Brix measurements and its role in plant nutrient management


Brix is a measure of the dissolved solids (TDS) of a liquid (in our case plant sap), predominantly the sugar content but also minerals etc. (including amino acids, lipids, and any suspended particles or colloids).

A Refractometer and the calibrated brix scale

Brix is measured on a scale that quantifies the amount of light that is bent (or refracted) when passing through a liquid. The amount of light refraction depends on the density of the liquid (which is influenced by the TDS). The unit of measure is degrees Brix (oBx); i.e. 1 gram of dissolved solids per 100 grams of solution. Brix levels in crops will generally vary from around 4 to 20. 

Brix measurements are taken with the aid of a brix refractometer. The more sugars and dissolved solids in a sap sample, the more the mixture bends the light that passes through it. A brix refractometer reads how much the light bends (refracts), and displays the results as a percentage of sugars in the sap.

And it’s easy to use—just take a leaf sample, roll it into a ball and squeeze a couple of drops onto the glass slide of the refractometer. Then look through the hand-held device towards a light source, and read the brix number on a graduated scale. 

The more efficiently your plants take up water and nutrients, the higher the brix. 

Therefore, the determination of the plant’s sugar levels, (as well as other dissolved solids like minerals) is known as Brix. The sugar levels in a plant are like a gauge of photosynthetic activity. They are also a gauge of the health of the plant; the higher the sugar levels, the healthier the plant.

Measuring brix levels is very quick and helpful, because it gives clues as to the health of the plant and the subsequent likelihood of insect pest attack, frost susceptibility, possible plant growth limitations and more. It can also help alleviate nutrient deficiencies before the first signs of deficiency appear on the leaf. Taking brix readings and making adjustments will help prevent problems before they happen.

High brix crops are the cornerstone of sustainable farming. Resistant to disease and unappealing to insects, healthy plants with high brix levels require fewer inputs and improve profitability. They are also better for human consumption and health. 

Furthermore, there is a direct proportional relationship between brix and the quality of the finished produce. High-brix plants are healthier, tastier and higher in nutrients than low-brix plants, and brix offers an objective measurement of how well plants are doing. 

What level of brix is considered ‘high’?

  • 0 – 2 brix: Very low brix; the plant is essentially unable to ‘look after itself’. Insects will move in quickly to consume these plants and disease will run rampant.
  • 3 – 7 brix: Mid-level brix; the plant has a chance of survival. 
  • 8 – 11 brix: Higher brix; natural resistance begins. Most sucking insects will not tolerate a brix of 8 or higher; chewing insects that eat the roots or leaves directly will start to lose interest once the plant reaches a brix level of 10 or 11.
  • 12 – 20+ brix: High brix; virtually no insects will attack a plant with a brix level of 12+. 

Brix Indicators

  1. Low brix levels are often linked to high nitrate levels in the plant. It is impossible to achieve nutrient density in the presence of excessive nitrate nitrogen. This form of N is only ever taken up with water, so the higher the nitrate levels the greater the dilution factor. A watery, mineral deficient plant is a calling card for insects and disease, so this could also be called a stress meter.
  2. High brix plants will have a higher specific gravity. They will weigh more and, if you are paid by weight, this is a good story.
  3. Shelf-life and brix are directly related. The higher the brix levels of fresh produce, the longer it will last on the shelves.
  4. Good brix levels can confer enhanced protection against frost. A denser sap will have a lower freezing point, therefore protecting the plant against lower temperatures.
  5. The line that divides the two visible hemispheres can offer an indication of calcium levels in the plant. If the dividing line is clean and sharp, this indicates a calcium deficiency. It can actually be a sign of generalised mineral deficiency, but as calcium is “the trucker of all minerals”, this mineral is the chief suspect. A fuzzy dividing line is an indication of mineral density and desirable calcium levels in the plant.
  6. Brix levels can also offer a warning of damaging storm events. Typically, the plant builds brix levels with photosynthesis throughout the day. At around 5 pm this process stops and, soon after, the plant begins to pump sugars down to the roots and the beneficial organisms surrounding those roots. Therefore, Brix levels will always be higher in the late afternoon than in the morning. If there is a sudden drop in brix levels outside of those times, it may be a warning of a sudden change in the environment. Brix levels should never fall during the day and, if they do, it may be linked to a survival strategy where the plant pumps down as much sugar as possible to the roots, as an energy reserve to fund the possible rebuilding process.
  7. The refractometer can also provide an indication of boron levels in your crop. If the brix levels of your crop do not drop overnight, then you may have uncovered a serious boron deficiency. Early each evening, there is a transfer of glucose in the chloroplasts down to the roots. The opening of that important doorway is governed by boron. The absence of the “door opener” means that sugar is trapped in the leaves and the workforce beneath the roots is effectively starved of energy. The wheels begin to fall off shortly after that. Regular monitoring with your refractometer can prevent this boron-based problem and the resilience of your crop and soils will improve.
  8. Finally, brix levels can offer an indication of likely weed pressure. The brix of the weed should always be substantially lower than the brix of the crop. Otherwise you have created conditions for the weed rather than the crop. High brix crop plants are often produced in soils with less weed pressure. This is because calcium and phosphate are the chief brix-building minerals and many weeds (particularly broadleaf weeds) grow in soils that are lacking calcium and phosphorus.

