To help plants thrive, attention needs to be given to the subsoil and topsoil. Subsoil is what you are generally planting into, and what your plant’s roots will establish in. Topsoil is the layer that helps feed your plants.
Soil Categories
Garden soil exists on a spectrum from sandy soil on one end to clay on the other.
Sandy soil: has large particles which don’t retain water, so it’s very free draining. It also tends to have a higher acidity level.
Clay soil: has small dense particles which means it’s not free draining and prone to flooding. It’s also quite alkaline.
Loamy soil: sits in the middle, and is the ideal combination of sand, clay and nutritious organic material. The particles are medium size, it holds water without getting boggy, and has a neutral PH level, which are the ideal growing conditions for most plants.
Changing your soil conditions
It’s best to improve an entire planting area all at once, rather than the soil in individual planting holes. For example, if you dig a planting hole in clay soil, then drop in a plant and amend only the soil you’re using to backfill, you have essentially just created an in-ground flower pot, that becomes a water trap during winter, which can drown your plant.
Clay soil
Soil with a high clay content takes the longest to move along the continuum, but the process itself is easy. Add some organic matter, and gypsum. As gypsum dissolves, it releases calcium sulphate which helps to separate and break down the fine clay particles.
Add a good dose of gypsum and organic matter with each change of season.
Depending on how clay-heavy your garden is, it can take a number of years to break down. Planting into it will help this process along.
It’s a good idea to PH test the soil before you start work on it, and then test again later to make sure your hard work is paying off. The aim is to move it to a more neutral state between 4.5 and 7.5.
Sandy soil
To make sandy soil loamier and more fertile add compost and organic matter.
Soil troubleshooting
The following signs will tell you that your soil needs attention:
In winter, water will puddle, instead of soaking in
In summer, it’ll be hard with cracks through it
In spring it will be slow to warm up and you’ll see your plants will struggle to grow
It may be compacted and hard to plant into
Here’s what you can do to improve your planting conditions:
Dig through compost or mulch in autumn to boost nutrients before spring planting
Don’t tidy up too much, let leaves and plant matter decay in your beds
Sow green crops like lupin and mustard to naturally top up nitrogen levels
Attract beneficial insects and worms to naturally improve soil conditions
Turn over your soil to aerate it
On slopes, dense planting will help prevent run off and avoid leaching, which is the loss of nutrients
If your lawn is boggy in winter or cracked in summer then aerate the soil, sprinkle with gypsum, and add a top dressing
Planting for your soil conditions
When you’re planting it’s best to choose plants that like the soil conditions your garden is prone to. Here are a few examples:
Clay tolerant plants are:
NZ Natives such as Pukas, pseudopanax and Sophoras
Shrubs including Westringias, Hymenosporums, Grevilleas and Cannas
Perennials such as Hostas, Heucheras, Day Lilies and Asters
Fruit for the garden including Guavas, Blueberries Feijoas, Apples, Peach and Nectarine trees
With sandy conditions, go for:
NZ Natives such as Pseudopanax, Flaxes, Griselinias, Astileas, Dietes Coprosmsa or Pohutukawas
Grasses such as Lomandras, Toe toe, Carex, or Dianella.
Groundcovers such as Convolvulus cneorum
South African plants such as Proteas or Leucadendrons
Cacti and succulents
Nearly all garden plants grow best in loamy soils with the exception of cacti and succulents.
However, plants are fairly adaptable, so if you want to grow something and your soil conditions don’t match, now you know how to change things to help them get established. — Courtesy of Mitre10
