Danger in applying too much lime

Press, Volume CXI, Issue 32565, 26 March 1971, Page 11

Danger in applying too much lime

■ Autumn is traditionally considered the best time to apply lime to the garden. This has perhaps come about because it is at this period of the year that the vegetable garden carries least crops and is usually dug over to lie fallow during the winter.

The use and value of lime have been fully dealt with on a previous occasion so will not be elaborated on again. Regular applications are beneficial in most soils and result in improved fertility. It must, however, be applied with some discretion because it can be overdone, resulting in serious problems. Too heavy a dressing of lime can induce excessive alkalinity. ■ Most plants prefer a slightly acid medium for optimum growing conditions and some, notably the ericaceous plant family members such as rhododendrons, azaleas, and ekianthus, most definitely are intolerant of all but an acid soil. They will often register their displeasure of high lime content by failing to thrive, turning yellow of leaf and even dying if the situation is not corrected.

Organic matter in a soil abundant in lime can break down rapidly and soluble minerals (nutrients) thus released may be quickly lost Certain diseases favour alkaline conditions such as scab in potatoes but the most serious problem associated with too alkaline a soil is induced mineral deficiencies.

Particular elements can be abundant in a soil and may be readily available to the plant within a particular range of soil acidity. When, however, the soil tends more and more to a higher level of alkalinity (or acidity) these elements gradually become converted to complex compounds which are less and less aysiiable to the plant.

Of these elements, iron is perhaps the most important and the one most seriously affected. Iron deficiency is a fairly common complaint on alkaline soils and is vital to the plant in the production of chlorophyll, the green colouring pigment. Lack of iron induces a chlorotic or yellowing condition in the leaves, particularly on young foliage which can result in die-back of the growing tip in severe cases. ■Manganese can be a serious problem, as in tooalkaline soil conditions there may be accelerated uptake of manganese, and toxicity symptoms may appear. A deficiency may be caused if the soil is too acid.

All plants are not equally sensitive to such problems and although it has been mentioned earlier that most subjects prefer slightly acid soil conditions, there are some which will grow in calcareous soil. Some of these are cistus, fuchsia, forsythia, and euonymus. Lime has most use and

value in the vegetable garden and needs careful use in both the fruiting area and the ornamental part of the garden. If in doubt as to

■ whether and how much to i apply, a soil test will help to 1 solve not only the liming i problem but also the need i or otherwise for fertilisers.