Marijuana – Northern Lights

I will be growing a Cannabis indica strain called ‘Northern Lights’.  The type I will be using has been hybridized with an autoflowering strain, meaning that the plant will flower on its own schedule, independent of photoperiod length.  It is also feminized, meaning that the plant will be female and will therefore produce the desired flower buds.  These seeds are expensive, so in order to maximize the size of the harvest from each seed, the growing conditions will be a bit more complicated than my usual simple Kratky buckets.  I will be using a growing method commonly referred to as Deep Water Culture (DWC), using a separate reservoir bucket.  Here is the setup:

  • Connect two 5 gallon buckets together using PVC tubing and fittings as described here: Two Bucket System.
  • Use a water pump (PonicsPump PP09205, 92 gallons/hour) to circulate the fluid between the two buckets.
  • Use an air pump (Whisper Model 10, 0.5 L/min) and an air stone to elevate the oxygen levels in the fluid.
  • The main source of lighting will be a 200-Watt LED grow light.
  • Use frozen jugs of ice to lower the temperature of the fluid to the desired level (64-68 °F, 18-20 °C).  Frozen jugs will need to be replaced every 24 hours.
  • Wrap the buckets in towels to provide some temperature insulation, and put the whole assembly inside of a 27-gallon storage tote, to contain the fluid in case of leaks.
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The Two-Bucket System, showing a water pump (purple) for fluid circulation and an air pump (yellow) for aeration.  Fluid changes and other system maintenance is performed in the reservoir bucket (left), while the plant can grow undisturbed in the other bucket (right).

Nov 27 = Day 0.  Plant started from seed (Blimburn Seeds, sourced from SeedSupreme).  Seed sowed in 1.5-inch rockwool cube in 2-inch net-pot.  Moistened with Seedling Blend, a dilute blend of fertilizers.  N-P-K (in ppm): 22-29-16.

Nov 29 = Day 2.  The seed has germinated.  I can see the taproot emerging from the seed, but the leaves have not yet emerged.  Nonetheless, I have placed the plant directly under a fluorescent light (spiral bulb, 23W, 6500k) for 18 hours per day.  The bulb is positioned 3-4 inches above the plant.  The bulb generates a lot of heat, so I placed a small fan about 3-4 feet away from the plant to blow air on it during the day.  I also placed the plant on top of a heating pad (set on ‘low’), which cycles on/off every 30 minutes during the night to keep the plant warm.

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Dec 1 = Day 4
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Dec 2 = Day 5

Dec 7 = Day 10.  Plant is about 1-inch tall, and the main root is about 4-inches long with many branches.  To ensure that the root system has enough room, the plant was moved into a slightly larger 3-cup container containing the same nutrient solution as above.

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Dec 7 = Day 10

Dec 10 = Day 13.  To acclimate the plant to a higher concentration of nutrients, the solution was changed to the following half-strength solution (per gallon of tap water): 1 g Masterblend 4-18-38, 1 g calcium nitrate, 0.5 g magnesium sulfate, 0.1 mL Dyna-Gro Pro-TeKt, 1.3 mL pH Down.  pH = 6.0.  N-P-K (in ppm): 51-47-101.

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Dec 13 = Day 16.  The first set of real leaves is turning yellowish, but the rest of the plant is green.

Dec 13 = Day 16.  Plant transferred to the Two Bucket System.  The system contains a total of 9 gallons of fluid, which results in having the fluid level just at the bottom of the net-pot in the plant bucket.  For nutrients, the Regular-Strength Blend was prepared.  N-P-K (in ppm): 103-95-202.

For lighting, a 200-Watt LED grow light was positioned 18-inches above the plant, running 18 hours per day.  A fan also blows on the plant during the hours that the light is on.

Going forward, daily maintenance of the system is conducted as follows:

pH
If the pH is below 5.0 or above 6.5, the pH is brought back into the range of 5.5-6.0 by the addition of either pH Up or pH Down.

Temperature
If the temperature of the fluid rises above 68 °F (20 °C), then a sealed jug of ice is added to the reservoir bucket.  The ice cools the system down to its lowest point in 2-3 hours, and then the temperature slowly returns to the starting point after 18-24 hours.  I add enough ice to bring the temperature minimum down to about 60-65 °F.  To determine how much ice to add, I use the following guide:

Reservoir Volume Ice Volume Cooling Achieved
9 gallons 1/2 gallon 7 °F
9 gallons 1/4 gallon 3.5 °F
6 gallons 1/2 gallon 10 °F
6 gallons 1/4 gallon 5 °F

A spreadsheet containing all of the daily measurements of temperature and pH can be found here: Temperature and pH Measurements.

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Dec 19 = Day 22.  Plant is 2 inches tall.

Dec 19 = Day 22.  LED grow light was lowered to 12 inches above the plant.  Going forward, the light will be raised as needed to maintain of height of 8-12 inches above the plant.  Here is what the entire growing system looks like:

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Dec 19 = Day 22
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Dec 28 = Day 31.  Plant is 4 inches tall, 12 inches across.
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Jan 7 = Day 41.  Plant is 8 inches tall, 20 inches across.
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Jan 19 = Day 53.  Plant is 12 inches tall.

Jan 27 = Day 61.  The fluid in the buckets was entirely replaced.  All remaining fluid (6 gallons) was removed from the system.  7 gallons of new fluid (Regular-Strength Blend) was added.

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Feb 3 = Day 68.  Plant is 16 inches tall.

