By Jeanne Austin
Spring is the ideal time to give your garden its annual feed. But with so many different products and formulas around, how do you know which one to use? Jennifer Stackhouse shares her tips on fertilisers and when to use them in your garden.
This is the first part of the “Gardening Tips” series, brace for more tips in the future.
Soil and sunshine work together to make plants grow. In nature, leaf litter, animal manure, and other goodies that fall on the soil continually break down to replenish soil nutrients and keep plants growing. In a garden, it’s a whole different ball game, where plants are often competing for nutrients and replenishments, gardeners needs to add fertiliser to the garden soil or potting mix to keep their plants growing.
Whether its organic or fertiliser to your soil, you provide them with three basic building blocks, which are nitrogen (N), phisphorus (P), and potassium (K). Packaged fertilisers list the amount of these building blocks, often showing it in a ratio format.
It’s quite complex and varied on the way plants use the nutrients provided. Some neeeds more of one nutrient, but little of another, while others needs a three way split. Understanding which nutrient does what gives you a rough guide to selecting the right fertiliser for your plants.
Determining the growth patterns
As a general rule of thumb, nitrogen encourages leafy growth, phosphorus stimulates overall growth and plant development, while potassium assists with flowering. Lawn food, which are designed to stimulate leafy growth, have much higher levels of nitrogen compared to the levels of phosphorus and potassium they contain.
A plant food for general garden plants may have the equal ratio of N,P, and K, to encourage growth and flowering.
Citrus food on the other hand, has smaller amounts of nitrogen and higher amounts of phosphorus and potassium. Most native plants can’t tolerage high levels of phosphorus, so the NPK ratio for a native plant food will show little or no phosphorus.
Fertiliser products that are derived directly from seaweed have little or no nitrogen but are rich in phosphorus and potassium.
As well as the top three nutrients, plants require smaller amounts of other elements including sulfure, calcium, and magnesium, which all play an essential part in plant growth.
Some additional elements are also needed in very small quantities and are referred to as trace element. They work to correct the occasional deficiencies in particular plants or soils. Trace elements, which include, zinc iron, boron, copper, manganese, and molybdenum are usually packaged and sold together.
But not all nutrients stimulate plant growth alone. Products such as humic acid, compost and organic matter encourage the growth of microbes in the soil, which in turn aid root growth. These products can alter soil pH, improve drainage and create a better texture.