The Best pH For Your Cannabis Plant

Last updated: 26 February 2020

pH for weed

There are a number of important factors that go into growing a cannabis plant. Air temperature, soil temperature, humidity and light all have a huge impact on a cannabis plant’s healthy development. However, even if all these conditions are perfect, there’s one variable that affects a plant more than any other – potential hydrogen, commonly known as “pH.” This plays a crucial role in how plants uptake their nutrients. If a grower can’t dial in the pH for their weed, their plants won’t make it to harvest day.

What Exactly Is pH Value?

pH level for weed

Essentially, pH is a 14-point scale that measures the alkalinity or acidity of a solution. The pH of distilled water is 7 – dead center in the pH scale. If a solution is more acidic, it’ll have a lower pH value ranging from 1 to 6. Lime juice and vinegar are common acids. The opposite is also true: if a solution has a higher pH, ranging from 8 to 14, it’s a basic alkaline. Milk and bleach are two examples of alkaline solutions. pH is a logarithmic scale – meaning that a solution with a pH of 5 is ten times more acidic than one with a pH of 6 – and it plays an important role in several functions essential to life on earth, including how plants eat.

Why pH Is So Important

Three macronutrients – nitrogen, phosphorus and potassium – are the essential building blocks that make up any plant. However, if the pH level for a weed plant’s medium (soil or hydroponic) is too high or too low, the plant cannot absorb these nutrients. Without these crucial components, a plant will essentially starve to death. This condition is called “nutrient lockout”, and it can quickly turn a healthy plant into sickly, wilted mess. This is why every grower must understand the relationship between pH and nutrient uptake. In the short term, nutrient lockout can cause a plant to stop growing. If a grower doesn’t fix their pH problem in time, their plant will die. Even if a plant is otherwise completely healthy, it will eventually starve to death if the pH of its medium is too high or too low. It’s therefore extremely important for growers to understand how pH works and what the ideal pH should be for their cannabis plant.

What’s The Ideal pH Value For Cannabis?

When a grower cultivates any plant (including cannabis), it’s best to mimic the types of conditions that the plant would enjoy in nature. In the places where cannabis grows in the wild, the soil is slightly acidic. However, there’s no “magic number” when it comes to the best pH for weed. Instead, the best pH for cannabis plants will depend on several factors, including growing medium.

Best pH For Soil: Keeping It Within 6.0 – 7.0

best ph for cannabis

The best soil pH for cannabis plants is between 6.0 and 7.0. Soil is significantly more forgiving than hydroponic media, and because of this, a plant’s pH can deviate slightly when planted in soil. For instance, if a grower feeds their plant a nutrient mix with a pH of 6.3 one day and 6.7 the next, they probably won’t notice any difference in their plants. Drifting pH like this can actually be beneficial to a cannabis plant, because weed absorbs different nutrients at different pH levels. However, once a plant’s pH begins to drift outside of the 6.0 to 7.0 range, a grower may start noticing some problems with their plants like droopiness, dryness or change of color.

Best pH For Hydroponics: A Goal Of 5.5 – 6.5

how to lower ph in water for cannabis

When growing in a hydroponic medium, the correct pH for cannabis is between 5.5 and 6.5 – slightly lower than in soil-based gardens, because hydro starts with pure water – free of any nutrients as compared to soil. Additionally, in a hydroponic garden, a grower applies their nutrients directly to the roots. Because of this, the pH issues in hydroponic gardens can damage a plant’s health extremely quickly. However, it’s still important to make sure that pH fluctuates slightly in a hydroponic garden. Because plants absorb different nutrients at different pH levels, growers should make sure that their pH isn’t always the same, although still of course within a safe range.

Ways To Accurately Measure pH

how to check ph of soil for weed

Because regulating pH is so critical to the growing process, it’s important to measure it accurately. To that end, every grower needs a pH measuring kit. There are several different types of pH kits, including test strips, droppers and digital pH meters. Different growers have different opinions on which type of pH testing kit is the “best.” For example, digital pH meters offer the most exact reading and are easy to use, but require constant calibration. There are two different pH levels that a grower needs to check. First, they’ll want to test the pH of their nutrient mix to ensure that it’s within the correct range for their medium. Second, growers should also know how to check the pH of soil for weed plants. The advantage of digital Ph meters here is that some of them can do it all and test the pH of both liquid and solid media. While pH strips and dropper kits are simpler and don’t require any maintenance, they aren’t always as accurate as a digital meter. They’re also more susceptible to human error.