Feb 15 = Day 80.  The fluid in the buckets was entirely replaced.  All remaining fluid (5 gallons) was removed from the system.  6 gallons of new fluid (Extra-Strength Blend) was added.  This new fluid has a slightly higher nutrient concentration than the old fluid.  N-P-K (in ppm): 124-114-243.

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Feb 19 = Day 84.  Plant is 22 inches tall.

Feb 25 = Day 90.  Added 1 gallon of new fluid (Extra-Strength Blend).

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Mar 6 = Day 99.  Plant is 28 inches tall.
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Mar 6 = Day 99.  Plant is starting to flower.  This plant is female, as evidenced by the white strings (pistils).

Mar 6 = Day 99.  The fluid in the buckets was entirely replaced.  All remaining fluid (4 gallons) was removed from the system.  6 gallons of new fluid (Bloom Blend) was added.  N-P-K (in ppm): 74-114-243.  The Bloom Blend has a lower N content than previous blends, to discourage vegetative growth and encourage flowering.

Mar 20 = Day 113.  The fluid in the buckets was entirely replaced.  All remaining fluid (3.5 gallons) was removed from the system.  6 gallons of new fluid (Bloom Blend) was added.  N-P-K (in ppm): 74-114-243.

Mar 31 = Day 124.  The fluid in the buckets was entirely replaced.  All remaining fluid (4 gallons) was removed from the system.  6 gallons of new fluid (Bloom Blend) was added.  N-P-K (in ppm): 74-114-243.

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Mar 31 = Day 124.  Plant is 36 inches tall.

Apr 10 = Day 134.  The fluid in the buckets was entirely replaced.  All remaining fluid (4 gallons) was removed from the system.  6 gallons of new fluid (Bloom Blend) was added.  N-P-K (in ppm): 74-114-243.

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Apr 14 = Day 138.  Lots of buds still developing.

Apr 24 = Day 148.  The fluid in the buckets was entirely replaced.  All remaining fluid (3 gallons) was removed from the system.  5 gallons of new fluid (Bloom Blend) was added.  N-P-K (in ppm): 74-114-243.

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Apr 26 = Day 150.  Plant is stabilized by addition of support straps.

May 5 = Day 159.  The plant has reached its maximum height (3 feet 5 inches) and is not growing any taller.  Also, the leaf tips all over the plant are starting to burn, which indicates that the nutrient concentration is too high.  The fluid in the buckets was entirely replaced.  All remaining fluid (2.75 gallons) was removed from the system.  5 gallons of new fluid (2/3-strength Bloom Blend) was added.  N-P-K (in ppm): 49-76-162.

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May 5 = Day 159.  Leaf tips are burning, which indicates that nutrient concentration is too high.
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May 5 = Day 159.  Plant has reached maximum height of 3 feet 5 inches.

May 15 = Day 169.  The fluid in the buckets was entirely replaced.  All remaining fluid (2.75 gallons) was removed from the system.  5 gallons of new fluid (2/3-strength Bloom Blend) was added.  N-P-K (in ppm): 49-76-162.

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May 23 = Day 177.  The buds are covered with trichomes, which is where the cannabinoids are found.  Most of the pistils have turned brown.  The plant will likely be harvested soon.

May 25 = Day 179.  The fluid in the buckets was entirely replaced.  All remaining fluid (2.5 gallons) was removed from the system.  5 gallons of new fluid (5/6-strength Bloom Blend) was added.  N-P-K (in ppm): 62-95-203.

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Jun 5 = Day 190
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Jun 5 = Day 190.  The terminal bud (cola).

Jun 5 = Day 190.  Many of the fan leaves are yellowing, especially near the terminal bud.  Upon inspection of the trichomes with a 30x magnifying glass, there are a few trichomes that are turning amber, but most appear to be clear or cloudy.  Almost all of the pistils on the plant have turned brown.  I think the time has come to harvest this plant, since I do not want the cannabinoid quality to deteriorate.  It has now been 13 weeks since this plant started to flower.

For the final step of the growing process, I will be performing a “flush”, which involves removing all nutrient fluid from the system and replacing with plain water (adjusted to pH 6).  This can help to clear out any accumulated nutrients, resulting in a cleaner burning, better tasting final product.  For the DWC system I am running, the flush only needs to occur for 1-2 days.

All remaining nutrient fluid (3 gallons) was removed from the system.  5 gallons of plain water (pH = 6.0) was then added.

Jun 7 = Day 192.  After 2 days of flushing, the plant was harvested.  All fan leaves were removed.  The remaining stems (covered with trichome-laden buds and sugar leaves) were hung upside to dry.  A small fan was used to keep the air moving around the drying pieces, but was not pointed directly at them.

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Jun 7 = Day 192

After 5-6 days, the buds and leaves were mostly dry, so they were carefully trimmed off the stems and placed into a glass dish.  The dried buds were allowed to sit in the open for another day, and were then transferred into glass quart jars.  For a few weeks, the jars will be opened daily to allow air exchange.

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The final product.

Overall, the marijuana plant consumed and transpired 26.5 gallons of nutrient fluid.  In the future, it might be more convenient to grow the plant in a much larger vessel (such as a 32-gallon trash container) rather than the smaller Two Bucket System that I used here.

Ideally, the temperature of the fluid would have been kept within the range of 65-68 °F for the entire growing period.  I did my best to control the fluid temperature by adding jugs of frozen ice everyday.  During the winter months, it was easy to keep the temperature in the desired range, but as the spring came, the grow room got warmer, and the temperature cycled out of the desired range on a daily basis:

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