How (and When) to Measure BRIX

When I took my first BRIX reading on my farm—which had been an alfalfa field for over 20 years—we came in at a 7. A refractometer reading of 7 °BRIX means that the sugars in my plants’ sap were at about 7%.

That number doesn’t mean much on its own unless you know your target. Most scientists agree that the ‘sweet spot’—where plants reach optimal health and enjoy the greatest resistance to pests and diseases—is a BRIX level of 12 or higher.

So how do you take that first reading to see where you stand and figure out your next steps?

Measuring BRIX is simpler than it sounds. You don’t need fancy lab equipment. A handheld refractometer, a garlic press, and a little muscle are all you need to get started.

All that's really needed to take a BRIX reading. There are different kinds of refractometers (digital ones with probes), but this is the one I use to take readings on our farm.

Measuring BRIX on our farm using a handheld optical refractometer:

1. Pick the right leaves. Choose healthy, mature leaves from the middle of the plants. Avoid new growth or stressed leaves. For one reading, we take leaves from about 4 plants spaced randomly througout the field to get an idea of the general health of our dahlias.

2. Extract the sap. Squish the leaves into the garlic press and—here come the muscles—squeeze the press to extract sap from the leaves.

3. Place on the refractometer. Drop this sap onto your clean refractometer prism until it's mostly covered (2 - 3 drops). Close the plastic daylight plate over the sap to spread it evenly across the prism.

4. Read the number. Point that baby at a light source and look where the number is where the background colors meet. That's your result.

   
   
   
   

And… that’s it! In just a couple of minutes, you’ve got a snapshot of your dahlias' current health (which, we'll learn in future posts, is really a snapshot of your soil health).

By taking readings every week throughout the growing season, you’ll gain valuable insight into how your plants are responding to your farm practices—from watering to soil care.

And fair warning: BRIX readings can be a lot like stepping on a scale. The data isn’t linear—it can fluctuate a bit from one reading to the next.

So instead of obsessing over small up and down changes, record your readings and pay attention to overall trends over time. That’s where the real insight comes from.

When to Measure BRIX

To keep those fluctuations down and get more reliable readings, you need to know a few things beforehand. Measure in the afternoon on a sunny day, ideally between 11:00 AM and 4:00 PM.

Why afternoons?

Plants photosynthesize throughout the day, producing sugars and storing nutrients. Early morning readings are almost always lower because the plant hasn’t had time to build energy yet. So do your feelings a favor and don't measure first thing in the morning!

Tips for More Accurate Readings

• Consistency is key: Test at roughly the same time of day if you want to track trends over time.

• Optimal conditions: Choose sunny, dry days. Cloud cover, rain, or recent watering can dilute the sap.

• Leaf selection: Healthy, mature leaves give the most reliable readings.

• Daily cycles: Remember, BRIX is lowest at dawn and peaks in the late afternoon.

And Finally, Because This Can't Be Overstated...

Testing BRIX is about tracking plant health and trends. Over time, you can see how your soil, fertility, and care practices are affecting your plants. If BRIX levels are climbing over time, your plants are loving what you're doing. If they're on the decline, then it's time to make some adjustments.

Next time, we’ll dive into the soil—and the microbes that help boost BRIX and plant health.