Need help watering your cannabis plants? You’re not the only one. It’s one of the more common issues cannabis growers encounter, probably because it seems so basic on its face that people trust their own instincts.
However, there are several factors you should take into consideration before giving water to your cannabis plants. For example, what’s the best time of day to water cannabis? How often should I water cannabis seedlings?
Keep reading below for answers to all of your cannabis water related questions.
What Type of Water Is Needed For Cannabis Plants?
Cannabis plants are a lot like Goldilocks in that they like their water not too hard, not too soft, but “just right.” They prefer water containing between 100 and 150 parts per million (ppm) total dissolved solids, which is classified as “slightly hard” on the scale of soft to hard water.
The terms hard and soft water simply describe the amount of dissolved solids in the water.
You might be able to skip the filtration system if you have regular access to water in the 100-150 ppm range.
Understanding Total Dissolved Solids (TDS) in Water for Cannabis
Home growers need to buy a Total Dissolved Solids (TDS) meter so you can determine if your water is too soft or too hard. Measuring total dissolved solids is as simple as taking a sample of water from the water source you’re interested in using to water your cannabis plants, and using the TDS meter to measure it.
If the water is within the 100-150 PPM range your next step would be to check the pH. If the water is not within the 100-150 PPM range, it’s not suitable for use and you’ll need to come up with filtered water.
Filtering Water For Cannabis Plants
Best Method: Reverse Osmosis
The most common method of filtering water to make it usable for cannabis plants is reverse osmosis water filtration. Sounds complicated but Amazon sells an easy to install reverse osmosis kit for home use.
Installing a reverse osmosis home filtration kit is probably the best option if you’re growing more than a couple plants. Once you get past the initial cost you get as much water as you need until the filters need replacement.
Make sure to get a kit that includes a step for carbon filtration, which will remove chlorine and other contaminants that a regular reverse osmosis system without the carbon filtration stage would miss.
Add CalMag after Reverse Osmosis Filtration
Once you receive water from your reverse osmosis kit, the PPM will be at or near 0, which is too “soft” for cannabis plants. So you’ll need to add some Calcium and Magnesium (CalMag) to the reverse osmosis water until the PPM reaches the acceptable 100-150 PPM range. At that point, it’s ready to be fed to your cannabis plants.
Budget Watering Method For Only A Few Plants:
Another option is to buy your water in an already filtered state, such as distilled water. If you go this route you’ll still need to add calcium and magnesium (CalMag) to the water in order to bring it up to the 100-150 ppm range.
Using distilled water may be practical for small grows, but can become costly the larger your grow is, and the more grows you use it for. So it may be worthwhile to invest in a reverse osmosis system from the outset.
Cannabis Water Filtration Methods To Avoid:
There are other less efficient water filtration methods available, such as ion exchange, activated alumina, and activated carbon, but they all leave the water in an imperfect state for use on cannabis plants.
Running your water through any type of activated carbon filter will remove some of the contaminants but it won’t remove minerals, dissolved solids, or salts. This means you’d risk the water being too hard for your cannabis plants, despite filtering it.
I know people are growing cannabis on a budget, so this would naturally be one of my questions when it comes to watering cannabis as well.
What’s A Good Water pH For Cannabis Plants?
The pH of the water you provide to your cannabis plants will affect the pH of the growing medium, which ultimately affects the plant’s ability to absorb nutrients. The pH of the water used on your cannabis plants can be easily adjusted with this affordable General Hydroponics pH control kit. This kit works for both soil and hydroponic applications.
There are two different water pH ranges you should aim for depending if you’re growing in a solid medium such as soil or coco coir, or growing hydroponically.
The proper pH for growing cannabis in soil is 6.3 to 6.8. If your soil tests inside the 6.3 to 6.8 range, the water you provide your cannabis plants should be in the 6.3 to 6.8 range so nothing changes.
But if your soil tests slightly too alkaline or slightly too acidic, you’ll need to adjust the water pH towards the opposite direction during your next watering, so when the water combines with the growing medium, the medium’s pH adjusts in the proper direction.
The proper pH for growing cannabis hydroponically is 5.5 to 6.1. The pH of your reservoir will gradually change as your plants grow and absorb nutrients. This requires regular monitoring of the reservoir water pH. Whether you decide to replace the entire reservoir or re-adjust the pH, you should add a small amount of pH adjuster, test your water, then add more adjuster if necessary.
How Often Should I Water Cannabis Seedlings?
This is a very common question I receive from new growers, and over-watering cannabis seedlings often the first fatal mistake a new grower will make. There’s no preset watering schedule you can use for cannabis at any stage of growth.
