I know that we are still well into winter, but as we all know gardening is about planning ahead. Spring will soon arrive and with it up will go the sales in fertilizer and compost. Many gardeners may question the value of fertilizer or compost and when looking at a bag it is important to understand what all the figures on the bag mean.

There are different fertilizers namely organic and synthetic. Organic or those made from natural materials such as composts, seaweed, manure, fish extracts, chicken manure, animal by-products and sewerage waste. Synthetic fertilizers are those made from chemicals. There are also some specially “designed” slow release fertilizers (most of these synthetic).

Organic fertilizers are usually not as concentrated as synthetic fertilizers, they also often leach out slower than inorganic fertilizers. The use of organic fertilizers are beneficial to the soil structure and some have the added benefit of changing the soil structure to be able to absorb more water for longer. Organic fertilizers are also less harmful to soil organisms such as earthworms (which are vital in their role of decomposing fallen plant material in the garden, for creating compost in the soil and for aerating the soil) and even the smaller micro-organisms. In fact it promotes their growth which is beneficial for soil structure and for making the chemical elements available to plant roots.

Synthetic and many organic fertilizers are sold indicating a formula for example 2:3:2 (21) or 3;1:5(28). This stands for the chemicals N:P:K. N is for Nitrogen, P for phosphate and K is for potassium. The amount in brackets indicates the percentage of the actual nutrient in the whole mixture i.e. how concentrate the mixture is. The remainder of the fertilizer is carrier.

Nitrogen (N) is mainly for lush leaves and promotes rapid vegetative growth, it is especially good for leafy crops and for evergreen plants that have small flowers. All plants require nitrogen to produce their green growth/leaves (chlorophyll) and branches. Lack of Nitrogen can be evident by yellowing of leaves and stunted growth. Too much N results in soft sappy growth and lanky stems that are more susceptible to frost and fungus diseases (therefore slow down in use towards the end of summer to allow them to harden before winter).
Phosphorus (P) encourages strong healthy roots, promotes blossoming, ensures crop maturity and seed development. Plants also need this to enable their cells to divide.
Potassium (K) promotes flowering and fruiting, increases disease resistance, effects water intake by plant cells, helps translocation of things such as sugar and starches around the plant as well as the strengthening of plants. It also promotes general plant health.

The figures 2:3:2 will therefore indicate the parts of each macro nutrient in that fertilizer. Therefore there will be 2 parts of Nitrogen, 3 parts of Phosphate and 2 parts of Potassium. This is a very broad range balanced fertilizer aimed at general growth of lawns, shrubs and flowering plants. It is good to use this in-between the use of other fertilizers.

Most fertilizers are very easily identifiable by the name and picture on the bag. Fertilizers with a higher N and K value e.g. 3:1:5 or 4:1:6 will be better for fruit and flowers.

Many organic fertilizers (due to their origins and production processes) will contain a fairly wide range of other micro-elements which are also really beneficial for plants and there is no need to buy sperate micro nutrient fertilizers.
Balanced feeding of plants is essential and never apply more of the fertilizer than the recommended dosage. Any fertilizer (granule or power concentrate) spilt onto plant leaves must be washed as soon as possible to prevent burning of leaves. This burning is caused as a result of the elements in the fertilizer being more concentrated that those in the plant leaf and water must therefore move from one to the other by means of osmosis. It can and will kill plants in high enough concentrations.

Foliar fertilizers (applied over the plant foliage) are in a liquid form and useful as they are absorbed very quickly and therefore available to the plant at “short notice”. It is best to apply these fertilizers in the evening or early morning as this is when leaf stomata are open.
Do not store fertilizers in areas that are wet or damp as this can cause it to go hard and compact. As a safety advice, never store fertilizer together with your lawnmower petrol, as the contact between the two could result in a fatal accident.

In my opinion, rather apply fertilizer in small doses thus allowing plants time enough to absorb it rather than over fertilizing and allowing excess to run off into our local river and polluting the environment. Excess nutrient runoff from farms also contributes to alien invasive aquatic plant explosions on Hartebeespoort dam and the Vaal River Barrage.

As usual there is so much more to share on this topic, but that is for another day. Remember that responsible gardeners are Water Wise gardeners.