Is it true that pests won’t attack healthy plants? And that you can determine the health of your plant through one simple measurement? These ideas have been circulating for years, often going viral in gardening circles when a new video or blog post draws attention to them.
The claims revolve around the Brix levels of your plants. Brix measures the sugar content—essentially the sucrose—in a liquid. Technically, it measures the soluble solids, but in gardening, sugar levels in plant sap or juices usually dominate, making Brix effectively a measure of sugar concentration. The scale has long been used in the food and beverage industry to test sweetness, and it’s named after Adolph Brix, dating back to the mid-1800s.
In the garden, people have started using Brix as an unconventional measure of plant health, with some claiming that high Brix levels mean healthier plants, higher nutrient density, and even pest resistance. Let’s break down these claims and see what’s really going on.
High Brix Levels and Nutrient Density
One of the claims is that high Brix levels indicate a higher concentration of nutrients, such as vitamins and minerals. While it’s true that these nutrients are part of the soluble solids measured by a Brix refractometer, the sugar content is typically so much higher that it overwhelms the reading. As a result, a Brix measurement isn’t a reliable indicator of nutrient density. Some argue that higher sugar levels correlate with better nutrient availability. This seems like a hypothesis that would be easy to test, but hasn’t been.
What studies we have—and there aren’t many of them—don’t support the correlation between Brix levels and nutrient concentration. A 2019 study on tomatoes published in the Journal of Plant Nutrition concluded that “Brix readings showed no correlations with nutrient concentrations.” Similarly, earlier research on lettuce found no connection between Brix readings and calcium concentration. Despite these findings, proponents continue to assert that high Brix levels imply high nutrient density without presenting substantial evidence.
Does High Brix Mean Better Plant Health?
Another claim is that measuring Brix levels can give you an idea of a plant’s overall health, essentially serving as a proxy for photosynthesis efficiency. The idea is that healthy plants produce more sugars through photosynthesis, which should be reflected in higher Brix readings. While this sounds plausible, there’s no concrete evidence to back it up. Healthy plant growth involves many factors—nutrient availability, soil health, water, and sunlight—and reducing this complexity to a single number is overly simplistic.
Pest Resistance and Brix Levels
Perhaps the most appealing claim is that plants with high Brix levels are immune to pests, with a specific number often cited: a Brix level of 12 or above. The idea is that pests avoid plants that are healthier and more nutrient-dense, as indicated by high Brix.
However, what may be the only study on this topic, conducted nearly 30 years ago at California State University-Fresno, found no consistent connection between Brix levels and pest numbers—in this case, leafhoppers. The study didn’t find evidence to support the notion that pests avoid plants based on their Brix level. It’s just one study and it’s not like it thoroughly refuted the high-Brix-no-pest hypothesis, but no research has been presented to support it.
Where Did These Ideas Come From?
If it’s not based on science, then where did these ideas come from? The concept of using Brix levels as an indicator of plant health has roots in an alternative science or fringe science, tied to spiritual and mystical beliefs. For example, it believes that what we call pests have a divine purpose to eat what is garbage for humans, so healthy, nutritious plants—as indicated by high Brix levels—won’t attract pests. This philosophy also aligns with some more conventional ideas, like regenerative agriculture, a focus on soil health and organic matter, the importance of soil microorganisms, avoiding pesticides, and growing nutrient-rich food. Many of us share those same goals, but the use of Brix as a measure of plant health lacks scientific validation.
Should You Buy a Brix Refractometer?
A Brix refractometer is a simple tool that costs under $30, and it’s easy to use. Many gardeners find it fun to measure the sugar content of their plants, and there’s nothing wrong with that. However, if you’re expecting it to provide insights into pest resistance, nutrient density, or overall plant health, you might be disappointed. The claims about Brix levels being a magic bullet for pest-free, nutrient-dense gardening are not supported by current research.
Even if there was something to the idea of using Brix refractometer, it’s not clear what practical actions you can take based on those readings, other than adding more and different fertilizer. And often the nutrients that Brix supporters recommend you add are ones your soil test may have told you are already present in abundance (calcium and phosphorus, in particular).
If you enjoy experimenting in the garden and are curious about sugar levels in your plants, a refractometer can be an interesting tool. But if you’re looking for proven methods to improve plant health, focusing on good soil practices, like adding compost and other organic matter, will likely yield better results than relying on a Brix reading.
Conclusion
While the idea of using a Brix refractometer to gauge plant health or deter pests is intriguing, the science simply isn’t there to back it up. High Brix levels might reflect certain aspects of plant health, but they are not a definitive measure of nutrient content or pest resistance. Gardening is full of fun tools and experiments, and a Brix refractometer can be part of that. But the whole concept of using Brix readings in the ways we’ve been talking about comes from an alternative science with some dedicated followers, but little evidence to back it up.