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How to tell if a cannabis plant needs watering

October 7, 2016
Updated 03/25/19

Giving a plant the proper amount of water may be more difficult than you think.

There isn’t an exact science for watering a cannabis plant—you can’t observe the roots (in most cases) and don’t have a way of knowing exactly what’s happening in the soil. Also, a plant is constantly growing and the climate it’s in may fluctuate, so the amount of water it needs will constantly change.

Despite this, here are some tried-and-true tips and strategies to help keep your plants healthy and properly hydrated.

How often should you water cannabis plants?

When you think your cannabis plants might be thirsty, take time to observe:

  • Do the leaves look dark green or are they yellowing?
  • Are they vibrant, rigid and strong?
  • How does the soil feel?

A common mistake first-time growers make is to overwater a plant. A healthy cycle of wet and dry is necessary for the roots of a plant to grow out and reach deeper into the pot.

To see if a plant needs watering, stick a finger down a couple inches into the soil. If it’s dry, it’s time to water.

Related

How Homegrowers Can Keep Their Cannabis Roots Healthy

You can also pick up a pot and feel the weight of it to determine if it needs water. This will take some experience—be sure to lift up your pots after watering to get a feel for how heavy they are when full of water. This will give you a sense of what a light, or dry, plant feels like.

An underwatered plant looks droopy and weak, with yellow or brown leaves. There is no strength in the leaves and they feel lifeless. But an overwatered plant look similar, except that the leaves are dark green and the leaf tips will curl as if they are hiding from the water in their pot.

Obviously you don’t want your plants to ever be in either condition, but as you figure out your cannabis watering schedule, keep in mind that it’s better to underwater plants rather than overwater them.

Related

Stages of the cannabis plant growth cycle

Roots pull in oxygen as soil dries and when soil is too wet, the plant essentially can’t breathe.

Pay attention to timing and note the intervals at which you water your plants, and even write it down in a log. But keep in mind that as plants get bigger, they will need more water and need to be watered more frequently.

How much should you water cannabis plants?

Holding water rubber hose tube. Watering

The amount of water your plants need will depend on a number of factors, including:

  • Size
  • Outside temperature
  • Overall health
  • Stage of growth

You want to soak the pot and have run off through the drainage holes in the bottom of the pot. Water should pool up on the surface of the soil while you’re watering, but it shouldn’t sit on the surface after you move on to the next plant.

If a plant is very dry, water will run straight through the pot and quickly come out the drainage holes. If this happens, water the plant a little bit and come back to it after 10 minutes or so and water it again, and maybe even a third time. This will allow the soil to slowly absorb water incrementally, until all of the soil is thoroughly wet.

Take notes, make calculations, and get your plants on a watering schedule. Setting a cycle where the plant needs to be watered every two to three days is ideal.

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Straight From the Source: Clean Water Tips for Your Cannabis Homegrow

As the plants grow, so will their need for water. You might need to top-off individual plants in between their full waterings as they grow and you figure out a consistent watering schedule.

The sooner you find the sweet spot between too wet and too dry, the sooner you’ll see your garden flourish.

Is your container the right size?

cannabis pot

To properly hydrate a cannabis plant, it needs to be in the correct container size. If the pot is too big, the plant can’t drink water where its roots don’t reach. If the roots aren’t absorbing water, water will sit and take a long time to evaporate, which can promote unwanted insects, fungus, and root rot.

Conversely, if a container is too small, the roots won’t be able to stretch out, which will ultimately stunt the growth of the entire plant. You will also need to water the plant all the time, which will add to your labor.

Related

Choosing the Right Container for Your Cannabis Plant

Ideally, plants should start in a small pot and progress to bigger and bigger pots as it outgrows each container. For example, you can start a clone or seedling in a 4″- or 1-gallon pot, then move on to a 2-gallon, 5-gallon, 10-gallon, and so on.

Plants are ready to transplant when a healthy root structure encompasses most of the soil, but the roots aren’t bound. Transplanting is a good opportunity to see the quality of your roots: bright white roots, with a strong thick structure is a sign you have been watering your plants correctly.

Materials for a well-hydrated cannabis garden

Large Indoor Marijuana Legal Recreational Commercial Growing Operation

These materials will help optimize your plants and make the watering process easier and more efficient.

Perlite

Perlite comes from obsidian, which is a volcanic glass. It is produced when obsidian is heated to a high temperature and then expands. It’s light, porous, and organic, making it a great addition for your soil, as it prevents soil from clumping and promotes oxygen flow.

Smart pots

These pots are made with canvas, and the fabric helps roots breathe, allows heat to escape, and lets water drain. All of these traits will improve the quality of your plant roots and how they handle being watered.

Drip lines

Drip irrigation lines allow you to water plants consistently and distribute water evenly across the pot. They also prevent your pots from flooding on the surface when getting watered, which will cause perlite to come to the surface where it is useless. Drip systems also help prevent evaporation when you’re gardening in a hot climate.

Timers

It’s crucial that you measure how much water you are giving your plants. If you have an irrigation system, figure out the flow rate and set a timer so you can gauge when it’s time to move on to the next pot, ensuring every pot is receiving the same amount of water.

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Leafly Staff

Leafly is the world’s largest cannabis information resource, empowering people in legal cannabis markets to learn about the right products for their lifestyle and wellness needs. Our team of cannabis professionals collectively share years of experience in all corners of the market, from growing and retail, to science and medicine, to data and technology.

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  • Chris Newman

    The story didn’t mention what happens to plant roots when the soil dries out: There are two types of plant roots: The main root system and the tiny “feeder” roots at the ends that actually take up moisture and nutrients for delivery to the plant. If the soil dries out, these feeder roots die and it takes a week for them to regrow. In the meantime, while the plant may look healthy, it’s not actually growing much, and certainly not growing flower weight. If the soil can’t drain or is too dense, these feeder roots will drown and many may not even grow back.