How Often Do I Measure pH?

Every grower should check their pH every time they make a nutrient mix to feed their plants. One of the most important rules for cannabis growing is to always check the pH balance before feeding. If the pH of the medium is too high or too low, the grower can adjust the pH of their mix to fix it.

When pH Is All Wrong: The Symptoms

If you’re wondering whether the pH of your plants is too high or too low, don’t worry – they’ll tell you. When a plant’s pH is incorrect, it can result in stunted, gnarled plants that fail to develop. These plants will be more susceptible to nutrient deficiencies and other health issues. Come harvest time, pH imbalances have a significant effect on a grower’s final crop.

When pH Is Too High

When the pH of a plant is too high, that plant won’t be able to absorb iron and other nutrients. Often, a plant will show certain signs of deficiency. An astute grower may notice that their plant appears to be lacking in one of these nutrients – when leaves turn dark green, claw-looking and droopy – and make up for this discrepancy by adding more of that nutrient to the plant. However, simply adding more nutrients won’t fix the grower’s problem. That’s because regardless of how much of the nutrient the plant has access to, it won’t absorb this without the right pH levels. Instead, the grower needs to address the real problem – the pH imbalance.

When pH Is Too Low

If a plant’s pH is too low, it won’t be able to absorb nutrients like phosphorus, calcium and molybdenum. Phosphorus is crucial for bud development in a weed plant’s flower cycle. The plant’s leaves will appear droopy and develop tan, brown and yellow spots along its edges. Leaves may also take on a mottled brown and yellow complexion from calcium deficiency. These deficiencies can cripple a plant as it ages. However, if a grower catches them early, they can correct the pH problem and their plants will be able to recover.

how to lower ph in water for cannabis

How To Lower pH

To lower the pH of a grower’s medium when it’s too high, they’ll need to use one of two different approaches depending on the medium they’re using. Most experienced growers know how to lower the pH of the water in their hydroponic weed garden: by giving their cannabis something acidic. Common products like pH Down and acid-based fertilizers can lower the pH of a hydroponic grow. For soil grows, pH Down solutions, acid water and iron drenches can help lower the pH of a medium. However, it’s important to note that iron is also a cannabis micronutrient, so it’s important for a grower to be conservative if they want to lower their pH using iron.

How To Raise pH

Additionally, a grower needs to know how to raise pH in soil for their weed plants. To do that, they can use high-pH fertilizers, flowable lime or hydrated lime. These products all help to boost the pH in a medium and allow the plants to absorb nutrients again. Hydroponic growers can also use these tools in addition to products like pH-Up and potassium bicarbonate. However, similar to iron drenches, potassium is itself a nutrient. Therefore, growers need to make sure they’re not giving their plants too much of it when using potassium bicarbonate to raise the pH of a plant.

Wrapping Things Up

Now that you’ve learned the basics of pH control, you can apply these rules to your own grow. Mastering pH is a crucial step for any grower who wants to grow bomb weed. With enough knowledge and practice, you’ll get used to adjusting the pH of your cannabis plants for maximum efficiency. That way, you can ensure that you get high-quality, high-yielding harvests every time!

Easy to grow weed strainsOpen collection
Is there any potential problem with using white vinegar & baking soda as ph up & down?
I've been using apple cider vinegar as pH down since I started growing. Never needed a pH up though.
may i ask why do you want to use vinegar and baking soda? cash that tight ?
Yes I'm currently piss broke, somehow still learning to grow for personal & have been extremely lucky as a broke ass so far. I popped some bag seeds, made two grow boxes from scrap wood and Panda Film (one for veg & one for flower). Started vegging under CFL. Went to the hydro store and was given free samples of nutes, then went to the thrift store and scored an HPS on the cheap.
2 bottles of ph up and down is like $6 shipped on amazon and more than enough for an entire grow cycle in a medium setup
I’ve always had problems with pH, it could be always too high one summer or too low the next summer. I couldn’t figure the reason, but it stopped once I started using branded soils with nutes from the same brands only. They are developed specifically to create cannabis-specific blend with pH perfect for Cannabis. Never had any problems since. Just make sure to use pH neutral water
Good soil should not need to be PH'd, in fact it can ruin the soil bacteria which feed on the soil and release its nutrients for the plant to use. It is this bacteria which controls the PH to one in which it and the plant thrives. Soilless hydro on the other hand has no such bacteria so the PH is not controlled any other way then by the grower. Unless you have very bad soil, PH should not be causing any problems and changing the PH will be futile.
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