Testing a New Nutrient Line

By Grubbycup
Published: March 2, 2018 | Last updated: April 8, 2021 12:37:19
Key Takeaways

Nutrients are one of the most important variables in growing a successful crop. But with so many to choose from, how does a grower know which nutrient line is best for them? A simple controlled test, as explained here by Grubbycup, could hold the answer.

There are many quality nutrient choices on today’s market, and a few controlled experiments can give valuable information about which perform better during a harvest. Common indicators of improvement are increases in production, cost savings, or quality.


Although a larger sample is more accurate, the minimum number of plants needed for such experiments is two. One is the control plant, which is fed the current nutrient regimen, and one is fed with the new feeding schedule. Other than the different nutrients, the plants should be as similar to each other as possible and grown under exact, if not very similar, conditions. Cuttings (or, clones) are commonly used to minimize the impact of genetic differences.

If using more than two plants, the percentage of the crop to commit to the new feeding schedule is dependent on the confidence the grower has that the change will improve (or at least not hinder) production versus the proven schedule currently in use.


Keep Good Records

Keeping good records improves accuracy. Note the experiment’s start date because it will allow for the calculation of daily production after harvest. For the control group, feed as normal and track the amount of each nutrient used. For the experimental group, follow the manufacturer’s recommendations and again keep track of the amounts used. At harvest, make note of the harvest date, record the harvest weight from each plant, and calculate the totals of each nutrient used.

Production improvements are indicated by an increase in the average amount produced per day for the duration.

Subtracting the start date from the harvest date will give the total number of days for the garden. For example, a harvest on Aug. 1 minus a planting date of May 23 would be 70 days. If one group matures faster than the other, calculate each set of dates separately.


Then, divide the amount harvested by each plant by the number of days it took to grow them to calculate the grams per day (GPD) produced. For example, a plant that harvested 35 grams after a 70-day season produced an average of 0.5 GPD. A plant that harvested 30 grams after a 60-day season also produced 0.5 GPD, so this method allows for the comparison of harvests from the lengths of different seasons.

If the only concern is to maximize production, then simply compare the average GPD of the control group versus the average of the experimental group. Whichever method results in a higher GPD is more productive (within the margin of error). If the control group produced an average of 0.5 GPD and the experimental group produced an average of 0.75 GPD, the experimental group would have been more productive.


Other Factors to Consider

If expense is a concern, it can be factored in as well. Dividing the total cost of the nutrients used by the total number of days will give an average cost per day. If a gardener were to spend $140 over a 70-day grow, then they are spending $2 a day on nutrients. Dividing that number by the number of plants gives the amount spent on each plant per day. If an average of $2 a day on nutrients is spent to feed 20 plants, then each plant costs an average of 10 cents a day in nutrients.

Comparing the GPD and the cost of nutrients can give a clearer picture of the expense versus the return. An increase in the daily cost of nutrients should be at least matched with an increase in production to be cost-effective. Which is to say, any increase in price should be covered by enough additional harvest to offset the difference in cost.

Other improvements, such as the quality of flavor, may be less tangible and more subjective. Blind testing can help minimize bias when judging differences. To set up a blind test, start with an identical container for each sample. Have an assistant who won’t be involved with the evaluation prepare the samples. Have them write the identity of the sample on a small piece of paper, then fold the paper so it can’t be read and tape it to the bottom of the lid. Then, have them place the sample in the container and close, and repeat for each of the other samples. They should rearrange the sealed containers (which should appear very similar to each other) randomly and number each of the containers on the outside.

If done correctly, each container will have a name on a folded piece of paper taped to the bottom that matches the sample inside the container that is labeled with a randomly assigned number.

Then, each person judging evaluates each sample, and records results according to the number listed on the outside of the containers. Once all the samples have been rated, their identity can be determined. If one method or the other is substantially superior, it should be reflected in the results.

Calculations and testing can supply empirical evidence to suggest one method over another, but they aren’t the only considerations. Other factors may include a gardener’s feelings about the manufacturer, availability in the local area, the advice of other gardeners, and sustainability of production methods.

There are many fine nutrient lines available that perform well, and using experimentation and testing can help a gardener decide which is better for them.


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Written by Grubbycup | Indoor Gardener, Owner & Writer of Grow with Grubbycup

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Grubbycup has been an avid indoor gardener for more than 20 years. His articles were first published in the United Kingdom, and since then his gardening advice has been published in French, Spanish, Italian, Polish, Czechoslovakian and German. Follow his gardening adventures at his website

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