• Professor Sprout

Cannabis Grow Guide PART 2: What Causes Weed to Have Black Ash?

Updated: Apr 24


Read Part 1 


Professor Sprout’s Great Black Ash Experiment


My research into cigar production and tobacco farming seemed to point to the mineral content of the soil and the ratio of micro and macro nutrients therein as the main factors dictating ash quality. An additional consideration often mentioned was the quality of the roll on the cigar (in our cases, usually a much smaller joint) but more on that later.


So the goal of my Great Black Ash Experiment was to grow multiple identical clones under the exact same environmental conditions, but with completely different soil mixes and nutrient regimens. By controlling the environment and using exact genetic replicas I hoped to be able test which specific soil mixes created the whitest ash, and which ones left black ash. Once I had obtained this data I figured it should be pretty straight forward to deduce which elements were the causative factors in poor quality ash.


So to get on to the actual experiment; for every different soil and/or nutrient program I grew a pair clones to make sure I would have two examples to choose from and to ensure there were no major outliers in the group.


For example, if I grew the exact same clone in two equal sized containers of the exact same soil mix, and one plant grew tall and healthy, and the other short and sickly, it would signal to me that something was off (perhaps a root fungus or something), and this pair would be eliminated from the experiment to avoid skewing the data. Thankfully, all the pairs looked very uniform throughout the experiment, and no plants had to be disqualified.


Ultimately I decided on taking 24 clones of one of my favourite strains: Lucky OG Kush. Since I am very familiar with this strain and have grown it many times, I thought this would be a good starting point rather than using a strain I was somewhat less familiar with.


36 clones were rooted, with 24 of the healthiest and most uniform clones being selected to take part in the experiment. They were then transplanted into their final 3 gallon nursery pots of different soil blends and soilless mixes. The plants were then vegged for two weeks before flipping them over to the flowering phase.


The Three Testing Groups


The Great Black Ash Experiment is broken down into three groups - Synthetic Liquid Nutrients, Organic Liquid Nutrients, and Organic Soil Mixes.


Group #1 - Synthetic Nutrients (Advanced Nutrients)


This was a group of 6 plants (3 pairs) that were planted in Promix BX peat-based soilless mix and fed three different nutrient regimens. All plants in this group were fed on a fee-feed-water schedule. The first pair of plants received only the basic nutrients fed at 1000ppm (this was a comfortable nutrient strength for this particular strain as had been previously determined) The second was fed at the same overall concentration of 1000ppm, but during weeks 2,3,4 they were given a PK booster. The final group was also fed at 1000ppm, but with the addition of a ripening PK booster supplied during weeks 5 and 6. The goal of keeping the overall concentration of the fertilizer solution the same while adding different supplements to the mix was done in order to determine if using bloom boosters will cause black ash.


Plant Summary for Group #1

Plant A1 and A2 Synthetic: Advanced Nutrients Sensi Bloom Part A and B at 1000ppm with no additives.


Plant B1 and B2 Synthetic: Advanced Nutrients Sensi Bloom Part A and B at 1000ppm with PK booster (Big Bud) during weeks 2,3,4


Plant C1 and C2 Synthetic: Advanced Nutrients Sensi Bloom Part A and B at 1000ppm with PK booster (Big Bud) during weeks 2,3,4 and ripening PK booster (Overdrive) during weeks 5 and 6.


Group #2 - Soilless Mix with Organic Bottled Nutrients (General Organics)


This group was a pair of plants grown in Promix BX and fed with organic bottled nutrients from the General Organics Bio Thrive line at the full label dose on a Feed-Feed-Water Schedule


Plant Summary for Group #2

Plant G.O.-A1 and G.0.-A2: General Organics Bio Thrive Grow (4-3-3), Bio Thrive Bloom (2-4-4), General Organics CaMg+ (1-0-0) all fed at full label dose


Group #3 - Custom Organic Soil Mixes


These next 16 plants (8 pairs) were planted into a series of soil mixes based on pre-mixed dry organic “All-Purpose 4-4-4” and “Power Bloom 2-8-4” products from Gaia Green, high quality bagged growing soil from Sea Soil (“Sea Soil Essentials Soil” 1.7-.45-.21), and a popular “Subcool’s Supersoil" recipe found online. Additionally, I added a custom “Professor Sprout Mix” that I developed from scratch based on my soil and nutrient ratio research.


Each one of these soil mixes (and the soilless mixes for the bottled nutrient regimens) were blended, mixed well, and lightly dampened with compost tea. Each mix was then cooked (composted) for 60 days in warm summer weather prior to the commencement of the experiment.


Plant Summary for Group #3


Soil A1 and A2: Bagged Soil (Sea Soil) Only


Soil B1 and B2: Bagged Soil (Sea Soil) plus dry mixed Gaia Green Power Bloom and Gaia Green All Purpose at 1/2 label dose.


Soil C1 and C2: Soilless Mix (Promix BX) Amended with dry mixed Gaia Green Power Bloom and Gaia Green All-Purpose a full label dose.


Soil D1 and D2: Soilless Mix (Promix BX) Amended with dry mixed Gaia Green Power Bloom and Gaia Green All Purpose at half label dose.


Soil E1 and E2: Professor Sprout’s Mix custom organic soil blend at full strength.


Soil F1 and F2: Professor Sprout’s Mix custom organic soil blend at half strength.


Soil G1 and G2: Supersoil organic soil blend mixed per instructions found online.


Soil H1 and H2: Supersoil organic soil blend mixed per instructions + extra potassium.


Next week: How I was shocked to find that a completely non-flushed, non-cured, non-dried, over-fertilized organic cannabis bud could still burn to a clean white ash!


-Professor Sprout


Read Part 3

DISCLAIMER: WE ARE NOT DOCTORS. THE OPINIONS AND INFORMATION PROVIDED ON THIS SITE ARE NOT MEDICAL ADVICE. THE CONTENT OF THIS WEBSITE IS INTENDED FOR LEGAL MEDICAL MARIJUANA PATIENTS, CAREGIVERS, AND LICENSED GROWERS ONLY. SEEDS ARE FOR PATIENTS 18 YEARS PLUS. KNOW AND FOLLOW YOUR LOCAL LAWS.