pH 101: The Crash Course
Lesson One: The Basics
So, what exactly is pH? It stands for "potential hydrogen," and it basically tells you how much hydrogen is hanging out in a solution and how active those tiny particles are.
The pH scale goes from 1 to 14. Think of it like this:
1 is super acidic.
14 is very alkaline (the opposite of acidic).
7 is perfectly neutral.
Here's where it gets interesting: every single jump on this scale represents a ten-fold change in acidity or alkalinity. For instance, water with a pH of 5 is 10 times more acidic than water with a pH of 6, and a whopping 100 times more acidic than water with a pH of 7! This is why keeping a close eye on your pH is so important.
The pH of your plant's growing medium—be it soil, a soilless mix, or water—directly impacts how easily nutrients dissolve and become ready for your plant to use.
Generally, for plants in soil, the sweet spot for pH is 6.5 to 7. That said, some plants are a bit picky and prefer slightly more acidic or alkaline conditions.
If you're into hydroponics, the ideal pH range for your nutrient solution is 5.5 to 6.5. Again, some specific plants might be okay with more acidic solutions.
Lesson Two: How pH Affects Plant Growth
Plants are just like us—they need a balanced diet to grow big and strong! While most growers know about the big three (nitrogen, phosphorus, and potassium, or “NPK”), there are actually thirteen additional nutrients that are vital for your plant's development.
If the pH is either too low (too acidic) or too high (too alkaline), those essential nutrients can't get into the plant. What happens instead? The unused nutrients can build up and form salts, which then make it even harder for your plant's roots to take in water.
Before a plant can absorb a nutrient, that nutrient needs to become soluble, meaning it can dissolve and be absorbed. Each nutrient has its own special pH range where it becomes soluble. If the pH falls outside this perfect range, you can run into something called nutrient lockout. This is essentially your plant starving, even if there are plenty of nutrients around, because it just can't access them.
Also, if your soil is too acidic, it can discourage helpful soil microbes from doing their job. These tiny helpers are super important for assisting your plant with nutrient and water uptake.
Lesson Three: How To Measure pH
Knowing where your pH stands is the first step!
Measuring pH in Soil or Soil-less Mix
Soil pH Meter: This is arguably the quickest and easiest way to get an accurate pH reading right in the root zone. These handheld meters use a probe to measure hydrogen ions. Just make sure your soil is moist for an accurate reading.
Runoff Method: This method is great for potted plants. First, water your plant with your usual water and let it drain completely. Then, place a saucer under the pot and pour distilled water (which has a neutral pH) into the soil. Collect the runoff and test its pH using test strips or liquid drops.
Dilution Method: Take one part of your soil sample and mix it thoroughly with two parts distilled water. Let it settle, and once all the particles are at the bottom, test the water with a pH test kit.
Measuring pH in a Hydroponic Solution
For hydroponic systems, you'll usually test the nutrient solution in the reservoir. However, you can also install in-line monitors in systems where the water circulates, or test the runoff in certain setups.
pH Meters: Just like with soil, handheld meters are a fast and easy way to get accurate readings here.
pH Test Kits: These kits (or strips) involve taking a small sample of your nutrient solution to figure out its pH.
Lesson Four: How To Adjust pH
Okay, you've measured your pH and found it's off. Here's how to bring it back into line.
Adjusting pH in Soil
To INCREASE pH (make it less acidic):
Dolomitic Lime: This helps stabilize soil pH and keeps it near neutral when mixed in.
Hydrated Lime: This dissolves in water and changes pH quickly. Be careful not to use too much, as its fast action can harm plants. Sometimes growers use a mix of both hydrated and dolomitic lime for both quick and long-term effects.
Egg Shells, Oyster Shells: These can increase pH in acidic soil, but they take a long, long time to break down and affect the pH.
Wood Ash: Wood ash is pretty high in pH (usually around 9-10) and it's easy to overdo it. Make sure you know where the ashes came from to avoid adding bad stuff to your soil.
To DECREASE pH (make it more acidic):
Elemental Sulfur: Sulfur lowers pH in alkaline soils and is generally safe and easy to use if applied correctly.
Adjusting pH in Hydroponic Solutions
pH Up and Down Solutions: These commercial solutions are designed to be added to your nutrient reservoir as needed. Always follow the label instructions. A good starting point is usually about 1mL per gallon. Mix well and retest the pH after about 20 minutes. Using these commercial mixes is often recommended because they contain a "buffer" that helps prevent wild pH swings.
For quick, DIY adjustments (use with caution, as they lack buffers):
To raise pH:
Potassium Hydroxide
Baking Soda
To lower pH:
Vinegar
Citric Acid (like lemon juice)
Crash Course Graduation Day
Now that you’ve made it through our crash course, you’re ready to tackle the pH in your own garden. Understanding and managing your pH is a game-changer for plant health. By keeping these levels in check, you're setting your plants up for success and ensuring they get all the good stuff they need to truly thrive. Good luck and happy growing!
