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- Armchair gardening this week is soil pH and what to do about it. The pH is
the level of acidity or alkalinity in your soil and how it has a profound
effect on the vigour of many of your favourite plants, especially in this
area. First step to solving your pH problems is to buy a pH testing kit.
- In this region of Adelaide, with its predominantly heavy alkaline clay
soil, we do not have the luxury of picking up exotic gardening books to get
ideas on plants to grow, without using some considered reasoning. ‘Will it
tolerate the pH of my soil?’ That’s the question you should ask every
time. While some plants are quite adaptable across a wide range of pH, most
are very specific.
- Carnations, Tomatoes and Beets all like alkaline conditions, where as
Camellias, Azaleas, Gardenias and Rhododendrons need acidic soil reactions
or they fail to thrive and usually die in a short time at a pH reading in
the range of 8-9. Seven is neutral and pH6 is about as good as you could
hope to maintain in this region even with lots of help.
- Compost and some organic mulches are slightly acidic, but with Adelaide’s
tap water on them, your soil will soon become alkaline. Leave Almond husks
and shells right alone, at pH10 they are dynamite in this area!
- If you are intent on maintaining a mildly acidic soil apply iron chelates
on a monthly basis at the rate of 10 grams per 5 litres of water and water
it in the soil around your acid loving plants. It acidifies the soil and
makes iron available again, which it will not be at a pH of more than 8,
which is common in this area. The indicator is when you leaves turn yellow,
but the veins stay green. It’s called "lime-induced-chlorosis"
and iron fixes it. Not nails or horseshoes though that sort of iron is
useless to plants! You can also use it on the foliage as a foliar spray and
effects are immediate.
- Other ways of acidifying your soil or container plants are to use iron
sequestrine, but it’s very expensive and hard to find (Australian Plants
Society sell it), flowers of sulphur works and its cheap, but does not have
a long lasting effect, but then most remedies don’t either, so try it.
Some plants don’t like too much sulphur though, get tricky doesn’t it?
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