fan speed generally needs to be adjusted down. 750 rpm is a good starting point and can be adjusted until the sample is clean and loss off the sieves is eliminated.
Combine settings by model
These settings are recommendations and not the rule, changing crop conditions mean it is important to monitor the progress and adjust as necessary.
Case IH 8520
- Sped up rotor discharge chopper knives and engaged to 1 notch to prevent wrapping.
- Disengage straw chopper, ran chaff spreader.
- Concave – medium wire – 28 – Likely could have been open further.
- Fan 800 rpm
- Rotor 550 rpm
- Pre sieve 8
- Top sieve (chaffer) 10
- Bottom sieve 11
- Rotor vanes – fast
- Air bar on 40 ft Gerringhoff draper was valuable to prevent header loss.
- Hemp settings included in book
- Concave – 0.4″ – Likely could have been opened further.
- Fan opening – 3-6
- Top sieve (chaffer) – 0.625″
- Bottom sieve – 0.313″
- Chopper speed – fast
Lexion 760 – not recommended due to rotor wrapping
- Concave – small grain – 24mm
- Fan – 1100 rpm – wetter colas require higher fan speed.
- Cylinder – 640rpm
- Rotors – 650 rpm
- Top sieve (chaffer) 7
- Bottom sieve 4
Disable the straw chopper and windrow the straw. Every combine is different and through inspection within the first acre is recommended to find potential problem areas.
Drying and Cleaning Grain
Wet hemp grain can begin to heat up and spoil in a matter of hours. Do not leave wet hemp in the grain tank or truck overnight. Wet hemp must get put on aeration within several hours – the wetter it is the more urgent the need for aeration becomes. In conditions with low humidity, forced air can be enough to dry hemp grain. In humid climates hemp may require heated air.
- Drying equipment should be appropriate for the size of hemp seed.
- Seed drying for direct harvest should start within 2 hours of harvest.
- If sample contains excessive amounts of leaf and stem matter, screening prior to drying will improve the drying time and help prevent spoilage.
- Seed should be dried to less than 10% moisture
- Air temperature in grain should not exceed 95° F
Ensure product matches processor or contract specifications before shipping. Seed processors may require that steps and other large material be screened out of seed prior to shipping.
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This area of hemp production agronomy has the lowest level of optimization – many different approaches are being explored. This is due to the nascency of the CBD industry, following legalization of hemp production. Many of the agronomic practices for flower production are similar to grain production – refer back to the previous section for topics such as planting date, fertility and weed management.
When to Harvest
CBD concentration tends to increase with the time the crop is in the field. Samples can be taken as harvest approaches to judge the crop’s readiness. Harvest Recommendations for grain are also a guide for flower harvest – when approximately 70% of female bracts are open showing mature seed the crop is ready for harvest.
Equipment for Harvesting Hemp Flower
Many different harvest approaches have been used for cannabinoids from hand harvest to fully mechanized. With mechanized harvest of ABOUND varieties, harvest is similar to collecting chaff and grain at the same time. The primary consideration with flower harvest is to minimize handling and loss of trichomes throughout the process as much as possible.
The following is a brief overview of some mechanized harvest options available currently:
- Direct Harvest – plants stand in the field until maturity. Grain is approximately 15-20% moisture, flower is approximately 70% moisture which helps reduce trichome losses but requires drying. In wet conditions hemp will dry faster standing than in a windrow.
- Windrow & Pickup – plants are cut and windrowed at maturity and left to dry in the field before being picked up and threshed. Flower moisture rapidly decreases and reduces the need for drying but is more prone to trichome loss. This method is only suitable for arid environments and more research is needed on ideal moisture levels for threshing.
- Combine – the preferred method for harvesting multipurpose ABOUND varieties. Cutting and threshing are the same as grain hemp, but the separator is modified to collect the flower as well as grain.
- FarmMax Interceptor: modifies John Deere S-series combines to separate grain, flower, and stalk on the combine and eliminates the need for post-harvest separation.
Farmer modified combines
Modified combines exist in different forms but the general changes are to disable the cleaning fan to allow chaff to be carried to the grain tank or strait to a conveyor with the grain. Some modification of clean grain elevator and grain tank cross-augers may be necessary and post-harvest separation is required.
- Forage Harvester – Forage harvesters are capable of harvesting hemp biomass. They are not recommended for ABOUND varieties unless grain is not an end market product.
