Ericaceous compost can’t be used on just any type of plant in your yard or garden. This compost has a low pH or high acidity, which can damage some plants that don’t prefer acidic soil.
Most compost isn’t ericaceous, and if you measure your soil’s pH levels regularly, you’ll already be aware of which of your plants like which type of soil. When you buy it in the store, it will be labeled as ericaceous, but when you make it at home, close attention should be paid to the materials that go into your compost to be sure it’s the right pH level for the plants you’ll use it on.
What’s The Difference Between Ericaceous Compost And Normal Compost?
The difference between ericaceous compost and normal compost is the acidity level. Regular compost has a slightly acidic to slightly alkaline range between 5.5 and 8 (with 7 being neutral), while ericaceous compost has a pH between 5.5 and 4. Many plants like slightly acidic to neutral soil, but certain ones prefer more acidic soil.
The word ‘ericaceous’ comes from its Latin root, Erica, which refers to the plant family, also known as heath or heather. These are short, woody evergreens that grow in acidic soil, and the word has come to also describe the acidic conditions that those shrubs like to grow in.
Why Does PH Level Matter For Compost?
In nature, some locations have more acidic soil than others. In general, areas that get more rain have more acidic soil because rainwater contains some acidic compounds naturally from the atmosphere. Forests and rainforests tend to be more on the acidic side, while grasslands and arid regions have more alkaline soils.
Since plants are conditioned in nature to live in a certain soil type, they need those conditions recreated in our gardens. The soil pH affects which nutrients are available in abundance and which the plant must be particularly efficient with. For plants that like only slightly acidic or neutral soil, a low pH has certain nutrients available that are toxic to those plants in higher amounts than they’re used to.
For example, nitrogen starts to become less available below a slightly acidic level of 6, while iron becomes increasingly available below the same pH level. For plants that aren’t used to it, acidic soil can be toxic with iron and leads to a deficiency in nitrogen. Both, in the correct amounts, are vital for photosynthesis and many other plant life processes.
What Makes Compost And Soil Acidic?
Aside from rainfall, certain other plant compounds add to the acidity of the soil. Some plants, like oak, pine, and walnut trees, have high tannin content, a bitter compound that has a low pH level. When materials from these kinds of plants break down, the tannic acids are released and can lower the soil’s pH, making it more acidic.
In compost, as in soil, these materials take the longest to break down, and the material will slowly release tannins and lower the pH level of the immediate area.
Humic acid also lowers soil pH, which is produced as organic material gets broken down. It’s present in abundance where there’s lots of organic material and a high rate of decomposition, but it’s found in all soil and is an important way that nutrients get released from organic material.
What Plants Can You Put In Ericaceous Compost?
Certain plants do best in high-acid soil, and these include many common flowers, trees, and foods:
- Azalea
- Hydrangea
- Rhododendron
- Hosta
- Holly
- Dogwood
- Oak
- Pine
- Magnolia
- Potato
- Pumpkin
- Leeks
- Broccoli
- Celery
- Raspberry
- Blueberry
Oak trees, for example, are native to the northern hemisphere, and they can live in soils between a pH of 5 and 7. Berry bushes are native to forested areas around the world, which have lower pH levels on average. Blueberry bushes, for example, like ericaceous soil between 4.5 and 5.5, as do rhododendrons and azaleas.
Can I Put Acid-Loving Plants In Regular Soil?
Hydrangeas, in particular, will subtly let you know if they need more acidic soil: their flowers are pink or white in only slightly acidic soil, but they have purple and blue flowers when the soil pH is between 5 and 4.5 when aluminum starts to become increasingly available (and provides the dark blue coloration).
In general, however, if you put acid-loving plants in regular soil, they may end up not being able to get enough iron, which is most available in soils with a pH below 6. An iron deficiency, or chlorosis, leads to yellowing and wilting as the plant is less able to perform photosynthesis. Acid-loving plants are used to the high availability of iron and low availability of nitrogen, which is most able to absorb at a pH level between 6 and 7.5.
Without enough iron, however, the plant is unable to use nitrogen, even when it’s plentiful. Without photosynthesis, sugars and starches aren’t made, and the plant weakens and eventually dies off.
How Do You Make Ericaceous Compost?
The best way to make ericaceous compost for your acid-loving plants is by using the leaves, twigs, and other clippings from those plants in your compost heap. Compost made with these materials will release more tannins into the mixture while their materials slowly break down. The carbon-rich parts of the plants, like dead leaves and stems, last particularly long to keep the soil at a lower pH. Once the organic matter is completely decomposed, however, the materials are neutralized.
To make acidic compost, mix a 50/50 balance of carbon-rich materials like dead leaves, sawdust, cardboard, and woodchips with nitrogen-rich materials like vegetable and fruit scraps from the kitchen, grass clippings, and other herbaceous yard waste. The green, nitrogen-heavy materials will break down first, and the carbon-rich materials will last longer, providing the ericaceous compounds that acid-loving plants like so much.
