All about ericaceous compost

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Whether you’re a keen all-round gardening enthusiast or a reluctant weekend weeder, if you’re hoping to get the most out of your flower beds and borders this spring, then you’ll need to swot up on some basic chemistry – the pH scale. In gardening terms, any reference to pH levels normally refers to the acidity or alkalinity of soil, however it’s also important to understand the significance of pH levels in compost.  Granted, who knew plants were picky when it came to compost?!?! However, this is the case and different plants like different composts and soil conditions. Ericaceous plants are plants which are averse to lime and so thrive in acidic growing conditions; these include common UK flowering plants such as rhododendrons, camellias and azaleas. These lime-haters will require an ericaceous (acidic) compost. 

Ericaceous compost has a pH balance of less than or equal to 7, ideal for growing acid-loving plants including blueberries, azaleas, camellias, rhododendrons, and heathers; it serves up a generous dose of low-ph nutrients to keep your favourite flowers thriving. If you’re beholden to existing flower beds and borders filled with alkaline soil, ericaceous compost is a great way of counteracting the high pH of the soil, while also feeding and nurturing plants, regulating moisture and serving as an aesthetically-pleasing top layer. 

If the soil in your yard is only slightly alkaline, you can try to modify the pH level by counteracting the alkalinity by adding ericaceous compost. If you’re new to the idea of composting and pH levels, this information article should help you in understanding the basics and finding a suitable compost for you, your budget, your soil and your plants. 

HUMAX Ericaceous Compost 40L
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HUMAX Ericaceous Compost 40L
  • Brand: Humax
  • Usage: cuttings and planting out of pots, tubs, window boxes and creating acid beds and bog gardens.

Only got 5 minutes 

The pH of compost and soil controls how effectively the nutrients in the soil can be absorbed by the roots of plants. Despite the fact your garden soil or compost may be teeming with goodness, if the pH level isn’t compatible with the plants you’re trying to grow, they may not be able to absorb the nutrients from the soil and so your plants will not thrive and, worst case scenario, they may be killed off completely. 

Just having a basic understanding of the role of pH levels in compost can help avoid costly, time-consuming mistakes, and ensure you’re giving your plants the best possible chance of thriving, even in not-so-perfect soil conditions. 

What is ericaceous compost?

Ericaceous compost is an acidic soil-improver, which tends to be defined by the ‘lime-hating plants’ best suited to its acidic composition. 

These include:

  • Rhododendrons
  • Camellias
  • Azaleas
  • Heathers (sun-flowering)
  • Pieris
  • Blueberries
  • Japanese maples 
  • Tomatoes
  • Rhubarb

Suitable for use in flower beds, garden borders and pots, ericaceous compost not only promotes strong root development through its ability to retain moisture and enhance drainage, it also contains long lasting nutrients to encourage optimum growth and eliminates the need for additional feeding i.e. adding additional ericaceous fertiliser. 

The best ericaceous composts will contain lasting growth boosters; be weed-free; contain added iron to assist in the production of chlorophyll and enzyme production; and be sourced from British sustainable materials, with no added chemicals. 

Ericaceous compost facts

  • Ericaceous plants are also known as ‘acid-loving’ or ‘lime-hating’ 
  • In order for ericaceous plants to grow and thrive, they need to be in the correct soil (acidic) or at least have ericaceous compost added to the existing soil 
  • Ericaceous plants depend on nutrients which are inaccessible to them in high pH (alkaline) soil 
  • Ericaceous compost allows the release of iron and other essential nutrients needed by acid-loving plants
  • These essential vitamins can be bound up in the structure of normal soil, depriving the roots of your ericaceous plants of the nutrients they need
  • Soil which is lime-rich and has a pH level of above 7 binds iron and other essential nutrients which are essential for the healthy growth of ericaceous plants 
  • If planted in alkaline soil, ericaceous plants produce weak, yellow leaves; growth is stunted and overall appearance is poor 
  • The term ‘ericaceous’ originates from the Latin term for heather ‘Erica’ 

Do I need ericaceous compost?

