Your Tutor For This Course:

BSc in Applied Plant Biology (Botany) Univ. London 1983. City and guilds: Garden Centre Management, Management and Interior Decor (1984)

Susan Stephenson is a passionate and experienced horticulturist and garden designer. She has authored three books, lectures at 2 Further and Higher Education Colleges, teaching people of all ages and backgrounds about the wonders of plants and garden design, and tutors many students by correspondence from all over the world.

Susan studied botany at Royal Holloway College (Univ of London) and worked in the trading industry before returning to her first love plants and garden design. She is therefore, well placed to combine business knowledge with horticulture and design skills. Her experience is wide and varied and she has designed gardens for families and individuals. Susan is a mentor for garden designers who are just starting out, offering her support and advice and she also writes, delivers and assesses courses for colleges, introducing and encouraging people into horticulture and garden design.

In 2010, Susan authored a complete module for a Foundation degree (FDSC) in Arboriculture.

Susan holds the RHS General with Distinction. She continues to actively learn about horticulture and plants and (as her students will tell you) remains passionate and interested in design and horticulture.

IRRIGATION

WHEN TO WATER

Plants will need more water in hot, dry or windy conditions, but it is also easier to use water incorrectly at these times.

Naturally, you’ll need to water your plants more often when it’s hot but good watering involves more than turning on the sprinkler every couple of days or standing around with a hose each evening.

TESTING TO SEE IF IT NEEDS WATER

One of the biggest problems in gardening is not watering when it is needed.

Not only can plants suffer from not enough water, they can also suffer when they are watered too much and too frequently.

A simple technique of pushing your finger into the soil can help determine if the soil needs watering. If the finger comes out dry, then it most probably is time to water. If the finger comes out moist and cool, then it could forgo the watering till a little later.

The Dos and Don’ts of Watering

• Avoid watering in the evening – Although this is often a pleasant activity, evening watering isn’t a good idea as it encourages fungal diseases in plants. The water droplets remain on the plants overnight, providing the perfect conditions for the spread of many common fungal diseases, including black spot on roses.
• Don’t water in the middle of the day – Some foliage burns in strong sunlight if water remains on the plant. African violets, gloxinias and newly planted seedlings are particularly susceptible to foliage burn.
• Don’t spray plants lightly with water each day – The water is unlikely to penetrate down to where the roots need it. Over time, the roots will only grow in the top couple of centimetres of soil, where they are subjected to the extremes of heat and cold.
• Don’t apply water faster than it can be absorbed – It will simply run off the surface.
• Don’t waste water by using sprinklers on windy days.
• Don’t position a sprinkler where the water will be sprinkled on roads, driveways, etc.
• Do water early in the morning – The water will have a chance to soak deeply into the soil before the sun gets too hot, and water on the foliage will have evaporated before the hottest part of the day reducing the risk of foliage burn.
• Do water deeply – This encourages the roots to grow downwards, giving a healthier and stronger plant. This reduces the likelihood that the plants will suffer from water stress, particularly if you are unable to water for a few days in very hot weather (e.g. if you are away on holidays).
• Do add plenty of organic matter to soils before planting. This helps improve soil structure allowing better water penetration into the soil, as well as improving the ability of the soil to hold water.
• Do use mulch – This will make a big difference to the amount of water you need to apply. Evaporation of water from the soil can be reduced by up to 70% or more. Be careful though, that you do not use too thick a layer of mulch, as the mulch can act like a sponge when you water soaking up a lot of water preventing it from reaching the soil beneath.
• Some mulching materials, particularly fine materials such as sawdust, can also pack down creating a barrier to water penetration. Use a mixture of coarse and fine materials, and periodically check, using your fingers, to see if the water is penetrating the mulch.
• Think about installing a drip irrigation system. Micro-jets and drippers use much less water than sprinklers and hand watering.
• To take care when applying fertilisers dissolved in water in summer, as they are more likely to burn the foliage in hot weather.
• If you are going to use a sprinkler, use one that produces large drops rather than fines ones which are more readily blown around in the wind, and are more readily evaporated.

Other Ways to Reduce Watering Needs

• Group plants with similar watering requirements together. This allows you to only provide the amount of water all of a group requires, rather than the level of watering the most water-hungry of the plants require.
• Avoid cutting your lawn too low (less than 2-3cm), as the grass won’t have enough leaf material to protect itself from burning.
• Use timers on irrigation systems to ensure they are turned off in case you forget that they are on.
• When washing your car, try and wash your car on your lawn so that the water from the car washing can also water the lawn). Wet the car first, then turn the hose off (either at the tap or at the nozzle), then soap down the car.
• Do one section of the car at a time to prevent the car detergent from drying. Once you have finished “soaping up”, turn the hose back on, and wash the car down.
• Use a broom and shovel to clean your hard surfaced areas (e.g. road gutters), rather than washing them down with water from a hose (which can waste more than 1000 litres of water per hour).
• Create windbreaks using plants or permeable materials such as trellis, or picket fences to reduce the effects of drying winds.
• Don’t over fertilise your plants, including lawn. This encourages a lot of growth, which increases the water needs of the plants, and results in soft growth that is more easily damaged by mowing and/or harsh conditions.
• Add wetting agents (found in a garden centre), to your garden beds. This helps improve water penetration into and through the soil, reducing water lost through evaporation and runoff.
• Soil wetting agents, and water storing granules, can be added to potting mixes to reduce the need for watering containerised plants. Be sure the size of any container is suitable for the plant/s in them. If the container is too small, they will require very frequent watering.

