Do Hydrangeas Need Ericaceous Soil? Understanding Soil Preferences

Understanding Hydrangea Soil Preferences

Hydrangeas are popular flowering shrubs grown for their showy blooms and ability to adapt to different garden settings. While they are often associated with ericaceous, or acidic, soil, the reality is more nuanced. Not all hydrangeas require acidic conditions, and their soil preference depends largely on the specific variety and the desired flower colour.

Ericaceous soil is acidic in nature and is typically recommended for plants that prefer a low pH, such as rhododendrons, azaleas, and camellias. Some hydrangeas can benefit from such conditions, but others are far more adaptable. Understanding how soil pH affects hydrangea performance is key to growing them successfully.

How Soil pH Influences Flower Colour

One of the most well-known characteristics of hydrangeas is their ability to change flower colour based on soil pH. In particular, this applies to Hydrangea macrophylla, also known as mophead or lacecap hydrangeas. In acidic soil, where the pH is below 6, these hydrangeas tend to produce blue or purple flowers. In neutral to alkaline soil, with a pH above 7, the flowers shift towards pink or red.

The reason for this change lies in the availability of aluminium in the soil. In acidic conditions, aluminium is more soluble and available to the plant, which influences the pigments in the petals and results in blue tones. In alkaline soil, aluminium is less available, and the flowers take on pinker shades. This phenomenon does not occur in all hydrangeas — it is specific to certain cultivars of macrophylla varieties.

When Ericaceous Soil Is Beneficial

Ericaceous soil is most useful when the goal is to grow blue-flowering Hydrangea macrophylla varieties. For gardeners looking to achieve or maintain strong blue or purple tones, lowering the soil pH using ericaceous compost, pine bark, or sulphur-based products can make a significant difference. Growing in containers using ericaceous compost offers more control over soil chemistry and is often the best option in regions with naturally alkaline soils.

Hydrangeas grown in acidic soil may also show better uptake of micronutrients like iron and manganese, which supports greener leaves and overall plant health. However, these benefits are most apparent when pH is a limiting factor in plant performance.

Not All Hydrangeas Require Acidic Soil

While some hydrangeas benefit from ericaceous soil, many varieties are perfectly happy in neutral or even slightly alkaline conditions. Hydrangea arborescens, such as the popular ‘Annabelle’, and Hydrangea paniculata, known for cone-shaped blooms, are not sensitive to pH in the same way. These types will bloom reliably regardless of whether the soil is acidic or alkaline, and their flower colour remains consistent.

For these varieties, the structure, drainage, and organic content of the soil matter far more than its pH. Well-prepared, moisture-retentive soil with good organic matter will produce healthy plants and vigorous flowering without the need for specialised compost.

Managing Soil pH for Container-Grown Hydrangeas

When growing hydrangeas in pots, it’s much easier to manage the pH of the growing medium. Using ericaceous compost gives an instant low-pH environment, and applying rainwater instead of tap water helps maintain acidity over time. Adding a hydrangea feed formulated for acid-loving plants can also support stronger flowering in blue varieties. If pink blooms are preferred, a more neutral compost and alkaline fertiliser will help reinforce that tone.

Because container soil can change pH over time due to watering, feeding, and leaching, regular monitoring is useful if flower colour is a priority.

The Role of Aluminium and Iron Uptake

When gardeners aim to produce blue hydrangea flowers, the focus is often on making the soil more acidic. But the real driver of colour change is the plant's ability to absorb aluminium, which only happens when the pH is low enough — typically below 5.5. Even in slightly acidic soils, if aluminium is not present or not soluble, flowers may stay pink. This is why aluminium sulphate is sometimes added alongside ericaceous compost to reinforce blue tones.

Iron uptake also becomes more efficient in acidic soils. If hydrangeas are grown in alkaline or even neutral conditions, they may develop chlorosis, a yellowing of leaves caused by iron deficiency. This isn’t universal across all hydrangea types, but it’s more likely to appear in pH-sensitive varieties like Hydrangea serrata and Hydrangea macrophylla. This is another reason why ericaceous conditions benefit certain hydrangeas — not just for colour, but for leaf health.

Soil Biology and pH Interaction

Soil pH doesn’t only affect the plant directly — it also influences the biological activity within the soil. In more acidic soils, the microbial population shifts. This can affect how organic matter breaks down and how nutrients are made available to the plant. Certain beneficial fungi and microbes thrive in slightly acidic conditions and help make phosphorus and trace minerals more accessible to roots.

If your goal is long-term health and resilience for your hydrangeas, improving not just pH but overall soil biology through compost, leaf mould, or other organic inputs may be as important as selecting ericaceous compost.

Rainwater vs Tap Water

In alkaline regions, even if you plant your hydrangeas in ericaceous soil or compost, you may gradually undo the acidity by watering with hard tap water. Tap water in many parts of the UK contains calcium and magnesium, which raise soil pH over time. If you're growing hydrangeas in containers and trying to maintain blue flowers, using rainwater instead of tap water is a simple and highly effective step. It helps preserve the acidic environment without needing to constantly reapply acidifying products.

Seasonal Changes in Flower Colour

Even with perfect soil conditions, hydrangea flower colour can shift slightly over time or across seasons. Changes in temperature, light exposure, rainfall, and nutrient uptake can all influence how pigments express. You may notice blue blooms fading to lavender or pink as the season progresses, even in acidic soil. This is a natural variation and doesn't necessarily indicate a problem with your soil.

Because of this, colour control in hydrangeas is best approached as a range, not a fixed outcome. You can aim for blue, but expect some natural variation — especially as the plant matures.

Misconceptions About Ericaceous Soil

Many gardeners assume that ericaceous soil is necessary for all hydrangeas, which leads to unnecessary effort and cost. In fact, most hydrangeas will perform very well in neutral soil with good structure and moisture retention. It’s only when the specific goal is blue flowers — or when growing clearly acid-loving species like Hydrangea serrata — that ericaceous soil becomes essential.

For the majority of white, green, or pink-flowering types, including Hydrangea arborescens and Hydrangea paniculata, soil pH has little to no impact on performance.

Final Word

Hydrangeas do not universally require ericaceous soil. Only specific varieties, mainly Hydrangea macrophylla, depend on acidic conditions to produce blue flowers. Other types are more pH tolerant and will thrive in a range of soil types as long as drainage and organic matter are adequate. Ericaceous soil is a helpful tool for those who want to control flower colour, but it is not essential for healthy growth in all hydrangeas. Knowing your variety and your goal will help determine whether acid soil is truly necessary.