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Archive for January, 2012

If you’re in the business of trying to grow anything, the weather we’re having isn’t making it easy! And even if you’re not a commercial grower, the twists and turns of the weather lately makes it really hard to get the best from your plants.

I downloaded the weather data from Medina Research station for last December to today. The daily evaporation for that period ranged from 1.5 mm for the day up to 11.4 mm! That’s a ten fold difference. And I bet the settings on your irrigation controller haven’t changed in that whole time! When you sum up the evaporation over a week it doesn’t look quite as variable – 44.1 mm, 44.2, 57.9, 63.4, 54.2, 66.2 and 58.4 – which is only about a 50 % variation. Actually last week would have been less because I haven’t subtracted off the rain we had, which at home was 42 mm but for Medina was about 30mm. So you really need to take that off the weekly evaporation. Incidentally, from a commercial point of view we don’t regaard anything under 4 mm as being effective ie its not regarded as beng enoguh to do any good.

Anyway, what I’m trying to say is that unless you vary your irrigation you are either going to run into trouble with plants drying out, or you are overwatering like mad to cater for the worst case scenario, wasting water and probably washing away most of the fertiliser you put on into the bargain.

Commercial growers vary their water on a daily basis if they are doing their job properly. And at this time of year, depending on their crop they may be watering anything up to four times a day in amounts that will add up to the total daily evaporation – plus or minus depending on crop and stage of growth. Now, no home gardener can be bothered with that, plus if you have to abide by the two or three time a week watering edict, you simply can’t water every day unless you hand water. And in sand that’s a problem because it does not hold water and actively growing plants will dry the root zone out in well under a day and get stressed or even die – particularly if they are small seedlings.

What can you do to help this? Amend your soil with clay and organic matter. Be wary of the source – you get what you pay for! Don’t run the risk of getting dieback with your clay and remember that compost has quite a lot of phosphorus in it relative to nitrogen. Much of this is explained in previous posts.

The other thing you can do is mulch. But remember to use coarse chunky and COMPOSTED material (again to prevent importing disease and weed seeds) so any applied water runs straight through or you will end up with wet mulch and dry plants. Keep mulch away from the collar of the plants. Mulch does a good job of moderating soil temperatures and the trials we have been running at Murdoch TAFE show that if you start with a nice wet soil profile, mulch can do quite a good job of helping to maintain the soil moisture. Don’t layer the mulch on too thick though, keep it in proportion to the size of the plants it is around. And don’t add the same amount to it each year, just maintain the thickness you need.

Still though, if you are having trouble with plants not thriving in the garden, the best thing you can do is get out with a spade and dig. You may be surprised. I have been. Beds I thought should have been well wet have shown dry patches and even been dry about 25 cm down – well within the root zone of any plants.

Always beware of newly planted plants. Inferior potting mixes (you get what you pay for) and simply the type of mix, may mean the root ball of your plant dries out before the soil around it.

In my experience many plant problems come down to the basics and on our sands its odds on its watering or lack of nitrogen and those two are inextricably tied together. Too much watering means you wash all your nitrogen away. Assuming you had enough in the first place – nitrogen is the one nutrient always in short supply on our sands, and manures and composts never have enough of it while at the same time they are overloaded with phosphorus.

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