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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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