Understanding Your Soil

The Start Of The Growing Season Is A Great Time To Prepare And Ameliorate Your Soil

Whether it is your potager (where heavy cropping can quickly reduce fertility) or in your decorative borders where plants are growing long term; you need to refill their store cupboard so that they have access to a balanced range of nutrients for the first flush of growth.

Soil is composed of many different elements and in a well-balanced soil these should be 50% mineral elements, 5 to 10% organic matter, and the spaces in between these solid elements should be 50:50 air and water. The minerals and the organic matter will hold the nutrients that the plants require and release them slowly for plants to take up. There should also be a healthy community of beneficial microorganisms that help to break down the organic matter as well as larger organisms such as worms and insects. Soil chemistry also plays a part in the availability of nutrients. If your soil is very alkaline, the calcium in the soil will bond with some of the essential plant nutrients and make them unavailable to plantseven if there is a good supply, the plants are unable to access them. Iron is the nutrient most affected by this leading to plants becoming stunted, with yellow leaves, and poor flowering and fruiting. This is because iron is a major constituent of the chlorophyll molecule and without it the plant cannot create enough for the leaves to be green, the reduced ability to photosynthesise leading to poor plant growth and development. Finding out the pH of your soil is key to understanding nutrient requirements.

Soil texture will also tell you a lot about the fertility of your soil. If your soil is predominantly clay, then you are likely to have good nutrient and water retention because the clay particles have a slight magnetic charge which attracts water and some of the main nutrients, but your soil will be harder to work and can become compacted easily leading to a lack of air in the soil. Plant roots need oxygen and therefore the structure of the soil can also affect healthy growth. Sandy soils are lighter and much easier to work but they drain very quickly and cannot hold onto water or nutrients because the particles are inert.

The solution to both of these problems is to add organic matter. In heavy clay soils it will break down the large cloddy lumps of clay creating more air spaces. In sandy soils it will help to bind the loose structure together and because, like clay, organic matter has a small magnetic charge, it will improve water and nutrient retention. This could be well rotted manure or garden compost, leaf mould or very well composted bark. For alkaline soils manure is best because it will help to lower the pH or, if you can get hold of them, composted pine needles. For acidic soils leaf mould or garden compost will help to raise the pH.

Most soils will be lacking nutrients after a long growing season and a wet winter, and organic matter breaks down over time, so it needs to be replenished. Late winter to early spring is the best time of year to replenish the supply. For clear areas such as your potager, or new beds and borders that have not yet been planted up, dig in generous amounts of organic matter. For established beds you can add a thick layer of organic matter as a mulch on top of the soil making sure that you do not bury the crown of the plants. You can top this up throughout the growing season. We continuously mulch our borders starting with well-rotted garden compost in late winter, topping it up with grass clippings throughout the summer, and then a mix of grass clippings and autumn leaves in late

Caroline has been a lecturer in horticulture for 20 years and now runs a nursery and ‘garden craft’ courses in the Haute-Vienne at Le jardin créatif autumn which we collect with the lawn mower. Grass clippings are high in nitrogen, the most important plant nutrient, which they release as they break down; they do not look attractive when you first add them but they soon mellow to a dull buff colour.

The addition of organic matter will also help to support a healthy population of beneficial microorganisms which feed off it, breaking down the organic matter into the basic elements that plants are then able to access. In addition, the increased water retention in the soil will help plants to survive through the dry summers. Mulching the surface of the soil is invaluable for reducing evaporation of water from the soil surface and keeping the root zone cool.

If your plants are showing signs of particular nutrient deficiency (such as yellowing leaves, yellow between the veins, purple or blue discoloration to the leaves) you may also apply a slow-release fertiliser at the beginning of the growing season and again in June/July. There is a wide range of organic fertilisers available in the garden centres, bricos, and even supermarkets. A general purpose fertiliser with trace elements will suit a wide range of plants.

You can buy home soil test kits to find out the pH of your soil, or you can bring a small soil sample along to Le Jardin Créatif on Saturdays when the nursery is open - we will do a pH test and a texture test and give advice on your soil and planting solutions. You will need just a small handful of soil taken from around 10cm below the surface. Our nursery and garden will open for the 2023 season from Saturday 4th March. We are open every Saturday until the end of October 10am - 4pm.

See our updated plant list and details of our craft and sculpture workshops: www.lejardincreatif.net