You’ll need ericaceous compost if the soil in your garden is alkaline but you intend on growing acid-loving plants. It might sound complicated but it really isn’t – you’ll first need to check the pH level of your soil by:

  • Using a soil-testing kit; this is the most reliable way of obtaining accurate results
  • Adding a soil sample to distilled water and testing using litmus paper 
  • Looking at your neighbours’ gardens to see if they’re growing lime-hating plants such as rhododendrons or azaleas!

A pH reading greater than 7 means you may struggle to grow ericaceous plants in your current soil type; you’ll need to grow them in pots using ericaceous compost instead. There is the option of adding chemicals to your soil, which can increase the acidity, but the change in pH level is often short-lived, especially if the soil was particularly alkaline to begin with. To some extent, it does depend on the specific type of plant and how ericaceous the species is as some plants are so strongly ericaceous they won’t grow in soil that is only slightly alkaline! 

Rhododendrons and azaleas tend to be more tolerant to slight alkalinity, but blueberries are very particular, preferring a pH of below 5.5. As a result, in the UK, frustratingly fussy plants such as blueberries are only likely to be seen growing in pots. 

It’s worth remembering that UK tap water is slightly alkaline and so shouldn’t be used to combine ericaceous compost with your existing soil, or be used to water ericaceous plants. An alternative is to use a water butt in your garden to collect rainwater. Using this instead of tap water will help maintain the level of acidity in your soil/compost. During prolonged dry periods when rainfall is minimal, you may have no choice but to reach for the vinegar in order to reduce the alkalinity of tap water!!! When all else fails, it’s certainly worth giving it a go, however it’s advised to test the pH before applying it to your ericaceous plants to check you haven’t overdone it with the barley malt!!!

Lime-hating, acid-loving plant types 

FlowerGenusFlowers in…Description
AzaleasRhododendronSpring Have shallow roots so require a well-drained soil Dense flower coverage, available in a large variety of colours Bright and summery feelRequires partial shade 
BlueberriesVacciniumSpring Produces ornamental bell flowers  Foliage hage has good autumnal colourRequires well-drained, moisture-retentive, acidic soil of pH level 4.5-5.5Blueberries contain high level of vitamin C, fibre and phytochemicals 
RaspberriesRubus Varies depending on variety Requires well-drained, slightly acidic soil Dislikes waterlogged or shallow, chalky soils Thrives in full sun or partial shade 
ParsleyPetroselinumLate spring Traditional and versatile herb Fresh, peppery tasteFlowering plant native to the MediterraneanMost common types: French curly-leaf and Italian flat-leafHealth benefits include lowering blood pressure and has been known to treat inflammatory conditions 
CamelliasCamelliasEarly spring Glossy evergreen Dramatic, stunning, elegant flowers in a range of red, white, pink, and yellow shadesThrives in full sun once roots are established Best planted in autumn 
TomatoesSolanaceaeSpringYellow flowersRequire 6-8hrs of sun each day, and plenty of water  Requires a rich, well-drained soil Sweet, fresh, slightly bitter scent 
Heather Callunas Mid summer to autumn Low-growing perennial shrub (around 2ft) Narrow, mid-green foliage with long spike-like,  4-petalled pink or purple flowers Requires well-drained, moist soil and full sun 
EnkianthusDeciduous shrubsLate spring to mid summer Deciduous shrub Bright and colourful feel; in autumn produces an amazing variety of browns, reds and yellowsSmall, alternate elliptic leaves Produces clusters of small cream or reddish, bell-shaped flowers 
KalmiasEvergreen shrubs Spring & SummerDense, bushy, medium-sized shrub Glossy, leathery leaves, deep green in colourPrefers moist but well-drained soil in partial shade Produces large clusters of bowl-shaped dark to pale pink flowers 
Pieris (Forest Flame)Evergreen shrubsSpringElegant but hardy Young foliage is red in colour, turning pink and cream before turning dark greenProduces small white urn-shaped flower clusters 
RhubarbRheumEarly spring to late summer Hardy perennial Grows up to around 2.5ftFleshy, edible, vitamin-rich stalks – pink, red or greenLarge, triangular-shaped leaves

Loam-based V peat-free ericaceous compost

Loam-based ericaceous compost

Loam-based ericaceous compost is soil-based and consists of a blend of loam, sand, grit or peat with increasing amounts of fertiliser added depending on the stage of growth.  It contains generous amounts of iron to support enzyme functions such as energy production and to encourage healthy leaf growth – ericaceous plants benefit from a helping hand when it comes to producing chlorophyll, which is needed for green and healthy leaves. 

