World-renowned cultivation expert Jorge Cervantes lays out the details on drying and curing, including the best ways to maintain the fragrance, flavor and potency of your buds, in this excerpt from his new book, The Cannabis Encyclopedia.
Read It and Reap: An Overview
A bountiful harvest of consistent, disease- and pest-free cannabis is the reward for your financial investment and hours of work and worry in the garden. Strong, healthy, well-grown clones and seedlings yield the heaviest harvests. A well-organized harvest will cut your workload, and a basic knowledge of what’s happening in the cannabis plant will help you to preserve its medicinal qualities during and after harvest.
Cannabinoid levels increase as plants approach peak ripeness. Proper timing is essential to achieving the desired cannabinoid levels. Indoors, the peak harvest window is normally open for about five to seven days, but not all flower buds are ripe at the same time. Some gardeners harvest their crops early—after 45 to 50 days of flowering, and before the buds reach peak maturity. The vast majority of gardeners, however, harvest their gardens at peak maturity. Cannabinoid profiles, especially THC content, are highest at this time.
The bulk of cannabinoids, including THC, are found in resin glands that cover the flowers and leaves; lesser amounts are present on stem surfaces and in the interior cells of the plant. Stems and roots may smell like they have cannabinoids, but they actually contain much lower levels of the desirable ones. Male plants contain much lower quantities and levels of cannabinoids than do female plants, and so they are normally harvested before they can pollinate the females.
Unpollinated female plants (sinsemilla, or “without seeds”) have the greatest amount of resin glands and cannabinoids, and are harvested when resin glands show peak ripeness. After harvest, leaves and flower buds are separated, manicured, dried and cured.
Growth stops at harvest, and thereafter the THC content cannot increase. Some plant processes will continue until the plants run out of energy stores. Overall cannabinoid levels are fixed, but change with harvest from inactive cannabinoids to active ones or back again.
Drying removes about 75% of the water weight found in foliage. Drying concentrates the cannabinoids in relation to the plants’ overall weight. The actual cannabinoid content of the resin glands will remain the same or decrease after harvest. Proper handling is key to retaining cannabinoid potency. Prolonged periods of light, temperatures above 80°F (26.7°C), friction from excessive handling, and damp, humid conditions should all be avoided, because they degrade resin glands and cannabinoids.
Washing the branches of harvested flower buds in a mild solution of H2O2 (hydrogen peroxide) has become a popular technique. We wash vegetables before consuming them, and cannabis is no different. A gentle bath of H2O2 removes surface bacteria, mold, dirt, dead pests and their feces, and other bad stuff. Such a bath also creates free radicals.
An H2O2 free-radical drench changes anything composed of carbon, just like using ozone in a garden space or curing room. Washing treated buds with plenty of fresh water is essential. No studies have been done to determine the potential for damage to the carbon chains in cannabis after an H2O2 bath.
Avoid excessive damage to resin glands by manicuring fresh flower buds immediately after harvest. Manicure the harvested plants when the foliage is still supple, by hand or using a trimming machine, to remove the outer, less-potent foliage from flower buds. Once manicured, flower buds are dried slowly to equalize their moisture content, preserve cannabinoids and remove chlorophyll.
After drying, flower buds must be cured to achieve full aroma and flavor. Too often, beautiful buds are dried too quickly or in an area with too much heat and thus are not cured properly. Handling cannabis too roughly may rupture the resin glands and degrade resin and terpenes. Flower buds maltreated in this way lose their bouquet. As the resin glands degrade, their cannabinoid content decreases. Also, poorly and quickly dried cannabis still contains various amounts of chlorophyll, starches, nitrates, etc.
Once the cannabis is cured, proper storage will ensure that it retains all of its essential qualities.
Do not water your plants for one or two days before harvest. The soil should be fairly dry, but not so dry that the plants wilt. This will decrease the drying time by a day or more and will not affect the quality of the cannabinoids and terpenes.
The fragrance of flowering cannabis is often pungent before, during and after harvest. If the air in and around the drying and manicuring rooms is stagnant, odors will linger and accumulate. To help control fragrance, keep the drying and manicuring rooms well ventilated. If possible, allow plenty of fresh circulating air to pass through the drying room to remove fragrances quickly, and keep temperatures below 70°F (21.1°C) to minimize aroma.
The leaf stem (petiole) has few resin glands that contain cannabinoids. This image shows many cystolith glands.
Loss of Fragrance
“Terpenes, or terpenoids, are the compounds in cannabis that give the plant its unique fragrance. THC and the other cannabinoids have no odor, so marijuana’s compelling fragrance depends on which terpenes predominate. It’s the combination of terpenoids and THC that endows each strain with a specific psychoactive flavor.” —Martin A. Lee, “Talking Terpenes,” High Times
The aroma, taste and, ultimately, effects of smoked cannabis depend upon the mix of terpenes and cannabinoids in the plant. Often, cannabinoids and terpenes volatize and are destroyed during flowering, harvest and storage as a result of high temperatures and maltreatment. The absence of these compounds diminishes bouquet and taste. It can also change the overall effect of the cannabis when consumed.
