Ericaceous Compost: What is it & Which Plants Need it?

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The Ultimate Guide to Ericaceous Compost

Walk through the compost section of any garden centre and you will be overwhelmed by the vast selection of brands and products, all promising the best results for your garden.

But is it really necessary to use a specific soil type depending on what you are planting? The answer is yes!

Plants are like people, each one is unique and has its own requirements and preferences when it comes to light, food and soil. It may not seem like a crucial factor, but ensuring that your soil has the correct balance of nutrients and minerals for what you are planting will guarantee that your garden thrives all year round with little extra effort from you.

What Is Ericaceous Compost and Why Do I Need It?

In simple terms, ericaceous compost is acidic soil with a PH of less than 7. Generally, in high rainfall climates soil naturally tends to be acidic, whereas climates with lower rainfall levels have much more alkaline soil. If you are unsure of the PH of your soil, you can buy inexpensive testing kits online or at your local garden centre to determine whether your compost is acidic, neutral or alkaline.
It is important to use ericaceous soil if you are growing calcifuge (lime hating) plants. Failure to do so can result in yellowed leaves, and your plant may wither and die without flowering. So, checking your soil PH is a quick and easy job that is well worth doing before you plant!

Which Plants Need Ericaceous Soil?

Many common shrubs and plants prefer ericaceous soil, including:

  • Azalea
  • Rhododendron
  • Hydrangea
  • Camelia
  • Heather
  • HydrangeaJapanese Maple
  • Lily of The Valley
  • Japanese Iris
  • Trillium
  • Gardenia
  • Begonia
  • Blueberry
  • Lingonberry
  • Cranberry
  • Bilberry

Some trees also favour acidic conditions, such as:

  • Magnolia
  • Dogwood
  • Beech
  • Willow Oak
  • Citrus Trees

Do I Need to Buy Special Ericaceous Compost?

Ericaceous compost is widely available to buy online, but if you need to cover a large area, it can become an expensive outlay. Thankfully, there are a few cheap and easy DIY options for acidifying alkaline or neutral soil yourself.

Traditionally, peat was used to lower the PH of soil, however, it is no longer recommended due to declining peat reserves, and the negative environmental impact of intensive peat mining on the ozone and climate. Instead, the Royal Horticultural Society now recommends using sulphur, aluminium sulphate or ferrous sulphate to acidify your soil.

Acidifying Your Garden Soilsulphur powder for ericaceous compost

To acidify your existing garden soil, simply sprinkle sulphur powder directly on your beds. The amount of sulphur needed depends on how acidic you need the soil to be, and whether the current soil is sandy or clay. There are helpful online calculators which will work it out for you, but in general, to change the PH of a soil from slightly alkaline to slightly acidic, you will need between 135-270g of sulphur per square meter.

As the sulphur particles are extremely fine, this should only be done in calm weather conditions and goggles, gloves and a dust mask should be worn for safety. If your garden soil is very alkaline, you may be better off planting your lime hating flowers in pots or raised beds with pre-mixed ericaceous compost.

If your existing garden soil has a PH of 6.5 or less, cutting it with a pre-mixed ericaceous compost will give it a slight acidic edge. However, you will need to monitor the PH to ensure you have the correct balance.

How To Make Your Own Ericaceous Compost

If you are a fan of composting and already have your own pile or bin, you can cultivate your own ericaceous mix. Adding pine needles, bark chips (from a good garden shredder), leaf mould, sawdust, citrus peels and coffee grounds will boost acidity, although these components take longer to break down than regular compost materials.

If necessary, sulphur chips can be added for extra acidity. One important difference from regular composting is that you won’t be able to add calcium or lime to minimize smells and discourage flies, as this will neutralise the PH of the compost. Regular monitoring of the PH levels of your compost will ensure it remains acidic.

Another option would be to blend your own ericaceous potting mix. This can be done by starting with a 50% peat base (or a peat substitute such as coir if you want it to be environmentally friendly), adding 20% perlite, 10% compost, 10% garden soil and 10% sand. Unfortunately, peat substitutes are less acidic, so you may still need to add sulphur to lower the PH of the mix.

coffee grounds

Some Points to Remember

If you lay your ericaceous compost over existing soil, it will gradually lose acidity over time as it mixes with the earth below. To maintain the acidity, it is a good idea to regularly add acidifying materials to your beds. Sounds like hassle, but it really is as effortless as throwing your used coffee grounds, tea bags and citrus peels on the soil. Alternatively, spreading a layer of mulch every so often will have the same effect. You may want to consider a mulching lawn mower to help with this.

It is also worth remembering that treated tap water is normally alkaline, so using it to water your beds could potentially negate the benefits of your ericaceous soil. The easiest solution to this would be to collect rainwater (which is more acidic) and use this to irrigate your plants. If you are stuck, adding a small amount of vinegar to a watering can of tap water will acidify it, but again you will need to check the PH before watering.

Once you have done the initial ground work and added the ericaceous compost to your garden, maintaining it is straightforward, and you will reap the rewards with blooming fruit plants and stunning vibrant flowers year after year. Keep your plants happy and they will reward you generously!

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