Improving your Irrigation

Would you like to improve your irrigation?  This blog post compares and discusses six food-garden irrigation methods, their advantages and disadvantages, what works and what does not work.  This might help you decide what irrigation system will be best for your food-garden.

1. Low-tech and effective

Nothing wrong with using the good old watering can, but if you have a large garden it can be hard on your arms and back because of the weight of water and the need to bend over. It is also very time consuming. Because you put the water precisely where it is needed, water costs will be low. It can be very satisfying and effective because you give every plant your personal attention.

One way of spending less time watering without much infrastructure is to bury unglazed clay pots called Ollas next to each plant and filling them with water perhaps once a week.  It is an an ancient method of plant irrigation that feeds water to plant roots gradually through the porous surface of the pots. It works well for watering of permanent plants, not short-term or seasonal crops. Food Garden Group members Dirk and Pauline put next to every young grape vine in their garden a terracotta tube with a wooden lid (see photo below).

Without a bottom the water would disappear in about ten minutes. With a bottom that closes off that end of the tube completely the terracotta is just moist on the outside and slowly releases the moisture to the surrounding soil. Dirk and Pauline fill each tube once a week with about one litre of water.  
They found the terracotta tubes at The Train in Margate.  The second-hand shop there had a pile of them (another place that might have them is Uptons, Max commented). Pauline gave each tube a bottom with Jovi Air dry clay purchased at Spotlight. The finished product is called an Olla (pronounced Oya). If you would like to know more about Ollas, have a look at a very good article here.

A wicking bed is a garden bed with a water reservoir under it. Water gradually siphons up to the roots of plants by capillary action. It is 'irrigation from below'.  Replenishing of the reservoir may need to take place once a week, so it is much less time consuming than watering by hand.  Building a wicking bed is covered in Food Garden Group blog post How to Build a Wicking Bed

Deep Hay Mulching involves covering your soil with a 20 centimetre thick layer of hay and keeping it covered all year round.  This stops evaporation and results in a major boost to microbial life in your soil. You will have to water far less frequently with less water.  The method is described in detail in blog post Deep Hay Mulching   

A watering wand (photo below) attached to a garden hose is a modern improvement on watering with a watering can. It saves a lot of time because it allows you to hand-water without having to fill your watering can.  Also, it allows you to water without having to bend over much.  It makes it easy to water under the foliage of plants and you can put exactly the right amount of water precisely where it is needed.

The best watering wands allow you to select type of spray, how far you open the throttle and how much water you get when the throttle is fully open.

Water Pressure

Before we have a look at other methods of irrigation it is good to discuss water pressure.
Water pressure is measured in Kilo Pascals (Kpa). Whether you are on town-, tank-, dam- or bore-water, it is good to know what the pressure is of your water when it comes out of the tap.
If the pressure is too low, the best irrigation method will not deliver.  If the pressure is too high, parts of your system may crack or literally be blown away.
Water pressure at our place was 1200 Kpa before a plumber installed a pressure reducer for the whole property.  To put that in perspective, most washing machine warranties become void if the washing machine is used with more than 500 Kpa water pressure.
You can ask a plumber to check the water pressure at your place or, for less than the cost of a plumber, you can buy a water pressure meter at Irrigation Tasmania at 43 Derwent Park Road, Moonah (phone 6272 2400) and measure the pressure yourself.
To get pressure down to acceptable levels you can attach a pressure reducer  to individual taps.  Pope sells 100Kpa and 300 Kpa pressure reducers (see photo below). Using them where needed avoids a lot of trouble.

If you find that water pressure at the end of a hose or poly-pipe is too low, consider using 19mm. (3/4 inch) hose or pipe instead of the standard 12mm. (½ inch).  It will make a big difference!

2. Overhead irrigation

At her farm at Richmond Food Garden Group member Tara uses overhead irrigation for root crops that can cope with watering from above.
I used two rotary sprinklers on stands for many years (see photo below).  I had them on for half an hour twice a week in summer when there was no rain.  In that time an area with a diameter of around 8 metres is watered thoroughly.  I used to then put the sprinklers in different spots and repeat the process.

Overhead irrigation is very effective as it allows watering of a large area with relatively little effort. As I said before I used it for many years.  That means that I also very much realise the disadvantages of overhead irrigation.  I will mention them below.

If you choose overhead irrigation, consider having multiple sprinklers on permanent stands (see photo below), rather than sprinklers that you move around (see photo above). There is nothing worse than finding that the sprinkler fell over and is lying flat on the ground with a muddy pool around it, while nothing has been watered. Below is a photo of a fixed irrigation stand. The hose goes up the star picket, then poly pipe goes to the spray head at the top.

