Now’s the time to apply the lime
THERE are several reasons why lime is applied to parts of the garden in autumn and early winter. The most important one is because it must be kept separate from high- nitrogen fertilisers, most of which are applied later in early spring.
Lime must never be used at the same time as high- nitrogen fertilisers such as fish emulsion or poultry manure because they don’t mix. They tend to collide and much of the benefit from each is lost into the atmosphere.
We also apply lime at the start of the dormant season because those hardy vegetables which are planted in, or keep growing through winter, such as broad beans, onions, garlic, English spinach, globe artichokes, asparagus and most brassicas all happen to be lime- lovers.
In other words, they prefer a sweet soil and detest acidic conditions.
Lime is not a fertiliser – it makes acidic or sour soil more alkaline and sweeter and many Tasmanian soils are acidic.
This can be a problem because when soil is too acidic, many of the minerals needed by plants become unavailable, or locked up.
So lime can also be a great un- locker for lime- loving plants grow healthier, crop better, are more disease- resistant and less attractive to insect pests.
Lime also has another vital role. It enables many soil organisms, especially the different types of bacteria, moulds and other fungi to operate more efficiently. This is why it is always a good idea to apply lime generously around most apple, pear, peach, nectarine, apricot and plum trees in early winter.
Right now, the ground around these trees is covered with fallen leaves and the halfdecayed, increasingly acidic remains of fallen fruit.
However, this debris is also the main winter habitat of some of the most persistent and destructive disease organisms such as acidloving scab and brown- rot.
So the act of sprinkling lime over this fruit tree debris is to rapidly increase its rate of decomposition, which in turn destroys many disease organisms.
Even better, earthworm populations thrive in well- limed soil, so they too multiply and play a vital role in converting all organic debris into valuable worm casts.
In the ornamental garden I sprinkle lime generously around lilac trees every June. They grow better, stronger and bloom brilliantly every spring.
But keep it away from lime- haters such as rhododendrons, azaleas, camellias, ericas and most Australian plants.
Lime is calcium and there are several forms. Much of the stuff we use on our gardens is nothing more than finely ground limestone, commonly known as “agricultural lime”.
The finer the particles, the more effective it is. Sometimes this limestone also contains another essential mineral magnesium.
This magnesium limestone is usually available as dolomite. It is particularly valuable for use on heavily leached, light or sandy soils at the normal rate of a handful to the square metre.
However, when lumps of hard limestone rock are placed in kilns and then brought to a red heat, a remarkable change will have taken place after cooling.
The limestone not only changes to a greywhite colour but becomes soft and powdery.
The most dramatic change is with the extraordinary volatility of this powder.
It has become quick- lime and it can be dangerous and difficult to handle. Even if stone- cold, quick- lime will immediately heat up to boiling point producing clouds of steam and swell rapidly when sprayed with water. This is why it is no longer available for public use.
Just the same this wetting or “slaking” process is deliberately carried out at lime quarries because the final result after cooling a second time is the super- fine, white “hydrated” lime used mainly by builders.
I prefer to use it on the garden because at around $ 15 per 20kg bag it is wonderfully cheap. It also does the job of soil- sweetening far more rapidly than ground limestone or dolomite and far less is needed to do the job.
In short, builders’ lime is half the price, twice as fast and less is needed.
The problem is it may cause problems with people with sensitive skins and the fine particles can be irritating if breathed in.
Just the same, many building workers use this stuff every day of the week and most get used to it.
I’ve used this fine lime for half a lifetime, chucking it about with great abandon with no ill effects.
In spring, I also spray builders’ lime mixed with water over our apple and pear foliage in October to control scab disease. Another application in early December also controls pear and cherry slug infestation.