Beat the Heat! Water-wise edible gardens

Everything you need to know about keeping your garden alive and thriving in the heat. Topics include choosing drought tolerant plants, providing shade and windbreaks for veggies, storing water in tanks and in the soil, using mulch and compost to retain water and drip irrigation.

Course Notes

www.veryediblegardens.com

Tanks – how big?

Pace out your house to figure out how much water you can capture. For every square metre of roof you can capture about 600litres of water per year in Melbourne in a decent year. So a 250m2 house can capture 250x600=150,000 litres of water a year. To really make use of this you probably need a minimum of a 20,000l tank. Any size helps, but a good rule of thumb is to figure out the biggest tank you can fit or afford and then get one slightly bigger. More info: http://www.veryediblegardens.com/iveg/water-tanks

Garden beds – how much water?

Depending on how well you condition your soil, how much shelter your plants get, how water hungry your type of plants are, they may need anywhere from 6-20 litres of water per day per square metre on top of natural rainfall in mid Summer. With good design and other strategies discussed in this course we minimise this quantity. A well designed 10m2 garden might use less than 10,000l in a year, the vast majority of this in the Summer months. You may use over 3,000l of this in a single hot rainless month, and none at all in colder wet months. Plan for three hot dry months.

Soil

Healthy soil can be the most important store of water in your system. It needs lots of mulch and organic matter (esp. compost) to build and maintain its water-holding capacity.

Swales

A ditch dug on contour (without fall). They are used on sloped ground. The loose soil from the ditch is formed into a mound which runs parallel to the lower side of the ditch. Used for planting trees. Swales slow and infiltrate water. Another good idea on slopes is to dig ditches on contour and fill with mulch for paths. Build garden beds also along contour below the path for maximum water infiltration.

Mains water

Source: Melbourne Water.

Irrigation

Use subsurface or below-mulch irrigation such as leaky hose, drippers, or 'wet pots'

Greywater

In most cases careful use of greywater can take care of much of your garden watering.
There are two basic ways you can go:

Low-tech, unfiltered, 'passive' greywater systems can be very cheap and have relatively low embodied energy and materials – these are the solution we usually favour. Shower water has the disadvantage of uneven distribution and can only water down hill plants in passive systems. For laundry we can use the washing machine pump to more evenly distribute, and can water plants up to about the height of the top of the washing machine. Greywater from these passive systems needs to be released into mulch-filled pits.
Commercial systems by comparison, include filters, storage tanks and a pump. They generally require more maintenance than a well designed 'passive' system, and perhaps ironically, are subject to more regulations. Because they include pumps, the water can be distributed up slopes. Because they include filters, purple greywater dripline can be used which makes for very even distribution.

In either case, greywater should not be used on veggies, especially root vegetables or things eaten uncooked. We usually use it on fruit trees, other perennial crops, and support species, and this works well in your case.
For laundry water alone, probably the best approach is the 'Laundry to Landscape' method outlined by US greywater guru Art Ludwig here: http://www.oasisdesign.net/greywater/laundry/
It uses the washing machine pump (without placing extra load on it) and an even and difficult-to-clog-up distribution system.
All of these systems use pits or trenches in the ground filled usually with a course non-fibrous mulch. The mulch will eventually rot down and become compost and need to be replaced every couple of years, so you can also use scoria which won't rot. If using scoria, you should put a layer of geotextile fabric on top of it and finish with crushed rock or some other surface that is nice to walk on.
The depth of the pit depends on the depth of your topsoil. You don't want the pits to be dug into heavy clays, where water will sit and stagnate. If you have no topsoil at all or very heavy clay soils, pits may not be appropriate at all.

Greywater regulations

Under EPA guidelines any system without filtration and which can be turned off during wet months has few regulations:
Untreated greywater (reuse)
Untreated greywater from the bath, shower and clothes washing machine can be bucketed or diverted to water lawns and gardens, as a temporary supply of water during dry weather.
Diversion and bucketing of untreated greywater does not require a council ‘septic tank’ permit. However, to protect public health and the environment, untreated greywater should be reused in accordance with the most recent version of EPA Publication 884, Greywater use around the home, and not stored for longer than 24 hours.

Choosing laundry and shower products

We recommend that you be very careful about what you use in the shower and laundry, to avoid certain chemicals and salts. This is also good for you! The soil can be damaged over time if grewyater safe products are not used. See www.lanfaxlabs.com.au for a comparison of salts in various washing detergents which can help you choose what to buy.

What to plant

Relatively drought hardy fruit and veggies:

Veggies: Eggplant, Capsicum, Pumpkin, Zuccini, Basil, mediterranean herbs, to lesser extent Tomatoes, corn handle heat and days without water. Other things such as beans struggle. Consider perrenials like rhubarb, sorrel, artichokes etc for deeper rooted crops.

Trees: Peaches, Nectarines, other stonefruit. Pomegranates. Feijoa (survive but fruit better with water). Mulberry. Figs. Grapges. (Apples ok but not so great with full exposure to hot sun. Tropical stuff like avocados don't deal so well with hot sun.)

Vegies: Eggplant, Capsicum, Pumpkin, Zuccini, Basil, mediteranean herbs, to lesser extent Tomatoes, Corn handle heat and days without water. Other things such as beans struggle. Consider perrenials like rhubarb, sorrel, artichokes etc for deeper rooted crops. Trees: Peaches, nectarines, other stonefruit. Pomegranates. Feijoa (survive but fruit better with water). Mulberry. Figs. Grapes. (Apples ok but not so great with full exposure to hot sun. Tropical stuff like avocados don't deal so well with hot sun.)

Innovative ideas

Wicking beds: watered from a reservoir below the soil and literally wick water upwards for low water use.
Aquaponics: organic hydroponics with fish in the mix. The most water efficient from of gardening but high on the materials input and engineering.

Save water in the home

Pee bucket. Instead of flushing water away, pee in a bucket and water it down 10:1. It is a high value fertiliser, your plants will love you for it. Really.

Books

Water: Not Down the Drain by Stuart McQuire. A Melbourne guide to using rainwater and greywater at home. Excellent overview of legalities and options, but very 'to the book'.
Create an Oasis with Greywater by Art Ludwig. US book but very good at home DIY solutions. The guru of greywater.
Harvesting Rainwater by Brad Lancaster. (2 volumes) Great ideas for captureing and directing rainwater where you want it with plumbing and simple DIY hand dug earthworks.