The Perils of Over and Under Watering Cannabis

Gardeners with a green thumb seem to have a feel for it. How do they intuitively know exactly when to water, and how much? But to the rest of us, the chore of watering isn't as straightforward and logical. Yet watering is critical to cannabis cultivation. Without the right balance, too much or too little water will slowly kill your crop. 

Getting it right is one of the first steps to a successful grow. If your plants are two wet or to dry, you need to know how to correct it.

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 This is a loaded question. Are you growing indoors or outdoors? Hydroponically or in soil? How large are the containers you have the plants growing in? There are so many factors that differentiate one set up from the next, that there is no easy answer that covers them all. 

But even if you'll always need to customize the watering schedule to your specific grow setup, there are a few rules of thumb to follow:

• When to Water Soil: Water when the soil has dried out one to two inches under the surface. Use your finger or a moisture meter to test.
• When to Water Coco Coir or Other Soilless Medium: Coir should never entirely dry out. Typically requires more frequent watering than soil.
• Container Size: The larger the container, the more water required to maintain ideal moisture content, but the better the moisture retention.
• Read the Runoff: During watering, the excess water (runoff) is an easy measurement for when the soil has reached peak moisture absorption. Aim for 10 to 20 percent runoff.
• Moisture Meters Simplify Matters: Not sure about how you can tell the ideal moisture level? Rely on a digital moisture meter to do it for you. 

• Droopy or wilted leaves
• Yellowing leaves
• Stunted growth

There are two reasons why your plants might be showing the signs of overwatering. The first is you are watering too much. The second is that you are watering too frequently.

The first signs appear immediately after a good dosing. You'll notice the leaves begin to drop. Although they still feel supple and healthy, they begin to wilt. Over time, with continued overwatering, you'll start to notice lower leaves turning yellow—eventually, chronic overwatering stunts the plant's growth. 

Overwatering saturates the root system to the extent that the roots cannot breathe. Although we often assume plants absorb all the oxygen they need through their leaves, much of the oxygen absorption happens underground through the root system. A cannabis plant will literally drown if the soil doesn't have enough space between the soil particles for oxygen to exist. Overwatering is a surefire way to suffocate your plants.

• Droopy or wilted leaves
• Yellowing (or browning) leaves
• Leaves curling under
• Leaves feel papery, slightly crispy

Yes, some of the very same signs and symptoms of overwatering turn out to be similar for the signs of underwatering. It's the subtle details that help you determine what the specific problem is.

If you see droopy and wilted leaves before you water, and the soil is dry out, chances are this is now a case of underwatering. If you see wilt happening after watering, then this is a problem with too much water. Over time, continued underwatering will cause some leaves to yellow, and eventually die off. You also may notice the leaves become brittle, almost papery. Curling leaves is the second sign of ongoing underwatering.

If you suspect you have overwatered your plants, how can you reverse the damage? Unsurprisingly, you'll have to start watering less. Use the finger test to begin checking the moisture of the soil (near the roots). Check every day until you notice a pattern. Only water if the soil feels dry roughly inches below the surface. 

Also, don't forget to consider the soil. Certain mixtures simply contain too much clay and have extremely high moisture-retention. While it may be too hard to fix for the current setup, consider a new mixture with better aeration and soil structure for your next crop.

A final tip for reducing the risk is ensuring your containers do not sit in standing water. If you collect runoff in a dish or tray under each container, make sure to drain them every time.

The first step to curing a case of underwatering is to water more. But what does that mean? During the first attempt, water thoroughly until the container is well saturated. You should water your plants until there is a significant natural runoff to ensure that you've completely rehydrated the container.

Following this initial reset, you'll want to check back daily. Using the finger test, ensure the soil still feels moist underneath the surface. If it has dried out, it's time for another watering. Although this time, it should require less. 

Whether you are experiencing a case of over- or under watering, it will take a week or so to settle into a new schedule. That means checking the plants every day, assessing the soil's moisture level, and watering if needed. Most soil-based operations will require watering every few days, but again this varies wildly based on the specifics. You can simplify everything with an irrigation system like the Blumat Automatic Watering Kits, or even a simple Digital Moisture meter.  

Watering is supposed to be the easiest step to growing cannabis, but as many growers have found out, that's not always the case. For new growers, it can be extremely challenging to determine the ideal watering schedule. Yet, even experienced growers could run into issues when they tweak the growing environment or head off on vacation. Nothing is as heart sinking as returning to the grow room only to see unhappy plants.

Knowing the signs of overwatering or underwatering help, you take control of the grow room. Making little adjustments to frequency and timing can make all the difference. With daily checks, and a routine schedule, a watering wrong can soon be righted.