About the Experiment
In partnership with Cornell Cooperative Extension, Brooklyn Botanic Garden is conducting a controlled experiment in the Herb Garden as a demonstration for visitors. The hypothesis is that pepper plants receiving targeted soil amendment will produce more numerous, larger, and higher-quality peppers.
Farmers and gardeners often obtain agronomic soil testing in early spring, to allow time for adjustments before planting. In March, we sent soil samples from this section of the Herb Garden to a soil lab for analysis. The results showed that while most nutrient levels were already optimal for most vegetables, certain crops—including peppers—could benefit from added potassium. In this section of the Herb Garden, potassium (K) levels measured around 120 to 150 pounds/acre. Peppers perform best with K levels around 250 to 300 pounds/acre. This suggests that adding potassium may improve our pepper crop.
You can also add too much of any nutrient. Excess phosphorus, for example, is often lost as runoff, which can then enter waterways and cause toxic algae blooms. By testing soil, then adding only the nutrients needed, we can get the most out of our plants without the side effects of excess nutrients. The goal is to optimize plant health without overfertilizing, which is not only wasteful, but on a large scale, can lead to significant environmental issues.
Methods
In early May we planted five pepper cultivars (a cayenne, habanero, Serrano, and two jalapeños) in two distinct areas of the Herb Garden.
In the treatment bed, just before planting the peppers, we raked in an amendment (potassium sulfate, also called sulfate of potash) to add plant-available potassium to the soil. We added at a rate of 150 pounds/acre, which was 30 grams for this 20 square-foot bed.
We didn’t add anything to the control bed. Otherwise, the two beds are being managed in all the same ways.
Hypothesis: The peppers growing in potassium-amended soil (the treatment bed) will produce more total pounds of fruit than peppers in the control bed.
We also want to observe if the plants grown in potassium-amended soil produce peppers with longer shelf life, brighter and/or more uniform color, and higher Brix levels (an indicator of sugar content and fruit quality), and if there is a difference in plant height between the two beds.
Each week, we harvest peppers from both beds and record their weights. We’re also exploring some other measurements; for example, we’re using a refractometer to measure Brix levels, since potassium deficiency has been shown to reduce Brix in some fruits.
Potassium deficiency has also been shown to negatively impact shelf life of peppers and other harvested fruit. We’re comparing the shelf life of peppers from both beds by tracking the percentage of weight lost each week for peppers that were harvested at the same time.
Check back to see the outcomes, and on your next visit, look for interpretation of this experiment in the Herb Garden.
Further Reading
Nutrient Guidelines for Vegetables (PDF), Cornell University, 2019.
A Summary of N, P, and K Research with Pepper in Florida, George Hochmuth and Ed Hanlon, University of Florida Institute of Food and Agricultural Sciences, 2020.
