Wouldn't it be great if you could have a reliable, consistent, and precise schedule for watering your cannabis plants?
While that would certainly make growing cannabis simpler, the truth is that these living plants are constantly growing and evolving throughout the various stages of their life cycle, while also responding to the variables of their growing environment. Watering cannabis plants is not a precise science and as a cannabis grower, it's your job to learn the language of the plants.
“Get to know your plants personally," said Lauren St. Pierre, a Harvest Associate at the New England Cannabis Corporation. “Study their behavior, reactions to the environment, and your impact when watering and caring for them."
Of course, if you're new to growing cannabis — even if you're a seasoned Master Grower — becoming attuned to the subtleties of each crop, grow environment, and season is as much an art as it is a craft.
Below, check out professional insights, tips, and tricks for learning how to water weed plants.
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How much water do weed plants need?
Not surprisingly, the answer is: it depends.
Overwatering is a mistake that many new cannabis growers make — and understandably so. Water is essential for the health and development of all plants, so better err on the side of too much rather than too little, right?
While underwatering can be detrimental to plant health, overwatering brings a whole host of problems, too, like the impact it has on roots. In the presence of too much water, roots can not get enough oxygen, they become susceptible to rot and disease, and they cannot provide the rest of the plant with what it needs to thrive.
“Overwatering may result in wilting, yellowing leaves, stunted growth, electrolyte imbalances, and root rot," explained Brody Hall, Certified Horticulturist with The Indoor Nursery. “Don't overdo it. Err on the side of caution when it comes to watering — check the soil often and only give just enough so that the top inch is moist."
What impacts the water needs of cannabis plants?
There are several variables that can impact how much water any particular weed plant needs on any particular day.
Plant size and stage of growth
Larger plants have larger root structures and need more water. Seedlings and young plants will need small amounts of water more frequently because they have such small root systems. As they mature and move through the vegetative stages, the volume of water they need will gradually increase.
Generally speaking, cannabis plants need more water during the vegetative stage and less during the flowering stage. “During the pre-flower 'stretch' they'll consume extra water as the mature plants grow quickly and prepare to flower, then toward the end of the flower stage, they use less water," explained Ed Geis, owner and cultivator of organic hemp at Bald Mountain Botanicals.
Indoor vs outdoor growing
Growing indoors, where there is less variability in the environment, can offer a little more predictability — especially if the environment of your indoor grow is highly controlled and relatively consistent. With outdoor growing, you will have to contend with changes in light, temperature, and humidity while accounting for rainfall and soil conditions.
Growing medium
There are lots of ways to grow cannabis plants and lots of different growing mediums in which to do it. Whether you're using soil, coco coir, rock wool, or another soilless option, how water saturates the medium and how well it is retained will impact watering needs.
Container size
If you're growing cannabis in containers, the size of the container will impact water needs. A general rule of thumb when watering container plants is to aim for about 30% of the volume of the container.
“One major aspect to look out for is using the correct pot size at certain stages of growth," explained Tom Bruggemann, inventor of Tom's Tumbler. “For example, growing a small seedling in a large pot may reduce the plant's chances of getting enough water, as the small root system doesn't have a chance to uptake water before it drains away."
Most growers recommend starting out in a small container and increasing pot size as needed throughout the life cycle.
Temperature and humidity
Not surprisingly, temperature and humidity, whether indoors or out, will impact how much and how often you need to water. The hotter and dryer the environment, the more water your plants will need.
Light intensity
Light intensity may also impact your watering schedule. If, for example, you're growing indoors and using high-intensity lights such as HPS bulbs or CFL bulbs, the extra heat they give off can increase the grow room temperature and may impact your water needs.
When to water weed plants
While some large commercial cannabis cultivation setups may use sensors in the growing medium to know precisely when to water — and have an automated system to then provide said water — there's still an ongoing debate among both commercial and home growers as to the best method for knowing when to water.
Whether you're growing indoors or out, many agree that the plants should go through a wet/dry cycle. That is, allowing the growing medium to dry out before watering. When the growing medium becomes dry, it encourages the plant to extend its roots downwards to look for more water. A large and robust root system helps support healthier and more robust plants.
“A general rule of thumb for watering indoor and outdoor cannabis is to water when the top 1 - 2 inches of soil are dry," said Hall. Here are the common methods for assessing when soil is dry enough:
- Nuckle method: Stick a finger into the soil down to the knuckle, if it feels dry, it's time to water. The same thing could be done with a ruler — if it comes out clean, it's time to water.
- Container weight: The second method involves becoming acquainted with the weights of your containers (if using them). Freshly watered containers will be much heavier than dry containers. You can either learn through repeatedly lifting pots to get an innate feel for them or use a scale to actually measure weights for future reference.
- Moisture meter: Another tool you might want to consider adding to the mix is a moisture meter. These digital devices can be stuck into the growing medium to measure the water content. The probes are generally several inches to a foot long, thereby reaching deeper than your fingers can. The price and quality of these meters vary, and not all meters are appropriate for all growing mediums, so be sure to do a little homework if you want to invest in a good moisture meter.
