Feeding time

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Spring's perfect combo of warm sunshine and rain means growth is at its most exuberant. All this activity needs fuel to keep it going, so now is the time to get feeding.

What do plants need?

The three 'major nutrients' that plants need in biggest volume are nitrogen (N), phosphorus (P) and potassium (K). As well, they need smaller quantities of a wide range of minor and trace elements.

  • Nitrogen is important for leaf growth and the conversion of sunlight into plant energy.
  • Phosphorous is critical in cell formation particularly in root growth and seedling growth, as well as flowering and fruiting.
  • Potassium plays an important role in a plants strength, water uptake and disease resistance. It enhances the quality of flowers, fruits and seed.

Plants grow best when they receive all the nutrients they need without one overpowering the uptake of another. A complete balanced fertiliser is the simplest way to achieve this. To make it easy, a wide range of specific plant foods are available.

Organic or inorganic - what's the difference?

Organic fertilisers come from plant and animal waste. Inorganic fertilisers are manufactured from chemical reactions. Some products blend the two.

Organic fertilisers add to a soil's physical structure, improving water holding capacity and drainage, while promoting the activity of beneficial micro-organisms. They release nutrients over a period of time and are generally less concentrated than other fertilisers so need to be applied in larger quantities. The exact nutrient content of any one organic fertiliser is hard to ascertain, but using a range of different organic products helps to approximate a 'balanced diet'. Blood and bone, for example, is a highly effective and long lasting fertiliser for a wide range of plants, but it doesn't contain potassium. Exclusive use of organic manures works best when there is a local supply of free or low-cost manures, not always easy for city gardeners.

Chemical fertilisers do nothing to maintain the physical structure of the soil. However, because they are more concentrated, and we know from the label what's in them, they provide fast reliable results. The nutrient content in 100 grams of general garden fertiliser is roughly equal to 3 kg of organic manure. The risk is over-use, as high concentrations can burn plant roots. Also, any excess 'run-off' is bad for the environment. Over time, soils fed solely with inorganic fertiliser suffer reduced humus content and biological activity. This leads to reduced water and nutrient holding capacity, and the need to add even more fertiliser - a vicious cycle. It's important to strike a balance.

A tonic

A fast-acting plant food applied as a liquid or powder (washed in with water) will provide a quick boost to growth and greenness. Liquid fertilisers are especially useful for plants grown in containers, and should ideally be added little and often. Use them as a supplement to longer lasting fertilisers.

Longer term

Pelletised poultry and sheep manures, blood and bone, and inorganic controlled-release fertilisers release their nutrients gradually, more in sync with plant growth. They allow the convenience of feeding less often, while helping to avoid waste and damage from over use.

What about lime?

Adding lime to the soil has many benefits, but it must be used wisely. There are three main forms:

  • Garden lime is made from natural limestone and provides calcium in a slow-release form. It can be used to raise the pH and is also useful for breaking up heavy clay soil.
  • Dolomite lime contains calcium plus magnesium, which is good for leafy crops such as broccoli and lettuce. An ideal composting agent, dolomite stimulates rapid decomposition of organic matter, and can be safely applied with other fertilisers.
  • Both garden lime and dolomite will raise soil pH, which is also known as 'sweetening' the soil. In general, an acid to neutral soil (pH 6.0 to 7.5) provides the broadest availability of nutrients. If the pH gets too low or too high, nutrient availability and beneficial soil microbe activity will drop. Apply at the recommended rate and avoid overuse. If in doubt, test your soil with a DIY pH test kit available from most garden centres. Lime can be very effective in the vege garden and for many perennials, but keep it away from 'acid-loving' plants such as camellias, daphnes and rhododendrons.
  • Gypsum is a good source of calcium and sulphur. It is excellent for improving soil structure, and often used to loosen clay and compacted soil. Gypsum is a natural mineral, with a pH of about 7.0 (neutral). It does not affect the soil pH balance so is safe to use with acid loving plants. Use gypsum in compost to enhance microbial growth and decrease unpleasant smells.

Spring lawns

While not soley about feeding - Spring is an ideal time to get your patch of pasture into top notch condition. Support the spring growth flush with lawn fertiliser.

Feeding and frequent mowing is the best way to keep lawns free of weeds but if things have got away on you, spring is the time to act with a selective lawn weed spray. Prickle weed killer is best applied in October or November. Alternatively, try Fiskars Weed Puller for easy chemical-free weed extraction.

Thin or lumpy lawns can be revamped by top dressing with a mixture of topsoil and compost. Small packs of lawn seed are ideal for fixing bare patches.

Regular mowing promotes thick, healthy growth. But if cut too short, lawns are vulnerable to weed invasion. Keep mower blades extra sharp for a clean cut. In spring it's best to use a catcher as excess build up of clippings can invite disease.


Look for these products, tips and advice at a Go Gardening Store near you.



A summer crop

Feeding Time