Carol shows how to get the most from acid soil
Far from being a problem, acid soil opens up a whole range of captivating plants you can grow. And many will thrive in pots. Carol Klein shares her favourites.
If mophead hydrangeas have blue flowers, the soil is likely to be acidic; if pink, it’s probably alkaline
Many of us garden on acid soil, sometimes without even real ising it. When we’re trying to understand a new garden or even when we’re looking in more detail at one we’ve had for some t ime, we’re far more likely to be preoccupied with the aspect and situation rather than the pH of the soil. But what is pH? And why is it important to know the pH of our soil and to choose plant s that are happy in it? pH is a measure of the acidity and alkalinity of the soi l and whi le its chemistry is complex, simply put, as the number of hydrogen ions in the soil increases, the more acidic the soil becomes. It is measured on a scale of 0-14 where is neutral, below it is acid and above it is alkaline. All manner of factors govern the pH level, even within one garden. Here at Glebe Cottage the soil is more acidic on one side of the garden under the beech and oak trees than on the west side. You can buy a simple testing kit to measure your soil’s pH, which involves shaking up a soil sample with a so l ut i on and comparing it to a litmus scale. Less scienti f ic but much more exciting is to do some detective work and have a snoop around the neighbourhood and see what thrives over the garden fence and beyond. Hydrangeas, for example, are fairly ubiquitous and you’re likely to find them in areas of both acid and alkaline soils.
However, if mophead or lacecap hydrangeas have blue f lowers, the soil is most likely to be acidic; if they’re overwhelmingly pink then it’s a safe bet that conditions are alkaline. And if there are masses of rhododendrons and camellias in the vicinity and they’re doing well with healthy, dark green foliage, it’s a sure sign they’re on acid soil. Conversely, if these plants are not doing well the soil may be too alkaline to support acid lovers. Although there are many alkaline-loving plants that can cope with acid soils, if a plant needs acid soil it will never be happy on ones with a high pH. The pH of your soil is what it is and there is no point trying to change it – and why should you? Having acid soil means you can grow a huge host of plants that will love growing there, plants that have evolved in acid conditions from all over the world, and amongst their number, some of the most beautiful in the world. The magnolia tribe and some of its close relations in the cornus family are happiest in acid soils while hazels, beech and horse chestnuts will also grow there. Many
The magnolia tribe and its close relations in the cornus family are happiest growing in acid soils
shrubs that f lower in the early part of the year enjoy leafy, acid soils. Witch hazels ( hamamelis) love such venues and so too do pieris, skimmias, enkianthus and, most famously, camellias and rhododendrons.
Planting perfection
Gardening on a soil with a low pH is much the same as gardening on any soil, but there are a few points to remember. Many acid-loving plants have come from heathland, woods and mountains and have fine, fibrous roots and shallow rootballs so prepare an area much wider than the size of the rootbal l when planting but avoid making deep holes that may act as sumps. Dig in plenty of organic material, but definitely not fresh, unrotted manure, which could burn the roots, nor any material containing lime (e.g. mushroom compost, which is highly alkaline). After planting firm down to make sure plants are in intimate contact with the soil but avoid being heavy handed or using feet! The soil should be friable, so if you’re gardening on heavy clay, wait for dry conditions. After planting give plants a thorough drench and water regularly especially in dry spells, ideally with rain water if your tap water contains lots of lime. Help retain moisture and keep down weeds
with a mulch of home made compost, bark or pine needles. If leaves are yellowing don’t assume a plant is in need of lots of fertiliser – yellow leaf edges can mean that plants are unable to take up all the nutrients and trace elements, because the soil is too alkaline and an application of sequestered iron will help here. And if you find your soil isn’t acid, grow acid-loving plants in pots of ericaceous compost. So, if you’re gardening on acid soil think of it not as a problem but as an opportunity to grow some of the most gracious and gorgeous plants in the world.