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Soil: 6.0-7.0

In the wild, plants prefer a slightly acidic soil environment. For soil an optimum root zone pH for is between 6.0 and 7.0, with the most time spent with a pH between 6.2 – 6.9. It’s a good idea to let the pH cover a range instead of always adjusting to the exact same pH number.

In a soil environment that doesn’t use liquid nutrients, pH isn’t as important. When using liquid nutrients in soil, you will almost always need to manage pH to prevent problems and get the best harvest.

Hydroponics: 5.5-6.5

In a hydroponic setup, you will almost always be using liquid or powder nutrients, so save yourself a ton of trouble by watching and adjusting the pH as needed! The pH will naturally change over time, and you only need to correct it when it starts going out of the 5.5-6.5 range.

With hydroponics, it’s especially important to allow the pH to range slightly. Some nutrients absorb better in different pH levels.

What about soilless mediums like coco coir?

Most soilless growing mediums are completely inert, which means they don’t contribute any nutrients to the plant. Instead they act more as a support system for your roots while you provide all the nutrients through the water. When the plant is getting all it’s nutrients in the water, it’s considered a “hydroponic” growing setup.

However, some soilless growing mediums with a lot of organic matter may need a slightly higher pH to thrive. For example if you heavily amended your growing medium with worm castings (worm poop), you will want to aim for a pH between soil and hydroponic ranges since you’ve added “soil-like” components.

For hydroponic growing setups (as well as soilless growing mediums like coco coir) an optimum root zone pH is between 5.5 and 6.5. This is slightly more acidic than the optimal root pH for growing in soil.

It’s a good idea to let the pH cover a range instead of always adjusting to the exact same pH number.

No Need to Be Exact – Let pH Range Up & Down

The thing to remember with pH is that you don’t need to be exact. What you do need to be is consistent in keeping the pH from creeping too high or too low in your plant root zone.

As long as you stick within the recommended pH ranges above, you will prevent the majority of all nutrient problems caused by too-high or too-low pH.

Why is it a good idea to let the pH cover a range instead of always adjusting to the exact same pH number? Some nutrients are better absorbed at slightly higher pH readings, while others are absorbed better at lower pH readings. Not having to try to pinpoint an exact number also saves a lot of unnecessary frustration.

If your plant roots are experiencing the wrong pH, it’s recommended you react as soon as you notice, and not wait until you actually notice problems with the leaves. It can be tempting to ignore a pH problem, but you’ll often get the best results by acting before your plant displays a problem. That being said, if your plant is growing green, vibrant and healthy, sometimes the old saying applies, “if it ain’t broke, don’t fix it.”

Tips

  • Be consistent in making sure pH stays in the range

  • You don’t need to be exact, just keep an eye on things and react if you notice the pH is getting too high or too low

  • Add all of your nutrients to your water first before checking and adjusting the pH. Your nutrients will affect the pH of your water so it’s important they get added before making any adjustments.

 

Supplies: What Do I Need to Test & Adjust pH?

  • Digital pH Pen or 

  • pH Measurement Kit with drops or strips

Related: pH Testers 

  •  PH Adjuster

A bottle of “pH up” and a bottle of “pH down

PH Up & PH Down gives you one of the best ways to adjust pH in soil or hydro. They each come in a bottle that lets you easily measure how much to add to your water.

There are other methods of adjusting pH, but using pH Up and pH Down is the best method I’ve tried –  I know these products work great for growing, and they keep the pH more stable than natural alternatives like vinegar or baking soda.

  • Water

For many growers, tap water works just fine for growing.

I use a container that was originally made for drinking water to mix up my nutrients, but many different types of containers will work. Most importantly, avoid anything fragile, especially glass (which can break your instruments or shatter).

How much pH Up/Down do I add?

The amount of pH Up or Down you add will vary a lot depending on your water. If you’re using very soft water than you will need just a tiny amount of fluid to adjust the water’s pH since there’s not much “stuff” in the water to buffer the pH. However, if you’re using hard (well) water than you’ll need to add more.

