Make an Ericaceous Soil Bed for Acid-Loving Fruits

, written by Benedict Vanheems gb flag

Blueberry bed

Some of the very finest fruits come from the acid-loving berries, a family with members such as the blueberry, cranberry, lingonberry and heathland bilberry. The latter has a plethora of colloquial names, including blaeberry, whortleberry, whinberry and, somewhat confusingly, myrtle blueberry.

All these berries grow naturally in acidic soils somewhere between pH 4.0 and 5.0. Neutral soil has a pH of exactly 7.0, with acidic soils sitting below this level and alkaline soils above it. The particularly low range of ideal pH for these acid-lovers means that very few of us have soil that's a perfect match. The solution is to grow them in pots of acidic compost (also called ericaceous compost) or in a specially prepared ericaceous bed, which is the purpose of this article.

Acid test

Gardeners and growers have been tweaking the growing environment for millennia, so making an ericaceous bed to widen our palate of fruits isn't especially new. Soil that isn't acidic enough sees plants such as blueberries failing to properly absorb iron, an essential nutrient for unhindered growth. The result is a plant that's deficient in iron and stunted and poorly as a result. Few plants in this condition will produce much in the way of berries. A dedicated, permanent bed will serve you well, ensuring optimum results and plants that have no need to sulk in second-rate soil!

Blueberries and cranberries

The first job is to find out exactly how acidic or otherwise you soil is. You can look at what your neighbours are growing as a clue – rhododendrons, camellias and heathers are just a few of the ornamental plants that demand acid soil, so if they're growing these you are likely to have acid soil too. However, the best way is to test your soil is by using a simple soil pH testing kit or meter. This will give you an exact figure from which to work. A testing kit will also enable you to test your new ericaceous bed once it's finished to double check it's at the correct pH.

Making an ericaceous bed

The best way to make an ericaceous bed is to prepare a tailor-made growing environment within a raised bed. This will save you digging out your existing soil, which is no mean feat! Construct a simple wooden raised bed by screwing lengths of timber to corner posts. (Find out how to weatherproof your timber.) I have also seen old railway sleepers used to a most handsome effect; you could also use rocks, bricks or breezeblocks – anything to contain your planting medium. Raised beds should be at least 30cm (1ft) deep.

What you add to your raised bed very much depends on what you have to hand. The bulk of the planting medium should be ericaceous compost, which is purpose formulated for acid lovers. To this you can add garden-made compost, very well-rotted manure, composted bark, sawdust or wood shavings, leaf mould or pine needles. If your soil isn't too limey (pH 6.5 or below) you can cut in some of the soil to save on the cost of ericaceous compost. The object is simply to create an acidic environment that's rich in organic matter and that's springy and free-draining, just like the woodland floor and heathland environments where these plants grow in the wild.

Using ericaceous beds for cranberries

Please avoid peat at all costs! Despite what some experts might recommend, it's not necessary and leads to the destruction of increasingly vulnerable wildlife habitat. Use of peat is also akin to cutting down tropical rainforest as it's a natural store of carbon. When cut and used in gardens this carbon is simply emitted as carbon dioxide, contributing to climate change. Gardening should be green, not part of the environmental problem, so steer well clear. Check that your ericaceous compost is also free of peat – it should say this on the packaging. If you have trouble sourcing peat-free ericaceous compost, make your own. Use composted bark, bracken or a combination of both as the base then add three parts by volume to one part lime-free sharp sand or perlite.

Maintaining acidity

An acidic growing medium that's placed on top of soil will gradually lose its acidity as it mixes with the soil below. Maintaining an acidic oasis isn't difficult but does require regular additions of acidifying materials such as those used to make up the medium in the first place. The best way to do this is to add them as a mulch on the surface. Leaf mould (especially that made from maple trees), pine needles, bark chippings and more ericaceous or garden-made compost is just the ticket. Many gardeners also add naturally acidic coffee grounds or spent black tea leaves to the soil surface, though I haven't personally tried this.

Test the soil pH regularly to check whether you are still providing the correct root environment (remember, pH 4.0 to 5.0 is ideal). Towards the end of each winter apply a sprinkling of sulphate of iron to the soil surface ready for growth to resume. Depending on your soil pH you can also water on sequestered iron during the growing season to stop pH from creeping higher.

Blueberries with wood chip mulch

Final tips

Aside from offering ericaceous soil, blueberries, cranberries and other acid lovers must be kept moist to mimic their natural environments. Treated tap water is alkaline, so if there's one group of crops to prioritise for watering with rainwater it's the acid fruits. If necessary you can mimic the pH of rainwater by adding vinegar to a watering can of tap water, but it seems far more cost effective just to make sure you've plenty of stored rainwater to hand.

