What Compost is Best For Acers? Key Considerations

Anyone keen on gardening will know how crucial it is to make sure that your plants have good compost to grow in – and what counts as good compost varies depending on what you’re planting.

If you’re planning to grow an acer, it’s important to get the right kind of compost to keep your tree happy and healthy and ensure it has all the nutrients it needs.

So, what compost is best for acers?

Acers generally prefer slightly acidic soil, so if your garden is alkaline, you may wish to grow your acer in a pot or container so that you can control the soil that it is growing in. You can plant an acer into the ground and correct the pH, but you will have to keep doing this every few years to keep the acidity levels high.

What Kind Of Compost Is Acidic?

The right kind of compost for acers is called ericaceous compost, and this can be purchased from many garden centers and nurseries very easily. It’s suitable for all sorts of acid-loving plants and it will help to make the environment around your acer’s roots acidic enough for the plant to grow happily.

You might be wondering why acers need a special kind of compost in the first place. The answer is that certain nutrients become insoluble when they are in high alkaline soil, and that makes them unavailable to your plant – so if the plant needs those nutrients, it needs to be able to access them.

Iron is one of the key minerals that your plant needs access to which it won’t be able to get in soil with a high pH value. You need to adjust the soil so that your acer can get all the iron it needs by making sure it is acidic enough.

If your soil has a lot of lime in it (making it alkaline), you may notice that your acer gets sick and its leaves start to turn yellow. This is sometimes known as lime-induced chlorosis, and it can kill your plant, or at least stunt its growth. If you notice your acer yellowing, check the acidity of the soil to see if it is too alkaline.

Don’t add lime to the soil around your acer under any circumstances. Even acers that are more tolerant of alkaline conditions will not appreciate this addition! Ashes can also increase the alkalinity and should likewise be avoided.

Can You Make Ericaceous Compost At Home?

Yes, you can make ericaceous compost yourself, and if you have acid-loving plants, this is a good idea as ericaceous compost can get a little pricey, especially if you need a lot of it. However, making it isn’t a very quick process, so if you’ve got an acer waiting to go in the ground, you’ll need to buy some.

Making ericaceous compost is similar to making normal compost, but you need to consciously add lots of acidic ingredients to reduce the pH value. Over time, your compost will slowly revert to being somewhat alkaline, so it’s important to add lots of acidic ingredients early on, and to top up your soil with acidity over time.

So, what ingredients do you need? There are quite a few things you can add that you might have to hand. Coffee grounds are a good one; they are rich in nutrients and acidic. You can also include pine needles, oak leaves, wood shavings, leaf mold, composted bark, or well-rotted manure. Citrus peels – unsurprisingly – are also acidic and will reduce the pH levels.

All of these things will make the compost more acidic and fill it with goodness for your plant. In conjunction with this, you should work to keep down the amount of alkaline ingredients you add, such as lime or ashes. These will increase the pH value and pull the compost toward neutral as they decompose.

Once the materials have rotted down, you should have good, acidic compost – ericaceous compost. You should check the pH value to make sure you have successfully achieved a good level of acidity before using it to plant your acer.

How Do I Know If I Need Ericaceous Compost To Correct My Garden Soil?

If you’re wanting to plant your acer in your garden, rather than in a container, you should check the pH of your soil first. Often, you will find that it is not acidic enough for an acer, and you’ll need to add ericaceous compost.

Remember that neutral is at 7.0, and anything above 7 is alkaline. Ideally, acers should be planted at pH values below 7.0, although some will tolerate neutral to slightly alkaline soil. Most like values as low as 4.0.

To check the acidity, all you need to do is buy a pH testing kit. These are readily available, inexpensive, and easy to use. You should follow the directions on the kit you buy, but below are some guidelines.

All you need to do is take a soil sample from about five to ten centimeters below the surface of the bed that you want to plant into. Add this to the testing bottle, followed by the testing solution. 

Shake it up and wait for ten minutes or so, and then check the color of the solution against the pH chart. This should let you know how acidic the soil is.

Can I Plant An Acer In The Ground Even If It’s Alkaline?

The answer to this does depend a bit on how alkaline the soil is, but you may be able to plant an acer in somewhat alkaline soil – but it probably won’t thrive so well. It is much better to plant it in ericaceous compost, but that doesn’t mean you have to use a container if you don’t want to.

To plant in the ground, you need to dig a large hole for your acer. This can be lined with plastic as a means of trapping the acidic soil near the roots of the plant, but remember to add drainage holes so your acer doesn’t get waterlogged.

If you don’t want to put plastic in, try a natural material such as cardboard, but be aware that this won’t last as long. Again, make drainage holes.

Fill the hole with ericaceous compost and mix in some grit to improve the drainage. Next, plant your acer in it and water it thoroughly. This should be enough to keep the acer happy and ensure it isn’t sitting in very alkaline soil, even if the area around the tree is alkaline.

Do I Need To “Top Up” The Soil’s Acidity Over Time?

Yes, you will need to decrease the pH value and increase the acidity over time. You should check the pH every few years using a testing kit, and if the value starts to climb, you need to take action to increase the acidity and keep your acer happy.

Fortunately, this doesn’t mean digging the whole plant up and starting again! Instead, you should add a good thick mulch of an acidic ingredient, such as pine needles. As these start to break down and spread into the soil, they will alter the pH and give the tree the acidity it needs to access vital nutrients.

How often you need to do this will depend on where you live and the conditions in your garden, but if your acer is starting to look sick and you’re not sure why the pH value is one of the first things you should check.

If you find the soil is too alkaline for the tree, make sure you correct it quickly; it will take a little while for your correction to reach the roots, so don’t delay.

Even potted acers will benefit from occasional adjustments to the soil’s pH levels because over time, the compost will shift to neutral or slightly alkaline. You should mulch around potted acers with pine needles or oak leaves too.

Will Some Acers Tolerate Alkaline Soil?

If your garden is quite alkaline, you might be hesitating to add an acer because keeping the soil acidic involves a fair bit of work, and you need to do this every few years. That might make you wonder whether some acers cope better with alkaline soil.

The answer is that yes, some do. If you plant a paperbark or snakebark acer, for example, it will do much better in alkaline soil than some other members of the acer family. Choosing a plant that suits your soil type can massively reduce the amount of maintenance needed, so this is often a wise decision.

Summary

Acers like to be grown in ericaceous compost with plenty of grit to ensure they are well-drained and don’t end up waterlogged. You should make sure that you have some ericaceous compost available before you purchase an acer. You should also mulch the ground with an acidic ingredient every few years to help keep the soil acidic enough for this tree to grow happily and healthily.