5 soil & plant ad­di­tives

Gardening Australia - - KNOW-HOW -

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.

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