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The perfect PH value for a cannabis plant

In the world of gardening, pH both affects and is affected by everything. Indeed, the entire process of growing plants is a study in the physical dance of pH balance.

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So, you are on your way to growing great cannabis. Your seeds have sprouted, and a small cannabis plant is now eagerly growing. You have spent good money on quality nutrients, and have made sure to properly water and feed your precious plant baby. But something is wrong; you notice your plant appears sick. The leaves are getting discoloured and growth has come to a standstill. Before you know it, your plant is withering away, and you’re stumped as to how this could’ve possibly happened.

Among fatal flaws like overwatering and overfeeding, pH imbalances are one of the most common issues in the cannabis garden. To understand why pH is so important, let us first understand the concept in and of itself.

WHAT IS PH?

pH is a measure of how acidic or alkaline something is. The pH scale ranges from 1–14, with a pH of 7 being neutral (the pH of pure water). If pH is lower than 7, a substance is considered acidic (think vinegar or lemon juice). If the pH is higher than 7, the substance is alkaline, as is the case with soaps, bleach, and ammonia.

In more scientific terms, pH level has to do with the concentration of hydrogen ions, say in the water you give to your plants. The pH scale is logarithmic to the base 10, which means that water with a pH of 6 is already 10x more acidic than water with a pH of 7.

WHY IS PH IMPORTANT WHEN GROWING CANNABIS?

As you will already know, all plants require nutrients for healthy growth. They require macronutrients nitrogen, phosphorus, and potassium, as well as micronutrients and minerals including calcium, magnesium, iron, copper, and a whole lot more. If plants cannot access these nutrients, it will lead to deficiencies and other serious health problems.

The issue with cannabis plants is that they are only able to take up nutrients within a small pH window, which ranges from about 6–7 when growing in soil. If the pH is lower or higher than that, the plant cannot take in nutrients, even if they are present—thus spurring nutrient deficiencies via “nutrient lockout”.

In those places where cannabis thrives in the wild, the soil is normally slightly acidic; therefore, homegrown cannabis plants will also prefer a slightly acidic environment. However, the way that you grow cannabis also plays a role in the optimal pH level for your plants. Cannabis grown hydroponically or without soil needs an even lower pH than a soil grow.

WHAT’S THE BEST PH FOR GROWING CANNABIS?

SOIL: 6.0–7.0 pH

If you grow in soil, the optimal pH level for the root zone is between 6.0 and 7.0. However, there is no set number within this range that is “best”. Instead, it can be good to allow for some natural fluctuation within this window to support optimal nutrient uptake. So as you adjust, try a slightly different reading each time. You can, for example, adjust your pH to 6.2 for one watering, then 6.6 the next. As long as it stays within 6.0–7.0, you should be fine. Soil is also more forgiving when it comes to pH imbalances, but it can only give so much.

If you grow purely organically—where you do not administer liquid nutrients—pH is less of an issue. If you’re using amended and composted soil with organic matter, the microorganisms within will make the nutrients more available to the roots. However, most growers using standard potting mixes and liquid nutrients will indeed have to reckon with pH.

HYDROPONICS AND SOILLESS: 5.5–6.5 pH

Hydro and soilless grows are a different beast when it comes to pH. If you grow soilless, say in coco, the optimal pH level at the root zone should be somewhat lower than in soil, between 5.5–6.5. The same goes for all methods of hydro.

With these methods, it is just as important that you allow the pH level to fluctuate across the acceptable range to support nutrient uptake. For example, in hydro, calcium and magnesium are mostly absorbed at pH levels above 6, while other nutrients like manganese prefer a slightly lower pH.

Then again, this shouldn’t be an issue since pH levels will naturally change slightly with each feeding in a hydroponic setup. You will only need to correct if the pH level exits the optimal 5.5–6.5 pH range.

When growing in coco, perlite, or hydroponically, you are in charge of administering nutrients directly to the root zone via the water, which means that huge pH fluctuations are more of a risk than in soil. The inert media used in hydro and soilless grows merely retains water and provides support for the roots of your plants. So when administering nutrients, be careful that you don’t overload your plants.

