Last updated on May 10th, 2020
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Ericaceous compost is a type of compost that’s perfect for cultivating acid-loving plants but with the large mophead hydrangeas, you use ericaceous compost to make the flowers bloom blue. There are some plants that prefer acidic compost and hydrangeas are one of them. There are times when you should use ericaceous compost for your hydrangeas and if you do you can choose to make your own or purchase it from any local garden centre or online.
How to make compost acidic
There’s no single solution for making compost acidic as the recipe is really contingent upon the current level of pH in your garden. Thankfully you can make some form of the compost rather easily.
- Start off your compost pile with approximately 8 inches of organic matter.
- Add to that high acid matter such as pine needles, oak leaves, or coffee grounds.
- Compost will eventually go back to a neutral pH but the pine needles help to keep the soil acidified until the pine needles decompose.
- Mix approximately 1 or 2 inches of screened garden soil over your compost so that all of the microorganisms that you have in your soil will naturally help the decomposition process.
Once you have this done you can, of course, take from your compost pile to help with your hydrangeas and spread it along borders under hydrangeas you want to encourage a blue flowers from.
Ericaceous potting soil mix
If you are growing your hydrangeas in pots you can use a mixture of 20% perlite, 10% sand, 10% sterilised soil, and 10% compost and then add peat moss to account for the rest. This type of mixture is ideally suited for high acid content thanks in large part to the peat moss. It is a perfect mixture to utilize in pots.
You can of course just buy ericaceous compost from your local garden centre, if you take this route we recommend a John Innes soil-based ericaceous compost.
When to use ericaceous compost for hydrangeas
In order to change the color of your hydrangeas if you have a big leaf variety like a mop head or lacecap you can use ericaceous compost. Ericaceous compost will make your soil more acidic. Acidic soil produces blue flowers. Not all hydrangeas will produce blue flowers so make sure that you have a big leaf variety, like a mop head or lacecap. In general, white hydrangeas cannot change their colours.
If you’re going to use ericaceous compost to change the color of your hydrangea flowers to blue, get an at-home pH test kit and test the pH levels of your soil. Just because of hydrangea is called something with blue in it or is producing blue flowers at the nursery when you buy it doesn’t mean that you’ll get blue at home automatically. In fact the names hardly ever pertain to the colors you get and the color of the flowers when you buy your hydrangea in the nursery is a reflection of the soil at that nursery and not the soil in your home.
That said, test the pH level and then make changes with the compost as necessary. This is something that might take a few weeks or a month or more to fully change. This is especially true if your soil is very alkaline.
Bear in mind that your soil naturally returns to its original state year after year so if you want to keep your flowers blue you’re going to have to use this compost on a regular basis and regularly check the acidity to guarantee results.
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