Cannabis plants lose their fragrance for a combination of reasons, all of which involve the destruction of terpenes or the creation of a poor environment for terpene development. During flowering, plants that are subjected to heavy weather—including wind, rain, and hot sunlight or artificial light—are often less fragrant. Outdoor plants also accumulate surface dust, bacteria and other bad stuff. When allowed to remain on the plant, these pollutants can smell and may possibly speed cannabinoid and terpene degradation. Ironically, however, poorly ventilated indoor environments are often more polluted than the great outdoors. Such pollutants can also play a role in diminishing fragrance.
Terpenes and cannabinoids evaporate into the air under a wide range of temperatures. As temperatures climb, more and more terpenes evaporate into the air. Terpenes can be destroyed by high temps, humid weather, wind, rain, and rough or excessive handling. Also, terpenoids may not have a chance to develop properly in plants that grow under the stressful conditions caused by climate, poor care, or attacks by pests and diseases.
As stated earlier, cannabis can lose its fragrance when it dries too hot and too fast. Fast drying doesn’t allow enough time for chlorophyll and other pollutants to dissipate, and these may remain in the foliage. The lingering traces of these undesirable elements can impart detectable odors and tastes when the cannabis is consumed.
When poorly dried or allowed to stay too wet (as if in a compost pile), cannabis starts the process of anaerobic decomposition. This process causes the cannabis to smell like wet hay and, in extreme cases, to have an ammonia-like odor.
Plants can also harbor powdery mildew or other diseases within their tissue. Powdery mildew is impossible to detect without laboratory analysis. Such diseases weaken the plants and can also play a part in the deterioration of fragrance.
Genetically, some plants appear to be predisposed to have less aroma and to lose fragrance over time. In combination with climatic conditions, genetics could play a role in minimizing cannabis fragrance.
The use of negative-ion or ozone generators has little impact on the fragrance of growing cannabis. Ozone generators, used to control odors, introduce ozone (O3) into an enclosed area. The O3 converts to O2 (oxygen) within a few minutes. A free radical of O floating next to O2 becomes stable when they combine to form O2. However this O molecule can attach to any carbon it finds and strip it away. Much of the O3 is converted to O2 in the air, but the laws of equilibrium and diffusion also apply. If used, ozone generators should be located outside of any occupied drying or manicuring rooms.
The fragrance of cannabis can also be controlled through the use of carbon filters, and by sealing the drying and manicuring rooms. Set up a fan and carbon filter in the room to remove fragrances before venting the air out.
Hanging plants upside down to dry is simple, convenient and effective.
Feeding and Flushing
Avoid the taste of chemical and organic fertilizers in harvested buds by leaching the growing medium with plain water or a clearing solution to remove any residues that have built up in the soil or plant foliage. Five to six days before harvest, leach the medium with clean tap water or reverse-osmosis (RO) water. Use a clearing solution such as Final Flush to remove any built-up nutrients in the soil.
Leaching heavily will wash out any fertilizer salts that have accumulated in the soil, allowing plants to use up the balance of the nutrients in their system before harvest.
Some indoor gardeners fertilize with a liquid salt-based fertilizer until two or three days before harvest, and then use a clearing solution to remove fertilizer residues. They say this practice helps the plants retain weight in their flower buds. But it doesn’t make the buds grow any faster, and fertilizer residues are still present in plant tissue. The tradeoff here is that the fertilizer adds weight at the expense of medicinal quality.
Apply the leaching solution according to the directions on the packaging. Always let at least 10 percent of the solution (preferably more) drain out the bottom of containers. If you’re using a recirculating hydroponic system, change the water after the first four to six days of application. Continue to top off the reservoir with clean, fresh water.
Always irrigate in the morning so that the majority of water is used during the day.
How to tell when fertilizers are affecting taste:
1. Leaf tips and margins are burned.
2. Leaves are brittle at harvest.
3. Flower buds smell like chemicals.
4. Buds crackle when burning.
5. Buds taste like fertilizer.
Inspect your plants at night with a green or UVB light. Powdery mildew and insect feces and trails will be visible; they actually leap out at you, almost as if you were reading the eye chart in an optometrist’s office. Carefully remove all signs of powdery mildew before it can enter the plant tissue. Spray fungus with an organic fungistat before removing affected plant parts to ensure that the disease does not contaminate the rest of the crop. This method works only when there is very little mildew.
A green light or UVB lamp makes pest trails and diseases very easy to see.
Once the large leaves on a plant are fully formed, cannabinoid potency has generally peaked. Potency increases from the bottom of the plant upward. Old, large bottom leaves are not as cannabinoid-potent as younger, smaller leaves toward the top of the plant. The most cannabinoid-potent part of the plant during much of the growth stage is found at the tips of branches, in the small leaves and well-formed shoots.
When harvesting, cut the entire leaf, including the stem (petiole), and toss it into a bag; if left on the plant, the petiole shrivels and may attract fungus. Paper bags are best for this purpose, since they breathe well and can be closed by folding over the top. Plastic bags do not breathe and often “sweat” inside, so the top of the bag must be left open.
Keep the paper bag in a closet or area with 40% to 60% humidity and a temperature of 60°F to 70°F (15.6°C to 21.1°C). Reach into the bag once or twice a day and stir the leaves by hand. Leaves should be dry to the touch in five to seven days. Once dry, place small, resinous leaves in the freezer so that the resin glands will readily separate from foliage. Large leaves carry fewer cannabinoids and are most useful in making tinctures, food preparations and drinks.