You want water to reach the roots, and you want to avoid making the soil so wet that it takes forever to dry out. When the soil does dry out, it’s time to re-water. You can also use a soil moisture meter to help you determine when the soil has dried.
A shallow flat tray may require more frequent watering, but rockwool cubes and large deep soil pots retain water longer. This is where the moisture meter mentioned above can come in handy.
Also keep in mind you’re better off going light on the water, since your cannabis seedlings will already be absorbing water from the humidity in the air.
In fact, when cannabis is in the seedling stage it gets a large percentage of its water from the humidity in the air. That’s why the recommended humidity levels for seedlings is 60%-65%, higher than what’s recommended for veg and flowering.
How Often Should I Water Cannabis During Veg (Vegetative Stage)?
As the cannabis plants grow in size during the vegetative stage, their water requirements will also grow. Again, there’s no preset watering schedule for any stage of growth.
By the time your plants are a couple weeks into veg, you can expect the root system to occupy most or all of the planter or grow bag, so you should water the grow bag or planter until you see some water come out of the drainage holes at the bottom.
Keep in mind the more you water the longer it’ll take for the soil to dry. This is why the moisture meter can be so valuable, it takes away a lot of guesswork.
Another factor you’ll want to keep in mind is whether your grow pots have drainage and are air penetrable. Air penetrable grow bags and pots with drainage holes are at lower risk for over-watering.
Another factor to keep in mind is the plants won’t be absorbing as much water from the humid air at this stage, so you’ll want to bring the humidity down to about 50%.
How Often Should I Water Cannabis During Flowering Stage?
The flowering stage is when your cannabis plants will need the most water, due to their growing size. As soon as the plants begin flowering, they generally double in size from that point.
The watering advice for the flowering stage follows the lines of the vegetative stage. Even though the cannabis plants will be drinking more water, let the soil moisture continue to guide you during this stage of growth.
What Does Under-Watered And Over-Watered Cannabis Look Like?
Both scenarios can cause broad nutrient deficiency. In the images below, notice the difference between the two scenarios. The leaves on an overwatered plant are drooping downward. The leaves on the underwatered plant are hanging down, but not really drooping. The leaves are still straightened.
An overwatered cannabis plant will look similar to spoiling lettuce. It may look soggy, have a light brown tint in the leaves, and will be droopy. The leaves may also be lime green colored due to the lack of nutrients. The excess water washes away nutrients in the soil before the plant can absorb them. Excess water can also cut off oxygen from reaching the roots, causing root rot.
An underwatered cannabis plant (see image above) will look withered and dry. You may also notice that your plant has stopped growing. Cannabis plants do normally go through periods of slow and fast growth, so slow growth doesn’t necessarily mean underwatering. But having a moisture meter and keeping track of how often you watered will help you make an educated guess. You’ll notice the plant leaves look more lively within a few minutes of watering a thirsty plant.
Keeping on top of watering your plants is important. As noted in this study, the effects of short term water stress include serious plant changes such as reduced leaf area, and regulation of the stomata, which affects the plant’s essential life activities.
How To Fix An Over-Watered Cannabis Plant
There are no guarantees for recovery once your plant is overwatered. But there are some steps you can take to try to save the plant. First, if you dont have drainage holes, drill some in the bottom of your planter. Second, if the plant is still alive when the soil dries out, add a few teaspoons of hydrogen peroxide to your next water feeding. Hydrogen peroxide helps the roots absorb extra oxygen, which is desperately needed during an overwatering scenario.
How To Fix An Under-Watered Cannabis Plant
There are no guarantees when it comes to saving underwatered cannabis plants either. The drought can cause severe damage to the plant. The best method of action to treat an underwatered cannabis plant is to immediately provide it pH balanced water without nutrients.
If and when the plant has recovered, you can add nutrients in the water.
What’s The Best Time To Water Cannabis Plants?
Many growers agree the morning (or when your grow lights turn on) is the best time to water cannabis plants since the plant will have moist soil available throughout the day when it’s receiving light and performing photosynthesis, instead of night time when the plant is resting.
This doesn’t mean that you shouldn’t water your cannabis at night, it’s just what many growers think is logically the best time to provide water.
How Does Air Temperature Affect Cannabis Watering Requirements?
A hotter climate will make cannabis plants thirstier. Growers who use CO2 typically grow in hotter temperatures and should expect higher water requirements not only due to the environment, but due to the faster growth promoted by the CO2.
Your air temperature should be between 70-80 degrees Fahrenheit, or up to the mid 80’s when growing with CO2.
Check Out Our Other Growing Resources:
Thanks for reading my cannabis watering guide! Don’t forget to check out my other valuable growing resources such as my guide to maximizing cannabis yield, my cannabis nutrient guide, my grow light hanging height guide, and my seed buying guide!