• Reduce the amount of lawn you have by replacing it with beds of plants with low water requirements, or choose lawn species that have good drought tolerance.

Reducing the need to water your lawn can save you a lot of water. You can also allow your lawn to “brown off” during hot, dry conditions. It will generally regrow very quickly once conditions improve (higher rainfall, cooler temperatures).

• Fixing, or replacing worn or leaky hoses, nozzles, sprinkler heads, timers, etc. can save quite a lot of otherwise wasted water.
• Use part circle (e.g. quarter, half, three quarters, or adjustable radius) sprinkler heads to reduce waste from watering areas that don’t need it (e.g. paved areas).
• Selective pruning of very leafy plants after the spring growth flush can reduce the water needs of the plant during summer (the less foliage the less water lost through the leaves). This needs to be done carefully to avoid damage to the plant.

WATERING SYSTEMS
A watering system can mean the difference between your garden thriving or struggling. It can also reduce the time you spend bucketing or hosing water onto your plants.

Take Stock
Have a good look over your garden. Think about the things that required so much time watering last year, or the plants that suffered most because you never got around to watering them.

Every garden is different. For some people, it’s the lawn that suffered most; for others it’s the pot plants on the veranda; and for others it may be the vegetable garden.

Target those problem areas for an irrigation system that can deliver regular water. You’ll be delighted at how much difference regular watering makes.

DIFFERENT GARDENS NEED DIFFERENT WATERING SYSTEMS

Garden beds
The type and design of the irrigation system you choose for a garden bed will depend on a number of factors:

• The type of soil – Sandy soils will readily absorb water, whereas clay soils can only absorb a small amount of water at a time. Sprinklers and sprays usually work well in sandy sites, but you will probably need to install micro sprays or drippers for clay garden beds.
• The layout of the garden bed will determine where you can install irrigation outlets. Placing a sprinkler right next to tree or bushy shrub will prevent an even distribution of water.
• Established plants may not need any additional irrigation.
• Areas under trees may need extra water.
• Garden beds with annual plants and vegetable seedlings will need to be kept from drying out.
• Some plants, particularly roses, are prone to fungal diseases. Do not direct water onto the leaves of these plants.

For Hanging Baskets
Hanging baskets are very prone to drying out, especially when they are exposed to the sun and wind. Because sprinklers and sprays will wash out the potting mix, it is best to water them with micro sprays or drippers.

Tubs and Pot Plants
Like hanging baskets, pots are best watered with micro sprays or drippers.

Sprinklers
Different sprinklers have different features.

• Costs vary.
• Pop up sprinklers will slip back into the ground after use. These can be a blessing in areas with lots of people walking or running around.
• Depending upon specifications, sprinklers can be adjusted to send the water at varying angles and at variable arc.
• Different materials provide varying levels of durability.
• Some sprinklers will only operate when there is sufficient water pressure.

Designing Your System
The number of fittings you can attach to your irrigation system will depend upon how much water flows through each fitting. Calculate the flow rate through your tap (see below), divide this by the flow rate through the type of fitting you want to use, and this will give you the number of fittings you can attach to each pipe.

NEVER put different types of fittings (e.g. sprinklers and drippers) on the same pipe. The different flow rates will mean that one or other of the fittings will not work at its optimum level. If you require different types of fittings, use a separate pipe.

If you need to have more than one pipe, you will need to install a manifold at the tap. This is simply a mechanism for turning the different pipes on and off.

Remember, if the water has to flow up hill, you will lose water pressure, which will simultaneously lower the flow rate. The flow rate will also be lowered if you operate other taps when you are irrigating.

Alternatively, if the water is flowing down hill, the water pressure will increase. If the flow rate is higher than what is required for your system, you will need to be careful you don’t turn the tap on too hard as this may cause the fittings to break apart.

How to Calculate Flow Rates

• Turn off all taps around the house.
• Place a 10 litre bucket under the tap.
• Turn the tap on full.
• Time how many seconds it takes to fill the bucket.
• Divide the time taken by ten to give you the rate (litres per second) that water flows through your tap.

Dripper or Spray?
Drippers take a long time to water a garden area. Water from sprays can evaporate and/or be blown away by the wind.

Cheap Micro-irrigation
Micro-irrigation systems are easy to install yourself.

Use high density polyethylene (HDPE) pipe. This is flexible and easy to cut and join together. This type of material is best suited for use with micro sprays and drippers. Its flexibility makes it ideal for irrigating pots and hanging baskets.

There are some disadvantages to using HDPE pipe and fittings:

• Above-ground fittings are easily damaged.
• Pets and other animals can ruin fittings trying to get water.
• Sunlight can cause some plastic heads to go brittle.
• Reach may be limited.
• Small pipes may become clogged (this problem can be minimised by including a filter).
• Small pipes may be cut by spades, secateurs, picks etc.

Handy Hint!
When installing a new micro irrigation system, lay the pipe in the trench. Before you install the fittings, run water through the system. This will straighten the pipe and ensure that fittings will be correctly positioned.