Follow our easy guide to “all you need to know about fertilisers” including:
What is a fertiliser?
How does a fertiliser work?
What types of fertilisers are there?
When should fertilisers be used?
What fertilise should be used on what plant and when?
What nutrients does a fertiliser contain?
How to select the best type of fertiliser for your specific plant?
A fertiliser is any substance, either natural or chemical-based, that is applied to soil or plants to increase yield or performance and comprised of nutrients essential for plant growth.
To grow, plants need sunlight, water and carbon dioxide. To thrive they require essential nutrients referred to as macro (or major) nutrients and micro (or trace) nutrients. These essential nutrients are considered mineral nutrients and in an ideal world are absorbed by the plants through the soil. There are many contributing factors that can affect the uptake of these essential nutrients and unfortunately, most soils across the planet are deficient in one or more elements.
The use of fertilisers dates back thousands of years, but it wasn’t until the early 20th century that agricultural and horticultural practices changed forever with the development of artificial fertilisers. Almost overnight there was a product available to farmers that would increase crop yields, was easy to transport and apply and allowed the world to feed a growing population with the same land resources.
Fertilisers supply essential nutrients to plants for balanced growth. Broadly speaking a fertiliser is any substance that is applied to the soil or foliage that will increase the health, disease resistance, productivity and yield of a plant. There are many factors that contribute to the effectiveness of nutrient uptake by plants. These include:
Artificial fertilisers are specifically formulated to supply nutrients to a particular crop and usually are made up of macronutrients (Nitrogen, Phosphorous and Potassium NPK) and micronutrients. When artificial fertilisers are manufactured the available nutrients are concentrated and converted into a compound that a plant can absorb (or take up) readily. If a plant is unable to take them up quickly many of these readily absorbed nutrients are water-soluble and will leach through the soil to waterways.
Organic fertilisers are any substances that were once living such as manure, biosolids, leaf litter, crop residues and any by-products from meat production facilities such as blood and bone. These fertilisers have a lower NPK ratio than artificial fertilisers but also have soil conditioning properties.
Nutrients in organic fertilisers are not as readily available to plants as artificial fertilisers. Organic fertilisers require a conversion process so they can be absorbed by the plants;
This conversion process is carried out by;
The by-product of the conversion process is an improvement in soil conditions. These soil conditioning properties further improve the water holding capacity of the soil, increase soil structure and aeration. In addition, there is an increase in microbial activity, which in turn reduces the leaching of excess nutrients.
Artificial fertilisers nutrient conversion for plant availability happens in a factory.
Organic fertilisers nutrient conversion for plant availability happens naturally in the soil.
There are many different types of fertiliser available on the market and to the new gardener selecting the right formulation for the garden can be overwhelming.
Types of fertiliser;
Fertilisers are an essential part of a plant health and maintenance program. Most naturally occurring soils on the planet are deficient in one or more of the essential nutrients that plants require to grow. Many of the plants we choose to grow in our gardens occur naturally in very different soils to what gardens we have in Australia.
Fertilisers will not revive dead plants overnight. What they will do is provide a continual supply of nutrients to ensure plants build up a natural resistance to disease, perform to their potential and thrive.
Even after improving soils with organic matter, compost and manures most garden plants will require regular feeding to stay healthy and flower and fruit. As gardeners, we expect a lot from our gardens. Gardens can be likened to an intensive horticultural set up on a mini scale. Every flower, leaf or piece of fruit we remove from the garden is removing essential nutrients from the soil. For garden plants to continually thrive these nutrients must be replenished, either by organic matter or a specially formulated fertiliser.
Fertiliser should be applied throughout the growing season and depending upon the type of fertiliser used, it’s best to use a small amount regular rather than a lot once a year. When plants are actively growing, flowering and fruiting their nutrient needs are at their peak.
Applying fertiliser when plants are dormant is a waste of resources, especially if using soluble formulations, as there is potential for leaching of nutrients past the plant’s root zone.
