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Nutrient deficiencies in plants

Azalea Nutrient Deficiency

When our plants are looking unhappy, we immediately suspect they’ve been attacked by a pest or disease. It is, of course, important to rule out such problems but, if leaves are
discoloured or distorted and you can’t see an obvious cause, it’s also possible that the problem is caused by a nutrient deficiency.

What is a nutrient deficiency?

Plants must be able to obtain about a dozen nutrients that are found in the soil. The three they require in the largest amounts are nitrogen, phosphorus and potassium. Calcium, magnesium and sulfur are needed in slightly lesser quantities and the so-called ‘trace elements’ – iron, manganese, copper, zinc, boron, molybdenum – in even smaller amounts. But each nutrient is essential and if just one is lacking the plant will grow poorly.

Why do plants suffer from nutrient deficiencies?

Sometimes the soil is poor to start with. Many Australian soils fall into this category and, while the local natives that have adapted to these conditions will grow happily, as soon as you introduce plants with higher nutrient requirements, you’ll begin to have problems.

Pot plants are dependent on the nutrients in the container and it’s easy for these to dissolve and wash away as the pot drains. This is one reason why slow and controlled release fertilisers (as found in Yates Acticote) work so well in pots. As well, most modern potting mixes are made from composted organic matter. This organic matter can continue to break down in the pot and will use up nitrogen as it does so.

The pH – acidity or alkalinity – of the soil can also be a factor. Sometimes, if the pH is wrong for the plant, it isn’t able to take up nutrients from the soil even if the nutrients are in plentiful supply. For example, it’s quite common for plants to show signs of iron deficiency if the pH is too high. If you don’t know the pH level of your soil, it’s worth having it checked.

What to look for?

Unusual pigmentation and poor growth are classic symptoms of many types of nutrient deficiency. If the plant is lacking nitrogen, the oldest leaves can turn yellow, drop early or develop reddish tones. Magnesium deficiency, which shows up as yellow patches between the veins, also appears on the oldest leaves. Iron deficiency, by contrast, appears on the newest leaves, with the veins standing out as a distinct green.

How to have healthy plants

In most cases, a suitable all purpose fertiliser will supply the required nutrients. Organic fertilisers like Dynamic Lifter are ideal for slower-growing plants, and the fortified variants in the Dynamic Lifter Advanced range are suitable to meet the higher needs of fruit, roses, lawns etc. Fast-growing leafy plants need quick, liquid feeds with something like Thrive All Purpose. Yates Trace Element Mix can also solve some specific problems.

Plant nutrition is a complex, but fascinating, subject that is explained more fully in the Yates Garden Guide or Kevin Handreck’s Gardening Down-Under.


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