#10 - Oct 2017 - Garden Stuff - © Sandy Lang - slang@xtra.co.nz
PLANT NUTRITIONOctober/November: Mid/late spring. Much longer days, warm soil, new leaves, flowers everywhere. Young fruit are forming where flowers have dropped. Things are growing very fast… What do plants need for growth…?
Plant nutrition: In darkness, plants do what we do, they use up carbohydrates, take in oxygen (O2), give off carbon dioxide (CO2) and grow. In sunlight they do what we can’t do. Their green leaves (chlorophyll) are photocells that absorb light energy. They take in CO2 and give off O2 and synthesise carbohydrates. This plant chemistry takes place in water solution in green cells. So, the ‘absolutely-must-have’ plant nutrients are: water, light, CO2 (day) and O2 (night).
Macronutrients: Like us, plants must also have certain minerals. These are dissolved in the soil water and are taken up by the roots. Three minerals are needed in quite large amounts - nitrogen (N), phosphorous (P) and potassium (K). If the levels of N or P or K are low, a plant will grow slowly and be susceptible to disease. You can buy bags of NPK fertiliser or you can use mineral-rich composts/manures. Go to www.tuigarden.co.nz for expert advice…
Micronutrients: As well as the macronutrients, plants also need tiny amounts of many other minerals. These ‘micronutrients’ include boron (B), iron (Fe), manganese (Mn) etc… Although needed only in tiny amounts, these are still essential. If the soil is deficient in one of them, growth is badly affected - e.g., many NZ soils are B deficient but a half matchboxful of B is enough for the whole garden.
Garden centres sell bags of fertiliser that contain the macronutrients along with the micronutrients. Different plants have slightly different mineral needs so they also sell fertiliser mixtures optimised for lawns or roses or citrus etc…
Low CEC: A soil’s cation exchange capacity (CEC) measures its ability to retain minerals. Most Eastbourne soils are sandy and bad at retaining minerals (low CEC). Increasing soil organic content raises CEC. On our sandy soils add fertilisers in small amounts and often. Heavy applications are soon washed down below the root zone. Slow release fertilisers are ideal… ___________________________________