Understanding Soil pH

If you are new to gardening you might not understand the importance of soil pH levels in your soil. While it is still something I am learning about, I thought I would do some research and write a blog on it to also help with my understanding of the subject.

So first off, what is soil pH and why does it matter?

The nutrients that plants need to survive are absorbed through their roots. The way plants receive those nutrients is by absorbing them once they are dissolved in water. If the mixture of the water with the nutrients is either too acidic or too alkaline, the nutrients won’t be able to easily dissolve and the roots will be incapable of absorbing them, making the plant unable to grow.  This is where your pH level comes in. Soil pH is the measurement of the amount acidity or alkalinity that is in a soil.  pH is measured on a scale of 0 to 14, 0 being pure Hydrochloric acid and 14 being pure sodium hydroxide, which is alkaline. No plant can survive in either of the extremes, however some plants do better in soil that is more acidic than alkaline and vice versa.  Neutral pH is 7, and most plants do best when they are in the range of anywhere between 6 and 7.5.  You can find out the pH level of your soil with a test kit that can easily be found in any gardening store, nursery or online. So, soil pH level is important because if it is off, you're plants can't absorb any nutrients and they won't survive. 

That being said, it is important to test your soil to find out if you need to adjust your soil so that your plants have the best possible chance of survival. However, be aware of what you are planting. HERE is a link to see the list of plants that thrive best in certain levels.  If your test shows that the number is more than a .5 difference from what you need, you are going to need amend your soil.

Once you find out what level your soil is at, if it is not what you need it to be, you are going to need to figure out how to adjust it.  Be aware that it can take months to adjust the pH level of your soil.  You should test every 2-3 months and only expect about a .5 unit of difference in that time. Every time you test, you can add more amendments. Also, be conscious about the fact that adding extra amendments can cause more harm than good. If you are adding anything that comes from a bag, make sure to follow the directions exactly. Too much can be damaging.  It is usually best start testing and amending in the fall time so that hopefully by spring you are ready to start planting. You will make it easier for yourself if you choose plants that thrive best in the soil you already have.

Now, to adjust your soil, lets first say your soil is acidic. This means that the pH level is lower than 7.  With acidic soil it means that your soil is lacking in calcium and magnesium. The most common organic fixer for soil with high acidity is Lime.  There are two different lime amendments. Dolomitic limestone is for if your soil has tested low in magnesium, and calcitic limestone for if your soil is low in calcium. Other things that work well for acidic soil are eggshells, oyster shells, clamshells, calcite, or hardwood ashes.  

Next, lets pretend your soil is too alkaline. This means that your pH level is above 7 and that your soil is low in iron, phosphorous, and zinc.  The best way to handle high alkaline soil is to increase the nitrogen. Things that are good to add nitrogen are sulfur, acidifying fertilizers or peat moss. Again, make sure to follow instructions on your bag. However, you can never add too much organic matter such as compost, animal manure, or worm castings. You can add any kind of organic matter on as often as you want to because it will only continue to help your soil. It is also good because it is providing food for the microorganisms that are living in your soil, and you need microorganisms because when they digest the matter, they create nutrients for your plants and help create great soil structure. Click HERE to understand in depth why microorganisms are important.

Note: Peat moss is controversial because the way it is obtained is not very sustainable. Coco coir is a good alternative however it ‘s pH is closer to neutral so for using it to try and lower levels it might not do anything.

So, once you have decided what amendments to add to your soil, all you have to do is follow the instructions on the bag and apply! Or in the case of adding organic matter, just cover your bed completely. Then till it all in and you are good to go until you need to test again. Now, many people believe in no-till farming and that is another subject but I think technically if you leave amendments on top it’s considered mulch.  This will over time amend your soil but it takes much longer to decompose.

  I hope now you have a better understanding on what soil pH is and why it is important. I encourage anyone with a garden who hasn’t tested their soil to do so and maybe it will answer some questions if you are having growing some particular things! Thanks and have a great day!