Overhead irrigation is an inefficient way of watering because of water evaporation in the air, wind drift and watering of paths and fences. Overhead irrigation can cause mildew by putting water on leaves.

Overhead irrigation is best done early in the morning, so water on leaves evaporates soon after.  This also avoids leaf-burn.  The photo shows leaf-burn on a lettuce that was watered from above when the sun was too hot.

A leaf of a lettuce seedling burnt by the sun after overhead irrigation

A disadvantage of overhead irrigation is also that it is indiscriminate. It covers a large area, and whatever grows there, gets more or less the same amount of water. You can't differentiate between a bed that needs regular watering (eg. lush green vegetables) and a bed next to it that should not have any water at all (eg. potatoes that have died off and are ready for harvest). Your green vegetables might be very happy with your watering, while the potatoes next to them are rotting in the ground.

One last disadvantage of overhead irrigation I found to be that, if you have a trellis or bean-tripod or other high obstacle, the area immediately behind the structure misses out on water.  Just be aware of this and water that area by hand.

3. Drippers on poly-pipe

Drippers or micro sprayers on black poly-pipe (see photo below) are great next to (semi)-permanent plants, bushes and trees.  They are a bit fragile and are easily clogged up with soil particles, but that does not matter if you have them in spots where you won't tread on them, don't have to move the pipe out of the way regularly, and don't need to regularly till the soil.  Drippers and sprayers provide an efficient use of water.  They are also good for use with pots. They are not great on vegie beds for the reasons I just mentioned.

Where a poly-pipe is a bit far from where the dripper needs to be, attach a drip-line to the poly-pipe (the white narrow flexible line in the photo below) and attach the dripper to that.  

To avoid clogging it is best to put a filter on your tap.

I had 32 drippers of the type shown in the photos above on one line and found that they worked adequately, but not brilliantly.  When I divided that line into two lines with 16 drippers they all worked much better. Consider switching to 19mm. pipe if performance is lacklustre.

4. Soaker hose

Soaker hose (usually green) has been around for a long time and can be an effective way to irrigate.  It is hose with evenly spaced tiny holes. It is easy to install, but it is best laid in straight lines or gentle curves.  It is robust and it is easy to move out of the way if you need to dig.  If you buy quality ones they are reasonably durable and will last a long time.

In areas with strong water pressure it will be best not to open the tap completely when using soaker hose, or to install a 300 Kpa pressure reducer on the tap you run the soaker hose from.  Try to avoid water coming out in arcs that irrigate your plants from above because that might burn leaves if you irrigate on warm sunny days.

Soaker hose is not available in really big lengths. It is really meant to be used 'as is' without any adjustment.  With some brands the hose's entry connector and end plug can be put in different spots, so you can shorten the hose if you want to. Some brands allow you to connect up two soaker hoses. 

The best type of soaker hose allows you to clean out the hose if it is clogged up by removing the end plug and flushing through.

5. Weeper Hose

Weeper hose is porous right along its entire length (see photo below).  It is used together with standard poly pipe connectors. It provides efficient even drip irrigation all along the line on level areas, but not on slopes or areas with dips.

Weeper hose is made from recycled tyres.  It is great to see a great product made from them, but do not over-estimate the robustness of weeper hose.  I found that it won't last long if water pressure is too high! You can only repair it by removing the leaky part of the hose.  Install a 100 Kpa pressure reducer on the tap you run the weeper hose from, and your weeper hose may be fine for many years!

Some brands advise that their hose should only be used on top of soil. Other more expensive brands allow their weeper hose to be covered by up to 50 millimetres of soil or mulch.  The cheaper ones are mostly not worth buying unless you want some arty looking fountains popping up randomly in your garden!

Weeper hose is easy to install, bends easily so there is no need to use a lot of T-connectors.  It provides good drip irrigation on level areas.  It is  easily moved out of the way when you need to dig, also great for circular layouts.

Food Garden Group member Wendy's veggie garden consists of a number of long narrow beds.  She uses weeper hoses as follows:

The photo below shows pipe at the start of a bed, held in place with a stake, and connected to poly pipe by means of a standard poly pipe T-bit and sturdy metal clamps:

Some brands advise that you turn the tap on slowly when starting, and don't fully open it.  Generally a maximum length of 30 metres is recommended.  Weeper hose may clog up if your water contains sediments.

