Soil pH is one of the most important factors that can be overlooked in the garden. pH has impacts on the availability of nutrients and of the plants ability to take them up. If the pH of your garden soil is not in the optimal range for the plants you are trying to grow you may end up having issues. Often plants grown in a soil that does not have the optimal pH don’t produce or if they do their harvests are low while the plant may looks stressed.
On today’s joint episode between the Testing Garden Assumptions and Urban Garden Series I am going to take a look at soil pH, how to easily measure it and how you can adjust the pH over time if need be.
pH is measured in a 14 point scale with 0 being the most acidic 7 neutral and 14 the most basic.
Most common garden plants prefer a slightly acidic or neutral soil. There is a link in the description for a University of Vermont reference page outlining the optimal pH for a number of crops. 
After having consulted Maxxam analytics you have two options to measure your garden soils pH. The most accurate is to run a sample through a lab or University Extensions office to get the pH reading on your soil. Alternatively you can do it yourself however it is quite a bit less accurate but should provide you an indication if your soil is in the right ballpark.
You will need two things to do this. The first is a pH meter. This one was under 20$ and should be accurate enough for our purposes. This meter also helps me keep an eye on when I need to water my garden helping me conserve the water from my rain barrel.
The second is distilled or deionized water. You can pick this up at most drugstores. It has a neutral pH whereas your results might be skewed by tap water that is slightly basic and rain water slightly acidic.
pH varies through the soil and changes over time. This meter is also not as accurate as the equipment in a lab. So you will want to pick a number of sites so you can average the results imporving the reliability. For this roughly 1 meter by 1 meter bed I have selected 4 spots that are representative for the bed. The more sample locations you measure the more accurate your numbers will be.
I chose locations that are in the proximity of the crops that I am interested in making sure to not be too close as to disturb roots. Today I am making sure my new blueberry and lingonberry bed has the acidic pH both crops need.
Pull back the mulch and the top inch or 2-3 cm of soil. Most roots are below this initial soil and the mulch I add over the course of the season can temporarily impact the pH of this less used rooting zone.
Mix the soil in the hole down to 6 inches or 15 cm making sure it is as close to a consistent mixture as possible or homogenous.
Flood the area with your deionized water. This will help the meter get a proper reading on the soils pH.
Turn on the meter making sure the probes are clean. Insert and wait for 1 minute until taking a reading. Record the reading and repeat over your other sample locations.
Once you have finished up average the readings. That is the most representative pH of your soil.
If your soil is within the range for the crops you are growing you are good and can rest assured that the pH wont cause any issues and is unlikely to shift too much over time.
One of the most common mistakes new gardeners make is applying store bought products to fix a nutrient deficiency without knowing if that will actually fix it. As I mentioned earlier if the pH is not in the optimal range nutrients may not be available or the plant cant take them up. This is when you may need work to change the pH.
If your pH is very low and you need to raise it gypsum or lime can be added to bring the pH up.
If your soil is too basic and you need to add acid you can add elemental sulfur or flowers of sulfur. You can also mix in peat.
Compost that is made with higher carbon content such as leaf mold does have a lower pH however it is not as effective as peat or elemental sulfur for lowering the pH of soil but does help make up a good base that maintains an initially lower pH.
There are quite a few myths related to lowering the pH of your soil. Amendments such as cold coffee and pine needles are themselves acidic however too weak or neutralize before they can transfer the acidity to the soil.
If your soil does need amendments to bring it into the right pH range you will likely have to continue to amend over time as the soils pH will recover. This is through what is called the soils buffering capacity. Essentially chemical reactions will return to the original pH over time.
If you do have to amend the pH of your soil take it slow. pH changes of more than 1 point per month can have a huge impact on the plants you are growing. Quick shifts in pH can destroy the microorganisms that run the nutrient cycle in your garden. If the nutrient cycle is disturbed your plants may struggle to get nutrients especially if their roots get burned in the process.
When working on amending the pH of your soil I would recommend doing it once a month during the growing season measuring the pH before and a few days after each time.
Having a pH in your soil that is initially in the right range is one of the reasons why I chose to grow in raised beds. Starting with the right pH helps me avoid the cost of testing and amendments to adjust the pH over time.
I started my beds with a large portion of the soil being compost and when I knew there would be acid loving crops like my lingonberries and blueberries I admixed in peat to keep the initial pH lower. Peat is not a renewable resource however when I looked into amending the beds with elemental sulfur it too is not renewable. So I made the decision to use peat as it is a waste product here in Alberta and elemental sulfur is not. As the use of products in the garden is something I like many of you try to avoid I recommend you research the issue before making your decision.
If you would like to find out how to grow more at home or learn about other garden myths check out the links on screen now and make sure to subscribe so you can catch all future episodes in the series.
Testing Garden Assumptions Series Playlist:
Urban Gardening Series Playlist:
University of Vermont pH requirements for plant growth reference sheet: