Cannabis pH, EC and PPM: Getting the Root Zone Right

Everything your plant eats has to dissolve in water and pass into the roots, and three simple readings tell you if that hand-off is working. pH tells you if the nutrients are available, EC and PPM tell you how much nutrient is in the water, and the runoff tells you what the roots are actually getting. Get these right and feeding becomes predictable. Ignore them and you can starve a plant sitting in a full tank of food.

Key Takeaways

• These three numbers tell you if your plant can eat. pH decides if nutrients are available, and EC and PPM tell you how strong your nutrient solution is.
• pH decides availability. Aim for 6.0 to 7.0 in soil and 5.5 to 6.5 in coco or hydro, since the wrong pH locks out nutrients even when the tank is full.
• EC and PPM measure the same thing two ways. EC reads nutrient strength directly, and PPM is a conversion of that number, so pick one and stay consistent.
• The 500 and 700 PPM scales are the biggest source of confusion. The same solution reads 500 or 700 PPM depending on your meter, so match your meter's scale to your feed chart, or just use EC.
• Order matters when you mix. Set your strength first by adding nutrients, then adjust pH last, because adding nutrients moves the pH.
• Test the runoff, not only the input. What drains out of the pot tells you what is actually happening down at the roots.

At Barney's Farm, the same lesson comes up again and again: a cheap pH pen and an EC meter prevent more problems than any expensive nutrient ever fixes. Here is what each number means and the exact steps to measure and adjust them.

What pH, EC, and PPM Actually Measure

Three readings, three different jobs.

• pH measures how acidic or alkaline your water is on a scale of 0 to 14, where 7 is neutral. It controls which nutrients your roots can absorb.
• EC, or electrical conductivity, measures how well your solution conducts electricity, which tells you how much dissolved nutrient salt is in the water. It is read in millisiemens per centimetre (mS/cm).
• PPM, or parts per million, is a conversion of the EC reading into a nutrient concentration number. It is convenient, but it depends on which scale your meter uses.

The relationship is simple. pH decides if food is available, and EC or PPM decides how much food is on the table. You need both in range for a plant to feed well.

Why the Root Zone Runs the Whole Grow

A plant does not absorb dry fertiliser. It absorbs dissolved ions, and it can only do that inside a narrow pH window. Push the pH out of range and nutrients lock out, which means they are present in the medium but chemically unavailable, so the plant shows a deficiency while surrounded by food. Feed too strong and the high salt level pulls water back out of the roots, which burns the leaf tips. Feed too weak and the plant runs short. The whole job of these three readings is to keep the root zone in the range where the plant can drink and eat freely.

pH Targets by Medium

The right pH depends on what your roots sit in, because soil buffers swings while soilless media do not.

Aim for the middle of your range on most feeds, and let the pH drift slightly across that band on successive waterings, since different nutrients are absorbed best at slightly different points. Soil is the most forgiving medium here, and a resilient strain like Pineapple Chunk shrugs off minor swings, though the numbers still set your ceiling. Seedlings and late flower do a little better slightly higher, around 6.1 to 6.3 in coco.

EC and PPM: Reading Nutrient Strength

EC and PPM both answer one question: how strong is this solution? EC measures it directly. PPM takes that EC number and multiplies it by a fixed factor to express it as a concentration.

Here is the part that trips up almost everyone. There are two common PPM scales, and the same solution reads differently on each. The 500 scale multiplies EC by 500, and the 700 scale multiplies EC by 700, so a solution at 1.0 EC reads as 500 PPM on one meter and 700 PPM on another. Both are correct. They are simply different scales. US meters like Hanna and most pocket pens use the 500 scale, while Bluelab and Truncheon meters commonly use the 700 scale.

The safest habit is to work in EC, since it never changes between meters. If you use PPM, always check which scale your feed chart and your meter use, and keep them matched. To find your meter's scale, measure a solution and read both values. If 1.0 EC shows 500 PPM you are on the 500 scale, and if it shows 700 you are on the 700 scale.

Target EC and PPM by Stage

Your plant wants more food as it grows, then less at the very end. These ranges suit most soil and coco grows, using the 500 PPM scale. Hydro usually runs a little lighter, and different strains vary, so treat them as a starting point and watch the plant.

Start light and build up. Lighter feeding is safer, and many growers find it improves flavour, so it is better to feed a little under and raise the strength than to burn the plant and have to nurse it back. Your starting water matters too, since hard tap water can already read 200 to 300 PPM before you add anything, so keep your base water below about 0.3 EC or use filtered water.

The Tools You Need

Two cheap meters cover everything, plus the solutions that keep them honest.

• A pH pen reads the acidity of your water and runoff. A digital pen costs little and beats color-drop kits for precision.
• An EC or TDS meter reads nutrient strength. Many pens combine pH and EC in a single unit.
• pH Down and pH Up adjust your solution. pH Down is usually phosphoric acid, and pH Up is usually potassium hydroxide.
• Calibration solutions keep both meters accurate. You need pH buffers at 4.0 and 7.0, plus an EC calibration standard for your meter.

How Often Should You Test?

How often you check depends on your medium, because the buffer in the medium decides how fast things drift.

• In soil, test your input water on every feed and check the runoff about once a week. The medium holds steady, so daily readings are rarely needed.
• In coco, test the input on every feed, since coco holds almost no buffer and the pH can move quickly between waterings.
• In hydroponics, check the reservoir daily. With no medium to steady it, the pH and EC can drift within hours, especially as the plants drink the tank down.

How to Measure Your Values, Step by Step

Do this every time you mix a batch. It takes two minutes and saves whole grows.