Different plant groups have varying requirements for nutrients.
The correct balance of nutrients is important for optimum plant growth. It’s a case of more isn’t better as excessive amounts will have detrimental effects on plants and often result in death.
Macro (or major) nutrients are those nutrients required by plants in greater quantities than micro (or trace) nutrients.
N Nitrogen is required for leaf growth and protein formation. Too much nitrogen results in soft weak growth and susceptibility to pests and diseases. Plants over fertilised with nitrogen will not survive drought conditions and are often referred to as ‘thirsty’, at the first sign of drying conditions they will collapse.
P Phosphorous is essential for strong root development and fruit and seed production. Phosphorous deficiency in plants manifests itself as a red or purple tinge on foliage and stunted root and tops growth.
K Potassium contributes to a plant’s resistance to pests and diseases. This nutrient plays an important role in the vascular system and the translocation of vital plant sugars. Potassium thickens cell walls and is responsible for strong stems in all plants. It will also intensify flower colour and perfume, an essential element for roses.
Potassium deficiency will be identified by scorching of leaf edges and tips, reduction in flower size and early leaf shedding.
Calcium, Sulphur and Magnesium are known are secondary nutrients and are important elements required by plants:
Ca Calcium is essential for building cell structure and cell walls in a plant and plays a vital role in the uptake of many nutrients.
Calcium deficiency results in stunted roots, distorted growth and stress symptoms on new foliage.
Mg Magnesium plays an important role in the photosynthesis process and is an important part of chlorophyll, the compound that makes leaves green. Magnesium is movable within the plant, so deficiency shows up in lower and older leaves.
Magnesium deficiency shows up first as pale leaves and often leads to chlorosis on foliage that takes on a patchy appearance with yellowing between veins.
S Sulphur is now thought of as the 4th macro nutrient, even though it is only required in small amounts it is essential for plant growth. Sulphur is found in organic matter however isn’t available to plants until it has been converted by microbial activity in the soil. It is a building block of protein chains and essential for chlorophyll formation.
Sulphur deficiency is first noticed in plants as pale leaves. It is not mobile around the plant, so deficiency will show up in new leaves. Sulphur deficient plants are small and stunted.
Fe Iron is essential for plant enzyme systems and chlorophyll production.
Mn Manganese is essential for photosynthesis.
Zn Zinc is needed for the plant hormone that is responsible for stem and leaf expansion.
B Boron assists in the formation of cell walls in the rapidly growing tissue.
Mo Molybdenum helps bacteria and soil microbes convert nitrogen from the air to a soluble form available to plants.
TIP: Avoid fertilising plants when they are water stressed, have experienced transplant shock or have sustained damage in some way. Roots are susceptible to burning.
Selecting the right fertiliser can be a little daunting as there are so many choices on the market.
There are a few questions to ask:
Answering these questions will make fertiliser selection easier. It will also ensure your fertiliser choice will live up to the expectations and will do what it was purchased to do.
Achieving even coverage is important when applying fertiliser. There is less risk of over feeding and causing damage to plant’s roots. It is important to follow the directions on the container as over fertilising can cause long term damage and even death of plants in extreme cases.
When fertilising trees and shrubs apply granular formulations around the drip line of the tree, this is the area directly under the circumference of the branches and leaves. Do not apply granular fertilisers to close to the trunk or stem or the plant as this may burn it. If applying over the top of mulch apply before a shower of rain or water, it in so the granules are in contact with the soil surface.
When fertilising pots sprinkle evenly around the soil surface and water in well. Always wash any fertiliser off the foliage after applying to reduce the potential of burning delicate leaves.
Liquid fertilisers can be applied via watering can or a pressurised garden sprayer. Watering cans apply high volume quickly and are the ideal choice for watering pots in or feeding and watering at the same time.
Pressurised sprayers are lightweight and easy to cart around. They are the ideal choice for applying soluble nutrients that will be absorbed by foliage only.
TIP: When applying granular fertiliser, a handful is roughly 30-50grams.
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