Managing pH in Your Greenhouse Naturally
by Adrian White
20 December, 2021 by
Managing pH in Your Greenhouse Naturally
Lucija Johum

You’ve heard the term used among farmers and gardeners everywhere. 

But what exactly is pH? If you want to get deep into the technical stuff, “pH” officially means “potential of hydrogen.” In more layman’s terms however, this translates into a measuring method for acidity.

When determining what types of soils are best for your plants, taking pH into account can be important. In a greenhouse environment especially – where soils used within are introduced and managed differently than out in a field – it’s crucial that growers have some awareness and control of these smaller, more isolated soil environments within their structures. Certain plants thrive better in a specific soil acidity level over others, since pH can also indicate more of certain nutrient minerals are available, though not always. 

The great news is that growers can have some control over the pH of their soils, and using just natural and organic means. Even better: the key to optimizing pH does not have to be through constant testing. Being aware of soil biology and nutrition, and even paying attention to plant health, can all give you some indicators of how your soil acidity needs to be tweaked, if at all. 

With that said, how do you get acquainted with your soil’s pH? Understanding it to begin with is a real help and a great first step, in addition to a simple test. Then, once you grasp the science of it, working with it for the benefit of your greenhouse plants can be a walk in the park.


As stated above, pH is the measure of hydrogen present in soils, which in turn gives one an idea of acidity. The more hydrogen that is concentrated there (in relation to other elements present), the more acidic it will be. On the opposite end of the spectrum, the less hydrogen around, the more basic it is (or alkaline).

Typically, the more acidic soils are, the more revealing it is of less elemental nutrients available to plants such as magnesium, calcium, and potassium. Soil that acidifies over time as more hydrogen gets concentrated there – something that happens naturally the more plants absorb nutrients into their roots – naturally lowers the amount of nutrient availability. To measure this, the pH scale runs from a general range of 0 to 14: 0 being very acidic, and 14 being extremely basic.

The most important thing to remember: acidity can be very telling of your soil microbiome – that is, the diversity of microscopic life present, an element that is very important to plant health according to Lowenfels and Lewis: authors of Teaming With Microbes. Soil life can be greatly affected by acidity, and every grower should pay attention to balancing this aspect of their growing medium for the best results. Healthy soil biology is everything!

Now, what precisely happens when soil becomes very acidic, as opposed to very alkaline? How can you tell the difference? But more importantly: how do you bring it all back into balance?

ACIDIC (0-7)

Having more acidic soils can mean a number of things. On the one hand, more acidic soils signal the presence of more fungal life, and less so bacterial life. It can also indicate the presence of less nutrients important to plants because hydrogen levels have increased so much over time.

In some cases, finding acidity in your soils means nutrient availability has been stripped somewhat, with no organic nutrient matter having been returned over the years. For most plants, this is definitely not ideal, and you’ll want to bring pH back into balance. However, for some plants – such as nursery trees, shrubs, and hardy, woody perennials – having fairly acidic soil is a real boon (raspberries, fruit trees, and evergreens are good examples).

These plants evolved over time to have better relationships with fungal-rich microbiomes near their roots. All the same, however, even a too-fungal, excessively acidic environment can be tough on these acid-lovers, too – so be careful and attentive.

BASIC (7-14)

Also called alkaline soils, this state represents an excess of other elements and nutrients besides hydrogen – and most likely potassium, an element that tends to alkalize its surroundings. Magnesium, calcium, and other nutritive elements may be found in large amounts, too. On a soil biology level though, higher basicity means that soils also have a higher level of bacterial activity, which is not something that all plants will enjoy. 

Your average soft-stemmed plant however – such as most vines, herbs, and flowers – will absolutely love a growing medium that is slightly alkaline. That’s because these plants have evolved to interact with bacteria to get the nutrients they need in the soil. Though watch out: your woodier plants will struggle in such environments! 

Still, on the extreme end of things, very alkaline soils indicate a huge level of nutrient availability that can be exciting to some plants. Unfortunately, anything to the extreme will be harmful to any plant, no matter what it is. For that reason, avoid letting your soils veer towards extreme alkalinity.


The truth of the matter: most plants are like Goldilocks. They don’t want their porridge too hot, nor do they want it too cold. For the most part, they’ll want it just right: smack dab in the middle.

The definition of neutral on the pH scale hovers right around the number 7, exactly in the middle between 0 and 14. For the most part, even some plants that prefer “slightly acid” soils – like some vegetables – stick around the number 7, with 6.5 being the sweet spot. The same with slightly alkaline lovers, hovering around 7.5 or 8.

Since most plants don’t go to extremes, there’s a better chance than most that you’ll simply want to focus on furthering soil neutrality. The best way of doing this: taking care of the soil microbiome! Ensuring that there is a wide variety and diversity of microbial life for your plants right there in the dirt is always a wise step for your plants, no matter what.


Let’s say you’ve checked your soils, and you do see a deficiency or imbalance in the making. The soil is much too acidic for your greenhouse veggies, or maybe the alkalinity is way too high for your flower crops. Either way, how do you bring things back to the happy medium?


To bring highly alkaline soils back into balance, there are a certain number of natural methods and tricks to help you. Try these as soil amendments in your growing medium.

  • Calcitic lime – A version of lime that is high in calcium, amending this into your soils can help raise soil acidity levels when they’re too low. Make sure you don’t apply it to plants that dislike high calcium amounts. After application, one must wait up to an entire season before seeing the pH change.

