Understanding how pH affects cannabis plants

Understanding how pH affects cannabis plants

The need to maintain the right pH for cannabis growing is one of the most important fundamental cultivation parameters. pH is a measure of acidity/alkalinity. It affects many aspects of cannabis cultivation. Get the pH wrong and your plants won't be able to absorb the necessary nutrients even if they are present, a phenomena known as nutrient lockout.

Summary:
What is soil pH?
How does pH affect cannabis plants?
Understanding cannabis pH fluctuations
What’s the ideal pH level for cannabis plants?
How to test soil pH for cannabis?
Cannabis pH problems symptoms and cure
Choose from the most resistant cannabis seeds

What is soil pH?

The pH scale varies from ph 0 to pH 14. pH 0 is highly acidic and pH 14 is highly alkaline. pH 7 is half way between, it is neither alkaline nor acid. Therefore pH 7 is defined as neutral. Very acidic or very alkaline conditions can be hugely destructive to plant cells and tissue. That’s why many biological processes take place around neutral pH levels.

In the case of cannabis, pH is typically around 6-7 when grown in soil. In other words, a slightly acidic cannabis soil ph is preferred for optimised mineral/nutrient absorption by the cannabis roots. In the wild, cannabis plants will thrive in moist, nutrient rich soil with a slightly naturally acidic pH.

When grown in other methods/systems such as hydroponics, cannabis pH range may need to be even more acidic. Using hydroponics, water pH for cannabis is typically in the range 5.6 - 5.8. Just for comparison, Orange Juice has a pH around 3, milk has a pH around 6 and battery acid has a pH of 1.

Soil pH

How does pH affect cannabis plants?

Now you know a little more about pH for cannabis you may be curious to know why/how the pH of your chosen grow medium has such a crucial role in the health, development and quality of your cannabis plant.

All cannabis growers will be aware that cannabis relies on nutrients and minerals to grow. That means a good, usable supply of the main N, P & K macro nutrients (Nitrogen, Phosphorus and Potassium) within the soil nutrients. Carbon (C) Hydrogen (H) and Oxygen (O) are macronutrients which are absorbed via air and water.

In addition to the main ‘macro’ nutrients, there are also vital micro nutrients which are required to maintain and support the complicated cannabis plant biochemistry. The micro nutrients include elements such as Magnesium, which is vital for photosynthesis, as well as Boron, Calcium, Iron, Manganese, Copper and others.

Micro nutrients, by definition, are only required in small quantities. But the presence of these micro nutrients is essential to the long term and short term plant health. Without them, you won't be able to produce high quality cannabis. That’s why ph for weed is critical.

If the soil pH for cannabis is outside the preferred range the various biochemical pathways required for nutrient absorption and mineral assimilation simply don’t work. That means nutrient lockout. The nutrients may well be present in the soil, but the wrong pH for cannabis means that they can’t be absorbed and used.

Related:
Cannabis nutrient deficiencies and excesses chart

Understanding cannabis pH fluctuations

Maintaining ideal environmental conditions for your cannabis plants is the best way to ensure optimised harvest quality levels as well as generous harvest quantities. That’s why good cannabis growers like to maintain the best pH for cannabis. Many experienced cannabis growers monitor the pH of their cannabis grow medium. This allows them to check that the cannabis ph level is OK. It also allows the grower to catch any pH drift early, before it has had chance to cause too much damage.

When cannabis pH levels fluctuate it restricts the ability of the plant biochemistry to fully utilise the key nutrients essential to plant and bud growth. Resin production and THC levels will be reduced. To the cannabis grower, this will seem like the plant is struggling to grow/yield well. The plant may look discoloured. The growth may look inadequate and the buds won't have the same quality. 

What’s the ideal pH level for cannabis plants?

If you’re growing in soil, the best pH for cannabis is between pH 6.0 - pH 7.0
A cannabis pH chart is sometimes provided by the nutrient supplier. It shows the various minerals and nutrients and how they are best delivered at an optimum pH for the plant. Note that in soil-free cannabis cultivation, e.g. cannabis hydroponics, slightly more acidic conditions nearer pH 5.6 - 5.8 are often used.

Few soil growers are particularly worried about the specific pH level. So long as it is between pH 6-7 the conditions will allow good plant growth, assuming that the soil quality and other environmental conditions, lighting etc are also well controlled.

To some extent soil is ‘self buffering’ and provides a certain degree of tolerance and flexibility. Therefore you may not need to worry about precise daily pH checks on the pH of your local water supply (and final nutrient solution) in the same way that hydroponic growers might. Soil is forgiving, but can only self-buffer to a certain level.

Organic growers may have a little more latitude than most when it comes to cannabis pH. Although there is nothing wrong with growing cannabis in soil using concentrated liquid nutrients, many people prefer to forget about their pH meter and take a more organic approach.

Not only can this seem simpler, many cannabis connoisseurs think the best taste and aromas are produced from organic soil-grown weed. If this sounds appealingly simple, you are not alone! Dutch Passion recommend slow-release organic nutrients such as those from BioTabs.

These slowly release nutrients throughout the grow and also support a healthy root zone of beneficial bacteria and microbial life. This means, especially when growing in large soil containers, that you may only need to consider light general purpose bloom nutrients towards the end of bloom.

Note that many soil growers feel that allowing a certain natural variation between ph 6-7 is also healthy for the plant since it may allow certain minerals to preferentially absorb at different pH levels. Few soil growers are determined to maintain pH for cannabis at precise levels and many never bother checking the soil pH at all.

One of the beauties of soil cultivation is that you have more pH latitude and flexibility than you would with other grow methods. For some cannabis growers, keeping life simple in the grow room is one of the most important issues. Growing organically in soil is a great way to do just that.

pH scale

How to test soil pH for cannabis?

