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Water Use, Storage and Conservation

Growing vegetables (and fruit trees) need water.  A lot of the time this is supplied by the rain, but at times in many parts of New Zealand rainfall is in short supply.  The purpose of this page is to give you some tips on how to grow food successfully while still conserving water.

1) Water plants’ roots, not their leaves

Unless plants are dusty and would appreciate a wash, it is best to water the soil below the plants, not their leaves.  (This also helps to prevent mould or mildew problems;  curcubits (cucumbers, pumpkins, melons etc) are especially prone to mould if their leaves get wet.)

2)  Don’t water at midday!

It is best to water plants in the early morning or evening.  Watering in the middle of the day will result in substantial loss of water due to evaporation.

3) Water more, less often

Watering deeply two-three times a week (when necessary) is more efficient in terms of time and water use than watering lightly every day. Soaking the ground properly encourages plants to grow deeper roots which allows them to access moisture which is stored deeper in the  soil. (By contrast, if plants receive a small amount of water each day, they do not bother to grow deep roots.)

4) Mulch!

Applying a layer of mulch on top of garden soil is an effective way to prevent water from evaporating from the soil.  Grass clippings*, spoiled hay*, untreated sawdust,  wood shavings from chicken houses, pea straw, bamboo leaves etc can all be useful forms of mulch.  (Sawdust and wood shavings have the disadvantage that they can deplete soil nitrogen as it breaks down and cause your plants’ leaves to turn yellow and retard plant growth.  If you use these you may need to add extra nitrogen containing fertilisers to compensate.)

It is also important to leave a space around the base of plants:  Do not mulch right up against the base of plants (or trunks of trees) as this can cause the stems or trunks to rot.


NB: Please note that grass clippings and hay used as mulch (or added to compost heaps) should come from spray free lawns/fields. The herbicide aminopyralid can contaminate grass and hay – and manure from animals that have eaten contaminated grass and hay.  Using aminopyralid contaminated ingredients can poison soil (or compost) and kill many types of vegetable plants including lettuce, beans and tomatoes. (See http://www.compostgardening.com/ and http://www.guardian.co.uk/environment/georgemonbiot/2011/jul/15/vegetables-disease-aminopyralid-pesticide?INTCMP=ILCNETTXT3487 )   In NZ aminopyralid is sold by Dow under the brand names “T-Max” and “Tordon Brush Killer XT”.


At times of water shortages:

If water is in short supply, and your garden is in danger of dying, one option is to use grey water to water lawns, fruit trees and vegetables.  “Grey water” is water that has been used for washing.  Its use does carry the risk of potentially spreading disease such as those that are transfered via the “faecal-oral” route such as hepatitis A or other bacteria/viruses that may be present in faeces and that may contaminate grey water as bodies or underwear are washed.

To minimise this risk, the following precautions should be taken:

1)  If saving water from a shower (such as by putting a plug into the bath allowing the shower water to accumulate in the bath or catching it in a bucket) wash carefully around the genitals etc and rinse well before putting in the plug or collecting water in bucket.

2)  If saving water from a washing machine, do not include underwear or nappies in any load of washing from which you plan to save the rinse water. (NB:  If you decide to use water from your washing machine to water your garden, use only soap flakes (or grated soap) in your machine for these washes, or use the long life eco “laundry balls” – see  http://www.manaproducts.co.nz/laundry-balls.asp 

Do not use grey water from loads of washing which have been washed with modern washing powders and detergents that contain enzymes and toxic ingredients that may damage your plants.  It is also undesirable to water plants with laundry that was washed in washing soda as washing soda is high in sodium.)

3)  If using grey water, allow it to cool sufficiently that it will not stress your plants then use it immediately.  Stored grey water quickly becomes fetid as bacteria (from skin, dirt on clothes etc) multiply.  Stored grey water  should not be used for irrigation.

4)  If you water garden plants with grey water, ideally water only the soil beneath the plants, not the plants’ leaves.

Important:  If you decide to use grey water to water your garden, ensure that any produce your harvest is washed extra carefully and that children wash their hands after playing out doors. If someone in the household is immunocompromised, using grey water may pose an unacceptable health risk, even if taking the precautions outlined above.


Catch your own water!


Plants grow better on rain water!  If you are a serious gardener – and have the money to spare – it is worthwhile considering  a rain water tank.  There are a number of options ranging from concrete, plastic and steel.  Each of these types have advantages and disadvantages:  be sure that you are ware of these before you buy.   There are also do-it-yourself plans on the net.  If making any sort of rainwater storage tank yourself, ensure that it is constructed in such a way that it does not pose a drowning hazard for small children or pets or a breeding ground for mosquitos.  It is also a good idea to fence off the area surrounding water tanks as a precaution against the small risk of some sort of structural failure of the tank or its supports – such as during an earthquake.



Categories: Gardening Information, Water Use, Storage and Conservation

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