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Sensi Sermons: Reading Resin Heads and Flushing

Sensi Sermons: Reading Resin Heads and Flushing

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KNOWN SIMPLY AS “THE REV” TO HIS PATIENTS, fellow growers, and students of the art, this veteran of cannabis culture brings more than 34 years of experience in breeding and growing, both hydroponically and organically, to the table. Having produced some of the West Coast’s most carefully balanced medical strains, The Rev preaches that growing pot is easy but growing great pot-truly exemplary herb-isn’t. He’s passionate about sharing more than 30 years experience with others so they, too, can grow to the potential of their genetics.

In his debut contribution to SKUNK, The Rev shares some of his knowledge regarding harvest readiness and flushing, including the classic old school emergency flush.


SO BROTHERS AND SISTERS, you think it’s time to harvest the fruit of your labors, eh? Welcome to one of the most misunderstood areas of growing. Harvesting plays the role of the redheaded stepchild of the cannabis growing process. Many otherwise capable growers often fall short when it comes to finishing their crop. A great grow with a lousy harvest is akin to running a marathon at top speed and then walking the last two miles. A top-notch crop that ends in mediocrity when it could have produced superb herb if only it had been properly flushed and harvested at peak potency always saddens me.



First, to get top shelf herb, you must flush. Anyone who tells you that flushing is simply a way to improve already good herb is sadly misdirected. Flushing is really just a nutrient purge—nutrients that can be smelled and tasted if they aren’t expelled from the plant. Technically, flushing is leaching nutrients from the plant, including trace and secondary nutes, such as sulfur and the “heavy metals”: zinc, iron, and copper. These and potassium are notorious for creating harsh smoke if present in significant enough quantities at harvest.

If you’re container growing in either soil mix or soil-less mix your flush should involve hydrating with straight water until visible drainage occurs from the bottom of your containers. Be sure to do this each time you water, ensuring that any excess nutrients are truly leached out and carried away via the run-off. The flushing process will be visibly reflected by the appearance of leaves that fade to yellow, beginning at the bottom of the plant and migrating upward as the flush proceeds.

For about 7-14 days, feed your plants straight water or a very mild nute solution. Intelligently deciding between the two options and determining exactly how long to flush requires a bit of skill and experience. As you begin the flush, if you’re using plain water, the lower leaves may slowly fade out. This is fine; however, if they begin to fade and die at a more rapid pace, you’ll need to slow their cannibalization rate by utilizing a mild nute solution. Switch to straight water for the final 5 to 7 days of the flush.

It’s best to flush with distilled water or rainwater. The pH levels of your flush water aren’t nearly as important as during the grow; simply ensure that they fall between 6.0 and 8.0. If you need to alter your pH, avoid off-the-shelf products. To lower pH, I recommend distilled white vinegar or apple cider vinegar. To raise pH, try tap water or bottled spring water. (These methods also work well for pH adjustments during the vegetation and flower stages.)

It’s important to realize that there are no exact durations or numbers for flushing. Many factors influence the nature of the “perfect” flush. For example, how often were accumulated salts flushed out during the grow? What type and quality were the nutrients your plants were fed? At what ratios?

Personally, I flush my plants for a maximum of 7 days. This is because I flush well during the grow and use high-quality nutrients that leave fewer salts behind than the cheaper varieties. Also, I’m not a nuker (overdosing plants with fertilizers—this is far more common than growers think), so I don’t have massive accumulations of nutes and nute salts in the soil mix by the time it comes to flushing.

Some characteristics of flushing are strain-specific. For example, if you’re flushing a nutrient hog (such as Northern Lights) for a full 14-day cycle, you should begin with a very mild nutrient solution (about 1/8 of manufacturer’s recommended strength). Otherwise, the strain can lose 50 percent or more of its leaves in a matter of days, indicating that it’s dying too fast (and resulting in strange tastes and reduced potency); however, something like a 100 percent sativa South African (such as a Malawi Gold) can store a ton of nutrients. She’s capable of heavy feeding but will put herself on “rations” during a flush. With a strain like that, you can easily use straight water for the entire 14-day cycle.



There is, however, an important exception to the need to flush—organic growing. In 100 percent organics, true living
soil, you simply don’t need to flush. As soon as your plants are ready to go, you can harvest them right then, on the spot. They can be green as hell and it doesn’t matter (as long as they aren’t burning freshly added “hot” nutrients, such as guano or blood meal, which should never be applied within 30 days of harvesting).

Note that true living organics is different from regular organics in that the plant roots, in a true living soil mix, have adapted to work in total symbiosis with the micro-beasties (both fungal and bacterial), absorbing all nutrients via this partnership. Under this dynamic, plants are never fed raw nutrients (organic or otherwise). They simply receive water and some organic teas. In regular organic growing, you’re feeding the plant. In living organics, you’re feeding the soil mix (or, more specifically, the micro-life within).

