Learning how to water marijuana plants correctly plays an essential role to a healthy grow. Afterall water is like the blood of cannabis plants carrying all the important nutrients around the plant and delivering them to the right places.
How much should I water my plants?
This is a difficult question to answer because it depends on several contributing factors:
As the plant grows bigger it will obviously require more water. When cannabis plants are in the early stages of growth, they are small and delicate and prone to damage. Seedlings are too small to be watered in the conventional way and you should use something like a mister to gently spray them and moisten the plant and soil. After you have done this, wait for the soil to dry completely before watering them again. It should take 1-2 days for the soil to dry completely, however this depends on environmental factors such as temperature.
The type of growing medium you are using determines how much water you should use. For example, soil holds moisture more efficiently than clay pebbles so if you are growing in pebbles then the plants will require more frequent watering. Even when growing in soil you will find that certain types of soil will drain faster than others, adding soil amendments such as perlite can assist drainage by reducing soil compaction.
Types of pot
Another factor that plays into watering frequency is drainage, different types of pot expel excess water at different speeds, I always advise growing in smart pots of air pots. These types of pots are made purposefully to drain water faster and allow airflow, because they are covered in tiny holes it is almost impossible to overwater with them. However, you will need to water more frequently because they will dry out much quicker. Read our full guide on different types of growing pots for a more detailed explanation on this subject.
Different sizes of pot will also drain at different speeds, obviously if you have a small pot it will drain and dry out much faster then a large one.
Plants that grow in warmer climates are going to require much more water than if they are grown in mild climates. If you are growing indoors keep a thermometer inside your grow room so that you can keep an eye on the grow room temperature. If the temperature is very hot you can water them more often. However, try to bring the temperature down too by using an AC.
How do you know if your plants need watering?
There are a few signs you should look out for that indicate your plant needs more water.
Droopy or wilting leaves
When cannabis plants need watering the signs are obvious, if you ever see the plant looking generally unhealthy with the leaves drooping down it usually means that the plant is thirsty. However, it is worth noting that if a plant has been overwatered it will look similar. If you are struggling to tell the difference a simple way to tell is to feel the surface of the soil, if it is bone dry to the touch then it will most likely be underwatered.
Underwatered: Drooping leaves looking a little drier.
Overwatered: Drooping leaves that look dark and heavy.
It is much safer to underwater than overwater your plant. If plants have been underwatered, they can recover in just a few hours once they have been watered. Whereas if they have been overwatered it can take much longer for plants to get back to full health.
Another clear sign that your plants have been underwatered is if the leaves are discoloured or beginning to turn brown or yellow. It is fine the leaves of a plant to turn yellow during the end of the flowering stage, however if this begins to happen earlier then it could be an indication of underwatering.
Feel the soil
It may sound like the most obvious answer but just by simply feeling the surface of soil you should be able to determine if the plant needs watering. Make a shallow hole a few centimetres deep with the tip of your finger in the surface of the soil, this will give you a good idea of how dry the soil is.
If you want to be more accurate than this you can also weigh the pot to see how much water it is holding. To get an idea of if the plant needs watering, weigh the pot when it is relatively dry and in need of watering, this gives you an indication of how much it weighs with very little or no water. Then water the plant and weigh the pot again. You now know the average weight with and without water, make a note of these and make your judgements based on this.
To check if your plants are thirsty follow these three checks.
- Are the leaves drooping or turning yellow?
- Make a shallow hole in the soil, does it feel dry?
- Weigh the pot, how far off is the pot from its dry weight? If it is very close or below then you know your plants need water.
How to water marijuana seedlings
Marijuana seedlings are incredibly delicate, it is during the seedling stage that they are most vulnerable so it is important to be very careful when you water them.
Because of their size it is very easy to over water marijuana seedlings so follow these simple steps and learn how to water weed seedlings to avoid this mistake.
Use decent pots
Make sure your pots have good drainage to allow excess water to drain out, this will reduce the risk of over watering. Read our guide on the best pots to grow marijuana in. It is more difficult to water Seedlings that are in a large pot, this is because the pot will require more water than a small pot which leads to a greater risk of over watering.
Use a misting spray
When seedlings are very young they need a humid environment to thrive, use a misting spray to gently spray them and keep them moist throughout the day.
How often should I water my marijuana seedling?
