Watering Techniques

Sometimes even the most basic requirements are overlooked by cannabis gardeners

Growers have to find the perfect balance between overwatering and underwatering. Photo courtesy of Water Pulse.

On the surface, watering a cannabis crop seems fairly straightforward. But the subject is much more complex than “just add water” — particularly when it comes to growing the healthiest plants possible.

Different sources of water — wells, city systems and rainwater among them — require different treatment methods and filtering before they’re safe for cannabis plants. Getting water to the ideal pH level and temperature can also help plants absorb more nutrients to help unlock their full potential. Plus, there’s the basic fact that having a good handle on water can save money, says Tim Cullen, CEO of Colorado Harvest Company, a major Colorado grower.



The Hanna Instruments pH tester (HI 98100) has been a reliable friend for growers, due to its automatic calibration, just-add-water instructions, low maintenance and a suggested retail price of under $50.  Each model has a built-in automatic shut-off feature and an internal 1,000-hour battery life. The tester comes with its own cleaning solution that can be easily replaced by distilled or deionized water and a clean toothbrush.

To use the HI 98100, fill a small container with the test water, insert the sensor and wait for the LED screen to display the pH level. Growers should be aware that the scale for measuring pH is logarithmic, so each pH level is 10 times as potent as the one before and that “close enough” can be deadly to plants.

More information: hannaisnt.com.

Water Pulse

There are millions of square feet of WaterPulse watering mats being used in greenhouses and grow facilities throughout the United States, helping businesses save hundreds of millions of gallons of water every year. While most of the mats are being used in traditional agriculture, they also have the potential to help cannabis growers save water, reduce expenses and increase yields.

These easy-to-use mats take advantage of the natural capillary action of soil to deliver water and nutrients uniformly, for less plant loss, faster growth and higher quality crops. This uniform watering and reduced plant maintenance translates to lower water and labor costs, and increased yields.

More information: www.waterpulse.com.

“Water is a vehicle for nutrients,” Cullen says. “Plants need water, but in many cases, it’s the nutrient delivery system as well. And that water can become very, very expensive once you add nutrients. You really only want to water as much as you need to.”

Among the most common problems for gardeners of all plants is overwatering. There’s a tendency for amateurs to believe that if watering is good, a lot of watering must be even better. Overwatered plants tend to turn dark green, curl over and droop. Underwatering can look similar, sometimes with yellowing leaves that also curl over and droop. Overfertilization is another problem that can make the leaves flip over and curl into what looks like claws, Cullen said.

“Healthy leaves should be ‘praying to the gods’ — that’s what we call it,” Cullen says. “They should point up at the sky at a 45 degree angle.”

Adding nutrients to untreated water and overwatering are rookie mistakes that can waste a colossal amount of money.

“If water’s coming out of the bottom of your planters — if you use planters — then you’re wasting it,” Cullen says. “Root rot is another really common disease caused by overwatering. At our grow, we do a light water in the morning and a light water in the afternoon. Our rule is: Don’t put your plants to bed with wet feet. If you have too much water overnight, they will get root rot.”

Analyzing the water source and using the appropriate filters is another way to make sure plants are getting everything they need, says Rich Gellert, president of California-based Hydrologic Purification Systems, which makes a wide variety of filters for the cannabis industry.

Even rainwater collection — which tends to be the most pure form of H2O — sometimes requires a filter. If water is contaminated, vital nutrients like nitrogen, potassium and phosphorus may not be absorbed by plants.

“Rainwater is a unique thing, depending on where you are in the country,” Gellert says. “There aren’t a lot of minerals in there, but there could be particles or other contamination if it’s collected off a roof. There could also be bacterial contamination, which means you need to sterilize it with UV light or chlorination.”

In general, for rainwater, growers should use a sediment filter, a carbon filter, a sterilization technique like UV light, chlorination or ozone and a pH analysis, Gellert says.

Well water can be much trickier to use, because it’s not thoroughly regulated. Before using well water, Gellert recommends getting an expert analysis, because the water could have increased levels of lead, iron or even radioactive elements like cesium in it — and those are all potentially damaging to plants.

“It’s super important to know what you’re working with when you use well water,” Gellert says.

Surface water from a river or stream can also require extra work — it’s often flush with sediment that needs to be filtered out, and it also can be contaminated with bacteria and other biologic elements, he says.

Tap water, which is filtered at a city water treatment plant, is probably the most common water source, but it can have too much chlorine or fluoride, which can damage plants.

“Water is your vehicle, and you need to make sure your vehicle is in good working order before you add nutrients,” Cullen says. “It’s all about knowing your plants and treating them like little living creatures.”

Another critical element is to keep the water’s pH at the right level so that nutrients are properly absorbed. However, the pH level sometimes depend on the grow medium being used, says Robert Kressa, owner of Grow Contractors, a California consulting firm focused on design, build and operations for cannabis growers.

Generally, for hydroponic grows, the pH should be around 5.8; for outdoor soil, the ideal range is between 6.2 and 6.8 or so, Kressa says. (The pH scale is measured from 0 to 14, with 7 being neutral. A pH less than 7 is acidic; higher than 7 is basic.)

“We’re finding that it’s okay to let the pH swing a little though, because that allows different micro- and macro-nutrients that normally wouldn’t be available to become available to the plant,” Kressa says. “You can vary the level by about a point or so for a day or two and that helps plants get more nutrients, but you don’t want to do it for a prolonged period of time.”

Another factor to pay attention to is the temperature of the water.

“Temperature, as far as efficiency goes, you want the water to be 78 degrees,” Kressa says. “But there’s a bit more to it than that. Terpenes and odors tend to reduce as heat increases. So temperatures over 78 degrees with high humidity, plants grow faster and produce more, but you sacrifice flavor. And temperatures under about 72 degrees, the plants grow much more slowly.”

Cold tap water in winter seasons can be a big danger to plants.

“In the northern states, in winter, they have very cold tap water — and that’s going to shock your plants,” Gellert says. “You can’t water straight from the tap. Most people store in reservoirs and use a heater to get it to the right temperature (of about 65-70 degrees). And others use a chiller in summer if the water is over 80 degrees.”

Overall, the best thing to do is pay attention to your plants, because it’s fairly easy to notice when they droop or yellow or otherwise look unhealthy, Cullen says.

“Plants can tell you what they want — you just have to be able to speak their language,” Cullen says.




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