Feeding citrus trees

Green-leaved treet with flowering tangerines. Fedding citrus trees correctly is important.

Growing Citrus Trees Across Australia

Citrus trees are a staple of many Australian gardens. However, growing them to fruit successfully has different challenges, depending on the location. And feeding citrus trees correctly is vitally important.

The majority of home gardens in South Australia are blessed with great citrus growing conditions and so have trees heavy with fruit. In contrast, the eastern states can struggle with ‘Fruit fly’, which can make nurturing mandarin and orange trees a challenge. As a result, many gardeners don’tbother growing citrus because it becomes a constant battle with insects.

The ideal conditions for most citrus plants are warm sites, untouched by frost and with free-draining soil.

The Problem with Alkaline Soils

One of the biggest hurdles to overcome in feeding citrus trees is to do with soil pH.

There are pockets of Australia where the growing conditions are similar to the Mediterranean and citrus trees thrive like weeds. In areas like this, and even in the sub-tropical regions,you will soon discover that they have a few deficiencies which appear when growing in fairly alkaline soils.Alkaline soils are those with limestone in the lower profiles. In Mediterranean regions the soil profile generally gets more alkaline with depth, even if you mulch with acidic composts and leaf-litter on the surface.

A common problem found in citrus crops is the appearance on their leaves of a green vein pattern against a pale green leaf. This is lime-induced-chlorosis (LIC) and occurs when the alkaline soils that the plants are growing in fall within the pH 8 – 9 range. The issue isn’t unique to citrus varieties, with many native plants and acid-loving ornamental also being effected when planted in alkaline soils.

Please see here for a more comprehensive look at the ideal soil for citrus.

The Solution to Alkaline Soils

Though iron is often part of the composition of these soils, the alkalinity drastically slows the plants uptake of the available iron. The solution is to introduce iron chelates, which is fairly easy to do on a small scale. However, their extensive use only has short-term benefits.

For more on iron deficiency in plants and the pluses of iron chelates, see here.

A more efficient and longer-lasting answer is iron sequestrine, but it is very expensive to use on anything other than valuable container-grown plants. And a quick tip – be careful where you water your container-grown plants if you decide to go with the iron sequestrine – the liquid looks like a full-bloodied Shiraz wine and you really don’t want it staining your foot paths or paving stones!

Other solutions, include using ‘flowers of sulphur’ which are at least more economical, though the sulphur needs to be added frequently. And if you want to keep it ‘green’, the organic answer is to compost green matter and rely on the leaching of humic acid into the lower soil profile. It works, but takes time and many gardeners want faster results.

If time is not a problem, you can go old-school and bury iron filings and offcuts under your oranges, limes and mandarins. As the seasons pass, the iron will oxidise, and the soil will become more acidic and perfect for feeding citrus trees. But it takes a while to go from summer through to winter and back again, so be aware that this method really does require patience. Plus, both the organic and chemical remedies need warm soils. This means that in the colder months, there isn’t a lot happening.

A selectin of fruits and citrus fruits on an orange background. Feeding Citrus trees correctly is important.

Missing Elements

Another set of problems related to more alkaline soils is that the high soil pH can interfere with the uptake of minor trace elements like magnesium, manganese and zinc – all of which are needed for feeding citrus trees. In fact, a lot of other plants would barely miss these elements at all, but this is sadly not true of grapefruit and lemon trees.Even when you add a complete citrus fertiliser to your soil, the presence of potassium locks these minor trace elements up, so that they are not readily available to your citrus trees.

That’s why the experienced Riverland citrus blocker or Sunraysia blockies apply the minor trace elements of zinc, manganese and magnesium as foliar sprays, several times during the warm weather. Even this is not as straight forward as you would expect it to be. You cannot spray your crop with these 3 compounds in a combined hit because they seperate out into solids from the solution and so can’t be absorbed by the target plant.

The best plan is to mix zinc in the form of zinc sulphate with manganese sulphate and to spray the chosen plant in the late afternoon on a day when the forecast is no 3 rain-free days. Three or four weeks later, magnesium sulphate or Epsom Salts can also be applied – again at the end of the day and when no rain is expected. To assist the uptake of magnesium as a foliar spray, nitrogen has to be added to tepid water, usually in the form of urea, because it is extremely cost effective as it contains a massive 43% water-soluble nitrogen, so you don’t need to use much.

I know this all sounds like a lots of work and unnecessarily complicated, but feeding citrus trees the right nutrients is important and you’ll be rewarded healthy, lush trees with heaps of flowers followed by superior fruit.

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