    I solved this watering issue 20 years ago with “capillary watering.” This is how Mom Nature waters plants when it’s not raining: Automatically replacing moisture within the soil, molecule by molecule, on demand as the plant roots consume it, via capillary action. If you place a drop of water on a paper napkin and watch it spread out, that’s capillary action. This gives you the simplicity of soil with the performance of hydroponics, with almost no investment or maintenance.

    Cap watering is a simple, cheap and foolproof way, with no moving parts, to maintain the perfect growing conditions that the plants really need: Evenly moist soil at all times. Starting with excellent loose potting soil full of organic materials (i.e. peat moss or sterile compost, with some perlite), this is exactly what capillary watering does. If you’re not a soils expert, buying new professional potting soil with every crop is a worthwhile investment.

    Not top-watering also means that the soil doesn’t pack down, leaving the roots with plenty of air spaces within the soil to breathe. It also means that you’re not flushing nutrients out the bottom of the pot every time that you top-water.

    The only maintenance required is keeping the shallow bottom water reservoir, which can service countless plants, topped off once a week or so. If you automate that topping off with a float valve hooked to a faucet, after the first watering, you’ll never have to hand water again for the rest of the crop cycle.

    Check out YouTube videos for “capillary matting.” Lots of simple ways to engineer this, but keep in mind that capillary action will lift water, without moving parts, a maximum of about 6″. That’s all that you need.

    For smaller grows, I use a large mortar-mixing tub (10 gallons capacity for about $10) and place a 2′ X 4′ piece of 1.5″ styrofoam insulation board on top, resting on the edges of the tub – both are available from home improvement centers. Drill a 2″ hole in the middle of the sheet and feed a 12″ X 24″ piece of matting through it, with about half hanging down into the water reservoir and the other half spread out flat on top of the styro board. Cover the top of the board with more matting and that’s the total construction. I used the same system for years indoors and it never did wear out.

    (If you want to create a larger moisture floor, just make multiple units and gang the tubs together with simple fittings and 1/2″ tubing from the same home center. If you need to spread out the plants for more room as they grow, just reposition them as needed.)

    When you need to top off the reservoir, you can do so through the same 2″ hole. If the matting surface feels damp, it’s working. If you stick your finger into the hole and don’t feel water, it’s time to top it off.

    For each individual pot (say 5 gallon size) before adding soil, run a wick of cut matting about 4″ wide X 18″ long through the bottom of the pot drainage hole, with 12″ going up through the center and fill with soil, with 6″ hanging out the bottom. Tuck the lower part flat under pot and set it on top, where the weight of the plant will maintain good contact with the base matting. Moss is going to grow on top of the open matting, but no big deal.

    If you can’t find cap matting, which is spendy, old polyester blanket material from the thrift store will usually work just as well. If you dunk it in a bucket of water and it stays damp after lifting it out, it will work. You *must* start out with damp matting. If it won’t readily hydrate, try adding a little plant soap as a wetting agent to the hydration bucket water.

    But, I don’t bother to grow my own any more. I live in Washington state and when I need weed, I just stop off at the local legal pot store and pick up what I want, from 50 or more different strains. Not having to even think about getting busted is an incredibly liberating experience. 🙂

    • Greenleaf910

      The one issue I have with your capillary watering is that there is no run off, and if your feeding the plants with concentrated liquid nutrients you need to flush the salts out that are left behind once the nutrients are absorbed, if not you have a very good chance of getting nutrient lock out due to the high nutrient salt content. For every gal of soil you have, you should have a 1liter run off. I grow in 3gal. smart pots and I water every other day, and feed twice a week. When I feed, I pour about 7liters of nutrified water in each pot and get approx. 3 to 4 liter runoff. My Indica’s seem to love it.

  • Bridget Sparling

    wat do i get to really not have that home grown smell

    • Gordon Ross
    • Shawn Fitzsimmons

      Air purification system like a Carbon Filter

    • Steve Wescott

      Drying and cure correctly helps alot in getting rid of that. Also a proper flushing.. hope this helps

    • Gremblo

      you could pay for an air filter if you want a fool proof guarantee, or you could build a device I invented that ill call the ‘Grow Sploof’. essentially to make this, you need a circular fan, 2 pillow cases, and some sort of solid laundry detergent (the little pellets work perfectly). Take the first pillow case and fill it with the laundry detergent, then put the second pillow case inside and then attach the layered fabric to the fan so that it sucks the air around your plants and blasts it into laundry detergent purifying the smell.

  • moses

    On important Tips on watering which has been passed by my Indoor Gardeners team (Sijigreenhouse) was that If your cannabis plants shows signs of drooping, chances are you are over or under-watering.

    In order to prevent over or under-watering, make sure you water thoroughly every time (don’t just water a tiny spot in the middle of the pot, you should be getting 20-30% extra runoff water every time), and wait to water again until the top inch of the growing medium feels dry, up to your first knuckle or so.

    • Greenleaf910

      Exactly correct!

  • Pierre Blais

    Hi I would like to know if a total of 136 watts of LED lights is OK for 1 pot plant.Thanks

  • Brent

    That’s fine just be careful for mold. We use a leaf blower in the morning to get the access water of the heads.

  • Gary Sizemore

    I’m adjusting the ph on my water, but since I’m using tap water, I’ve been letting my water sit for at least 24 hours. I heard this lets the chlorine dissipate. Does anyone know if this is true, or am I wasting time leaving it sit?

    • Bob Johnson

      yes this is true