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Managing Alkaline Soil: How to Lower Your Soil pH
Growing plants in chalky or alkaline soil can be challenging, but the good news is that lowering soil pH is a straightforward garden project that will help you grow a much wider range of plants successfully.
Understanding Your Soil Test Results
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Your soil test shows a pH of 7.8, which is very alkaline (or limey). To put this in context:
- Average soil pH: around 6.5
- Acidic soil (such as peat): around pH 5.5
- Chalky/alkaline soil: around pH 7.0 and above
Why Does Soil pH Matter?
Each plant species has evolved to access nutrients at specific pH levels. For example, rhododendrons naturally grow in forest leaf litter, which creates acidic soil conditions. At this pH level, they can readily access the nutrients they need. At the other end of the spectrum, plants like daisies thrive in alkaline conditions.
Plants That Love Alkaline Soil
Before you invest effort in lowering your pH, it’s worth noting that many beautiful plants actually thrive in alkaline conditions. These include:
- Dianthus (pinks and carnations)
- Lavender
- Clematis
- Lilac
- Bearded iris
- Scabious
- Gypsophila
- Hellebores
- Box (Buxus)
- Viburnum
Your extremely high pH might be natural if you’re on chalk, or if you’re in a new build property, it could be caused by building materials like dropped cement mortar raising the soil pH.
The Solution: Lowering Your Soil pH
If you want to grow acid-loving plants or simply expand your planting options, the goal is to bring your soil pH closer to 6.5. You can achieve this using both natural and chemical treatments:
Natural Treatments:
- Well-rotted horse manure or farmyard manure – use as a mulch or dig into the soil. Both have a naturally low pH.
Chemical Treatments (available at most garden centres):
- Liquid tomato feed – apply as a liquid feed
- Growmore fertiliser – sprinkle one handful per square metre
- Iron sulphate – sprinkle onto the soil and water in well
The Good News
Looking at your soil test results apart from manganese levels, all other nutrients in your soil look fine. As you lower the soil pH, the existing nutrients will become more available to your plants, and you should see noticeably improved growth.