I am currently doing an internship with Deanne Bednar at Strawbale Studio in Oxford, Michigan. While here we a had a couple of guys come and do a biochar demonstration open for anyone in the community. Here is a summary of what I took from it along with a little extra research. First off, what is biochar? Basically, it's just charcoal that is used for soil amendment. It is created from the burning of wood or biomass (a renewable form of energy) under the exclusion of oxygen and is composed primarily of recalcitrant carbon which means that it stays in the soil for hundreds to thousands of years unlike labile carbon that will rot in matter of weeks to years.  (Labile carbon is usually root residue or plant debris, also known as compost, that provide an important source of energy for soil microorganisms) Biochar has a long history for being used as a fertilizer but in the last thirty years research and use has accelerated. Recently, production of biochar is being suggested as a strategy to remove global-warming carbon dioxide from the atmosphere because of it's ability to produce oil and gas byproducts that can be used as a fuel providing renewable energy, thus meaning it could possibly help alleviate climate change.

How does it work? Biochar has a microscopic composition of countless small channels that can absorb water and nutrients up to five times it's weight. This is helpful through dry spells allowing it to moderate drought. These microtubules can store important bacteria and fungi which are what transports nutrients from the soil to the plant increasing the biological life of the soil and creating soil fertility. The important thing to know about biochar is that because of it's ability to absorb minerals if you don't charge it prior to soil application it will steal nutrients from the soil and harm your crops. Charging your biochar means loading it with nutrients, this can be done in many different ways. A few of the most common ways to charge biochar would be mixing it with compost, manure, or compost tea and the duration of your charge should be at least fourteen days. Specific instructions on charging your biochar can be found here. Once this is done you should crush your biochar into grain sized material making your biochar ready to be added your soil. We did this by putting it into a five gallon bucket and crushing it with a board. This is going to help improve your plant growth similarly to compost. However, as stated above, because biochar is a recalcitrant carbon it will continue to provide the nutrients you are needing in your soil basically indefinitely unlike your labile carbon compost which you will need to continue to add over the season because of the rate in which it breaks down. If you would like a more in depth and scientific explanation of how biochar works click here.

Why biochar? Biochar can reverse soil degradation reducing the leaching of nutrients and creating a reliable source of fuel and food production enhancing plant growth in places with severely nutrient depleted soil. It can be helpful in places with limited resources or fertilization material and lack of adequate water with it's ability to retain water and nitrogen and raise soil PH level. It can make farm lands more fertile reducing the leaching of nutrients and fertilizer requirement for extended periods of time, provide thermal energy for cooking, and with the addition of an engine could produce kinetic energy for making electricity. Here is a more in depth list of benefits.

How do I make my own biochar? Easy! Biochar can be bought, but it's way more fun to make your own! The method we used in the demonstration was the Hawaiian luau pit. I am going to copy and paste the instructions from http://hawaiibiochar.com/biochar-burn-demonstration/ because they explain it better than I can. First, a fire is started in the bottom of a pit, then dry wood is then added as fast as the fire will allow – you must always push the fire near to the point of smothering it, yet without actually smothering it.  It is important to always keep a clean burning fire – no smoke.  If it becomes a bit smoky, back off, let the fire catch up.  If it is raging, add more wood to choke it out a bit.  In this way youare constantly covering the char that has been made with fresh layers of wood, which become char, which are soon covered with fresh layers of wood, which become char, and so on. When you near the top of the pit or the end of your wood supply, you finish with small diameter wood.  This chars quickly.  Let the flames die down a bit, then voila – a large bed of red hot glowing coals.  By this point, if you have done it right, the entire pit has turned to char.  You can either hose it down immediately, or cover it with soil to snuff it out. We hosed it down which seemed to be the most efficient. I was told that using soil you risk the chance of the fire restarting and turning everything to ash. We were instructed to use wood no more than two inches in diameter and once it got going the moisture content didn't seem to matter much as our wood was pretty wet. There are many different methods to making biochar, more can be found here and The Biochar Solution was a book recommended for learning about it more in depth.

I hope this post was informative and if you had little to no knowledge on biochar previously then you learned something new. Have a beautiful day!