How Often to Water Cannabis?

How Often Should Indoor Plants Be Watered

What do you need to know about watering your indoor cannabis plants? How much water do you give them? How often to water cannabis? Does the water need treating in any way?

This editorial will take a look at all you need to know about watering cannabis indoors. From growth stage to pH level. From watering mistakes to measuring PPM. Watering cannabis plants isn’t as simple as filling a bucket from your kitchen sink, but it’s not exactly rocket science, either.

The essentials of watering indoor cannabis plants

Indoor cultivation gives you far more control of the environment, meaning you can optimize 99% of the growing conditions. The flip-side is that more attention must be paid to watering frequencies, quantities and purities. In the absence of rain or other natural phenomena, indoor plants solely rely on the water provided by you, the cultivator.

Cannabis Water System

What sort of water do cannabis plants need?

Cannabis plants need a specific type of water to really thrive. Unsuitable or poor water quality can negatively impact processes such as transpiration and photosynthesis. When this happens, the plants will wilt and droop, ultimately leading to sickly plants with lighter, poor quality yields.

To prevent such problems, the Potential of Hydrogen (pH) levels and parts per million (PPM) of the water need to be monitored.

pH level. This is the numerical scale used for measuring the acidity or alkalinity of a substance. The pH level has a significant impact on how the plants absorb nutrients. As such, water that is too alkaline or acidic can cause problems with nutrient uptake. Your water must be kept within the ideal pH range of 6.0 to 6.8 so your plants can best absorb the different minerals they need for growth.

Your growing medium has pH levels, too, so it’s important to measure the run-off water. If it’s too acidic, dissolving garden lime can increase pH levels. If it’s too alkaline, adding white vinegar will decrease the pH levels. You can also buy products that raise or lower pH levels.

PPM. Parts per million is a measurement of nutrient minerals present in the water. It can be measured and monitored with the aid of a ppm meter. Too many minerals can cause burning, while too few can lead to deficiencies. Measuring ppm helps the grower stay within optimum ranges.

In the case of cannabis plants, optimum levels depend on growth phase. Plants in the vegetative phase do well with a ppm of 500, but 1000ppm is ideal during the flowering stage.

Not all minerals and dissolved solids are advantageous to cannabis plants. Harmful bacteria and pollutants could be contaminating your water, and these can only be removed with the use of filters. Reverse osmosis filters can remove 95% to 99% of dissolved salts and bacteria in the water, and they’re a good way to get your water to acceptable, pre-nutrient levels.

How often should you water cannabis plants & how much

Okay, so you’ve prepared some high-quality water for your cannabis plants, how much do you give them and how often? Cannabis plants have different watering requirements depending on things like growth stage, geography, pot size and growing medium. Let’s take a look at the things to think about when creating a watering schedule.

1. How does growth stage affect how much I water my cannabis plants?

Cannabis Seed Sprout

Cannabis plants in different stages of growth require different amounts of water. It’s impossible to say something like 2 weeks flowering = 2 gallons, because there are so many other things to consider.

  • Seedlings. Seedlings require less water less often. Their roots are small, the pot is small and the volume of soil* is small. 
  • Vegetative stage. During this phase, you need to start increasing your waterings according to how much your plants are consuming. The best way to do this is to cycle wet to dry. Plants can also absorb moisture from the leaves but taking on water this way doesn’t help to grow solid roots.
  • Flowering stage. During the flowering stage, volume and frequency of watering should be reduced to a minimum. Excess moisture will encourage mold in the buds. During late flowering, the plants need to be flushed with pure water so they use all their nutes. This will mean more natural-tasting flower post-harvest.

2. How does geographical location affect how much I water my cannabis plants?

In warmer climates, plants need to be watered more often. Heat causes moisture in plants to evaporate and transpire at a faster rate. In really hot climates, your plant could dry up in a day or less after watering.

Cannabis plants grown in cooler locations will lose less water through evaporation; they’ll generally need fewer waterings.

3. How does the size of the plant and container affect how much I water my cannabis plants?

New Grown Marijuana On Bucket

Generally, large plants like sativa-dominant Hazes and Diesels must be planted in big containers. The bigger the container, the more water you’ll need to cycle wet to dry. Smaller plants like certain indica-dominant Afghans and Kushes will sit in smaller pots and require less water.

Generally, seedlings are planted in small, square inch starting pots and given small amounts of water. Once their root systems develop, the plant is transplanted to a bigger pot to start vegging. This is an excellent opportunity to see if the plants have healthy roots. White, thick and well-developed roots are an indication that the plants have been watered well.

You could also plant the seedlings directly into a large (final) pot to avoid a future transplant. If you decide to do this you should be wary of overwatering. A huge mass of wet soil can put too much pressure on the root system, even when cycling wet to dry. 

Tip: Try watering to 50% of the pot’s capacity, focusing the water in column around the base of the main stem. Gradually increase the amount of water until the root system is big and healthy.

4. How does room temperature affect how much I water my cannabis plants?

Geographical location can affect the temperature of both indoor and outdoor cannabis grows. Growing indoors, though, has one significant benefit over the outdoors – you’re in control! With fans and air conditioning, you can maintain any temperature you desire (within reason).

