By Drew Cooper
Well, we’ve had quite an ordinary summer to this point, with a few warm days, not much rain and plenty of wind. Not the perfect conditions for the human species, but our gardens haven’t minded it at all. Lots of growth and beautiful flowers, albeit a little on the dry side.
With soil moisture one of the most important contributors to optimum growth, it is well worth having a look around the garden and taking note of what plants are doing well in different areas. You will probably find the plants that are irrigated are well outperforming the drier parts of your garden. This would seem obvious, but why?
The adage that native plants don’t need supplementary water is a bit of a furphy. True, many of our native plants in areas of low rainfall and sandy soil have evolved to require less water than their relatives in wetter areas, but without water most plants will suffer and at the very least just sit there and appear quite unhappy.
Native plants require more water than we’ve been led to believe. The cells in the plants need adequate moisture to maintain their turgidity – firmness of stems and leaves; water is one of the vital raw ingredients that a plant needs for photosynthesis, as we remember from school; and plants cool themselves through the transpiration process. This is all fairly straightforward.
What many people don’t really grasp is that plants need water in order to feed themselves. While there may be an abundance of nutrients in the soil, often supplemented by us fertilising, a plant cannot access this food without water. Most plants can only take up nutrients once they are dissolved in water, so without adequate soil moisture your plants will simply be waiting for some help. And that can only be from rain or us.
In heavier soils or soils with a good humic (organic matter) content, water is held for much longer than in the free-draining soils along our coast. Understanding this helps us make decisions on how often we need to help our plants access water.
A simple way to determine whether there is adequate moisture for optimum growth is to conduct a ‘ribbon test. Take a small handful of soil from at least 100mm below the surface and make a fist, squeezing the soil together. If the soil runs through your fingers when you open your hand, it is too dry; if the soil is dripping with moisture, it is too wet. What you want is for the soil clump to maintain its shape and only fall apart when you wriggle your fingers. It’s a very handy test for all gardeners to know.
We find that installing an irrigation system for your home garden is well worth the time, effort and/or money in order to keep your plants thriving. At the very least, give the plants a regular drink through hand-watering. You can determine if you have irrigated or watered enough by – you guessed it – a ribbon test.
