All plants need water, that’s an undeniable fact. However, cannabis plants give you their best performance when not just watered, but hydrated with pure water containing nutrients delivered in the correct amounts at the correct times and via the most apt watering methods.
While I’ve been growing cannabis for years, I’m still aware of how tricky watering can be, especially when growing indoors.
Unlike when cannabis is grown in its natural environment, the unique watering requirements for indoor marijuana cultivation mean that the root zone isn’t always as big, porous or expansive as roots need it to be.
In nature — or in 200-gallon porous grow pots outdoors — cannabis roots are able to expand as much as they need to. And water can go wherever gravity and root-zone porosity guides it.
This ample room and the ability of water to move into and out of the root zone freely facilitates healthy roots and optimized nutrient uptake, because roots need mass, branching, aeration and oxygenation.
In an outdoor setting where plants are growing in the earth or in large porous pots, the root zone has a wide top area, so plenty of oxygen is driven into the zone, along with water. Also, outdoor-grown cannabis root zones have a wider bottom/side perimeter, so water can pour all the way through the root zone, with some of it exiting the area from all sides and from the bottom. This creates strong hydraulic flow that cleanses roots and assists their function.
The flushing action of water moving into, through and out of a root zone removes root-zone debris, as well as excess salts.
When water can move downward and sideways, the roots aren’t waterlogged, and when roots are in a non-waterlogged root zone, they’re not drowning in moisture. This healthy flow of water in the root zone means an environment far less habitable for diseases that cause rot root.
What’s In The Water You Use To Hydrate Your Cannabis?
The information here is aimed primarily at people using soil, soilless mix, and coco coir in individual pots. There are different dynamics and strategies for marijuana watering in pure hydroponics systems, such as deep water culture, ebb and flow, aeroponics and with materials such as rockwool.
Of course, it isn’t just the amount of water and how often you water — it’s also what’s in your water. Unless you have access to tested well water, or rainwater with less than 50 parts per million dissolved solids that test 100 percent clean for parasites, poisons and contaminants, then you should be using reverse osmosis water.
Using regular tap water means you’re pouring minerals and contaminants into the root zone. Non-reverse osmosis water inevitably contains compounds that interfere with total control of marijuana feeding.
Starting with zero parts per million reverse osmosis water in a hydroponics garden with an inert medium such as soilless mix, rockwool or coco coir, the grower has to carefully dose the nutrient water to avoid under- or overfeeding.
Underfeeding results in slow growth, lack of vigor and nutrient deficiencies in your cannabis crop. Overfeeding is even more damaging. When too many nutrients are put into the water, the roots burn. Excessive nutrient salts block roots from taking in mineral elements, creating a caustic root zone that drains the life out of plants.
Most hydroponic nutrient brands have inadequate or generic dosing instructions, which likely result in overdosing your plants. This is especially true in grow phase for seedlings and clones.
One of the many reasons why I use Advanced Nutrients is that its grow-phase hydroponic base nutrients contain time-sensitive dosing instructions that acknowledge the fragility of young seedlings and clones. The base nutrient product labels instruct you to start with a small dose and gradually increase it to full strength during grow phase.
Water Outflow Is Essential For Cultivating Cannabis
Even if you’re not putting many nutrients into your water, your cannabis root zone can still end up salty and toxic, affecting root-zone pH and creating a cascade of negative effects that feed off each other.
I recently visited a grow room with a root zone that hinted strongly at watering-related problems. The grower had 14 plants in individual 7-gallon hardened plastic pots in his indoor grow room.
The root-zone media was Pro-Mix BX, a soilless mix. The pots were sitting on two tarps to prevent water from getting to the floor underneath.
The grower was watering 1–3 times per week, depending on plant size and grow-room humidity. In bloom phase, he was using an average of one gallon of water per pot at each watering.
You could lift the pots up before and after watering, stick your fingers into the Pro-Mix, and feel that the root zones weren’t waterlogged. It seemed as if the grower was using the correct amount of water and had a good watering schedule in place — but problems were on the horizon.
He was watering just enough per pot so that each was saturated from top to bottom — yet no nutrient water was running out the bottom of the pots. He didn’t want water pouring out onto the tarp to sit in puddles that create extra humidity and provide a messy milieu for bugs and bacteria. This puddling had happened before, when he used a higher volume of water per pot.
His plants were doing fine until about three weeks into bloom phase. Then they developed leaf-tip burn, which is a sign of over-fertilization, and bud growth had slowed to a minimum.
My friend had been conservative in his feed program, which was averaging less than 1000 parts per million at every feeding. He couldn’t figure out why his plants were burning.
When I observed him irrigating, I saw he wasn’t using enough water to flush about 20 percent of it out the bottom of the pots. No water was coming out at all. He admitted that he never flushed the root zones.
This meant nutrients had built up in the stagnant root zones and were burning his plants. I advised him to immediately flush his plants, but he resisted because he didn’t want a swampy grow-room floor.
Although the plants were large and some were supported by plant cages, they’d each have to be moved to a bathtub to be thoroughly flushed using six gallons per pot of Flawless Finish and reverse osmosis water, at 5.8 pH.
He purchased plant caddies to make the job of moving pots easier, and it took us an entire afternoon and evening to flush each plant, let the root zones dry out so they wouldn’t leak water onto the floors, and move the plants back into position under the grow lights.
Part of the reason it took so long is that his reverse osmosis system wasn’t fast enough in creating the new reverse osmosis water.
Also, for several plants, we stopped up the tub drain so we could capture the runoff and measure its pH and parts per million. The runoff parts per million were as high as 755 and the pH was all over the place, as low as 5.3 (way too acidic) and 6.7 (way too alkaline). These readings are an indication of how toxic and out of sync that root zone had become.
If he hadn’t flushed, his plants would have further deteriorated beyond burnt roots and an inability to intake nutrition, and he may well have suffered a total crop loss.
When It Comes To Hydrating Your Cannabis, Extra Work = Extra Reward
My grower friend had made a mistake by not doing a flush at the end of grow phase and for not planning another flush in the middle of bloom phase. When I explained to him that at every other watering he had to move his plants to the bathtub and use enough water so that about 25 percent of it dripped out the bottom of the pot, he groaned with dismay at the thought of all that extra work.
However, he was pleased to see his plants recovering within five days after our flush, and that switching from General Hydroponics nutes to Advanced Nutrients Sensi Bloom pH Perfect base nutrients had saved his season.
Picture in your mind an outdoor cannabis plant growing in well-aerated soil, where water comes into the root zone evenly throughout the ground diameter of the plant canopy.
In those circumstances, water easily finds its way through root-zone pathways, with some of it flowing out and away from roots. As new water comes in, it brings in fresh nutrition and oxygen, and as it exits the root zone, it carries with it debris and stale nutrients. Always try to duplicate that grow situation when watering your cannabis.
One final word of advice: Added enzymes to your cannabis root zones act as catalysts that help and protect root function.
No matter what kind of cannabis root zone you have, and even if you have to install a drain in your grow-room floor or carry your plants to the bathtub for watering and flushing, do your best to duplicate a dynamic inflow and outflow of water.