Citrus fertiliser – a New Zealand answer

Neil Ross’s advice is mostly spot on for citrus. However, treating yellowing of leaves with 500 g of MgSO4 7H20)(Epsom salts/Magnesium sulphate) seems excessive and he appears to totally miss the likelihood of nitrogen deficiency. I wrote this in response to a July NZ gardener article.

Curing yellowing of citrus leaves with 500 g of Epsom salts which contains about 10% Magnesium is an inadequate answer to citrus yellowing – suggested by Neil Ross in last months citrus 101. For a more balanced approach purchase a citrus fertiliser that will provide closer to the recommended (see web reference below) rates of elements, including Nitrogen. Ravensdown produce a citrus fertiliser (12.2% N, 4.5% Phosphorous, 4.5% Potassium (K), 6.2% Sulphur, 5% Magnesium and 4% Calcium.) The web reference below states for young citrus- two years old – they require about 120 g of N/tree each year. Given that you will be using plenty of organic manure – we hope- a reasonable rate would be 1 coffee mug of Ravensdown’s citrus fertiliser applied 3 times each year. I would spread that fertiliser around the tree, right out just past the drip line and cover with organic material. Don’t dig around the citrus- they are surface feeders. If the tree is getting plenty of water and lots of organic matter, it is unlikely it will need a fourth mug of this mixed fertiliser. By the way, Neil helped me understand that one should go easy on lime. Citrus prefer a more acidic soil.

Last year my mandarin in the glasshouse- I live in the cold of inland Canterbury, was a bit yellow. I took really fresh cow poo- at least 5 litres of poo, mixed that with another 5 litres of water and splashed the resulting mess over the leaves, the rest went onto the soil around the tree. Worked wonders. Loved the mandarins! By the way, the leaves were not coated in thick poo – rather they were rinsed in the poo mix and turned satisfyingly green and healthy.

http://www.hortnet.co.nz/publications/guides/fertmanual/citrus.htm

Here is a more detailed explanation-
For further quality information- check out http://www.hortnet.co.nz/publications/guides/fertmanual/citrus.htm but their recommendations are in units of element (eg N=Nitrogen) not a weight of fertiliser eg urea with 47% N in it. Not so helpful for a lay person. Refer below.

How to make sense of this?

Certainly organic manures are going to help, as they will provide a wide range of elements in a slow release form, while also improving physical properties of the soil. But if a chemical answer is chosen?

How much Mg is being applied in 500 g of Epsom salts? Due to the large amount of water tacked onto the Epsom salts only 10% is actually Mg. So Neil is suggesting 50 g of Mg be applied along with some Sulphur.

What might be a more appropriate application when leaves are yellow?

At least give an annual total of 120 g of urea spread over approximately 5 applications. But if we follow this simplistic advice we are now addressing N and Mg deficiencies, but failing to provide P and K. There’s the reason we use an already mixed citrus fertiliser. I’d follow recommendations on their bags or buy a larger quantity from someone like Ravensdown.
Ravensdown produce two fertilisers for citrus.
Here is what is in the 40 kg bag of the citrus fertiliser closest to Neil’s recommendation (The other mix made by Ravensdown focuses more on N and less on Mg). The one I would use has 12.2% N, 4.5% Phosphorous, 4.5% Potassium (K), 6.2% Sulphur, 5% Magnesium and 4% Calcium.

So by way of meeting our desire to provide an ordinary gardener with helpful recommendations- buy 40 kg of citrus fertiliser, use it elsewhere on your garden- it is a good general fertiliser mix! Or share with friends and save money by buying a decent quantity.

Annual amount to use on each tree – About 3-4 large coffee mugs each year. Ie. One mug 3-4 times a year, and plenty of organic matter spread over the fertiliser each time it is used. The N in the fertiliser is susceptible to volatilisation- a process where N is lost as ammonia. Reduce those losses by hiding the fertiliser under a screen of manure or straw or even newspaper that worms will love to degrade.

1 comment to Citrus fertiliser – a New Zealand answer

  • I have come to the conclusion that this article and supporting comments are quite fascinating. In my experience, this is a good site to find information on topics such as gardening. Will anyone here show me where to find more particular articles on this topic, please? Thanks a bunch!

Leave a Reply

 

 

 

You can use these HTML tags

<a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>