Clear Mountain Garden Treasures

Clear Mountain Garden TreasuresWater Wise

Water Wise

Summer is a time of plenty. Harvesting veggies and fruits from one's own garden is very rewarding.

Tomato: Sweet 100

Summer is a time of plenty.

However, summer is also very dry and without additional water, veggie and flower beds soon wilt, ruining the harvest. This article is on efficient water usage and how to plant to minimise the need to water.

All plants need water to survive and grow. Plants grow best if they are given the optimum amount of water for their growing conditions and season. Too little water and growth stops or the plant may die back, or even die completely. Too much water will also affect the growth and encourage diseases. Water logged conditions will certainly kill most plants.

Plants absorb most of their water through their roots. Tiny hairs grow near the tips of roots, and these help to absorb water. It is important that roots be kept moist or the hairs will die. Roots also need to breathe, so it is important that growing media or soil has plenty of holes for air to get to the roots. If the drainage is poor, water will fill up these holes, drowning the roots.

The key to efficient water use is to minimise water loss and maximise the use of applied water.

Water loss
Shelter and Wind
Soil Types
Growth Cycle
Drought Tolerant Plants
Succulents and cacti
Vegetables and Fruit
Plants in Pots
Using Rainwater

 Water loss

Most water is lost
through leaves.

The green dye in plant leaves, chlorophyl, uses carbon dioxide from the air and a small amount of water to convert energy from sunlight into sugars. The sugars then power the growth of the plant. In order for the plant to obtain carbon dioxide from the air, there are tiny pores (stoma) on the underside of leaves that open and close in respond to sunlight. These open to let air in when the sun is shining and close when it is dark.

The pores not only let in air, but allows water vapour to escape. Plants lose most of their water this way. As the leaves dry up, they soak up water from the stem. These are in turn, supplied by the roots. On a sunny day, the plant continuously loses water and sucks water from the ground. This process is known as transpiration and allows fertiliser to flow from roots to leaves.

 Shelter and Wind

The rate of transpiration is variable. On a hot summy day, it is expected that plants will lose more water. But what is less known is on cool windy days, plants can losse just as much, if not more water.

Manuka makes an excellent
shelter plant.

Shelter plants, such as shrubs and trees, can reduce the wind through a garden. They do not cut out wind altogether, and having some air movement is beneficial to plants. As a general rule, every metre height of shelter plant provides around 16 metres of protection. This means a 1m shrub will shelter smaller plants up to 16 metres away. A 2m tall row of shrubs planted near the fence on all sides will shelter most quarter acre sections.

Take care where shelter is planted. Take into consideration light, predominant wind direction and views. To allow more light, on the northern side, plant lighter shrubs or use deciduous shrubs. Deciduous shrubs have the advantage of allowing in more light in the winter months, where it is needed most, and provides some shade in the summer months.

 Soil Types

Soil in the garden acts as the primary water storage mechanism. Soils is created from broken down rock, and different sized rock particles make up different types of soil. Different soils can store different amounts of water. Clay and silt soils have very small particles and can store a large amount of water. Sandy soil, on the other hand, has very large particles. It drains well and stores the least amount of water. Often soils can be a mixture of different types.

The addition of bulk organic matter helps improve water retention of soils. For example, adding a generous amount of compost into sandy soils will help them retain more water than pure clay soils!


Soils can also lose water through evaporation. As water evaporates from the surface, deeper water up wickers up the soil, only to evaporate again. A 100mm layer of mulch can significantly reduce evaporation.

Mulch can come in many forms; leaf mould, lawn clipings, straw, rotten hay or bark. Straw (in particular, pea straw) and rotten hay are used in the veggie garden. Lawn clippings can also be used, thinly. Thick layers tend to become sticky and smelly. These mulches can also be used for flower beds.

Mulches break down and enrich the soil. They keep the soil cool, so veggie gardens should only be mulched from when the soil is sufficiently warm. This is usually towards the end of spring. Most mulches should break down by the end of autumn.

Bark is an excellent mulch for woodland areas.

Leaf mould and bark, on the other hand, are more suitable for perennial borders and woodland areas. They take longer to break down and hence do not need to be replaced as often.

Avoid using inorganic mulches such as pebbles. These tend to work their way into the soil and creates a top layer that is hard to dig.

Soil microbes use nitrogen to break down mulches, so it usually pays to add extra nitrogen fertiliser to compensate. This can be in the form of blood and bone. The soil should be moist before laying mulch. Some mulches can have a tatching effect, so it is best to water gently over longer periods.


The garden should only be watered when it is dry. Only apply as much water as the soil can hold. Excess water is wasted because most of it will drain away, leaching fertilisers from the soil. For clay / silt soils, this usually means less frequent watering, but use more water. For sandy soils, water more often, but use less water.

Garden irrigation comes in several forms. Apart from the obvious hand watering, there are sprinklers, soak hoses and drip systems to mention a few. In general, soak hoses and drip systems tend to be more water efficient. They deliver water to the soil where it is needed.

Evening and early morning watering makes efficient use of water. The sun is lower and the air is cooler, so there is less evaporation. It is also preferable to water when it is not windy. Windy conditions speed up evaporation.

Different soils can absorb water at different rates. Clay soils tend to be slow to absorb water. It is best to water deeply, meaning apply water at a slow rate over longer periods. This allows the water to soak into the soil. If the rate of water is too fast, some of the water will run off the surface and be wasted.

