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Why It’s Important to Test the pH of Your Run-Off

If you’ve recently noticed some leaf discoloration, mutation, or poor growth, it’s quite likely an inadequate pH range is the culprit behind these issues. pH is among the most important factors in the garden. But to understand it, we must first look at the basic biological functions of plants. In total, there are 16 essential elements that plants can absorb. These elements are divided into categories that contain nutrients that aim to support specific biological functions. However, to properly uptake these elements, plants must be fed within an adequate pH range. If you’re interested in learning more about the importance of testing your run-off, read the passages below. 

What is pH?

Potential Hydrogen (pH) is a unit of measurement that describes the acidity or alkalinity of any given substance on a scale of 0-14, with 7 being neutral. In the field of gardening, however, pH is the main factor that dictates the uptake of nutrients in the root zone. Depending on the pH of your nutrient solution, your plants may uptake more or less of a specific element. 

pH is the main factor that dictates the uptake of nutrients in the root zone.

The pH Scale and Nutrient Uptake

For plants to remain healthy and happy, they must be fed within an ideal pH range. For most plants in peat moss or soil-based systems, this pH range falls anywhere between 6.0 – 6.5. This scale can be thought of as the “sweet spot” for nutrient uptake. At this level, plants can uptake essential macro elements such as nitrogen, phosphorus, and potassium, while also having access to important micronutrients that help ward off common deficiencies and lead to the faster and healthier development of new growth. 

This scale can be thought of as the “sweet spot” for nutrient uptake.

Buffering Your Nutrient Solution

To maximize the rate at which your plant uptakes available nutrients, attempt to buffer your nutrient solution in the ideal range before irrigating your crop. Most fertilizers (but not all) will hold an acidic pH value, meaning the ingredients incorporated within the fertilizer will lower the pH of water (pH 7.0) once mixed at the recommended rate. So, after mixing your nutrients, test the pH of your solution, and if necessary, buffer your fertilizer into the appropriate range (pH 6.0-6.5). Use pH Up to raise the pH value of your solution, and pH Down to lower it.

pH Down

Only available in Canada

Tip: Dilute small amounts of pH Up or pH Down with water before adding it to your nutrient solution. This will help the solution adjust and decrease the chance of aggressive swings in pH value. 

Issues with pH

A variety of issues can arise if plants are not fed at an adequate pH range. For example, if plants are fed at a highly acidic rate, they will be unable to uptake and absorb valuable nutrients. This can lead to medium acidification, nutrient lockout, deficiencies, and the buildup of salts. If you’ve noticed worrisome growth patterns, it’s quite likely your plants are experiencing one or more of these issues. Follow the steps below to test the pH of your run-off and remedy the problem. 

Plants fed at a highly acidic rate will be unable to uptake and absorb valuable nutrients.

How to Test Your Run-Off

To test the pH of your plant’s run-off, start by collecting a sample. Begin by watering your plants with plain, neutral water (with a pH of 7.0) until roughly 20% of the water runs out of the bottom of your container. Then, collect the run-off into a container and test the sample. Ideal pH ranges for run-off should be between 6.0 – 6.5 in soil/soilless mixes like peat moss. However, any pH close to this range will be acceptable. If you test your solution and the pH deviates more than 1.0 from the ideal range, it’s clear that your plants are outside acceptable ranges of nutrient uptake. Remember, plain water acts like a solvent that rinses and neutralizes excess acidity. So, any number you receive from your run-off test is likely higher than the real pH value. 

Ideal pH ranges for run-off should be between 6.0 – 6.5 in soil/soilless mixes like peat moss.

How to Remedy pH Imbalances 

For any pH value under 5.5, consider feeding your crop at higher pH levels, or, buffer your medium with pH neutralizing compounds like calcium carbonate, dolomite lime, or oyster shell flour. After amending your medium with a neutralizing agent, the pH of your root zone should become stable over the next few irrigation cycles. As you water your plants, the pH neutral properties of either lime or oyster shell flour will slowly dissolve into the soil, thus raising the pH gradually over time. Resume your regular feeding schedule at a reduced rate and continue to re-test the pH of your run-off. When stable, your plants will be able to absorb all the essential nutrients offered to them. Soon, new, healthier growth patterns will emerge, and nutrient deficiencies will no longer plague the development of your crop. 

Feed your crop at higher pH levels, or, buffer your medium with pH neutralizing compounds.

Whatever your style of garden, chances are, GreenPlanet Nutrients has the perfect base nutrient program. To access the programs available at GreenPlanet Nutrients, contact a member of the GreenPlanet sales team, or your local garden supply store for product information and purchasing inquiries. 

Check out our Resource Centre for more product information

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Understanding Plant Nutrition

Choosing the right fertilizer for your garden can be as important as other factors that influence a successful harvest. However, choosing a “top tier” fertilizer as an input in the garden will not always guarantee a bountiful and quality-driven result. In order to produce a consistently healthy crop, gardeners must understand the connection between plant biology and the factors available which can influence a successful outcome. Understanding this connection, even at its most basic level, can help gardeners achieve faster periods of growth, and heavier, more quality-focused yields. Throughout this article, we will be examining the parts of plant food, as well as tools available to gardeners that ensure nutrient availability across periods of growth and bloom. 