• Calibrate your meters first. Dip the pH pen in the 7.0 buffer and set it, then repeat in the 4.0 buffer. Calibrate the EC meter with its standard solution. Recalibrate every few weeks, or sooner if readings look off.
• Warm and mix your water. Bring the water to around 66 to 70°F (19 to 21°C), then add your nutrients at the strength on the label and stir well.
• Measure EC or PPM. Dip the meter, let the number settle, and compare it to your stage target. This reading is your nutrient strength.
• Adjust the strength if needed. Too high, add plain water to dilute. Too low, add a little more nutrient. Re-stir and re-measure until you hit the target.
• Measure and set pH last. Only once the strength is right, check the pH, because adding nutrients changes it. Adjust to your medium's range, then re-measure.
• Feed, then test the runoff. Water your plants, catch some of what drains out, and read its pH and EC to see what is happening at the roots.

How to Adjust pH, Step by Step

Small moves, then re-test. It is easy to overshoot.

• Measure first. Read the pH of your mixed, nutrient-loaded solution, since the nutrients shift it.
• To lower pH, add pH Down. Add a few drops per gallon, stir, wait a moment, and re-measure. Repeat in small steps instead of dumping a large dose.
• To raise pH, add pH Up. Add it the same way, a little at a time, stirring and re-testing between additions.
• Land in range and recheck. Aim for the middle of your medium's target, then confirm the reading held before you feed.

Always adjust the strength before the pH, never after, because adding nutrients once the pH is set will move it again.

How to Adjust EC and PPM, Step by Step

Strength is even simpler to correct than pH.

• Read against your stage target. Compare your EC or PPM to the range for the plant's current stage.
• Too strong? Dilute. Add plain, pH-adjusted water a bit at a time, stirring and re-measuring, until the reading drops into range.
• Too weak? Add nutrients. Add a small amount of your nutrient mix, stir, and re-measure, building up slowly.
• Recheck the pH afterward. Any change to the strength can move the pH, so confirm it before feeding.

Reading the Runoff

Input readings tell you what you gave the plant. Runoff readings tell you what the roots are living in, which is what actually matters in soil and coco. Catch a little of the water that drains from the bottom of the pot and read it.

• Runoff EC lower than input. The plant is drinking and feeding well. This is what you want to see.
• Runoff EC higher than input. Salts are building up around the roots, so flush the medium with plain pH'd water to wash them out.
• Runoff EC about the same as input. The plant may not be taking up nutrients, often because the pH is off, so check and correct it.
• Runoff pH out of range. The root zone has drifted, which can cause lockout, so adjust your input pH to nudge it back.

How to Flush a Locked-Out Plant

When the runoff EC climbs above your input, or the leaves show signs of lockout, a flush resets the root zone. It washes the built-up salts out of the medium so the plant can feed again.

• Mix plain, pH-balanced water. Match the pH to your medium's range, with no nutrients added.
• Run it through slowly. Pour water equal to about two to three times the pot's volume through the medium, letting it drain fully each time.
• Test the runoff as you go. Keep flushing until the runoff EC drops back near your input reading.
• Let it dry back, then feed lighter. Wait until the pot lightens, then resume feeding at a lower strength than before so the buildup does not return.

Common Mistakes to Avoid

A few habits cause most root-zone problems, and all of them are easy to fix.

• Never calibrating the meters. An uncalibrated pen lies to you, so calibrate on a schedule and trust the numbers only when you do.
• Mixing up the PPM scale. A 700-scale reading against a 500-scale chart looks like overfeeding, so keep your scale and your chart matched, or use EC.
• Setting pH before strength. Adding nutrients after you fix the pH moves it, so always set EC first and pH last.
• Chasing perfect numbers. Small drift is normal and even helpful, so correct only when a reading sits well outside the range instead of fiddling constantly.
• Ignoring the starting water. Hard tap water carries a baseline of dissolved solids, so measure it first and factor it in, or filter it.
• Feeding too strong. More is not better, so start light and build up, since it is easier to add food than to recover a burned plant.

Frequently Asked Questions

What is more important, pH or EC?

Both, and they work together. EC sets how much food is available and pH decides if the plant can absorb it. A perfect EC does nothing if the pH is locking nutrients out.

Should I use EC or PPM?

EC, if you have the choice. It reads the same on every meter, while PPM changes with the scale. Use PPM only to cross-check a feed chart, and match the scale.

What is the difference between the 500 and 700 PPM scale?

They convert the same EC into different PPM numbers. A 1.0 EC solution reads 500 PPM on the 500 scale and 700 PPM on the 700 scale, so both are right, just measured differently.

Do I need to check pH in soil?

Yes, though soil is more forgiving than coco or hydro because it buffers swings. Checking your input water and occasional runoff still catches lockout before it shows on the leaves.

How often should I calibrate my meters?

Every few weeks for regular use, and sooner if a reading looks wrong or the pen has taken a knock. Store the pH probe in its storage solution, never dry, to keep it accurate.

Why is my runoff PPM higher than what I fed?

Salts have built up in the medium around the roots. Flush with plain pH-balanced water until the runoff drops back into range, then return to feeding at a lighter strength.

Where This Leaves Us 

pH, EC, and PPM are the dashboard for your root zone. pH keeps nutrients available, EC and PPM keep the strength in range, and the runoff shows you what the roots actually get. Calibrate your meters, set your strength before your pH, match your PPM scale to your feed chart or simply work in EC, and read the runoff to catch trouble early. None of it is complicated once you have done it a few times, and it turns feeding into a routine you can trust instead of guesswork. Get the root zone right, and the plant takes care of the rest.

Barney's Farm has been developing premium cannabis genetics since the 1980s, with over 40 Cannabis Cup wins. Explore our full seed catalog and find strains bred for every climate and skill level.