Like most scientists, we gardeners are curious about our natural environment. “Why does a plant behave in such and such a way, but only during hot weather?” we might ask ourselves, or “Why is one patch of potatoes covered in scab and not another?” And so the questions continue; the answers helping us to understand the world around us and, consequently, to improve our growing of plants.
Here in Greece, where I am holidaying, I am so obviously surrounded by lime that I can’t stop being curious about it: the water leaves a film of calcium on the bottom of the kitchen kettle, the sea is as soft as velvet, my shampoo wont lather, the village walls are coated in white wash, the caves are dripping in calcifications, and all the hydrangeas are pink! But what, exactly, does all this lime mean for the soil – and what are the consequences of having very little lime in your growing medium? In spite of being on vacation, I couldn’t stop myself from looking for answers.
Soils lacking in lime (or, at least, an adequate dose of it) spell trouble for many plants, including a wide range of vegetables (potatoes, tomatoes, peppers, peas, beans and onions being the major exceptions). Without sufficient lime, soil nutrients cannot be unlocked and made available for plants with the result being that such plants often display yellow and misshapen leaves. In lime deficient soils, microbes and worms fail to thrive and so organic matter is slower to break down and contribute to soil health. When acidic soil is corrected, plants are greener and stronger; they require less water, and are more able to resist diseases.
Unfortunately, just to make things more complicated, an excess of lime in the soil can cause similar problems. The only answer, if you are an anxious gardener, is to test (using a home soil testing kit) or have tested (through a laboratory) the PH levels of your soil. But before doing that, it pays to note that simple organic gardening methods may solve many PH problems. While non-organic fertilizers tend to rob soils of lime, compost, mulch, and leaf mould all help to smooth out PH levels.
It is also possible, to a degree, to ‘guess’ the PH levels of your soil. Ground previously used to ‘raise and graze’ animals, and which has had little, if any, lime added to it, is likely to be seriously lime deficient. That’s because animal bone growth is composed heavily of calcium and calcium is supplied to young animals through milk. Parent animals make milk by feeding off grass which, in turn, uses up calcium (lime) from the soil. Regions which experience high levels of rainfall (my Catlins home in South Otago is one of them) are almost certainly likely to be lime deficient because the lime will have been leached out of the soil. Clay soils are also likely to be lacking in lime as well as being resistant to changes in PH levels, which is why they need more lime than other soil types to raise their alkalinity.
Just how much lime to add to your garden, and in what form, depends on the soil type in your region. Visiting a site such as this Royal Horticultural Society liming advice can help you with decisions or, much more simple, you may like to pay a visit to your local garden centre. ‘Local’ in this case is of paramount importance as the person you speak to will be familiar with soil types in your part of the country.
When and if you do decide to apply lime to your garden, choose winter as the time to do it, and dig it in well. Over the colder months, it will take effect without damaging young growth. Bear in mind that lime applied only to the surface of the ground may take many years to break down (which is why it is best to add it to the soil at the time of planting lime-loving perennials).
As for me, after enjoying the soft pink displays of hydrangeas grown here in lime-rich Greece, I am away home to fill a few tubs with acid potting mix. These gorgeous (and rather fashionable) plants are PH barometres, and in my acid rainforest environment, every hydrangea in my garden turns blue!