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 potting soil (also called ericaceous potting soil) or in a specially prepared ericaceous bed, which is the purpose of this article.
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!
The first job is to find out exactly how acidic or otherwise you soil is. You can look at what your neighbors 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 cinder blocks – 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 mold 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.
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 potting soil is also free of peat – it should say this on the packaging. If you have trouble sourcing peat-free ericaceous potting soil, 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.
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 mold (especially that made from maple trees), pine needles, bark chippings and more ericaceous potting soil 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.
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 prioritize 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.