Well its cooler and there are showers around. Can I stop watering? And should I race round with soil wetting agents to fix the problem?
There are always two things to consider when it comes to watering. Well, fundamentally two things. The plant and the environment. Lets consider the environment – more specifically evaporation. Back in January and February the evaporation per day was about twice what it is at the moment. Say 8.5 versus 4.0 mm per day. On the hottest days in January it got up over 11 mm. So we are still losing about 4 L water per square metre of ground. So lets consider our plants. They may or may not be actively growing at the moment. If they are they will be using water. Remember we’ve had a couple of fairly heavy showers too so some plants may already be trying to grow and its important that we support them. If they are growing they will be sucking up water from the soil and drying it out and that moisture will have to be replaced or the new roots and shoots that are forming will die.
There are a few other traps at this time of year. If you’ve been watering with drip there may be a salt build-up around the edge of the wetted zone in the soil. The first showers of rain that come down may push some of that salt back into the root zone and so it is possible for plant roots to be damaged by that salt and you may see signs of that on the plant itself such as scorching round the edge of the leaves.
Irrigation is all about the water being where the plant can get to it – that is where its roots are. So if you’ve been watering through a dripper in one place, don’t suddenly move it to another because most of the roots will be back where the dripper WAS and your plant may die from lack of ACCESSIBLE water.
A really interesting paper was published in an irrigation journal last month. The authors looked at a range of wetting agents (five in all – granular and liquid) to see how well they worked on our sandy soils in Perth. Now bear in mind this is a refereed paper using good scientific methodology so the results are worth listening to. They found that only a few days after applying the wetting agent, soil wettability had declined back to OR EVEN WORSE than its previous level. Their conclusion was that many products DO NOT enhance long term wettability, in fact they even seem to make the original problem of non-wetting worse!
Food for thought? Back to clay amendments I think.
BTW the reference if you want to hunt it up is: Gross A, R Mohamed, M Anda and G Ho, 2011. Effectiveness of wetting agents for irrigating sandy soils. Water, April 2011, 154-157.
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So great to find a blog about WA gardening! You’re talking about the same problems, and unsatisfactory “solutions”, that I’m always complaining about to anyone that will listen. 🙂
My dad doesn’t know what I’m on about, since his block has 50 years of garden humus buildup, as well as the benefit of having had 30 of those years with daily summer watering and no water restrictions. It’s also in a bit more of a valley, and I’m on a hill — it just struck me the other day that I’m bound to have even more weathered, sandy, humus-free soil than a lower elevation. D’oh. 🙂
Thanks, and keep it up! I’ll be adding you to my bookmarks!
Hi Aileen,
Interesting about the wetting agents. Would you recommend a wetting agent or wetting agent type then?
No I wouldn’t! I’ve tried the same ones (recommended by Water Corp) as I guess everyone else has. I think I prefer to manage my organic matter and try to keep the soil moist. And maybe add some clay if appropriate.
I know I’ve used some wetting agents (it was a granular one) that I’ve attributed to killing plants – read the label because some have other things added – that may be good for some plants but not for others.
Its certainly been mentioned that water restrictions can be a bit of a farce if you have non wetting soil because it just takes so much more water to wet up the soil once it has dried out so it becomes false economy. I’m not sure if that’s been quantified/ratified but it wouldn’t surprise me!
Are you keen on Bentonite or Zeolite?
As a wetting agent or to hold water? Different things. Neither hold much water or give what they hold up to the plant well. But they may help non-wetting.