How to test soil pH cannabis? A simple pH probe is a useful and affordable investment. Just dip the probe below the moist soil surface and check the pH reading. You can also use paper pH strips. Simply take put some soil in a glass and mix with an equal volume of neutral water. Pour through a coffee filter and check water pH with a paper pH strip.

Don’t worry about getting the best pH meter for cannabis. A basic, affordable model should do the job. When you buy your pH meter also invest in some buffered pH reference solutions (e.g. pH 4.0 and pH 7.0) which can be used to check the performance/accuracy of your pH meter. When your pH meter can no longer be accurately calibrated to the reference solutions it’s time to get a new one.

Cannabis pH problems symptoms and cure

Knowing the best pH for cannabis is one thing. Maintaining it consistently can take some effort and checking. Cannabis pH problems will often arise if the nutrients/water pH is wrong. This could happen if there has been e.g. a mistake with nutrient preparation or nutrient additives.

One extreme measure for soil growers who feel that they have lost control of soil pH is simply to flush the soil with a large amount of water. If you have a 15 litre container of soil, perhaps you will flush with 20 - 30 litres of water. If you think there is a pH problem, don't delay, flush your soil with water before the plant is damaged.

Another option, perhaps for those with a little more practical experience with additives, is to use ‘pH Up’ or ‘pH Down’ to adjust pH levels in soil/water. If you are growing with a suitable hydroponics system you may be able to add ‘pH up/down’ additives drop by drop to your nutrient reservoir to correct the pH. Ensure that the ‘pH up/down’ additives have sufficient time to thoroughly mix in with the water in order to avoid false pH readings which will compound your problems.

Related:
What’s wrong with my cannabis plant?

How to tell if pH is too low

If pH is too low, indicating excessively acidic conditions, you will also see leaf discolouration as well as reduced growth/vigour. Outside of the optimum pH you will eventually see mineral deficiencies. A quick pH check is always worthwhile.

It’s important to find the root cause of the sudden pH issues. Has there been a dramatic shift in local water pH? Are your nutrients being correctly made up? Are you using pH adjustment additives excessively? pH adjustment additives will raise the pH (‘pH up’ makes it more alkaline) or reduce pH (‘pH down’ makes it more acidic). Incorrect use of these can be disastrous for your plants.

Many cannabis growers make up their nutrient solutions the day before and allow them to stand overnight. This allows the pH to equilibrate and stabilise. It also allows any chlorine smell (from mains water treatment) to disappear as well as allowing the nutrient solution temperature to equilibrate with room temperature.

Many soil growers, if they do need to test pH, do so on nutrients which have been prepared the previous day. One other useful tip is to stir and mix your nutrients thoroughly after using pH up/down in order to ensure that your pH readings are accurate and represent the real pH of the full solution.

How to tell if pH is too high

If pH is too high conditions are too alkaline for optimised cannabis growth. Elements like Iron are difficult to absorb when the pH is too high. Nutrient lockout and deficiencies will occur and the first signs of this will be on the cannabis leaves. The normal healthy vibrant green colour will often be replaced by yellowing leaves. Vigorous plant growth stops and plant health struggles until the correct pH for cannabis is restored.

How long does it take for cannabis plants to bounce back from high pH? This is a difficult question to answer with precision. High pH cannabis symptoms will depend on how severe the pH issue is and how long it has been present. Your plant could bounce back within a few days if you flushed the soil with plenty of water. Or, in the worst circumstances, your plant could be permanently stunted or die if left to sit in a very high pH feed for too long.

How to adjust pH levels

How to adjust soil pH for cannabis? Delicate use of pH additives to nudge pH up or down is not uncommon with cannabis growers. If pH control is something that worries you, take a look at organic soil growing. This minimises the need to worry about pH. The self buffering action of the soil naturally takes care of pH, up to a certain degree.

If you prefer to grow hydroponic cannabis (soil free) you will be in complete control of nutrient preparation and will need to be much stricter about pH control. That will require regular calibration and checking of your pH meter as well as the requirement to keep a spare pH meter for the inevitable day when the pH meter fails or starts to deliver incorrect readings.

Some organic growers find that pH can be gently and steadily adjusted using certain natural methods. pH can be reduced with the addition of compost teas, manure/compost, pine needles (these are slightly acidic). These natural additives may help with beneficial microbial action in the soil too. Lemon juice (mildly acidic) is a natural pH reducer. Lime/Limestone (mildly alkaline) is a natural way to increase pH.

Choose the most resistant cannabis seeds for your garden

Choose from the most resistant cannabis seeds

There are no particular cannabis strains which are particularly good at growing in extreme pH levels. Instead, focus on maintaining optimised environmental conditions for your plants. Perhaps that may be organic soil growing where pH concerns are minimal. Or it may be in a hydroponics system where pH stability and full pH control is essential in order to maximise the quality of your harvest.

Related:
Optimising your cannabis grow room conditions

If you’re growing organically in soil, the pH for cannabis is something that you may rarely concern yourself with. That means that you can choose freely from the Dutch Passion collection of autoflower seedsfeminised cannabis seeds or regular seeds. All will grow easily and deliver proven, high quality results.

Autoflowering cannabis seeds are particularly recommended for growers looking for the easiest grow experience. They grow from seed to harvest under 20 hours of daily indoor light, taking around 11 weeks. Grow them in large containers of soil e.g. 25-50 litres, with slow release BioTabs organic nutrients and you may only need to add tap water throughout the grow.

Understanding how pH affects cannabis plants
January 29th 2021
Categories : Cannabis Plant

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