What is N-P-K? 

N-P-K is an acronym for the most readily available macronutrients found in plant food. These important elements, nitrogen (N), phosphorus (P), and potassium (K), are the building blocks of plant nutrition and are an essential part of a plant’s diet throughout the periods of vegetative and flowering growth. Nitrogen, arguably the most important soluble macronutrient is responsible for creating the green parts in plant stems and leaf growth (Rienders, 2001, p. 108). Phosphorous and potassium, on the other hand, are utilized by the plant as energy, sugar, and essential oil carries, while also promoting plant disease and temperature hardiness, as well as early maturity and enhanced flavor and color in flowering plants (Rienders, 2001, p. 108).

Nutrient Availability and pH

What’s even more important than understanding the parts of plant food, is realizing the potential these elements have under ideal conditions. The unit of measurement which directly affects the uptake of fertilizer in any hydroponic and soil-based system is the pH, or, the potential hydrogen of a given nutrient solution or substance. pH is the measurement of acidity or alkalinity in any given substance on a scale of 0-14, with 7 being neutral. In the field of gardening, however, pH is the main factor that dictates the uptake of nutrients in the root zone; and so, depending on the pH of your plant’s medium and nutrient solution, your plants may uptake more or less of a specific element.  Author of The Growers Handbook, David Robinson, dives deeper into the subject of nutrient uptake, availability, and pH, by stating: 

pH is an essential factor in the uptake of nutrients. While available nutrients remain fairly stable in regular soil, pH fluctuations in a hydroponic garden will dramatically affect whether nutrients are more or less available. Study the chart provided to understand how different nutrients are more or less available on different sides of the scale.

(Robinson, 2012, p. 14)

The pH Scale and Nutrient Uptake

The chart that Robinson mentions can be found below; this guide illustrates a list of available elements that have the potential for uptake at various pH levels. As you can see, for plants, the “sweet-spot” for nutrient uptake seems to fall between the ranges of 6.0 – 6.5. At this level, plants have the ability to uptake essential macro-elements such as nitrogen, phosphorus, and potassium discussed in the former half of this article. Furthermore, at an adequate pH range, plants have access to abundant sources of micronutrients which help ward off common deficiencies and lead to the faster and healthier development of new growth. 

Tiers of Feeding: PPM

Another tool of measurement available to gardeners is PPM, or Parts Per Million, which measures the concentration of a nutrient solution (Robinson, 2012, p. 17). The affordances of this tool have led to some general conclusions about the tiers of feeding in the gardening community. For fruiting and flowering plants, for example, there is a general consensus regarding the scale at which plants in different stages of growth can be fed. Again, borrowing from The Growers Handbook, David Robinson illustrates this consensus in the lines: 

In most situations, plants do not require a PPM any higher than 1400. Often the same results or better can be achieved without exceeding 1000 PPM. It is very important to know the requirements of the particular plant that you are growing. Some plants are heavy feeders while others can only handle moderate food levels. The size of the plant also plays a role in the amount of food needed. Obviously larger plants can handle more food while smaller plants cannot..

(Robinson, 2012, p. 18) 

If you’re curious about acceptable tiers of feeding throughout the different stages of plant growth, consult the guide below for a general program (Robinson, 2012, p. 18). 

  • Cuttings – 300 PPM
  • Babies – 400-600 PPM
  • Vegetative 700-1000 PPM
  • Flowering 1000-1400 PPM 

Maximizing Nutrient Uptake: Connecting N-P-K, pH and PPM

To maximize the rate at which your plant’s uptake available nutrients, combine the knowledge of this article in your daily gardening practices. First, make sure you’re using a nutrient system with a well-rounded N-P-K ratio. Second, measure and buffer the pH of your nutrient solution to maintain an acceptable range; as stated above, the most common range for steady nutrient uptake is between 6.0 – 6.5. Lastly, utilize available testing equipment to measure the inputs of your garden. PPM is one among many ways of testing the content of your nutrient solution, and is, as Robinson states, “your eyes when it comes to mixing a nutrient solution” (2012, p .19). 

Cover Your Bases 

To ensure a clean, quality-focused crop, cover your bases with a GreenPlanet Nutrients feed program. To learn more about the base nutrient systems offered by GreenPlanet Nutrients, read the blog titled: Understanding the Parts of GreenPlanet Nutrients Base Fertilizer Programs. For all other inquiries, contact a member of the GreenPlanet sales team, or your local garden supply store for product information and purchasing inquiries. 

Check out our Resource Centre for more product information

Works Cited

Reinders, G. (2001). Secrets of High Yield Plant Growth. Cybo Press. 

Robinson, D. (2012). The Growers Handbook: Teachings of the garden sage. Hidden Tribe Publishing 

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