Battling with high Ph in your Garden

pH affects plant growth because a change in pH means a different availability of plant nutrients in the soil. When the pH rises above neutral (7) the availability of iron, manganese, copper, boron and zinc drops. Plants not adapted to a high pH are unable to get enough of these elements, particularly iron, manganese and zinc. This is shown in the yellowing of leaves. Affected leaves On alkaline soils plants get lime-induced chlorosis which shows up on the leaves as a dark green vein pattern against a pale green or yellow leaf. While iron is available in the soil the high pH slows the iron uptake by the plant.  

What to do 

There are many ways to decrease the alkalinity of a soil. Use compost to improve the soil and as it breaks down the humic acid will leach through the soil. A quick solution is the application of iron chelates, which is bought as a powder and watered onto the roots. New leaves will return to green in a week but the effect lasts only a few weeks.  If it works apply iron compost (see Iron Compost Recipe on Resources page). The cheapest material to use to acidify soil is sulphur. Apply about 25g per square metre to sands and up to 100g per sq m to clay. The sulphur is converted by soil bacteria into sulphuric acid which increases the concentration of hydrogen ions in the soil and so lowers pH. You can also use iron sulphate, using about twice as much as sulphur, however, since it is very salty only apply about a third of it at any one time. Water well after applying, wait a week and if necessary apply some more. These solutions work best in the warmer months of the year.