With a purpose-built bed you will be able to plant more than one of each type, which will dramatically improve pollination and berry set. For maximum visual impact plant your bed up so that lower-growing fruits such as the cranberry form an understory to taller blueberries. This will give a double layer of berries while creating a riot of colour in autumn/fall when the leaves of blueberries turn a spectacular crimson. In fact, acid-loving berries are every bit as ornamental as rhododendrons et al, so make a real feature of your ericaceous bed and celebrate this beautiful, blousy berries.

By Benedict Vanheems.

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Comments

 
"I have two blueberry bushes one in a built up area which sounds ideal but one at ground level.is it a good time to transplant into pots. The plants are two years old."
john haigherty on Thursday 16 January 2014
"Hi John. Now is indeed a good time to transplant into pots. Make sure you use ericaceous compost and appropriate-sized pots to give the roots enough room to grow further. If you are lifting plants from the ground make sure the soil isn't frozen or saturated."
Benedict Vanheems on Wednesday 29 January 2014
"Pine needles don't reduce acidity."
Martin on Thursday 30 July 2015
"i'm curious if a concrete large pot is used ,would high ph.leak from the concrete to the low ph. soil?? "
ira kaufman on Monday 12 October 2015
"Hi Ira. Yes, there might be a fish, so I would either line the concrete pot with plastic (including drainage holes at the base) or use a different pot."
Ben Vanheems on Tuesday 13 October 2015
"Thank you so much for including comments about the massive destruction of carbon sinks we gardeners are indulging in by using up the peat bogs! Almost no one pays any attention to this. Here's something I was surprised to learn: coffee grounds will improve the soil structure and add nitrogen, but they won't acidify the soil. They're actually almost pH neutral - all the acid ends up in the coffee! Pretty strange, huh? However, if you have some unperked ground coffee you want to get rid of, that might be another matter."
mkirkwag on Sunday 10 April 2016
"Hi mkirkwag. A bit thank you for sharing this useful snippet of information. I think it's so important that gardeners are part of the solution to climate change rather than another contributor to it. Avoid peat at all costs!"
Ben Vanheems on Monday 11 April 2016
"Hi Benedict, An explanation on how to make a simple ericaceous compost would be a great addition to this otherwise excellent article. Some of us would rather invest the time to make our own rather than head out to the store to buy a commercial product. Thanks, Matt"
Matt on Tuesday 24 May 2016
"Hi Matt. A recipe would be useful. The trouble is many recipes use peat moss, which destroys natural habitat and releases carbon dioxide into the atmosphere. You can easily buy commercial peat-free ericaceous compost, which we'd always recommend. I have come across one recipe, which comprises: 40% leaf mould, 50% grit and 10% composted bracken - but bracken doesn't grow everywhere! You could try substituting composted bracken with composted pine needles. I think a thorough search online should yield some useful leads for a suitable peat-free ericaceous compost recipe. Let me know if you go ahead and make your own."
Ben Vanheems on Tuesday 24 May 2016
"I am creating an acidic bed at ground level (no sleepers) Please would advise how deep i should dig, also what soil mixture i might use and how best to keep the bed at the right Ph? NB: have just been bitten by the gardening bug, (62yrs) it really is a joy! "
John on Saturday 11 June 2016
"Hi John. Great to hear you've been bitten by the gardening bug! For a ground-level bed I'd suggest digging down at least 30cm / 1ft deep. I would then consider lining the bed with a permeable membrane - to keep the acidic soil separate from the garden soil. You can fill the bed with ericaceous potting soil, or perhaps use a mix comprising 40% leaf mould, 50% grit and 10% compost bracken. But a bought-in ericaceous potting mix would be easiest."
Ben Vanheems on Monday 13 June 2016
"Can I put old ericaceous compost on soil currently growing raspberries and which is currently giving a good harvest? Also can I use it on ordinary soil in a veg bed?"
Allen Cole on Monday 3 September 2018
"Hi Allen. Raspberries prefer slightly acidic conditions, so adding ericaceous compost to the soil they are growing in shouldn't present a problem. For other veg beds, I'd exercise a little caution. If it's just a small amount it's not really going to have a dramatic effect on pH, though you may need to add lime for more alkaline-leaning crops such as cabbage and other brassicas. If it's quite a significant amount, it may be best to spread it elsewhere."
Ben Vanheems on Monday 3 September 2018

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