How to Flush a Sick Cannabis Plant

by Nebula Haze

Table of Contents

Why Flush Cannabis in the First Place?

How to Flush a Sick Marijuana Plant (without harming it)

How to Fix Incorrect pH Without Flushing


Why Should I Flush My Sick Marijuana Plants?

The main reason to flush your sick cannabis is to try to correct something wrong at the roots by leaching out extra nutrients or salt buildup in the soil or coco coir.

What about flushing plants before harvest to improve bud taste?
(How is that different?)

The most common reasons to flush sicks plants are…

  • Fix pH – The pH at the roots is several points too high or too low, causing major nutrient deficiencies

  • Flush Out Additives That Made Plant Sick – It's important to flush a plant that has been watered with something that has made it sick, for example if it is losing leaves because it was recently watered with a pesticide, nutrient or supplement that was too strong.

  • Leach Out Time-Release Nutrients – If transplanting isn't an option, sometimes a grower will flush a plant that is being grown in soil with "time release" nutrients (like Miracle-Gro soil). This idea is to try to leach out extra nutrients (specifically nitrogen) before the flowering stage begins. Too much nitrogen in the flowering stage can give buds a "green" taste as well as actually prevent buds from getting as big as they normally would. Since time-release soils slowly releases nitrogen for months it's important to flush that out before your plant starts making buds.

If your cannabis plant gets sick the day after you add a new supplement for the first time, you should probably flush your plant to "start fresh" at the roots

Sometimes you need to flush a cannabis plant because it's having nutrient deficiencies!

Which Growers Should Flush Their Plants?

Flushing sick plants is for…

  • Soil
  • Coco coir
  • Other soilless mediums

Flushing sick plants is NOT for…

  • Hydroponic or DWC grow setups – if you have a nutrient or pH problem, just change the reservoir so it has exactly what you want

How to Prevent the Need to Flush Your Plants

  • When hand-watering plants, always give plain water every other watering

  • Always start with 1/2 strength nutrients, and only increase nutrient dose if the overall plant is starting to look pale or lime green. Learn more about nutrient deficiencies. It's also a good idea to start any pesticides or supplements at half strength until you see how your plant reacts. 

  • Always check and adjust the pH of your plants every single time you give them water. Even if only giving plain water. Maintaining the pH is the #1 way to prevent nutrient deficiencies, and simply by doing this you'll dramatically reduce the chance you'll even need to flush (pH being too high or too low is the main reason to flush plants).

  • When plants are sick, try moving the grow light up a few inches or even a foot. This will help your plant recover more effectively from many nutrient problems, whether you end up flushing the plants or not.

Try to prevent nutrients problems before they happen so you never need to flush!

Example of a marijuana plant with a magnesium deficiency - try to prevent problems before they happen so you don't have to flush your sick plants!


How to Flush Sick Cannabis Plants

  1. Make up water with low levels of nutrients (1/4 strength or seedling dose). You want to take out the bad and replace with the good.

  2. Give 3x the pot size – Use enough water so that you're giving the plant 3x as much water as the volume of the pot. It may take a little while. Remove all runoff water immediately, you don't want your plant to suck the bad stuff back up!

  3. Give regular strength nutrients at the end – Make up one last batch of nutrient water at regular strength, and give this to your plants. You are replacing what you took out with what you want to be there – fresh, pH'ed nutrient water!

  4. Make sure there is a fan blowing over the top of the growing medium to help it dry out so plants don't get as droopy from being overwatered. There should be plenty of air circulation in the grow space, with access to lots of fresh air.

  5. Raise your grow lights up a few inches while your plant is recovering. Your plant definitely needs plenty of light, but you don't want to make it work too hard during the recovery period.

  6. Wait a few days for improvement – Although your plant may get droopy at first, you should start to see improvement within a few days. Try not to water it again until the top inch is starting to dry. It's not recommended to flush a plant two times in a row. After the first flush you should have flushed out what was hurting the plant in the soil. At this point, it's time to give your plants some TLC while you get things back on track.

How to Fix Incorrect pH Without Flushing

1.) Determine your target pH

  • Soil: 6-7 pH
  • Coco: 5.5-6.5 pH

2.) Collect runoff – Give your water at the correct pH, and collect runoff water out the bottom.

3.) Is the pH too high or low? If the pH is higher or lower than the correct range, don't panic! At the very least you're already giving your water at the correct pH from on top. That will help the plant stay healthy while you fix whatever is going on at the roots.

4.) Start correcting the pH the next time you water your plants. If you already have major nutrient problems, you might consider flushing as stated above. But if you don't see problems yet, or if you only see just a little bit of leaf discoloration or yellowing, there's no need to flush. Flushing is very stressful for plants and may prevent them from recovering as fast as they could, so it should be avoided if possible.

Most of the time, if your runoff pH was too high or too low, it's better to wait until your next watering to start correcting it.

5.) Always give water in the correct pH range, but at the opposite end. Next time you water your plants give water in the correct range, but at the opposite end of the range to start trying to get it to move in the other direction.

If your runoff water is coming out at 4.5 pH, it means you should water your plants at the high end of your desired pH range. So for soil you would water your plants at 7.0 pH, and with coco you'd water your plants at 6.5 pH.

This ensures that your roots are getting some amount of nutrient water at the correct pH, while also starting to leach out whatever is in the growing medium that's dragging the pH down.

Eventually, your pH is going to start coming out the bottom of the plant in the right pH range, even if it takes a few weeks.

I've found that correcting the pH this way seems to stop most nutrient problems within just a few days, while preventing your plant from getting stressed from a true "flush."

I wish I had known this before I started growing 🙂 I've done too many unnecessary flushes and unintentionally stressed out my plants!

Happy growing!



Jump to…​

Diagnose My Sick Plants!

How To Get To Harvest As Fast As Possible

Where to Get Marijuana Seeds Online

The Perpetual Harvest




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