If you're new to growing cannabis, consider all of these tools for figuring out when to water your plants. “As you maintain your garden, you will see there is a certain rhythm to it all," said Parker Curtis, cultivation expert at Homegrown Cannabis Co., “You will start to learn how often your plants need water and be in tune with them."
How to water a weed plant
Once you know when it's time to water your plants, how do you go about actually doing it?
As stated above, if you're watering seedlings or very young plants, it's best to give them small amounts of water more frequently since their root systems are small and relatively delicate. Misting them is a safe way to do so since a hard stream from a hose or watering container could damage or kill them.
For mature plants, most growers agree that it's best to take a slow and intentional approach that begins at the stem and works outwards. “When watering indoor and outdoor weed plants, it is important to adjust the water stream so that it is gentle and slow," said Mike Biggio, co-owner of Area 420. “This will help the water to absorb into the soil and prevent excessive runoff."
A slow and steady approach will also help maintain the structure and porousness of the soil. When soil becomes compacted, it's harder for water and nutrients to move through it. “Avoid watering with a wide spout watering can, container, or bucket, as this can lead to soil compaction," recommended Hall.
If you're watering plants in containers, aim for anywhere from 15 - 30% of the volume of the container. “I usually aim for about 15 - 20% of my total pot size," said Curtis. “So a ten-gallon pot will get around one and a half to two gallons [of water]."
Your growing containers will need drainage holes in the bottom, and you should start to see runoff water flowing through these drainage holes quickly and easily. If it takes several minutes for runoff to appear, your growing medium probably doesn't have proper drainage or you need more drainage holes in the container. When your runoff is collected in a tray under the plant's container, be sure to discard it promptly since it can be a breeding ground for pests and diseases. Don't let your plants sit in runoff water.
The best time of day to water cannabis plants
Another consideration is the time of day. Many growers and gardeners will water plants early in the day before the sun has fully risen or the indoor light cycle begins. This gives the plants the water they will need for photosynthesis and other essential functions performed throughout the day. Others prefer to water in the early evening when the sun is going down. Most agree it's best to avoid watering in the high sun and highest heat of the day.
How rain affects outdoor watering
One major difference between watering indoor and outdoor plants is rain. With indoor plants, you control the plant's access to water; whereas with an outdoor grow, you don't control the rain.
Depending on your location, climate, and the frequency of rain, there may be periods where you don't have to water your weed plants at all, and others where you might have to water several times a week. If you live in a hot and dry climate with low humidity, Brody suggests that you may need to water plants every 2 - 3 days. In milder weather with more frequent rain, watering every 4 - 5 days may suffice. “And if it's frequently raining, watering isn't necessary until the rhizosphere (the soil around a plant's roots) has begun to dry — typically this takes a week or more to occur," he said.
When growing his outdoor hemp plants, Bald prefers to water mature plants less frequently but more deeply to encourage deeper root growth. “With outdoor plants, once they're mature and well established, it's better to water less frequently but more deeply than frequent light waterings," he said.
Another thing to consider when growing outdoors is the condition and type of soil you're growing in. Sandy soil tends to have better drainage and will need more frequent watering than clay soil, which has better moisture retention.
Does the type of water matter?
There are different types of water that could be used for growing cannabis, such as tap, rain, bottled, or reverse osmosis, for example.
Many growers use good old tap water without issue, though the quality and contents of tap water vary from location to location. If you live in an area with hard water — that is, water that has a higher mineral content — it could impact the health of your plants. Some growers recommend letting tap water sit out for about 24 hours before using it so the chlorine used to treat it can evaporate. Rainwater can also be collected and used (if it's legal in your area), and it typically has a fairly neutral pH.
In both cases, you may want to test your water before using it to measure its mineral content and pH so you can adjust as needed. When growing in soil, the pH of the water should be about 6 - 6.5, while hydroponic and soilless grows should aim for a pH of 5.5 - 6.
Both bottled and reverse osmosis water are preferable for their purity, but they can be expensive — and in the case of bottled water, wasteful — options. In most cases, tap and rainwater will work well for cannabis plants, with pH and feeding being tweaked as needed to accommodate the quality of your particular water.
When watering, use cool but not cold water as this could shock your plants.
How can I tell if I am over- or under-watering my plants?
Much to the novice grower's chagrin, the signs of underwatering versus overwatering can look much the same: drooping and yellowing leaves, for example. It may take some time to be able to pinpoint the differences but there are nuances between the two.
Signs of overwatering:
- Drooping leaves that curl inwards
- Leaves that look swollen and feel firm
- Slowed or halted growth
- Soil is wet
Signs of under-watering:
- Drooping leaves that fall flat
- Leaves that look dry and feel papery
- Plants looking drab and lifeless
- Soil is very dry
Again, it's important to take cues from the plant. If the plant is giving signs of being overwatered, despite the soil being dry, it could be that the soil further down is still wet and you don't actually need to water. If you're using a moisture meter, consider drilling holes into the side of the pot near the bottom so you can use the meter to test there.
Bottom line
The water needs of cannabis plants will vary from crop to crop and season to season. While there is no strict schedule to follow when watering your cannabis plants, by understanding the environmental factors of your grow and paying close attention to the plants themselves, you can become attuned to their water needs. If you're new to growing cannabis, most novice growers tend to overwater, so be sure to only water when the soil is dry.