In the 1970s, the cannabis produced in Northern California really made a huge impression on the market. The growers during that period were some of the first truly bulk organic producers and would harvest their plants totally green. These guys created KGB (Killer Green Bud) and lime green Skunk (a.k.a. “Red Russian” because it was grown along the Russian River in Humboldt, California). Of course, harvesting green means that it’s even more important to properly dry and cure in order to remove the chlorophyll, which can give your smoke the alluring flavor and smell of a freshly mowed lawn: very “green,” vegetable like, and highly undesirable, especially for cash croppers and connoisseurs.



Typically, examining the color of pistils is how a grower judges the readiness of a plant for harvest (when a certain percentage have changed from white to orange, it’s time to chop); however, I prefer to determine peak maturity using a 20-power jewelers loupe to examine the heads of the trichomes (resin heads). You can’t use 10-power; it just doesn’t work. You need a loupe that’s between 20- and 30-power (a bit harder to find, but it’s a great investment for any grower).

You should start examining your trichomes when about 50 percent of the pistils have turned orange. You’re looking for the normally clear resin heads to turn amber. When that occurs, you’re witnessing the degrading of the resin within the heads. It’s no longer at peak. In fact, you’re actually a bit on the down side when the heads begin turning amber. But, don’t worry; you won’t be able to notice the difference (if you smoked one harvested right before the trichomes turned amber and another right after, you probably couldn’t tell them apart).



When about 10 percent of the trichomes on the entire plant are amber, it’s time to harvest. This, in my opinion, is peak potency. You can look at any section of the plant and get a roughly accurate ratio, but it will vary a bit, depending on strain. Plants are usually confined to two maturation patterns: from the bottom up or from the top down. Some strains, like Durban Poison and South African varieties, mature from the bottom up. Other strains, like White Russian and Matanuska Thunderfuck, mature from the top down. There are more exotic patterns that occur, but they’re pretty rare. (Vietnamese Black actually matures from the inside out.) But most growers don’t deal with those types of strains.

To determine the state of the trichomes, simply examine the main cola and a few buds from the bottom of the plant. If about 1 in 10 resin heads is amber, you should immediately begin your flush. Note, however, that it means you still have an additional 7 to 14 days of flush during which the resin will continue to degrade. Again, the degradation rate is nominal. But after about two weeks you can start to perceive the difference in the end product. The smoke gets heavier, thicker, and more narcotic (“sleepy time” weed).

See Also
cannabis world news organic growing vibrant green cannabis plant


A huge misunderstanding among many growers regards the difference between milky and amber trichomes. Sometimes resin heads change from clear/transparent to white/opaque (“milky”). A slowing of the resin production causes this. Think of resin production as lava. As long as it’s in production and being pumped out, resin is clear, transparent, and fluid. After resin production begins to slow, however, like lava cooling, it starts to form a “crust.”

Many cannabis plants do this at some point during flowering. It can be brought on by them being nuked, human error, or simply a genetic trait. In plants exhibiting this trait, resin production will slow for a time and then pick back up.

A milky state of the trichomes, however, is in no way an indication that it’s time to harvest. Many growers note the milky resin heads, misinterpret them as mature amber heads, and prematurely hack their plants. Say it with me: Trichomes that are milky indicate nothing more than a pause in resin production. They are in no way an indication of the maturity of the resin.


Personally, I don’t think herb is even worth smoking unless the pistils are about 50 percent withered and orange. At less than 50 percent, you’re losing so much of the good stuff.

If fewer than 50 percent of the pistils are orange, the herb will produce more of an “up” high, but it lasts only about a third of the time. Also, the potency is down by as much as 50 percent. I have to admit, though, that the high does hit the smoker very fast—a potential “gee whiz” characteristic that may help it sell—but the resin is simply immature at that point. The herb will retain the “up” it has if you don’t allow the resin heads to get more than about 20 percent amber globally (over the entire plant).

It should be noted, however, that some people prefer a very narcotic, med-type of high (especially those with particular ailments). They’re patients who want to get the shit knocked out of them. These folks (or their compassion growers) should purposefully allow their plants to go past maturity. If they wait until about 80 percent of the resin heads turn amber before they harvest, they’ll produce a severely narcotic version of the plant.



If you get creative, you can basically produce two different types of cannabis from a single plant by carefully monitoring the resin heads and harvesting the plant in sections. Assume you’re growing a Durban Poison, which matures from the bottom up. When the bottom branches become mature, you could purposefully not harvest them. When the upper colas became prime, you would harvest them, letting the bottom one-third or so of the buds go until they were about 80 percent amber. The difference between the prime mature herb on the upper branches and the lower branches, where the resin has been allowed to go past maturity, is going to be night and day!

Durban Poison is a classic sativa with a very “up” high. It doesn’t give you the munchies, wakes you right the hell up, and gives you millions of ideas of things to do in the universe. It’s that kind of a high. But if you let its resin heads get amber, past 50 percent or so, it becomes extremely narcotic. We’re talking opium narcotic. Ever have someone give you a sativa and you swore it was an indica? It could very well be that it was harvested late and the trichomes suffered more resin degradation than is considered optimum.

This article appears in Volume 2 – Issue 6 of SKUNK Magazine.

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