5. How does growing medium affect how much I water my cannabis plants?

Cannabis Sprout On Soil

Different growing mediums have different absorption and drainage rates. This will affect how often you need to water your cannabis plants when cycling wet to dry.

  • Soil. With soil, try poking a finger 1 to 2 inches into the soil. If it feels dry, then it’s time to water it again. When it’s time to water, make sure you add enough to saturate the soil – you will know you’ve added enough when you see water running out from the drainage holes.
  • Coco coir. This medium has excellent water retention with a watering requirement similar to soil. Use the same cycling but if the coco coir remains wet for more than 3 days, it means you overwatered and you should use less next time.
  • Rockwool. This medium has dense and porous fibers that allow for high water absorption and excellent drainage. This means, generally, less waterings.
  • Perlite. This pH neutral medium can trap water and slow down evaporation. It requires less frequent watering due to high water retention.
  • Vermiculite. Generally, vermiculite is a light medium that has excellent water retention. Hence, it’s often mixed with other media.
  • Clay pellets. This pebble-like medium has high water retention. Clay pellets, because of their porous surface, drain water quickly thus requiring more volume, less frequently.

6. How does humidity affect how much I water my cannabis plants?

The amount of moisture in the air mostly depends on the temperature and ventilation of the cultivation area. In an enclosed space with big plants, your humidity level can rise beyond optimum. If the environment is too humid, your cannabis plants will decrease transpiration and water will not evaporate from their leaves. Therefore, less frequent watering is needed. It is vital to determine the moisture level to prevent overwatering.

Drainage System

Your plant pots need to be able to drain. The simplest way is to make sure water can exit the pots via holes in the bottom. This allows run-off water to flow outside the container – preventing a build up of stagnant water around the roots. When water accumulates, the roots get submerged and can drown due to lack of oxygen. Excess water also puts your plants at risk of pathogens and diseases such as root rot.

To ensure that a pot or container has a proper drainage system, observe how long it takes for the water to drain out. If it takes more than a few minutes, the medium itself may be holding too much water. Try mixing dense mediums with lighter ones, such as perlite, to loosen the soil.

Flood-and-Drain System

The flood-and-drain system involves placing potted plants in a tub attached to a reservoir. When it’s time to water the plants, a pump is turned on until the entire tub is “flooded,” letting the plants absorb water through the drain holes. After a few minutes, the water is then “drained” back to the reservoir.

Healthy Roots Of Marijuana

This system is limited to plants with roots that have reached the bottom of the container. Also, the water needs to be replaced every week to prevent bacteria and pollutants from building up.

Cannabis watering problems and how to fix them

Overwatering cannabis plants

Excessive watering inhibits plant growth. Some problems that result are drooping and root rot. However, the signs are easily observed and corrective measures can be promptly applied.

  • Drooping. An abundance of water and lack of oxygen causes drooping. This is because overwatering can force plants to store more water in the leaves. This, in turn, causes the leaves to curl down and droop. Unlike wilting leaves, drooping leaves will look very firm with some discoloration. This condition negatively impacts the growth of the plant.
  • Root rot. This plant disease occurs when the roots of the cannabis plant are deprived of oxygen, as well as when there is not enough oxygen dissolved in the water. This will cause the plants to grow slower, lose strength and become prone to pathogens, causing the root to rot.

The solution to overwatered cannabis plants

When the symptoms of overwatering occur, it’s best to water less often. The key is to wait for the soil or medium to feel dry before watering it again. Make sure the plants have proper drainage to ensure no water accumulates at the bottom of the pots. Drainage helps expel water and leaves the soil with a healthy moisture level.

In case of root rot, adding a few tablespoons of hydrogen peroxide into the water helps to both kill bacteria and provide oxygen to the roots – solving two problems at once.

Underwatering cannabis plants

This problem occurs when the plants aren’t given enough water. It could also be caused by using a large pot for small plants or an environment that is too hot. Either way, it causes wilting and significantly slows down the plant’s growth. If you allow the soil to completely dry, your leaves will shrivel and shrink and the plant will very quickly die.

The solution to underwatered cannabis plants

Such predicaments can be easily remedied simply by providing enough water. However, it may be difficult – if not impossible – to revive severely damaged plants that have been underwatered for a long time.

Using water with a pH of 6.0 to 6.8 helps rehydration and recovery. Water can also be sprayed directly on the leaves to help revitalize the plant. Once the plant seems to have regained strength, use fertilizers to help restore any nutrients that were lost.

Maximize yields with proper watering practices

One of the goals of cannabis cultivation is growing huge, prolific yields. This will never happen if you do not know how and when to water your cannabis plants. Poor watering practices lead to weak roots, sickly leaves, smaller buds, light yields and weak cannabis. That said, if you can master the art of feeding and watering, of cycling wet to dry, your plants will have a great chance of producing big yields of top-quality cannabis.

High Potency Cannabis

About the author: Derek LaRose

Also known as Kronic from The Cannabis Kronicles, Derek LaRose is a young ambitious cultivator and a staple educator for indoor cultivation.

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