  • For PH Down – 1 mL/gallon of water will generally reduce your pH about 1 point. That’s just a very rough estimate, but gives you a starting point. In imperial measurements, that’s 0.2 tsp/gallon (1 tsp/5 gallons) will reduce the pH by 1 point. If you’re regularly measuring PH Down I highly recommend using a blunt-tip syringe with mL measurements, it’s much simpler because imperial measurements don’t have precise enough measurements for the small amounts needed with PH Down!
    Note: If you are starting with RO (reverse osmosis) or soft water, you likely need less PH Down than the specified amount; if you have very hard water you may need more!
  • For PH UP – PH Up is not potent stuff! It actually has a very weak effect. Compared to PH Down you will need to add much more PH Up to adjust the pH by the same amount. With PH Up, depending on how hard your water is you need to add 2-4mL/gallon of water to raise the pH 1 point. In imperial measurements that’s 0.4-0.8tsp/gallon.
  • The first time you’re adjusting, you don’t know what pH your water is, how “hard” it is, and how your particular nutrients and supplements are going to affect the pH. Initially, you’ll have to add just a little bit at a time and keep testing until you get an idea of exactly how much you’ll need with your tap water, and the nutrients you’re using. After 1-2 times this step will only take seconds!
  • It can be helpful to make a note of the total amount of pH up/down added. The total amount of used pH up/down will be about the same each time. Remember that number and write it down! It will make pH’ing easier in the future! The amount will change a little depending on which nutrients your plant is getting for its current stage of life, but having a ballpark figure is really helpful.
  • Unfortunately there’s no exact formula to adjusting pH, because factors such as the source of water, growing medium, nutrients, drainage and growing setup all have an effect on pH.
  • You will need to use trial and error to figure out what amount of pH Up or Down works for you in your setup with your nutrients.
  • If you’re new to adjusting pH, start small with pH Up and Down, and only work your way up to bigger amounts after you’ve gained some experience. Most growers will be able to figure out their personal measurements within 1-2 waterings.
  • The very first time you pH your water, it will take a little trial and error to figure out how much PH Up or PH Down to add to get to the right number, since everyone’s water is a little different. The general idea is to start with a little bit, maybe a few drops, then retest and add more if needed. Continue this until you get the water in the proper range. PH Down is much stronger than PH Up, so be extra careful with PH Down! After the first time, it will be much easier to measure out how much you need.
  • Tips for Nutrient & pH Management:
  • Don’t Go Overboard: With liquid nutrients, it’s usually better to give too little than too much. You can always add more, but it’s harder to take nutrients back. A good rule of thumb is to start out at half the recommended dose, and only raise nutrient levels if the plant needs it.

  • Never Mix Nutrients or Supplements Directly With Each other: Always add nutrients directly to your water. It’s bad to mix nutrients together. They can react with each other in a way that can make nutrients less available to your plants. Most nutrient bottles or pH adjusters will come with a clear warning that says the same thing. Always add any additives directly to the water – your plants will thank you for it. Example Anything marked as a “grow” or bloom” should be added to your water AFTER you add your supplements

  • Add “Micro” to Water First – If you’re using a 3-part nutrient series with a bottle for “Micro,” you should always add that to the water first. It will also say so on the bottle and on the nutrient schedule, but just something to be aware of.

  • Tap Water Can Be Easier to pH Than RO or Highly Filtered Water: Tap water or mineral water has an extra buffer of extra minerals and other “stuff” in the water. This helps prevent the pH from swinging up too high or too low quickly and can make pHing easier. RO water has very little buffer (it’s basically pure water) and tends to swing up and down in pH easily with just a little pH Up or Down.

  • Shaking Water Changes the pH: When checking and adjusting pH, some growers like to shake their water container to make sure everything is evenly mixed. This works well, and roots love the extra dissolved oxygen, but it’s important to understand that after shaking the nutrient water for a long time, the additional dissolved oxygen will raise the pH of the water. Don’t worry about this – don’t retest then readjust the pH. If you’re going to hand-water to your plant, you want to make sure you go by the pH of the water before it was shaken up. In hydro, the water is going to be oxygenated anyway, so shaking it before testing is ok. If water is allowed to sit for a while, it’s normal for the pH to change a bit. When it comes to mixing, make sure you mix water gently so nutrients and pH Up or Down are evenly distributed, but avoid vigorous shaking until after you’ve already adjusted the pH.

  • pH Drift is Normal. Try to keep pH in the suggested range and you’ll be fine, even if it’s on the higher or lower end of the scale.

How Does pH Stop Nutrient Deficiencies? 

  • PH is the measure of how “acidic” or “alkaline” something is, on a 1-14 scale. A pH of “7” is considered neutral, for example pure water has a pH of about 7. The measurements of pH has to do with the concentration of hydrogen in the sample.
  • Okay, so why is pH important to  growers?
  • Plants naturally like a slightly acidic environment at the roots. Soil with a slightly acidic pH is what causes plants to thrive in the wild. Proper pH at the roots helps plants get access to the nutrients they need. If the pH at the roots is too high or low, the plant can’t properly absorb nutrients and you end up with nutrient deficiencies!
  • Some growers get lucky and grow plants successfully without having to worry about pH. Perhaps they had just the right soil, and happened to have just the right water to create the perfect pH environment for the plant roots. If your plant is growing perfectly, without any signs of nutrient deficiencies, than managing the pH might not be something you’re concerned about.
  • Unfortunately, many growers aren’t so lucky and their setup naturally has a pH that is too high or too low for optimum growth. While there are ways of getting around testing pH for your grow, nearly all growers will do better by paying attention to pH.
  • What Are the Benefits of Managing pH?
  • By maintaining pH…
  • plants are less likely to suffer leaf problems or nutrient deficiencies
  • without nutrient problems, plants can grow faster and produce bigger yields
  • occasionally growers are alerted to possible issues before they become a problem, for example if you determine the pH is too high or too low, you can fix it before your leaves start suffering from deficiencies
  • The main thing to remember is that maintaining the right pH at the roots helps the plant absorb nutrients. Why is that?
  • Nutrients take different forms (on a chemical level) depending on the pH around them. Some forms are easier for the roots to absorb than others. When the pH is too high or too low, the plant can show signs of a nutrient deficiency even when the nutrients are physically there at the roots.
  • With pH, you’re helping plants get access to all the nutrients all the time. While pH is important for all grows, it is most important for growers using nutrients. The way that liquid nutrients are formulated, they are highly available to plant roots, but only in the right pH range.