Fertiliser guide for the year

The Science

Simply put, fertiliser is required for soils that are lacking in the nutrients that a plant needs to perform at its best. You can tell if a plant needs feeding by some of the de­ficiency symptoms they display, such as yellow leaves (lack of nitrogen), no flowers (lack of phosphorus), weak stems (lack of potassium) or localised necrosis, evident by stunted growth and possibly curling leaves (a lack of calcium).

The most common fertiliser ingredients include Nitrogen (N), which promotes vegetative growth and is responsible for the greening of plants, Phosphorus (P), which assists with the manufacture of chlorophyll and is critical for root growth, and Potassium (K), which is essential for vigorous growth and the manufacture of sugars and starches, and therefore improves flower and fruit production.

Plants also use several trace elements or micronutrients in small quantities, like boron, cobalt, copper, iodine, iron, molybdenum, manganese, selenium, zinc, silicon, nickel and chlorine. Some of these can be present in fertilisers, depending on the product and its intended use.

Nutrients can be recycled into the soil in natural ways, such as through decomposing leaves and plants. Soils can also be improved by crop rotation and planting green manures. It’s not always ideal to use fertilisers, and more fertiliser is not always better – a balance is essential.

A plant only uses what it needs, and absorbing more than it requires can result in abnormal growth. You may decide to fertilise a particular section of your garden before planting the next crop if you have grown and harvested plants there before and know that your soil will be depleted of nutrients.

Vegetable gardens

As a general guide, and we do mean general as di­fferent climatic zones and di­fferent products make a di­fference in what you need for your particular garden, use 2:3:4 every 4 – 6 weeks year-round for good roots. These numbers refer to the percentage of nitrogen (2), phosphorus (3) and potassium (4) in the bag’s total weight. For leafy greens like spinach, use a fertiliser high in nitrogen (for leafy growth), like 7:1:3, every second month.


You may think that all you need do for general lawn care is water and cut regularly at the right time and frequency during the year, but feeding your lawn is equally important. Like all living things, your lawn requires food. It is easy to remember this if you think of a lawn as many tiny plants grouped together to form a carpet in your garden.

When choosing a lawn fertiliser, make sure that it is suitable for the type of grass in your lawn, and follow the manufacturer’s instructions carefully. The products have been designed to give the best results when using as stated, and using more will not speed up the programme but will more than likely cause damage. Follow-up instructions are also important. As a general rule for a healthy lawn, apply a lawn fertiliser (7:1:3) at the beginning of spring and repeat every 4 – 6 weeks during the growing season.

If your lawn needs a boost of nitrogen to make it greener, use LAN (Limestone Ammonium Nitrate) from December to February.

In warmer climates, you can boost root growth by adding 2:3:2 in late winter.

Garden beds

Make sure that whenever you plant, your flower beds are well prepared with organic fertiliser, compost and superphosphate or bonemeal. This gives plants the best start. Extra fertiliser is, as a general rule, a 3:1:5 SR (N) or 8:1:5 fertiliser for fruiting and flowering and can be used every 4 – 6 weeks. In winter, in cold climates, only feed seasonal flowers.

Feeding and fertilising tips

• Always water well after fertilising. In fact, donning a raincoat and fertilising in the rain is ideal!

• Kraal manure is often used as a source of nourishment for plants. Use during the peak growing season, in conjunction with or as an alternative to chemical or organic fertiliser.

• Always trust the manufacturer’s advice when deciding how much fertiliser to use per square metre – they are the experts and adding more will not make the fertiliser work any faster, and it may damage your plants.

• Compost is usually used during the main planting seasons, from March to May and from September to November, for flowering annuals and vegetables during soil preparation. However, compost will also be of great benefit to the garden if used as a surface mulch every 3 – 4 months, particularly during dry spells when rainfall is limited and water scarce.

• When planting any plants, always add superphosphate or organic bonemeal to the planting hole to stimulate root growth, along with compost. An EXCEPTION is when planting plants that are phosphate-intolerant, like those in the protea family.

The Gardener