Soil for hydrangeas, rhododendrons and blueberries – how to give them acidic soil

Whether soil is acidic or alkaline is measured by its pH value. The lower the pH, the more acidic the soil. Most garden plants thrive at a pH of around 6-7, but acid-loving plants prefer a pH of approx. 4-5.5.

In acidic soil, acid-loving plants can absorb the nutrients – especially iron – that they need. In soil with too high a pH they cannot take up the nutrients, and the leaves turn yellow between the veins.

Typical acid-loving plants are rhododendron, azalea, blueberry, heather, pieris and skimmia. See more in our plant encyclopedia under ericaceous bed.

The easiest solution is a ready-made ericaceous soil. Rhododendron peat from Grobund™ is a blend of light sphagnum peat with a fine structure and rhododendron natural fertiliser. It has a pH of approx. 4 and is ready to plant in – both for new plants and for spreading around existing plants.

To make the soil more acidic and airy, you can also mix pure peat moss into the existing soil. Peat holds moisture well and is easy to work.

Blueberries have the same requirements as rhododendrons: an acidic, humus-rich and moist soil. Plant them in rhododendron peat or in an ericaceous bed – see also our guide How to plant fruit trees and fruit bushes.

Hydrangeas thrive in a moist, humus-rich soil and do well in rhododendron peat. Hydrangeas are, however, more tolerant than rhododendrons and can also grow in ordinary good garden soil.

The pH of the soil affects the flower colour of many hydrangea varieties:

• Acidic soil (low pH): Gives blue flowers, because the plant can absorb aluminium from the soil.
• Alkaline soil (high pH): Gives pink or red flowers.

White hydrangeas do not change colour. If you want blue flowers, the soil must be kept acidic.

1. Choose the location: Most acid-loving plants thrive in light shade or partial shade and in shelter.
2. Dig a large planting hole: Acid-loving plants have a shallow, fine root system. Dig a hole that is wide rather than deep – ideally 2-3 times as wide as the root ball.
3. Fill with ericaceous soil: Fill the hole with rhododendron peat, or mix it well with the excavated soil.
4. Plant at the right height: Plant at the same height as the plant stood in the pot – not deeper.
5. Water thoroughly: Water well after planting and keep the soil moist. Ideally use rainwater, as hard tap water can raise the pH over time.

A layer of bark mulch around acid-loving plants retains moisture, protects the fine roots and suppresses weeds. Pine bark is a popular choice in ericaceous beds. Leave a little space around the stem.

Every year or every other year, top up with a layer of rhododendron peat around the plants so the soil keeps its low pH and good structure. Avoid liming and using ordinary garden fertiliser in the ericaceous bed.

We recommend approx. 150 litres of rhododendron peat per plant for small plants and approx. 300 litres per plant for slightly larger plants.

If you are creating a whole ericaceous bed, allow 30-40 cm of ericaceous soil. A 6 m² bed with 35 cm of soil needs 6 × 0.35 = 2.1 m³ = 2,100 litres.

See more calculation examples in How much gravel, sand and soil do I need?, or use our quantity calculator. We deliver rhododendron peat in bulk bags directly to your address – read more about delivery.