Understanding Soil pH:
A Simple Guide
Soil pH is one of the most important factors in plant health. It controls how nutrients behave in the soil and how easily plants can absorb them. Even the best soil mix and fertilizer won’t perform properly if the pH is too high or too low.
What Is pH?
pH measures how acidic or alkaline something is on a scale from 0–14.
Below 7 = Acidic
7 = Neutral
Above 7 = Alkaline
Examples:
Lemon juice: ~2
Pure water: 7
Baking soda solution: 8
Most plants prefer slightly acidic soil.
Why Soil pH Matters
Soil pH affects:
Nutrient availability
Root health
Microbial activity
Fertilizer effectiveness
Water uptake
A plant can show nutrient deficiencies even when nutrients are present — simply because the pH prevents uptake.
Think of pH as the “nutrient gatekeeper.”
Nutrient Availability and pH
Different nutrients become more or less available depending on pH.
At Low pH (Too Acidic)
Calcium and magnesium become less available
Iron and manganese can become excessive
Root stress may occur
At High pH (Too Alkaline)
Iron deficiency is common
Phosphorus becomes harder to absorb
Micronutrient lockout can happen
Ideal pH Ranges for Cactus & Succulents
Generally 5.5–6.5
Some desert species tolerate slightly higher pH
Organic vs Mineral Soils
Organic-Rich Soils
Compost, bark, peat, and worm castings naturally buffer pH swings. These soils are generally more forgiving.
Mineral / Gritty Mixes
Cactus and bonsai mixes with pumice, lava rock, sand, and stone have less buffering capacity. pH changes happen faster and water quality matters more.
Water pH Matters Too
The pH of your irrigation water slowly changes soil chemistry over time.
Hard Water
Usually alkaline
Raises soil pH over time
Can cause mineral buildup
Rainwater / RO Water
Usually lower in dissolved minerals
Helps prevent salt accumulation
Signs Your pH May Be Wrong
Possible Low pH Symptoms
Slow growth
Leaf burn despite mild feeding
Weak roots
Calcium deficiency
Possible High pH Symptoms
Yellowing between leaf veins
Iron deficiency
Nutrient lockout
Pale new growth
How to Test Soil pH
1. Soil Slurry Test
Mix:
1 part soil
1 part distilled water
Let sit 15–30 minutes and test with a pH meter or strips.
2. Runoff Testing
Measure the water draining from the pot after watering.
Useful for container gardening, though less accurate than a slurry test.
3. Digital pH Meter
Fast and accurate when calibrated regularly.
How to Raise Soil pH
To make soil more alkaline:
Dolomite lime
Crushed oyster shell
Wood ash (small amounts)
Dolomite lime is popular because it also adds calcium and magnesium.
How to Lower Soil pH
To make soil more acidic:
Elemental sulfur
Acid-forming fertilizers
Peat moss
Pine bark fines
Changes happen gradually — especially in mineral soils.
pH and Soil Ingredients
Different ingredients influence pH differently.
Ingredients That Tend to Raise pH
Limestone
Hard water deposits
Oyster shell
Some composts
Ingredients That Tend to Lower pH
Peat moss
Pine bark
Sulfur amendments
Mostly Neutral Ingredients
Pumice
Perlite
Lava rock
Sand
Granite grit
The Role of Biology
Healthy microbial life helps stabilize pH naturally.
Beneficial fungi and bacteria:
Break down nutrients
Improve nutrient cycling
Help roots absorb minerals
This is one reason living soils are often more resilient.
Common pH Mistakes
Chasing Exact Numbers
Plants tolerate ranges better than constant adjustments.
Adjusting Too Quickly
Large swings stress roots and microbes.
Ignoring Water Quality
Your water source may be causing the issue.
Over-Fertilizing
Salt buildup changes root-zone pH over time.
Final Thoughts
Perfect pH is less important than stability. Healthy roots, proper drainage, quality water, and balanced nutrition all work together with pH to create a thriving soil ecosystem.
If your plants are struggling, checking pH is one of the fastest ways to diagnose hidden problems before they become serious.