Soil Monitoring Tips for a Healthy Cannabis Grow

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If you think growing cannabis indoors will be an action-packed adventure filled with constant excitement, you’ve got a big surprise in store. Although there will be some fun times (as well as stressful times), a grow op can often feel like watching grass grow.

Well, you won’t be watching grass, but you will quite literally be watching plants grow over the next few months. Paying close attention and monitoring the crop is an important way to ensure healthy, hearty plants and catch any problems early on.

But what many growers don’t realize is that it’s just as important to monitor what’s beneath the surface as it is to check in on stems, leaves, and buds. Keeping tabs on the soil health and root systems is vital, so here are some tips on how to do it.

Start Off Right With the Proper Soil

Before you even go about monitoring your soil, the first step is to choose the right one. The growing medium has a lot to do with overall plant health, and not all soils are created equal. There are several different factors to consider for choosing the right soil, including:

  • Texture
  • Water Retention
  • Drainage
  • pH Value
  • Nutrient Content

The way the soil feels, retains water, drains, etc. has a lot to do with how the plants will take up water and nutrients. Don’t even think about taking a shovel to your backyard and using just any old dirt from the ground. It’s crucial that you use high-quality soil from the get-go and continue doing so all the way through to harvest time.

Regularly Check Soil Runoff

In the list of traits to look for above, one of the things listed was “pH value”. pH is a measurement of how basic (alkaline) or acidic a solution is, ranging on a scaled from 0 to 14. A pH of 7 is neutral, anything below 7 is acidic, and anything above 7 is alkaline.

An indoor crop thrives at a certain pH level, and usually, anything between 6 and 7 for soil growing gets the job done. Since pH plays a role in the uptake of nutrients, your plants will suffer when the levels stray outside of this range. It’s really important that you monitor this, and the best way to do that is by checking soil runoff regularly.

How to Check Soil Runoff

To check the pH levels of the soil runoff, you’ll first mix your water with the proper nutrients.

Stir the water for a few minutes, then test the pH by using a pH pen/meter. This guide and reviews on pH pens can help you choose the right pH-testing tool.

If the pH reads anything between 6 and 7, you’re good to go ahead with the watering. If not, use either pH Up or pH Down solution to bring it in the proper range.

After you’ve watered the crop using the properly pH-ed water, the next step is to check the runoff. Since the plants will be in pots with drainage holes, the water should easily run through the plants and come out of the drainage holes.

Right after watering one of the plants, raise up the pot and place a small container (a solo cup works well) under one of the drainage holes to collect the water runoff. Then, using your pH meter, test it. If it’s in that ideal 6-7 range, great! If not, you’ll have to make some adjustments the next time your plants need water.

Soil pH is something that should be monitored throughout the entire grow op, especially after each watering. The good news is that if the pH is off, it’s fairly easy to get it back on track as long as you catch it early.

Flush the Soil Every Now and Then

Aside from pH, another important aspect of soil monitoring has to do with nutrients. If you’re giving the plants too many nutrients, the soil and root systems tend to get blocked up and can lead to something called nutrient lockout. It can also be caused by pH imbalances.

Nutrient lockout presents itself in a few different ways, but it’s almost always caused by high salt content in the soil from over-fertilizing. The best way to fix this problem is to flush the soil with clean, fresh water – just be sure to check the pH of the water before you flush!

It’s also a good practice to flush the soil in the final week of the grow right before it’s time to harvest. This pushes excess nutrients out, which is smart since nutrient buildup can negatively affect the final product.

Control Soil Water Content Throughout

Soil that contains too much water can actually be more harmful than dry soil. The root systems need oxygen to survive, so too much water essentially drowns the roots and keeps them from getting the oxygen they need.

You can monitor soil water content in a few different ways, like check the top level of the soil for over-saturation and lift the pots to feel if they’re heavy with water. Don’t forget to keep the room’s humidity at the right level – too much moisture in the air can actually affect the water content of the soil.


Jack has been a gardening enthusiast for many years and always known to have a green thumb. He's recently started diving more into the science behind how things grow and sharing his findings online.

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