  • Dolomitic lime – Another type of lime that is high in magnesium rather than calcium. As such, don’t apply it to plants that get overwhelmed by magnesium.

  • Evergreen needles – Evergreen needles – such as pine – are high in tannins and volatile oils, which have a way of encouraging acidity and fungal growth in soils by stifling bacterial growth as they biodegrade. Using them as a mulch or amendment can help acidify slightly over time.

  • Gypsum – Gypsum is known to slightly acidify soils when you really need it, though not by much. In addition it is quite helpful for excessively alkaline clay soils, since gypsum can help break apart clumped up, hard-packed soil matter.


How about soils that are too acidified? How can you take steps to alkalinize them, and in simple, natural ways? Here are a few good (and popular) ideas.

  • Wood ash – A small dose of wood ash can go a long way for upping alkalinity in your soil. Since it’s rich in potassium, this too can help make soil more alkaline – though be sparing. Mother Earth News encourages that only up to 25 pounds be used on 1,000 square feet of space per year.

  • Mulch – Certain materials that are popular in mulch can give your pH a little lift. Oak leaves are a very good choice according to SF Gate, along with most other leaves that come from any hardwood tree as mentioned by Fine Gardening.

  • Baking soda – A common way to boost pH up here and there is to add a very small bit of baking soda to your soils. This can alkalize soil rather quickly – add baking soda once per week, test the pH, then add more until it gets to the level you like.

  • Lime – While lime is known for acidifying soils, if they are likewise on the very acidic side, lime can actually alkalize them, too. Both dolomitic and calcitic lime will work this way – but remember that it takes a while to see the pH change.


Going back to that Goldilocks analogy, how do you get your soils to be “just right?” That’s easy: just focus on improving your soil’s microbiome. You can actually work on this no matter what state your medium is in: whether it’s too alkaline or too acidic.

“Neutralizing” soil – that is, supporting its microbiome – is a task for anytime, and should be a part of the daily work of farmers and growers everywhere. Taking care of your soil life means that you take care of your plants. And really: if soil life is flourishing around your plant’s roots, then pH tends to manage itself naturally over time, and more and more without your help!

How to neutralize:

  • Add live compost – Have a compost pile? If not, make one! Or, make friends with someone who does. Incorporating live, microbe-rich compost into your soil is the best way to maintain pH neutrality over the long term.

  • Use compost teas – Along the same lines, compost teas work as excellent natural additives, since they are alive with plenty of bacteria. They also provide extra nutrients as fertilizer.

  • Mulch, mulch, mulch! – In combination with compost, adding mulch in and around your plants can help balance the life there. Not to mention: it makes your growing space look neat, and keeps down weeds.

  • Use only natural fertilizers – It should be known that chemical fertilizers – pesticides and herbicides, too – can suppress or even throw out of balance the life that is naturally present in your soils. To maintain neutrality: stick to natural!


Is managing soil acidity levels any different within a greenhouse than, say, an outdoor growing operation or garden? The short answer: not really. The long answer: the steps aren’t too different, but you might have to work them in more often!

If you think about it, an outdoor operation – involving plants sown straight into the ground – only needs some pH checking once in a while. However, since the soil surface area is so expansive and in higher contact with the natural elements of the outdoors, it probably needs it only a couple times a year, depending on how intensively it’s grown.

With a greenhouse, your growing mediums are more or less cut off from the outside natural world. If you are planting straight into the ground under your cover, on the one hand, that’s a bit of a different story – but if you are utilizing raised beds, containers, growing benches, or isolated mediums of any kind, realize that you will have to work natural matter into your soils more regularly because they are so cut off.

The most important thing to realize, however: no matter where you grow – greenhouse or no – the more naturally you grow without the use of chemicals, the less you’ll need to check on pH. The more naturally and organically you grow on the other hand, especially while working compost and compost teas into your operation, the less you’ll need to check pH, because you can be confident that the microbes are doing it for you!

Some quick tips:

  • Choose live and natural – When selecting soil that you’ll be bringing into your greenhouse to plant – such as for containers within a greenhouse – favor ones that are organic, or which contain microbes. This will help keep pH neutral.

  • Tweak your soils yearly (if need be) – Each spring, depending on the pH, work in amendments to your mediums that will help bring it to the level you want (e.g. wood ash for more alkalinity, or lime for more acidity).

  • Hydroponic pH adjustments – Does pH apply to hydroponics too? Of course! Very specific formulas – both organic and inorganic – are available commercially for your setup, helping you control pH so you don’t harm plants.

  • Planting straightaway into the ground under your cover? – Check pH and amend just like you would with an outdoor field setup, though you’d be wise to check pH a little more often. With water erosion and other elements having no way to escape outside your structure, you can bet they’ll have some more impact on your soil pH than otherwise.


As you can see, pH is important. For any gardener and grower, even in a greenhouse, keeping tabs on which end of the spectrum your soils are leaning –acid or alkaline – can help you prevent diminished plant health, and make sure they’re getting the nutrients they need by bringing them back into balance.

For extreme alkalinity or acidity, there are natural, easy ways to help harmonize your growing medium. But the biggest trick of all: take care of your soil life! If you keep the bacteria and fungi at your plants’ roots alive and kicking by avoiding the use of chemicals and amending with compost, these little guys will do practically all of the pH-tweaking for you.

And – as a busy grower yourself – you know you can always use the help!

Managing pH in Your Greenhouse Naturally
Lucija Johum 20 December, 2021
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