How to test soil pH for hydrangeas?
Written by
Nguyen Minh
Reviewed by
Prof. Martin Thorne, Ph.D.Correct colour control with your hydrangeas relies upon accurate soil pH testing, which can be done using "instant" soil kits, a digital meter, or by sending a soil sample off to a laboratory. Each method varies in accuracy and price, allowing you to select the one that best suits your gardening needs. I happen to use them all myself for the blue hydrangea beds I tend each year. It pays to check regularly to save costly mistakes.
Soil Test Kits
- Provide instant color-based pH range results
- Cost-effective but less precise than other methods
- Best for quick seasonal checks between professional tests
Digital Meters
- Offer exact numerical pH readings to 0.1 precision
- Require regular calibration with standard solutions
- Avoid meters under $50 as they often give unreliable data
Lab Analysis
- Detects minor pH variations and nutrient levels
- Takes 1-2 weeks but provides comprehensive reports
- Use university extension services for affordable testing
Taking a sample as accurately as possible yields accurate results. You want to sample the soil correctly. Dig six inches deep around the root zone at four different sites around each plant. Then mix the four samples in a clean container for use with the testing kit. Avoid taking samples near concrete or in areas where you have previously fertilized. I once took a very wrong alkaline sample from testing soil near our path, made of crushed limestone. Taking a sample well, of course, avoids such mistakes.
We interpret this hot afternoon analysis correctly if we want to be successful hydrangea growers. An acid soil with a pH below 5.5 often results in blue blooms, which is often attributed to the presence of aluminium. A neutral soil with a pH between 5.5 and 6.5 will produce lovely purple colours. At the same time, a higher alkaline mark, such as 6.5 and above, will result in pink flowers. I have a colour soil chart in my shed, which I keep handy for deciding whether to amend (see over!) quickly.
Avoid common mistakes to ensure reliable test results. Always moisten the soil slightly before inserting the probes; never test dry earth. Use a toothpick to clean the probes between each sample, and remember to store the meter with clean probes. I had my first digital meter die quickly because I left it full of soil and contaminants. Proper care should extend the life of an instrument severalfold, a small price to pay for accurate data.
A mix of methods yields the best results. Use the quick kits for your monthly checks. Rely on the lab tests for changes that need to be made in the soil. Be sure to log readings for reference. My records show trends over a five-year history, allowing me to assess the changes in deficits and surpluses to make to the soil periodically.
Read the full article: Soil pH for Hydrangeas: Color Control Guide
