Growers appreciate our articles documenting the best marijuana seeds and grow gear, but wonder how we are so sure of our “opinions.” Today we explain how you too can be sure about what’s excellent and inferior in your marijuana growing by doing “controlled experiments.”

If you want to be a serious, successful, professional grower getting the most from every marijuana plant you grow, you must master controlled experiments. Here’s how…

A controlled experiment starts with a hypothesis or other question(s) to test. These queries may include:

  • Competition between two nutrients brands.
  • Germination rate of cannabis seeds.
  • Measuring performance and outcomes for grow lights, pH meters, light meters, and other growing marijuana gear, including brand comparisons.
  • Evaluating the effects of supplemental additives such as root boosters, silicon, seaweed, etc.
  • Gauging effects of different grow room temperatures, vapor pressure deficit, air exchange, C02 enrichment, and other grow room environmental traits.
  • Evaluating the effectiveness of potions and techniques for preventing gray mold, powdery mildew, spider mites, root aphids and other growing marijuana problems.
  • Evaluating results of cultivation techniques such as topping, leaf-stripping, etc.

Detailed record keeping is essential to getting good experimental data in your marijuana growing.

One key to a successful controlled experiment is to have only one variable. For example, if you are testing two hydroponics nutrients brands against each other, you must use identical clones all from the same mother, and ensure all conditions and inputs other than the nutrients are exactly the same.

In our hydroponics nutrients test example, you might test to see differences in growth rate, pH stability, EC, bud maturation, potency or harvest weight between the two brands.

Potential outcomes include: no differences in plant performance parameters; subtle but minor differences; major differences.

Using that data, and with cost of the nutrients programs and their ease of use in mind, your test may reveal that one nutrients brand is a better value than the other. Then you repeat the test at least one or two more times to see if the same results show up.

When we procured a new type of LED grow light made by the Austrian company SANlight, we had a variety of testing goals. One was to see how much photosynthetic photon flux density(PPFD) of photosynthetically active radiation (PAR) was generated per watt.

Another was to see how well a specific SANlight model, the EVO4-120, lit a standard four foot by four foot by seven foot grow tent, compared to other LED grow light brands in the same tent.

This experiment required serious attention to detail. You must only compare grow lights that draw equal wattage and are meant for the size space you’re lighting. You also need a precision PAR meter such as the Apogee EPAR unit.

After that, all you have to do is hang the lights one at a time in the exact same place in the grow tent, and measure PAR uniformity and intensity from side to side and top to bottom.

We tested SANlight, Fluence, Mars Hydro, Lush, California Lightworks, HLG, NextLight, Black Dog, Gavita, Iluminar, and Kind grow lights, ensuring equivalent wattage draw during testing. Although there were many differences in individual grow light performance, the SANlight unit by far gave the best overall coverage, most dense light footprint, and highest intensity of any model tested, with the highest electrical efficiency.

The SANlight gear provided high PAR for nearly double the canopy area that some of the less-professional competing brands provided, with all lights using the same amount of electricity. SANlight penetration was also superior.

Sadly, our experiments found that most grow light companies are exaggerating the coverage area, PPFD, PAR and electrical efficiency of their lights.

We weighted our grow light experimental results along with other factors, such as grow light cost, lifetime illumination longevity, warranty, customer service,  and spectrum to evaluate which grow light brand is going to give you maximum value for your hard-earned investment.

Another example of a marijuana growing controlled experiment happens when you grow identical clones under the same grow light using all the same inputs and conditions—except you feed a phosphorus/potassium (P-K) bloom booster to half the plants.

Harvest all plants the same time the same way. Dry the buds in the same conditions for the same length of time, being sure to segregate buds grown with P-K booster from the others. The potential experimental results are: no significant difference in dry weight, or one set of plants produced more or less harvest weight than the other.

If you repeat this experiment at least a couple more times using the same P-K booster and get the very similar results, you know for sure whether that booster is actually boosting.

Note that in our experiments, most P-K boosters did NOT create a significant increase in visible bud size or finalized dry weight, and some even decreased harvest weight.

Marijuana seeds germination testing is easy and important. We use Grodan rockwool starter cubes that are all neutral nutritionally and use identical water, light, seedling heat mat, and ambient conditions. We watch which seeds sprout fastest, slowest, or not at all. We watch how they handle their first two weeks of life.

This kind of testing has shown us that the vast majority of seed companies are selling inferior seeds. For example, seeds from Serious Seeds and a few other seed companies have 100% germination rate over multiple strains and years. Seeds from most other companies consistently do not. Seed viability and early seedling performance is an indicator of breeding skill and breeder professionalism.

Some controlled experiments are a lot more complicated than others. For example, experiments to measure whether flushing marijuana plants at the end of bloom phase creates “cleaner” plants without harming potency and/or harvest weight are more complicated than measuring PPFD of competing grow lights brands.

The complexity comes when growers want to measure the claim that using a hydroponics flushing product results in better-tasting buds, which is a subjective measure not easily verified by scientific testing.

What’s most important is now you no longer have to be a victim of inaccurate product claims or misleading online rantings of people promoting various growing marijuana potions, techniques, and gear.

Using controlled experiments, you’ll be more sure about what is and isn’t working and worth using in your marijuana growing.

(For more information about controlled experiments, watch the videos embedded below by clicking through to YouTube, even though the videos are listed as “unavailable.”)