Marijuana plants like all living things need oxygen to survive too. When you water your marijuana plants the soil becomes damp and water fills in any air gaps in the soil, the roots of the plants then begin drinking the water. As the soil gradually dries out more oxygen creeps back into the soil which the roots use to power growth. if you keep watering seedlings without letting the soil dry our enough the soil surrounding the roots becomes constantly wet and starved of oxygen. This prevents the roots from growing and effectively they drown.
Over watering is probably the most common problem during the seedling stage. A simple way to avoid this is to stick your finger in the top 2cm of soil each time before you water them to test how dry the soil is. If the soil is dry up to around 2cm then you should be okay to water them.
How to water marijuana plants correctly
It has often proved best for me to water cannabis plants less frequently but making sure when you do water them you give them a good soaking as oppose to little and often. There is no exact rule on how much and how often you should water them as this really depends upon the size of the pot, the growing medium, the size of the plant and the temperature. However I have found that following these four simple steps always works out well for my cannabis plants.
Four steps to healthy watering
- To prevent over watering your cannabis plants, you should first check that they need watering. To do this dig your finger into the top layer of soil around half a centimetre deep. If you feel a lot of moisture still, then you can probably leave watering for another couple of days. If it is dry, then they are ready to be watered.
- Fill up your watering can and check the pH of your water with a pH meter. The pH should be 6.3 – 6.8 when growing in soil or 5.5 – 6.1 in hydroponics. If the pH is too high or low add in a few drops of ‘pH up’ or ‘pH down’ and test it again until you get within the right range. It is very important to make sure your water is the correct pH as this helps the plant to absorb its nutrients. If the pH is too high or too low, it can cause nutrient lockout.
- When you water them aim for the middle of the soil/substrate first to ensure the roots get a good soaking. A ‘good soak’ should be roughly 25-30% of the pot capacity, this should be plenty of water for the plant while not over watering it. Once you have given the centre a good watering, move to the outer edges of the pot and work your way around to give an even spread of water. This will draw the roots towards the outer edges once the plant has had its fill.
- After you have watered your plants check the runoff trays are not getting too full. You do not want to leave your plants sitting in the runoff water for too long. This will eventually go stagnant and can lead to fungal issues such as root rot. You should have pots with holes in the bottom, and you should ideally prop them up off the ground a couple of inches to allow the water to drain out of the pots easily while still hovering above any runoff water that pools underneath.
How to water your cannabis plants when you’re away
Cannabis plants require constant care and attention, if you are away for even a few days without tending to them this could have a significant affect on the quality and yield of your plants. Ideally try to time your grows around your vacations, however there may be times when you just cant avoid being away for a few days so here’s what to do.
Away for 1-3 days:
If you are away for a weekend, make sure you give your plants a thorough watering before you go, this should last them fine for a few days.
Longer than 3 days:
If you are away for longer than a weekend, then ideally your first choice should be to ask a friend or someone you can trust to water them in your absence. I appreciate that this may not be an option for many stealth growers out there so there are a few solutions that could help.
DIY Drip System:
Make a drip system that will provide a slow but constant feed of water to your cannabis plants. This is very easy and many people do this in their garden before they go on vacation but it works equally well with cannabis plants too.
Away for 2-5 days:
- Get a wine bottle or plastic bottle.
- Wash it out and rinse it thoroughly.
- Create a hole in the surface of the soil for the bottle to sit in – To do this, while the bottle is empty, turn the bottle upside down and press it into the top of the soil/substrate about 1-2 inches deep so that it stands up, or can be supported against the edge of the pot.
- Take the bottle out of the soil and fill it up with pH’d water.
- Now cover the top of the bottle with your thumb.
- Holding the bottle over the plant pot, turn the bottle upside down and quickly press the top of the bottle into the hole in the surface of the soil that you previously created for the bottle top to sit.
- The end of the bottle should now be upside down and slightly plugged by the soil or substrate. The water will gradually drip out into the soil over two to three days.
TIP – Support your DIY drip feed: To get your bottle to stand up straight in your soil use a bamboo stake. Place it into the bottle before you turn it upside down on the soil, make sure the bamboo stake sticks out of the end of the bottle and into the soil 7-10 inches to give it a sturdy support.
Away for longer than five days?
- This time use two large plastic bottles but put the cap on and make a small hole in the cap about 3-5 mm wide (I use a 3mm drill bit for this).
- Use the exact same method as above and the water should take 5-7 days to fully leak out with two bottles providing just enough water to keep your plants going.
If you have a decent sized grow and want to do things a little more accurately you can purchase an automatic digital irrigation system that you can connect to a large bucket or reservoir for between $30 – $50. This will allow you to pre-program your watering schedule and precisely how much water to use.