Soil Requirements For Growing Vertical Gardens

Western Australia, with its hot, dry climate, is a particularly challenging place to grow what are called vertical gardens. Also known as living walls or green walls, this upward growing trend is very much in fashion and used often to save space but mostly to create decorative effects. They can absorb heated gas in the air, lower both indoor and outdoor temperature, providing a healthier indoor air quality as well as a more beautiful space.

To grow plants in such exposed positions makes it critical to have the right soil conditions especially if you want your display to look its best and last for a long time. Garden soil cannot be used as it is too dense and on its own doesn’t offer enough air, water, or nutrients.

The growing medium must be capable of holding nutrients and moisture but must not be too heavy. Clay, because of its density, retains moisture well. It also tends to be more nutrient-rich than other soil types. The reason for this is that the particles that make up clay soil are negatively charged, which means they attract and hold positively charged particles, such as calcium, potassium, and magnesium. Adding 1% of clay to vertical soil mixes mix has numerous benefits:

  • Added clay greatly increases soil moisture retention rates;
  • The clay can disperse with wetting and reacts with other soil components;
  • The clay has high cation exchange capacity which helps the positive and negative ions in the soil to work together;
  • You only need a small percentage to make a huge difference to the soil profile.

Deep Green Landscaping who have their own “in house” mixes use Bentonite in their rooftop and garden mixes to give the soil the best chance of holding onto water and nutrients, especially new plantings.

Richgro also adds 1% Bentonite to its Vertical Garden Mix as well as different raw materials used to blend up a mix.  These may include pinebark, sand, spongelite, bio char, perlite, coco peat, wetting agent and controlled release fertiliser.  This came after many years of trials to get the exact ratio of ingredients to get the plants to grow and the soil media not to ‘shrink’ when settled. This mix has been used successfully by landscapers such as Creative Landscapes, Earth and Water and Phase 3 Landscapes.

Landscape Gardener Tim Davies, explains how you can turn sandy soil into water-retaining, rich garden soil through Bentonite Clay.

Another challenge with walled or rooftop gardens is watering. A product that is really popular in this case are water crystals. Those are water-retaining granules that swell up to many times their size when wet and act as a helping hand with watering. Keeping lots of containers, walled garden and hanging baskets wetted can be very time-consuming but by adding granules to the compost at the time of potting it may reduce the amount of times you would need to water.

From their natural dry state, Water Crystals swell when placed in water up to 400 times their dry size. They dehydrate over time and will re-swell. They’ll do this thousands of times over the life of the product.

It is a product used in the horticulture industry throughout the world where there is a shortage of water and can apply to food crops as well as our native plants and ideal for rooftops and walled gardens.

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