Is Your Soil Lying to You? Runoff Checks Reveal the Truth

When you water your cannabis plants in pots, you probably trust your soil to hold nutrients, drain properly, and keep your roots happy. But here’s the kicker: soil doesn’t always tell the truth. It may look fine on the surface while silently holding too much salt, locking out nutrients, or swinging pH levels that make your plants suffer. The best lie detector? Runoff checks.

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What Is Runoff and Why Should You Care?

Runoff is the water that drains out of the bottom of your pot after you water. To most growers, it looks like excess moisture. In reality, it’s a snapshot of what’s happening in your root zone. By collecting and testing this water, you can measure pH and nutrient levels to see if they match what you think you’re feeding.

• pH tells you whether your plant can absorb nutrients properly. Even the perfect feeding schedule won’t work if pH is too high or low.

• EC (electrical conductivity) or PPM (parts per million) tells you how concentrated the nutrients are. Too high = nutrient lockout or burn. Too low = deficiency risk.

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Signs Your Soil Might Be Lying

Not sure if runoff checks are worth your time? Here are some classic red flags that your soil isn’t being honest:

• Yellowing leaves despite feeding → nutrients are locked out by pH imbalance.

• Crispy leaf tips → salts are building up in the soil, making the medium toxic.

• Slow growth or drooping → your plant’s root environment doesn’t match your feeding routine.

• Stubborn deficiencies → you keep adding nutrients, but your plant keeps asking for more.

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How to Perform a Runoff Check (Step-by-Step)

1. Water Normally – Use your usual feeding solution until water begins to drain from the bottom of the pot.

2. Collect the Runoff – Place a clean tray or container under the pot to catch 10–20% of the water.

3. Measure the pH – Use a calibrated digital pH meter. Cannabis thrives in 6.0–6.8 for soil.

4. Check EC/PPM – A digital EC or TDS meter reveals nutrient concentration. Compare it to what went in.

5. Interpret Results –

   • If runoff pH is far outside the 6.0–6.8 range → nutrient uptake is compromised.

   • If runoff PPM/EC is much higher than your input → salt buildup.

   • If runoff PPM/EC is much lower → soil may be “eating” nutrients, or your plant is extra hungry.

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Fixing the Lies: Solutions for Common Problems

• High Salt Buildup → Perform a flush with clean, pH-balanced water until runoff EC/PPM drops closer to your input.

• pH Out of Range → Adjust your nutrient solution gradually, or use soil amendments like dolomite lime (to raise pH) or elemental sulfur (to lower pH).

• Nutrient Depletion → Consider refeeding with a balanced solution, or top-dress with organic amendments to replenish the soil.

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Pro Tips for Consistent Truth Checks

• Test regularly – once every couple of weeks during veg and flower.

• Keep a logbook – track pH, EC, and what you fed that day. Patterns reveal themselves fast.

• Don’t rely solely on meters – trust your eyes too. Runoff confirms what your plants are already showing.

• Beware cheap soil mixes – some potting soils swing wildly in pH after a few waterings.

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The Bottom Line

If you’re only trusting the look and feel of your soil, you might be getting played. Runoff checks are like reading your plant’s diary—they reveal the hidden truth about pH, nutrient buildup, and root-zone health. By taking just a few extra minutes to test, you can prevent lockouts, save nutrients, and keep your cannabis plants thriving from seedling to harvest.

So the next time your plants start whispering for help, don’t just look at the leaves. Check the runoff—because soil doesn’t always tell the truth.

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👉 Whether you’re chasing bigger buds, fixing tricky problems, or just watering your plants without second-guessing yourself, we’ve got your back. Happy growing! 🌱✨ Check out our website for more helpful tips on growing great weed.