5 soil & plant additives
The following materials can be used to preserve water in your soil and benefit your plants in other ways. Compost or soil improver added to soil helps it hold on to moisture. They also improve the soil’s nutrient level and stimulate microbial activity.
Bentonite clay or kaolin clay incorporated into the top
30cm layer of sandy soil assist its water-holding capacity. Adding 5–7 per cent clay volume also cuts water repellency. Wetting agents are horticultural detergents that allow water to soak into the soil instead of running off. They break down the waxes created by the soil microbes and fungi, and allow the water to penetrate. Products include granules and liquids, which last from two to six months.
Water storage crystals are polymers that soak up water, releasing it gradually during dry conditions for up to 21 days. They don’t solve water repellency, and should be placed near the root zone of plants in baskets and pots, or mixed into the planting hole in the ground. They absorb up to 400 times their weight in water, so give them a good soak before using them. These polymers last for up to five years and are made from a petrochemical, so they aren’t recommended for use with edible crops.
Fertilisers are available with coatings of soil microbes and fungi. Mycorrhizal fungi work to extend plant root systems so that they can absorb more water. The microbes stimulate root growth and soil organic carbon, aiding water retention. Mulch stops water evaporating from soil by up to 60 per cent and acts to discourage weeds, which compete with plants for water. Inorganic mulches, such as gravel and pebbles or medium- to coarse-grade bark mulches, work best as they allow rainfall and irrigation to penetrate through to the soil. Apply organic mulches to a depth of 4cm and inorganic mulches 4–7cm.
Anti-transpirant sprays apply a protective polymer over the surface of leaves and stems to protect plants from water loss that arises from heat and drying winds. The invisible film stretches with plant growth, lasting up to 90 days, and reduces water loss by up to 50 per cent.