In the Garden: How acidic is your soil? You need to work it out!

THE garden is sinking fast into its winter slumber, trees are being stripped of their leaves, and melting foliage enables plants to disappear below the soil in hibernation for the months ahead.

There has been no major frost to speak of, which is unusual for the end of November, but no doubt the temperatures will drop in due course.

It is very damp and wet, which is not good news for plants, particularly tender perennials such as salvias, cannas and gingers that may be brought indoors to over-winter.

Ensure that they are stored in a cool, dry place with ventilation for the best chance of getting through the winter in good condition.

Dahlia tubers also come to mind. Traditionally, yellow sulphur was used to dust the tubers to prevent the spread of fungal infection.

It is a good idea to go through the tubers a few weeks after they have been dug up and dried out a bit and cut out any rotten or damaged one to prevent rot spreading before preparing them for their final resting place for the winter.

They need to be stored dry but the tubers kept moist, which is a bit conflicting - vermiculite or wood shavings are a good option to cover the tubers in crates and place in a dark location, like under shelving, in the garage or shed.

The necessity to dig up and store dahlia tubers really depends on your soil and the location where the plants are growing. If it is a free-draining, sandy soil in a sheltered spot, then covering the surface of the soil with a thick layer of bark or soil should provide enough protection to over-winter the tubers.

Heavy soils that do not drain quickly will be more risky as they may freeze if the temperatures plummet or become water-logged over the winter months, and both of these conditions may result in the demise of the tubers.

Everybody needs to weigh up their own situation based on the knowledge of their own gardens and growing conditions, which takes a few years to observe and familiarize yourself with.

It really is a worthwhile occupation as it can save you lots of money choosing plants that will do well with the particular conditions provided.

Soil pH, for example, has a huge bearing on what plants can be grown, with acid-loving plants such as rhododendron, azalea and heathers doing well on soils below a pH of 7, and buddleja, lavender and forsythia preferring alkaline soils with a pH of more than 7.

This was a major factor in the partnering of The National Botanic Gardens in Glasnevin, Dublin and Kilmacurragh, Co. Wicklow.

The soil in Glasnevin is alkaline, limiting the range of plants that can be grown here. Kilmacurragh has acidic soil, enabling the growing of a collection of rhododendrons and other acid loving plants in Wicklow which could not be cultivated in Dublin.

How can you tell the pH of the soil? There are soil pH testing kits that can be purchased at most garden centres, but practical observations such as looking at vegetation already growing in the garden or in proximity to the garden can also be a good indicator as to what the soil pH is.

Birch, gorse and foxglove are all indicators of an acid soil, ash, honeysuckle and clematis preferring more alkaline conditions.

Altering the pH can be tricky, the addition of lime will increase the pH, making the soil more alkaline, and the addition of coffee granules or pine needles will decrease the pH, making the soil more acidic.

Both of these effects will be short-lived and will require constant topping up as they will be used by the plant roots or leached out of the soil, so basically we need to make the most of the soil type that we have and grow what does well in it.

Right plant, right place is one of the best pieces of advice ever given in gardening as it provides the opportunity to make life much easier.

I do remember visiting Brian Cross’s garden many years ago and spotting a beautiful specimen of Enkianthus Campanulatus in flower in spring, which I felt I really needed in my garden. So I bought it and planted it, but alas I have alkaline soil and this plant likes acid soil and so it died gradually over two to three years.

Getting familiar with your soil and the conditions you are providing for plants is essential before investing too much in plant purchases.

Happy Autumn Gardening!

Plant of the Week

Betula pendula ‘Spider Alley’, or the corkscrew birch, is a cultivar of birch bearing contorted branches which reveal themselves in winter when the leaves have been shed.

It has peeling white bark with patches of pink and brown on the younger wood.

It produces beautiful, golden autumn foliage with the silver bark and twisted branches taking centre stage for the winter months.

During winter, when flowers and foliage are not in as plentiful supply in the garden, we need to look at other elements for interest and trees with attractive bark rank high on the list, particularly as they mature.

Other valuable characteristics are brightly coloured stems such as dogwoods, strongly scented flowers like daphne or sarcococca, and of course evergreen trees and shrubs like holly and box.

This tree will grow best on acid soil but will tolerate alkaline, although it may not reach its full potential.

Best grown in full sun, it will get to an eventual height of six metres and spread of four metres in ideal growing conditions. An interesting tree for autumn and winter interest in the garden.