Plants for alkaline soil
This section features the best climbers, conifers, hedging plants, perennials, shrubs, trees and other types of plant that will succeed on alkaline soil. Alkaline soils, also known as “sweet” soil, are those with a pH of greater than 7. A soil with a pH of 7 is neutral. Anything below 7 is acidic or “sour” and anything above 7 is alkaline or “sweet”. Alkaline soils tend to be those with some chalk content which increases the pH and makes them naturally free draining. They tend to have more moderate to low fertility compared to neutral soils and the depth of soil over chalk can vary considerably. Chalky soils generally dry out more quickly, although deeper alkaline soils or those where clay is also present can be more moisture retentive. The pH of alkaline soils can be reduced, bringing it closer to neutral, by applying sulphur or ammonium. However, we generally recommend choosing types of plants that are well suited to the alkalinity of your soil, rather than trying to change it. Any artificial change to acidity will only be temporary and will need to be repeated over time.
Some of the best plants for alkaline soils are campanula, ceanothus, geraniums, lavender and dianthus. Campanula plants are cheerful perennials with nodding, bell-shaped flower heads, typically in shades of lavender, light blue, pink and white, held high on tall stems above toothed, mid-green leaves. Hardy geraniums are renowned for adding colour and beauty to the garden from late summer through early autumn, just as many other flowers are starting to fade. They produce masses of beautiful, saucer-shaped flowers, often with distinctive veins and sometimes a block of contrasting colour in the centre. Lavender has been a favourite of English gardens for centuries, prized for its rich, fragrant flowers and aromatic foliage. The distinctive purple, pink or white flowers are produced on long stalks above a compact mass of grey-green leaves between July and September. Whilst the most scientific way to measure the pH of your soil is with a soil testing kit, the easiest and cheapest way is to see how samples of your garden soil react to the addition of, firstly, vinegar and, secondly, baking soda (using separate samples for each). If your soil froths up when vinegar is added, it is high in chalk/lime and alkaline in nature. See our article on understanding your soil for more details.