Soil pH – The Master Variable

The UConn Soil Nutrient Analysis Lab tests for and analyzes multiple soil parameters; but none as critical, and as often overlooked, as pH. Soil pH plays a crucial role in the growth of vegetation planted, as well as ground water quality. Before we start talking about soil pH, I think it is a good idea to try to define what exactly pH is, and how it is determined.

When most of us think of pH, a pool probably comes to mind. I remember growing up, watching my mother apply different chemicals to our pool, and impatiently wondering why I had to wait to go swimming. She would tell me that she was adjusting the pH of the water to ensure it was safe to swim in. The basic understanding is that pH is tells us how acidic, neutral, or alkaline something is. To get a little more technical, pH is the measurement of the activity of Hydrogen Ions (H⁺) in an aqueous solution. The equation for determining and quantifying pH is:

pH = -log₁₀ (a_H+)

(a_H+ = Hydrogen Ion Activity in Moles/L)

We express pH on a logarithmic scale of 0-14, where 0-6 is considered “acidic”, 7 is “neutral”, and 8-14 is “basic”.

(Image from: http://www.edu.pe.ca/gulfshore/Archives/ACIDSBAS/scipage.htm)

Mineral soil pH values generally range from 3.0 – 10.0. There are numerous factors that determine soil pH including climate, parent material, weathering, relief, and time. Texture and organic matter content also influence soil pH. Most Connecticut soils are naturally acidic. Nutrient availability is directly influenced by pH with most plants (with some exceptions) thriving at pH values between 6 and 7. A majority of nutrients are available within this range.

(Image from: http://www.pda.org.uk/pda_leaflets/24-soil-analysis-key-to-nutrient-management-planning/)

Our lab measures pH using an 1:1 soil-to-DI water ratio. The saturated soil paste is mixed, then is analyzed using a glass electrode and a pH meter. We calibrate our meter using 2 solutions with known pH values, 4 and 7. We use these values because we expect most Connecticut soils to fall within this range. Once the initial pH value is obtained, a buffering agent is added. In our lab we use the Modified Mehlich Buffer. A second pH reading is obtained, and from these two values plus crop information, we are able to make limestone and/or sulfur recommendations.

The Buffering Capacity of a soil is the resistance it has to change in pH. Soil buffering is controlled by its Cation-Exchange-Capacity, Aluminum content (in acidic soils), organic matter content, and texture. A soil with a lot of organic matter and clay will have a higher buffering capacity than one with little organic matter that is mostly sandy.

If the soil pH is lower than the target range for a particular plant, limestone would be recommended. Whether you use pelletized, ground or granular limestone, the application rate would be the same. Once the target pH is reached, a maintenance application of 50 lbs/1000 sq ft would be applied every other year to maintain it.

If the soil pH is higher than desired, sulfur recommendations are made. Typically only powdered sulfur is available locally but granular sulfur could be mail ordered. Aluminum sulfate can be substituted for sulfur and used at a higher rate. Check out this list of preferred pH ranges for many common plants.

Monitoring your soil pH is essential to ensure that it is falling within the range best suited for the vegetation you are growing. The Standard Nutrient Analysis performed at our lab gives you a pH value, a buffer pH value, a lime/sulfur recommendation, available micro & macro nutrient levels, and a fertilizer recommendation. For more information on pH, you can contact Dawn or myself (Joe) at the UConn Soil Nutrient Analysis Lab (www.soiltest.uconn.edu)!

Test, don’t guess!

Joe C.

 

CT Flower & Garden Show Provides a Breath of Spring!

From this past Thursday morning until last night, the UConn Home & Garden Education Center, the Soil Nutrient Analysis Laboratory and Master Gardener Coordinators and Volunteers staffed our booth at the CT Flower & Garden Show. We weren’t sure how big a turn out to expect as in the past we have found that the more severe the winter, the greater the show attendance – probably because folks really needed encouragement that spring was on the way. This year, however, despite the warm winter, the show was packed! We must have performed more than 250 free soil pH tests and answered hundreds of gardening questions. The large number of soil pH tests was obviously due to the fact that most soils were not frozen solid – in fact there are many areas that only have frost in the top inch of soil – and that’s only on colder days.

Answering questions at the Flower Show

There were a lot of vole and deer control questions and many folks wanted suggestions for dealing with some of the diseases their vegetables, especially tomatoes, had been plagued with last summer because of all the rain. Moss in lawns was also a frequent topic of discussion and many visitors have heard of the boxwood blight that is infecting these lovely evergreens and wanted to know more.

The CT Flower & Garden Show has a lot to offer, from incredible landscapes to a multitude of vendors of largely garden related items, to the creative arrangements by Federated Garden Club members. I think I counted over 200 exhibitors in this year’s flower show program! The work that goes into some of the landscape displays is awe-inspiring! Years ago a company I worked for had an exhibit in the Boston Flower Show and the amount of time, effort, gardening expertise, and physical labor that went into designing, growing and setting up a landscape display left a team of us exhausted but happy with the outcome.

The CT Flower Show also gives local plant societies a place to introduce themselves to potential new members and give folks advice. One could find out information on African violets, bonsai, rhododendrons, orchids, carnivorous plants and much more. Representatives from UConn’s EEB Greenhouse and Invasive Plant working group were there to share their resources.

The theme for the juried Federated Garden Clubs of Connecticuts floral arrangements was ‘The Fabulous Fifties’ and there were so many creative, fun and artful entries it was hard to pick favorites, never mind winners. I would have had a tough time deciding who the awards should go to as all the entries were wonderfully creative.

Here’s some that caught my eye!

The above 3 pictures taken by Clinton Morse, UConn EEB

Till next time,

Happy Gardening!

Dawn