- New Holland Coppice header – the Coppice header was originally designed for biomass crops such as willow but has recently been used for harvest of hemp (generally feminized CBD production)
- Rotary heads are commonly used to harvest hemp biomass. An effort should be made to cut as high as possible to minimize the amount of stalk material chopped, diluting cannabinoid content.
- Headers – whether a combine or forage harvester is used, header choice is an important consideration.
- Draper – the crop flow is smooth and the cutting bar can be raised to minimize the amount of stalk material ingested.
- Stripper header – a rotating drum with fingers picks the seed and flower off the cola to be threshed, leaving the stalk behind. The drum is prone to wrapping and sending decorticated fibers through the harvest equipment.
- Hemp Harvest Works SuperCleanCut – similar to an all-crop header but without the auger. The snoots help raise leaning hemp plants that could be unharvestable with a conventional draper.
Flower Harvest for Efficiency
As with harvesting any product, the method must maximize harvest of biomass per unit area harvested while minimizing the loss of trichomes which contain the highest cannabinoid concentrations (See FAQs: What do we know about cannabinoids?). Trichomes are small and fragile so their loss during harvest is a legitimate concern. Finally, the method must incorporate a step for effectively sorting seed from flower. Hemp seeds have no cannabinoids so if they are present in the flower, the cannabinoid content of the seed/flower mixture will decrease. The following are brief descriptions of the methods we have reviewed. NWG does not endorse any of these methods (yet!) We will continue to update this page with our own data as we complete our experiments.
- Head or whole plant harvest: the principle here is similar to straight cutting grain except that rather than threshing the head, it is harvested into a truck for indoor drying and threshing. By threshing indoors, more control can be applied to trichome loss by collection with vacuum system.
a. A video of a head harvesting system: Watch Video
b. A video of a whole-plant harvesting system: Watch Video
- Harvest with a combine: like grain harvest except the combine settings are modified. The specific settings are not well-established but the main changes include lowering fan speeds and removing sieves with the intent to minimize loss of product other than the stalk. In this case the flower or flower/seed bulk is augered into the grain bin and then moved indoors for drying and processing. The crop can be windrowed in dry climates to expedite drying but care must be taken to harvest the crop before it becomes too dry in order to minimize trichome loss.
a. A video of flower harvest with a combine: Watch Video
- Stripper header: a stripper header is not a common implement on US farms but it has some practical benefits for harvesting a hemp field. It operates just as the name would imply, the header strips the flower (and grain if present) leaving the stalk remaining in the field.
a. A video showing a stripper header harvesting wheat: Watch Video
b. A brief video showing what a field might look like after harvest with a stripper header: Watch Video
- Silage bags: This approach is built upon the practice of wet preservation commonly used in fodder production. In short, a forage harvester is used to chop and collect the entirety of the hemp crop. This means that the stalk, stems, the leaves, the flower and any seed that may be present are all harvested. This is expected to lower the cannabinoid percentage considerably since stalks, stems, leaves and seeds are considerably lower in cannabinoid content than the flower. The chopped, wet biomass is then placed into silage bags and the air is removed. What is unclear is the quality of the final product. Watch Video
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Harvest timing and method will differ depending on the end-use. The hemp fiber market is still developing and there are few accepted industry standards for quality. It is important to have clear specifications from the processor to guide your management decisions.
When to Harvest for Fiber
It is important to get clear instructions about harvest timing from your fiber processor. Generally, hemp grown at high populations to produce bast fiber for textiles is harvested at flowering before seed set. Bast fibers undergo physiological changes as flowering progresses that may make them less desirable for fine textiles. Hemp grown to maximize hurd or for dual purpose can be left standing until the crop begins to senesce or when it is ready to be combined.
Retting is the controlled decomposition of hemp stalks in the field to make decortication more effective. The processor will dictate whether retting is required and how they want it to be carried out. Generally, stalks are left laying in the field for a period while microbes work in moist conditions to begin separating the bonds between fibers.
Cutting and Baling
The most proven way to cut hemp stalks is with a sickle mower. Growers have had mixed success with mower-conditioners. Most can cut the plants but wrapping can occur on discharge augers or conditioning rollers if they are present. Hemp can be baled with a variety of round and big square balers. Coordinate with the processor to be sure their equipment can handle the bales you plan to produce.
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