Loam-based ericaceous compost is well-suited to growing rhododendrons, azaleas & camellias.

Peat free ericaceous compost 

Traditionally, ericaceous composts were peat-based; widely used due to its ideal structure (the perfect balance of coarse and fine particles) and impressive water, air and nutritional content. The problem is that peat is primarily sourced from lowland raised bogs – a habitat that is now increasingly rare across the UK. Consequently environmentalist organisations have stepped in and raised the awareness of protecting and conserving such habitats. 

Compost manufacturers have responded by producing an increasing range of peat-free and peat-reduced composts made from a variety of base ingredients, such as wood or coconut fibre, composted bark and green manure.

100% peat-free ericaceous compost is ultimately the best option when it comes to the environment however it’s regarded by experts as not being as nutritionally rich as loam-based ericaceous composts. That said, manufacturers are working hard to improve the quality of peat-free ericaceous compost, and, for most amateur gardeners, it should prove sufficient for neutralising the alkaline soil in our home and domestic gardens.

Westland Ericaceous Planting & Potting Mix 10L
  • Size: 10 Litre
  • Slow release iron to maintain acidic root environment
  • Promotes chlorophyll production for greener, glossier foliage
  • Added zinc complex helps build plant resilience
  • 6-month slow-release feed for sustained growth

Using ericaceous compost in pots 

  • No flower beds or borders? Balcony or yard? No problem. You can still brighten up your outdoor space using pots.
  • If your soil has a pH reading of 7 or greater, this may prove difficult when it comes to growing ericaceous plants. The solution? Ericaceous compost in pots.
  • A wide variety of ericaceous plants can be grown in pots, even the larger shrubs such as camellias. 
  • Both the dwarf versions of rhododendrons and azaleas are a great choice of ericaceous pot plant – they’re small, colourful, and flower reliably year on year. 
  • Camellias are a popular choice but can grow to be pretty big so careful not to over-plant your pot!!
  • When choosing pots for your ericaceous plants, always choose a pot that’s just a little bit bigger than the pots they’re currently housed in. 
  • Choose a pot that’s too big and the soil is likely to go sour before the roots have spread and anchored.
  • General rule of thumb – the diameter of the pot should be around 10cm bigger than the diameter of the rootball; place the rootball in the pot centrally.
  • If bigger pots are your thing, then overcome the problem of potential soil souring by putting several plants in one pot. 
  • In spring, feed your ericaceous plants with ericaceous fertiliser to help encourage healthy growth. 
  • Ericaceous plants in pots will need repotting around once every 2 years as ericaceous compost loses its structure and the nutritional content reduces over time. 
  • The biennial re-potting of ericaceous plants is the ideal time to transfer them into bigger pots if required and/or prune the rootball. 

Frequently Asked Questions

What is the pH level of compost?

Mature compost generally has a pH of around 6 – 8 (neutral to low-alkaline). As compost decays, its pH level will change from initially being fairly acidic, to becoming more neutral as the organic matter breaks down.  If you have acid-loving plants, you will need to consider adding some ericaceous compost to soil which has a pH level of 7 or above.  

What are ericaceous plants?

Ericaceous plants are plants and shrubs which don’t like growing in soils that contain lime and so require planting in acidic or neutral soils and composts. Common ericaceous plants include rhododendrons, blueberries, heather, camellias, conifers, magnolias, acres, pieris, hydrangeas and azaleas.

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About Francesca Fitton 108 Articles
I have a passion for gardening and being outdoors. I blog about plant care, technology and tools that I love to use outside and invite you along to watch.

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