Brix Test A Tomato

Continued from What Is Brix?.

The second reason we may conduct a brix test is more practical and useful in our vegetable gardens.

First, we take our refractometer and measure brix in a leaf or especially a fruit from one of our plants, for example a tomato.

Note that a “fruit” is just the reproductive part of a plant, so botanically-speaking, many foods we call vegetables are fruits, such as tomatoes, pumpkins and avocados. So we test the brix, then foliar feed that tomato plant, wait 30-60 minutes, and measure the brix again.

If the brix meter shows an increase of at least a couple of points relative to a control plant that we also brix test, the tomato liked that fertilizer and we should spray the whole crop. If it stayed the same or even went down, the tomato might not want that fertilizer today.

Even good organic fertilizers are sometimes not wanted by our plants.

This is an advanced technique that takes some practice. It isn’t as useful for organic gardeners with small gardens growing many different kinds of vegetables, with just a few of plants of each variety, because it might not be worth the time to brix test, say, one tomato plant in order to spray the other three.

Or maybe it would. If you’re trying to grow the best tomatoes and you want to get many dozens of tomatoes from each plant, it could be worth it. If you have a huge bed of something like potatoes, go for it.

For many plants, you need 12 brix in all parts of the plant, so if you’re still getting plant predator damage above 12 brix in the fruit, test the leaves. They may be the weak link. Other plants need even higher brix. You also need to make sure you measure from the same place on both the test and control plants.

The way to get brix up long term is through improving the health of your organic soil. Phosphate is especially correlated to brix, so if you get your phosphate availability consistently up, your brix test will move up.

I’m not going to get into the details of using a brix refractometer, as those instructions come with the device, but it’s really simple. Use a pair of pliers or a blender to get a little bit of juice out of the fruit or leaves and place it on the glass plate.

Look through the hole like you would look through a kaleidoscope and you have your brix measurement.

A refractometer can also tell you if you have enough calcium. A blurry line where the upper and lower part of the scale join tells you calcium is sufficient. A sharp line indicates deficiency. Not everyone agrees with this seemingly strange methodology, but I’ve found it to hold true much of the time when compared to a soil test.


  1. Robert Foster on December 18, 2011 at 3:09 pm

    Hi Phil,    Who could have imagined a refractometer would become such a practical tool to have in the organic gardening shed.   This is fascinating stuff.  In your first writing you mention the need to understand the ‘dissolved solids’ to look for beyond sucrose and fructose.   Can you recommend a reading that may help me understand brix and how to practically apply various refractometer readings?  Sounds like I will need one in order to practically understand their application in the garden.  Some are better than others, no doubt.  Which one do you use?  By definition thus far, it sounds like we can monitor nutrient density and uncover our plants true dietary needs.   I look forward to hearing more on this subject.   Thank you…great work !  

    • Phil on December 19, 2011 at 12:27 pm

      Here’s a fantastic little book that was put online for free:

      • Bob Foster on January 27, 2012 at 3:27 pm

        Thanks Phil,   The online book was exceptionally helpful.  I will also be purchasing a refractometer to initiate that new learning curve.  Am deep into “Teaming with microbes” and enjoying the many scanningy electron microscope images.  Sure hope these little fellas don’t turn on us :).   Where do you get E.M? . ..if you even need it any longer? In most circumstances, do you think ‘compost tea’ may suffice to encourage benificial microbes? ..or would you suggest an initial treatment of E.M. to ‘clean house’  ?       

        • Phil on January 28, 2012 at 2:24 pm

          Properly aerated compost tea can be amazingly beneficial. If you’re making it, EM probably isn’t necessary, but will still be beneficial. EM is from in the U.S. and in Canada. I use it more than compost tea because it’s much faster to use.

    • roldan on September 27, 2017 at 9:13 am

      I need refractometer for my undergrad thesis. is there any laboratory in the Philippines? or else the store?

  2. Amy Pearson on January 27, 2012 at 5:17 am

    Eating organic food is a great step towards a healthy lifestyle. Unfortunately, many organic fruits and vegetables are a bit more costly. To combat the increased cost, and to ensure that the food you are eating is 100% organic, you may want to start your own organic garden.

  3. Shuetrim on February 4, 2012 at 11:21 pm

    Thanks for links Phil, you’re a wealth of knowledge that we all need so much these days!

