In this post we will tell about the health of plants. We’ll show you how you can test the nutrient levels of fruit, vegetables, and plants in general. You can do this test at home with simple, low cost tools. You can test produce from the grocery store, a farmer’s market, and/or your own garden.
Are you wondering if your food is healthy and packed with nutrients? Do you want to know if your plants are robust enough to resist disease and dissuade bugs from eating them? We can answer these questions using a refractometer.
A refractometer is a tool that is used to test sugar content in the sap of a plant. The level of sap sugar correlates to the level of minerals the plant is using. The test is best done at a time of peak growth during the day and in full sun.
What does a sap sugar test tell us about plant health?
The main purpose of a plant is to use sunlight to make sugar – the process called photosynthesis. A plant that is healthy is making a lot of sugar. The time of peak sugar manufacturing is between 10am and 3pm on a sunny day. This is the time of day that we should be testing our plants.
The unit of measure of a refractometer is called Brix (pronounced ‘bricks’). It’s pretty much the percent of sugar in the fluid you are measuring.
If we know the Brix what does that tell us about the plant? If a plant has a high Brix level it means it’s doing what it was made to do: grow and make fruit or seed. Only healthy plants do this well.
A healthy plant will turn away insects, disease and weeds. Really? Yes! God made insects and fungus to clean up sick or nutritionally deficient plants. Insects only want to eat low Brix plants.
Different insects prefer different Brix levels. When a plant measures above 12 Brix very few insects will want to eat it. Simple sap sucking insects such as aphids are the first to leave your plants alone when the Brix reaches 6 to 7. Other insects leave at around 9 Brix. Grasshoppers are the last to leave at above 12 Brix. See the chart below developed by Dr. Tom Dykstra.
Some people teach that since a bug does not have a pancreas that sugar in its body will ferment and kill the bug. This is partially true. A healthier plant will also start producing ‘secondary plant metabolites.’ A plant makes various chemical compounds such as carbohydrates, fats, proteins, and nucleic acids. Some are essential to plant development. Others are not essential and are referred to as Secondary Plant Metabolites.1 Some metabolites play a role in attracting pollinators, or repelling pests, herbivores. Bugs coming to eat sick plants don’t like these metabolites, so the healthier a plant, the less bugs want to eat it.
A healthy plant is also resistant to disease. The coatings a plant puts on its leaves to protect against diseases are much thicker on healthy plants. A plant with a Brix reading over 9 will start to be quite immune to disease. There should be NO need to spray fungicide on these plants.
What about repelling weeds? A healthy plant releases up to 60% of the sugar it makes out through its roots. These are called root exudates. Root exudates feed soil microbes and fungi. They love it. Weeds do not like to live in soil that is high in sugars. Weeds also do not like a higher carbon soil and sugar in the soil is broken down to carbon. So healthy soil and plants suppress weeds.
High Brix means lots of sugar and lots of minerals. This means the plant will taste great and be very nutritious! This means high quality hay for animals, delicious carrots and onions, apples and cherries. High Brix food is more filling when you eat it. High Brix food also has a much longer shelf life.
Benefits of nutritious, high-Brix food:
- Tastes great
- Richer in nutrients and minerals
- More filling (cows need less hay if it’s high Brix)
- Less prone to rot during storage
- Heavier / more dense seeds
- Fatter seeds
- Better germination of seeds
How do Brix Levels Affect Harvest Time?
Since plants have their highest Brix/nutrition content in the middle of a sunny day you should harvest during this time. This means strawberry picking, apple picking, produce for putting by and cutting hay for the livestock should all happen around lunch time, not at 5am when you want to get a good start on the day. Use the early morning and evening hours to do other work besides harvesting.
How to test plant Brix
Tools needed:
- Garlic press (We use this one from Ikea. It’s tough and low cost.)
- Refractometer (Lee Valley’s is less expensive)
Directions:
- Pick a half dozen leaves from the plant you want to test or multiple plants of the variety you want to test. (If testing fruit or vegetables, skip to step 2.)
- Place the leaves, fruit or vegetables in the garlic press.
- Close the press and squeeze down on your plant test material until some drops of juice appear from the press.
- Open the plastic cover on the Refractometer.
- Put 2-3 of the drops of plant juice from the garlic press on the flat glass surface that the plastic cover covers.
- Gently close the plastic cover. (If you slap it shut, some juice will splash out and make a mess.)
- Look through the eyepiece of the refractometer. Where the color in the eyepiece changes from white to blue (the point of reading) and where that is on the vertical scale shows your Brix.
Example: The image below shows a Brix reading of 13 Brix.
Note: Sometimes you will notice that the edge of the blue zone is fuzzy. This often happens when your Brix level is higher. It can also be an indication of your Calcium levels. Lower levels will have a sharper line. (2)
Cleanup
Refractometer: rinse and wipe dry the prism end including the plastic cover.
Garlic Press: Clean out, rinse and dry before storage.
Important: Write down your test results including:
- The date and time
- Testing location (which row or test spot in the field)
- What you tested and where on the plant you got it from
- Stage of plant growth
- Your Brix reading
- Other observations such as:
- Sky conditions
- If it has rained recently
- Soil conditions
Make a chart in a notebook that you will use for several years. As you keep track of your tests over a number of years of soil improvement you’ll see the progress you are making.
Test your Brix 1-2 times per week. You will get to know the health of your plants throughout the growing season. Also, test plants in the same area. On the field level, put a stick in the ground that you can come back to so you are testing plants in the same area. Soil changes from one area to the next, even 20 feet away. Take note of where you are testing.
Once you own this equipment, testing is free. It costs nothing but time to do a few or many tests.
Have Fun! You are going to learn a lot!
Footnotes
2- https://blog.nutri-tech.com.au/the-beauty-of-brix/
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