In the world of gardening, pH both affects and is affected by everything. Indeed, the entire process of growing plants is a study in the physical dance of pH balance.

How to Adjust pH When Growing Organic Cannabis

Question: What’s the Best Way to Adjust pH If I’m Growing in Organic Soil?

How do I manage the pH of my soil when growing organically?

More info: I’ve heard that many pH control kits can kill beneficial bacteria in the soil.

I was watering my cannabis plants tonight, and I mixed in a half strength dose of bloom nutes. So I test the PH and it is right in range, about 6.5. When I tested the runoff, it was really acidic at around 5.5.

What am I doing wrong, and how do I correct pH in my organic soil without hurting the micro-organisms the help the roots?

Answer

1.) Usually You Don’t Need to Worry About pH When Growing Cannabis With Organic Soil

As long as you’re starting with a good water source, usually you don’t have to think too much about pH during your grow.

However, when growing cannabis in organic soil, some of the most important things happen before you even germinate your plants. The more effort you put into starting with great organic super soil, the less you’ll have to worry about during the actual grow itself. If you’ve set things up properly, pH won’t be a problem for you!

When growing marijuana organically in a super soil environment, there are tiny organisms in the soil that break down nutrients and “feed” them directly to your roots. When you enlist the microorganisms to do the work of making nutrients available to the roots, pH management stops being something you have to do!

When growing organically, you also depend on your soil and the various components to automatically buffer the pH. Starting with the right soil will make things a lot easier for you!

Learn how to make organic super soil (custom-formulated soil for cannabis plants – for those who want to do organic growing the “real” way and just water their plants, without having to worry about pH or giving nutrients)

Unless you are noticing actual symptoms of nutrient lockout (nutrient deficiencies) than pH adjustment is probably not necessary.

Don’t let your nutrients run out!

If you’re starting with regular (non-composted) organic soil, than your plants will quickly use up all the nutrients in the soil and you will either have to transplant to new, fresh soil every 3-4 weeks or supplement with a proven organic nutrient line like the GO box. It’s especially important to make sure your plant doesn’t run out of nutrients in the flowering stage or it will dramatically lower your yields! Once of the cool things about composted soil is the nutrients break down slowly over the course of your grow, giving your plants the right amount of nutrients at the right time.

But if you are using liquid nutrients, it becomes important again to make sure you’re testing the pH of the water going in and out. Even organic liquid nutrients are only readily available to your plants if the pH is in the right range. But since you don’t want to disturb the microorganisms in the soil, try to only actually adjust the pH if you notice pH nutrient problems in your plants.

In general with organic growing, it’s recommended you do not adjust or try to manage pH until you know something is wrong. In organic growing “if it ain’t broke don’t fix it.”

2.) Organic Ways to Adjust pH – For When There’s a Nutrient Problem!

If you’re seeing nutrient problems on your plant, and you know your plant hasn’t used up all the nutrients, the first thing to always check is the pH! Check the pH of the water that’s going into your plant, as well as the runoff water that’s coming out the bottom. In soil you want to maintain a pH of 6-7.

If you do notice nutrient problems, the first thing to do is check the pH of the water going in and out!

If your pH is outside the 6-7 range, you may need to adjust the pH to avoid further nutrient lockout on your cannabis plants. But since you’re growing in organis soil, if you do want to adjust pH, you should use an organic source.

Luckily, there are natural sources of PH Up and PH Down, many of which you can actually find around the house!

Organic “pH Down”

Note: Dolomite Lime acts as a natural pH buffer and will help keep the pH constant when added to your soil during the compost process. It can also help correct acidic soil up to a certain point. If you have just realized your soil pH is too low, try to find powdered dolomite lime, as the larger chunks take longer to break down, though be careful that you don’t add more than instructed, lime is “hot” (has relatively high levels of nutrients) and can burn your plant in too-high doses. The larger chunks should be okay if you’re just looking for a pH buffer.

Using an inorganic pH adjuster (like the pH Up and Down that come with most pH adjustment kits, for example the General Hydroponics pH kit) may actually damage your microherd (beneficial bacteria) and can set your marijuana plants back as far as nutrient breakdown / absorption is concerned.

Learn the best ways to adjust soil pH using purely organic methods.