  4. Ben on September 10, 2012 at 6:03 am

    G’day Phil, back again with a quick question. Having heard that most large chain grocery store tomatoes in particular are picked green and gas ripened, have you tested or do you know of any recorded Brix reading’s of tomatoes picked like this or even a typical store bought tomato that is red on the outside with that washed out looking greeny/ orange colour on the inside? I will compare these myself when I buy a Refractometer however your thoughts would be interesting… Cheers Ben. btw your book is great so far!

    • Phil on September 12, 2012 at 9:10 pm

      Thanks Ben, I find most tomatoes from the grocery store to be low brix, and most from local, organic growers to be higher brix, although still not usually great.Even looking at my own tomatoes this year, they range from poor to excellent, with most of them being between average and good.Raising consistently high-brix crops seems to take a number of years of getting your soil right and getting your plant sources right, which generally means saving the best seed every year. It’s not a fast process, but it sure is rewarding!

  5. Cherie Proctor on April 24, 2013 at 2:02 am

    Phil are you able to give any advice on buying a good quality refractometer? I’ve found cheap ones on eBay for $30, and one for over $400 – what’s the difference?I know you said you can get a good quality one for $100, but since you’re talking US$ I’m sure that will probably equate to at least $300 or more in Australia where we are. For some reason we tend to get royally ripped off in Australia with the prices of everything, especially electronics! Even though the exchange rate isn’t anywhere near that bad :/Any advice? Is digital better than not? The ones that say they are for wine or brew sugar measuring (with %Brix) – are they the same thing you need for fruit / veges or are they different?Thanks!!

    • Ben on April 24, 2013 at 4:20 am

      Hi Cherie, I bought the one that Phil has/recommended. It is the Vee Gee BX-1 and I got it from Pike-Agri. The cost was around $97 and the shipping was about $48 from memory. The thing is you have to make the purchase first and then they send you the postage costing’s. You can pull out on the sale if you’re not happy with the postage price they offer you. I’m in Sydney btw.I’m happy with the refractometer thus far. No prob’s at all and it’s pretty robust.I must say I didn’t do much research in the way of Sydney/Australian supplier’s which I perhaps should have done, but…Hope this helps,Ben

      • Cherie Proctor on April 26, 2013 at 12:00 am

        Thanks heaps Ben! Good to know I don’t have to spend an absolute fortune.. 🙂 I’m in Brisbane, so I assume it’ll be a similar cost. Thanks again..

  6. Kim on March 29, 2014 at 4:56 pm

    does anyone have a recommendation for a digital refractometer, or thoughts on digital versus not?

    • Phil on March 29, 2014 at 5:57 pm

      I don’t have a link right now, but I’ve used several $30 models that have worked well. You can find them online.

  7. Carolyn on September 3, 2016 at 9:05 am

    How come I can’t find pumpkin on any brix charts. Don’t we have an Australian version. I know Americans don’t really eat pumpkin but I would like to know what rates, poor, average or good for jap or butternut pumpkins.

    • Phil on September 4, 2016 at 11:48 am

      We call them squash – they’re on the chart 🙂

  8. Larry on May 24, 2019 at 5:16 pm

    I know this post is very old, but I just found it – and found it very informative. Your comment about the calcium level agrees with an article I read on the site, titled “Brix Readings, and What They Tell Us”:

    “Brix readings can also indicate soil fertility needs. If soil nutrients are in the best balance and are made available (by microbes) upon demand by plants, readings will be higher.

    You will find that when the phosphate levels in the soil are not up to what they should be, the sugar in the plants will vary from the bottom of the plant to the top. In other words, the Brix reading at the bottom of the plant will be higher than the top of the plant. The better the phosphate levels in ratio to potassium the more even the Brix reading will be all over the plant. Also the better the phosphate levels in ratio to potassium the less fluctuation there will be in the brix reading in any given 24 hour period.

    You will also note that when you are looking into a refractometer you will sometimes be able to see a very sharp line which is very easy to read, while at other times it may be a very hazy line and not well demarcated and so difficult to read. The very sharp and dark and easy to read line means the crop is lower in calcium and higher in acid. A very diffuse and hard to read line tells one that the calcium is higher and the acid is lower in the plant. This is why a lower Brix reading on a plant will actually taste sweeter when there is high calcium than one that may have a little higher Brix reading and a low calcium. The available soluble sugar is what gives taste and sweetness to food. The more calcium in the crop along with the sugar, the sweeter the taste even though the Brix reading will be the same on two samples.”

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