How to Increase Brix 

If higher brix levels can have such benefits to us and our crops, then we also want to know how we can increase brix levels.

Since biostimulants improve the uptake of minerals, the careful use of additives such as amino acids, humic and fulvic acids, and seaweed extracts can help improve brix. The proper balance of 

minerals in the nutrient solution can also have a positive effect, particularly the potassium-to-nitrate ratio. Here are some suggestions for improving the brix of your favourite crops.

1. Nitrates and Potassium to Nitrate level

So to ensure high brix, don’t give plants more nitrates than they need. Excessive nitrates produce large cells with thin cell walls, making them a target for pests and diseases. If nitrates are adequate but brix is still too low, it may be beneficial to increase the potassium levels. Potassium is a catalyst for carbohydrate metabolism, helping to increase brix. 

A grower has three choices for increasing the potassium-to-nitrate ratio: lower the nitrates, increase the potassium or do a little of both. Once you find the sweet spot, no pun intended, the brix should start to improve.

2.Apply Trace Elements

Since trace elements activate enzymes in the plant, the plant is able to do more chemical reactions per second, resulting in higher brix. Iron uptake is especially important. Iron is a catalyst for chlorophyll synthesis, the green pigment in plants that actually manufactures sugars during produce more chloroplasts to hold the extra chlorophyll, turning the plant into a more efficient sugar-making machine. The result? Higher brix.

3. Use Humic and Fulvic Acids

Humic and fulvic acids are intermediate chelators, helping plants take up important trace elements. In nature, humic and fulvic acids hold onto iron ions like a claw and make them more available to the plant. 

4. Use Amino Acid Blends

Amino acids are also intermediate chelators, improving the uptake of minerals. In particular, amino acids improve the uptake of calcium. Calcium strengthens the stems and vascular system of the plant, allowing water and minerals to be taken up more efficiently. The more efficiently water and minerals are assimilated by the plant, the higher the brix.

5. Use Seaweed Extracts

Seaweed extracts also have a positive effect on brix. Seaweed extracts include mannitol, a natural sugar that chelates micronutrients and makes them more available to the plant. Seaweed extracts are also loaded with natural plant growth hormones that stimulate cell division. Seaweed extracts have numerous phytohormones, nutrients and other constituents that stimulate plant growth, therby increasing brix. Seaweed extracts work synergistic with other organic biostimulants, so using a combination of additives is better than using any single additive alone.

Remember, plant growth is part of a complex system with many variables, so there is no magic bullet to increase brix overnight. Instead, use the refractometer along with other management tools. Light levels, air flowpHelectrical conductivity and nutrient balance all affect brix in one way or another, and continuous improvement is the goal.

COMPO EXPERT has a range of products suitable for complete nutrient and brix management. Contact us today to assist you with growing better, more nutrient dense crops while having a greener footprint.  We are your EXPERTS FOR GROWTH.

Guide to Brix levels of different plants

As a basic guide, leaf sap brix must be above 12 for insect resistance and better yield quality.


Bell Pepper46812
Corn Stalk4101822
Corn Young8101824
Cow peas481214
English Peas8101214
Field Peas461012
Green beans481012
Hot Pepper46810
Potato Irish86710
Potato red86710
Potato Sweet681214

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