6. Drip-line

Drip-line (see photo below) is plastic tubing with inbuilt drippers at 30 centimetre intervals.

The 'hoses with holes' discussed in method 4 and 5 are fine if your garden bed or area is level and without dips, but if not, you have no control over where in the line water will come out.  The in-line drippers in drip-line (see photo below of a drip-line opened up) achieve even watering, even if the line is on a slope.  The photo below shows what you would see if you would cut open a pipe.

Many professionals use drip-line. It is very durable. It is effective and reliable.  It is not exciting to watch though, while it delivers water.  It just drips out of each hole, without water coming out in an arc or anything spectacular.

Staff of Irrigation Tasmania (43 Derwent Park Road, Moonah, phone  6272 2400) explained to me that the key to success with drip-line is to first make sure your soil is evenly moist, then keep it moist with regular - ideally daily - short watering sessions.  Drippers are spaced at 30 centimetres because if you use them this way they will keep a circle with a diameter of 30 centimetres around the holes moist.

Drip-line can be purchased in long lengths.  It is best covered with mulch or soil, although some brands claim to be 'UV resistant'.  Recommended water pressure is 50 - 250 Kilo Pascals (Kpa).

The tightest circle that can be made with this type of pipe is one with a diameter of around 30 centimetres, so for a garden bed you could consider the following layout:

In the diagram above drippers in every second line are offset by 15 centimetres so they cover different territory.

You terminate the drip line by folding the pipe on itself or by installing a valve that is normally closed. To clean out the pipes you open the valves or undo the folded ends and flush with water. Drip line can also be bought with drippers at 40 or 50 centimetre intervals. Thinner more flexible drip line of 6 millimetres thickness is also available.

At Food Garden Group member Tara's farm at Richmond they lay the drip line in straight long lines right where potatoes have just been put in the soil. As a result of subsequent hilling the drip-line gets buried right above where the water is needed in the top part of the hill. 

Food Garden Group member, Gordon, on Bruny Island is on tank water. He used drip-lines and watered for 8 minutes per day, but would have liked to water longer.

I recently realised how dry the soil under the foliage of my peach tree was, in spite of regular overhead irrigation. I now realise that the dense foliage of the tree stops the water that comes from above from reaching the ground. Drip line, arranged in circles under the tree, would wet the soil much more effectively, and it uses far less water.

For a few years wherever I replaced irrigation lines I installed drip-lines. I began to think that it would be the only type of irrigation line I would install from there on. It was easy to install, reasonably priced, effective, and durable. But then I saw that drip-line, like everything, has limitations.

I found that drip-line only disperses water evenly if it touches the ground. It needs to be on the ground, or below ground level. If drip-line hangs above the ground (as the pipe in the first photo under Method 3) and is not perfectly level, the drip will travel down the line, to the lowest point of the line, and it will then fall onto the ground. Water will not be evenly dispersed. Drippers on poly pipe (Method 3) are the solution if your irrigation line needs to be above ground level.

Other irrigation issues .....

To cover or not to cover your lines: 

Hoses or pipes covered by mulch or soil will last a lot longer than those exposed to UV. Your garden will look a lot neater without visible hoses and pipes, and no one will trip over them. On the down-side, it is a lot of work to put them underground. Also, you might forget about them and one day damage a pipe or hose while digging. Any leak will be harder to locate. I hope that I solved this problem in my garden by putting my 12mm. poly pipes and hoses inside hard-plastic plumbing pipes under pathways. Food Garden Group member Mandy put pipes leading to her raised beds under bricks, so she knows where they are, and can fairly easily regain access to them (photo below).

Best times to water: is at or just after dawn, because there will be low evaporation, water landing on leaves will not stay there long to give mildew a chance, and the sun is not strong enough to burn leaves.

Avoid connecting/disconnecting:
The fewer hoses and pipes you need to connect and disconnect every time you water, the less wear and tear will be on connectors (see photos below).

Marg's way to avoid having to connect and disconnect hoses

Wendy's quite artistic way of solving the problem

Water filters are not expensive to buy and help avoid blockages in drippers and sprayers.  If you use tank or river water in-line filters are a must.

Buy quality gear: whatever irrigation method you choose, do not go for cheap materials.  I found out the hard way that water is very good at finding the weak spot in your system and exploiting it. Setting up a system with low-grade materials may be a waste of time, a waste of water, and a waste of money.

Automating your irrigation: through the use of automatic water timers allows you to get your food-garden efficiently watered and ready for the next dry or warm day, even before anyone gets up in the morning!  The subject is fully discussed on this blog here.