When watering take care to check your local council water restrictions, especially on the days and times when watering is allowed. A water timer / computer makes it easier to control watering. Some water computers can even be connected to a soil moisture sensor, and can be programmed to only water when the soil is dry.

 Growth Cycle

Hippeastrums requires a
dry period to flower.

It is also important to understand the growth cycle of plants. A plant that is dormant will not need as much water, if at all, as when it is growing.

It may even be detrimental to water dormant plants. For example, hippeastrum requires a dry rest period to flower. If this dry period is not given, chances are the plant will not flower. With plants such as gloriosa, the tubers will rot if kept in a wet environment during dormancy.

 Drought Tolerant Plants

Cyclamen hederifolium
does not need additional
water once naturalised.

Coreopsis is drought tolerant.

Plant natives to really conserve water. Natives that naturally grow in your area will most likely grow in your garden without needing much additional water, once they are established. Cabbage trees, kowhai and pittosporum will tolerate drier conditions, although they grow better if given adequate moisture. For warmer coastal areas, pohutukawa is hard to beat. Once established, it will grow without without attention. Natives that come from the forest will tend to need some water, as it is usually a lot more humid in forest conditions.

There are also exotic plants that can cope with New Zealand's climate without being watered. Spring bulbs grow in the winter, when it is wet and go dormant in the summer. They do not need to be watered. Cyclamen has a similar growth cycle and will not require watering once established.

Drought tolerant plants such as cosmos, coreopsis (annual flowers), rosemary and lavender (shrub) do not need to be watered much once established. Cistus (or rock rose) is particularly drought tolerant and will forn low mounds that provide a splash of colour in the spring. Australian banksias are particularly tough and a number of species are also frost hardy. The other members of the protea family from South Africa are also particularly drought resistent, for example, protea and leucodendron.

 Succulents and cacti

The succulent Fucraea longaeva
is long lived and produces a
huge spike of flowers then dies.

There are a number of hardy succulents and cacti that will grow outdoors. These are naturally drought tolerant. It is best to plant winter growing ones as these will grow in the wet of winter and become dormant in the summer. Summer growing ones may need some protection from excessive winter rains. It is best to grow succulents and cacti in free draining soils. The following are a few examples, agave, dracenea and yucca.

 Vegetables and Fruit

Vegetables, on the other hand, tend to require a lot more water. On extremely dry days, most leafy vegetables need to be watered every day. Vegatables that are grown quickly to maturity tend to be tender and tastes best. This requires a lot of water. Vegetables that are water stressed tend to taste bitter.

Cucurbits (melons, cucumber and pumpkin) require a constant supply of water. If allowed to dry out, they become suceptable to powdery mildew.

Vietnamese mint requires
plenty of water

Fruit trees require less water, especially if they are mulched. They tend to have deeper roots that can seek water from far below the surface. The exception is citrus. Citrus have surface roots and is sensitive to drought conditions. They will need more frequent watering.

Most herbs, especially, perennials, require far less water. There are exceptions, for example, mint is a bog plant and loves plenty of water.


Lawns perhaps require the most water to keep green, especially in dry East coast areas. When mowing in the warmer months, set the mower to cut higher. In the spring, start by cutting the lawn at around 5cm to encourage good growth. Progressively move up to 10cm in the summer. Grass that is growing well will have deeper, more vigourous roots, that in turn, will be better at absorbing water. Higher lawns also suppresses weeds.

Mow often, and mulch the short clippings back to the lawn. This provides a temporary mulch that reduces water loss, and breaks down quickly in the summer heat, releasing nutrients back to the lawn.

For warmer areas, kikuyu lawns require virtually no watering. It is hard wearing and repairs itself very well. However, it will easily invade flower beds and can easily smother small shrubs. It is very vigourous and will require more frequent mowing.

 Plants in Pots


Pots provide flexibility
allowing interesting plants
to be grown.

Pots provide a flexible way of growing plants. For example, plants that are in flower can be relocated to where the blooms can be appreciated. Different plants requiring different soil and / or watering regime can be catered for. Pots though, dry out faster than the soil and in the heat of summer, most will require daily watering.

Daily watering, while onerous, and may seem like it uses a lot of water, is actually very water efficient. Water so that only a small amount of water comes out the bottom of the pot. This means that all the water that goes into the pot is used up by the plant and very little is wasted. Mulch can also be used to reduce water loss from the pot.

Clay pots dry out faster than plastic. Plants can be grown in plastic pots and the plastic pot placed inside a clay pot. Alternatively, paint the inside of the clay pot with a water impermeable sealant.

 Using Rainwater

Collecting rainwater for the garden is an effective way of reducing mains water consumption. Rainwater collected from a typical house in a moderately wet area ought to be sufficient to supply the watering needs of most gardens. The problem is when it rains, the garden does not need to be watered, so some form of water storage is necessary. This can be as simple as a large barrel, or at the other end of the scale, underground water storage tanks with pumps, etc.

The most common way to collect rainwater is diversion from the gutter down pipes. Make sure the water tank has an overflow that is connected back into the stormwater drain. A small pump can be use to move the water to where it is needed, or if you are on a hill, use gravity. Tank water is typically low pressure, so it is best to connect to drippers or soak hose.







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