Interpreting Brix Level Readings
Here are a few good things to keep in mind when interpreting your brix readings:
Each degree of a brix scale measurement is equal to 1 gram of sugar in 100 grams of solution. Yes- some other tiny bits of organic material may be present in your sample, but they have not been found to significantly change a reading.
It is recommended that you take your measurements in the afternoon - around 4pm, or before daylight really starts to go down. That way you get a full understanding of the capability of your plants to produce sugars through photosynthesis. Remember, if you take a brix level measurement early in the morning, the levels will be low, due to the plant having been at rest overnight. We need to give them some time during the day for photosynthesis.
Know also that where you are growing your plants can impact your brix readings. Plants that are grown under cover, such as in a greenhouse or tunnel are likely to have lower brix readings than plants grown outside in full sun, with good established soil microbiology.
This simple scale can help us correct for temperature differences. If you are taking your measurement with an analog (manual) tool and you are taking it below or above 20°C (68°F) you will want to do some simple subtraction or addition to determine a true brix scale reading. If your temperature is lower, you will be SUBTRACTING from your measurement. If you are taking your reading at a higher than optimal temperature, you will be ADDING to your brix measurement.
Plants that are heavily fertilized with a nitrogen-rich fertilizer or that are growing in soil that has been over-fertilized (and high in salts) may have lower brix readings. The balance for the plant is best achieved naturally when there is a healthy relationship between the plants and the microbes in the soil. Try taking some readings from happy, perennial plants and trees on your property (in wooded or untouched areas if possible) in addition to the plants that you are cultivating with intention.
Now, what do the numbers mean?
Researchers are finding that certain pest families are less interested in plants when brix levels reach a certain range. For example: Aphids lose interest/cannot tolerate sugar levels once plants reach up to 6 to 8 degrees on the brix scale. Sucking insects can tolerate a bit more sugar, but they begin to be dissuaded at 7 to 9 degrees. Chewing insects will back off when brix is 9-11 degrees. And lastly, grasshoppers stop around 10-12+. You can find a chart with this information here.
It has been suggested that adding sugars (even just household kitchen sure in solution) to the soils when watering plants with low brix levels can help the microbes along by giving them a source for food, that in turn allows them to deliver more nutrients to plants. This method can have very quick results, but it may only be a short-term solution. Healthy plants deliver that nutrients to the microbes themselves - and it’s the symbiotic relationship that we’re hoping to build. Molasses has sugar, plus additional nutrients. In particular, molasses has iron, calcium, magnesium, potassium, phosphorus, vitamin B6, and antioxidants.
Adding sugar in this way may help you get through a shoulder season or a few weeks. The microbes consume that sugar source and plant readings improve, but then they will run out of their food source and you can expect plant health to dip again. You might have to “feed” the soil weekly in order to try and achieve the balance you’re hoping for. Obviously- these kinds of short term solutions are not ideal.
The best course of action is to use a low brix reading as an alert to work on your soil. A soil test may be able to tell you what is missing from your soil. Plant tissue tests can help you learn of deficiencies in the plants themselves.
For more on brix levels and understanding this field of study, see the work of Thomas Dykstra, Ph.D. or check out this post.