Phosphate Of Iron - confusion

Cottage Compost · December 2023

Hoping someone may be able to help.

I'm wanting to purchase a bulk bag (20 - 25kg) of Phosphate of Iron. Buying this in 1 - 1.5kg boxes from local garden centres is going to prove very expensive indeed.

It's possible to get a variety of products in larger bags, but they are described very differently and some contain added chemicals too. Some are described to be used for the lawn to feed the grass and get rid of moss but also say they are suitable for acid loving plants too.

But it's the chemical makeup that i'm finding confusing, but do these product variations matter?

I have a number of Acers, Maples and two Gum trees that were purchased because they deliver excellent Autumn colours, specifically red. But they are not turning red, they are turning yellow with a slight hint of orange. These trees are growing away well and are greening up as they should over the summer.

Two different Nurserymen working for two different arboretums have suggested that i apply Phosphate of Iron once a month for 12 months then every two months for the second year then spring and mid-summer thereafter... This is a lot of Phosphate of iron, a single 1.5kg box is just enough to apply to the trees i have following the dosage in one application.

Do you buy Phosphate of Iron in bulk bags for your trees and or acid loving shrubs or plants?

Balgay.Hill · December 2023

I wouldn't rush to apply anything. It's been a strange year for weather, and many trees are colouring up differently from usual.

Cottage Compost · December 2023

Balgay.Hill said:

I wouldn't rush to apply anything. It's been a strange year for weather, and many trees are colouring up differently from usual.

They haven't turned red in autumn since they were planted three years ago (two autumns) since.

Nollie · December 2023

I’ve never heard of it used in that quantity or that context.

I use chelated iron on acid-loving plants or those liable to chlorosis in my alkaline soil and hard well water, such as certain roses and a lemon tree. You don’t need very much at all, in fact if you use too much the leaves go a horrible dark olive colour and it impedes photosynthesis. Never had to use any on an acer.

Consistently poor autumn colour is more likely down to genetically poor specimens or weather conditions not conducive to the production of anthocyanins (for red colour) rather than needing large quantities of a corrector product.

More info here:

https://www.rhs.org.uk/prevention-protection/poor-autumn-colour

punkdoc · December 2023

This sounds a really strange idea, there is no reason I can think of why this would work, it is much more likely it would be harmful.

Braidman · December 2023

Hi!

I think there is a bit of confusion, or else you have been sold a bum steer.

It is Sulphate of Iron you should be using, never seen Phosphate of Iron for sale!

Below is a list of SoI uses taken off the internet!

Sulphate of Iron improves soil conditions and cultivation for acid loving plants: azaleas, rhododendrons, magnolias, camellias, hydrangeas, Japanese maples, conifers, many heathers, alpines, blueberries, raspberries, currants, gooseberries and many more.

And you do not need to use very much of it!

Hope this helps!

Cottage Compost · December 2023

Yes, most if not all local garden centres sell Sulphate of iron, but it can also be called Phosphate of iron too, both products containing ferrous iron (Fe).

Having phoned two online bulk retailers for help and advice, they both said Phosphate of Iron and Sulphate of Iron are the same thing, both containing soluble ferrous iron (Fe).

To add to the confusion, some products contain as little as 12% to as much as 30%+ ferrous iron.

Some products describe the ferrous iron differently, created by a different process or by using a different raw material. Some products seem to have added chemicals and so on too.

All i have done so far is feed them with a little fish, blood and bone in March and keep them well watered through the summer.

Two Gum Trees (liquidambar 'slender silhouette') brought as different ages / sizes from two different nurseries, one online and one from a local nursery. Two Acer Freemanii's again, one bought online and one from a local nursery. Two Acer shirasawanum 'Autumn Moon maple' bought separately.

My trees were purchased specifically for their autumn colour that i hope to achieve somehow, either by waiting or by doing something. They are growing well and look very healthy.

These tree species are present in local arboretums, and there are specimens in local school grounds and parks. These trees turn red every year, well certainly as far back as i started noticing, which will be a good few years now. These same local trees turned red this year, but not as well as they have in previous years, i admit. A friend bought a 1ft tall gum tree in a pot from a local garden centre late last autumn, it turned red this year in a 1ltr pot, and it's just 18" tall now and probably no more than two years old at the very most. My trees are at least 5+ yrs old.

I refuse to believe or accept that so many trees each bought from different nurseries are all 'bad specimens' together in one garden. If i had just one that wasn't turning red, i could accept that as a possible reason, but not all of them.

How many years do i wait before i dig them up and sell or get rid and try again, or do i do / try something?

On visiting two local arboretums and having asked for help both advised that i should apply Phosphate of Iron (They didn't say Sulphate), are they both wrong? Their recommendation was offered confidently, without hesitation and with little additional questioning. One of them said they feed their specimen trees with the stuff every year to make sure they turn red in the autumn for paying visitors.

Because none of them are performing as expected, i feel that i should try something rather than do nothing.... i could dig them up and sell them whilst it's still possible, before they become so large they and may have to be chopped!

I could try feeding just one tree for a year and see what happens!

punkdoc · December 2023

FeSO4 is well known for helping acid loving plants thrive in slightly alkaline conditions, however there is no evidence that it improves autumnal leaf colour.

Cottage Compost · December 2023

punkdoc said:

FeSO4 is well known for helping acid loving plants thrive in slightly alkaline conditions, however there is no evidence that it improves autumnal leaf colour.

I agree, but why do two local arboretums use it?

Perhaps there's something happening indirectly in some way.

I've decided that i can afford to lose one tree if things go wrong as a test. If the trees or the test tree don't do their thing next autumn they'll have to go and i'll plant different trees in their place.

steephill · December 2023

Iron sulphate and iron phosphate are most definitely NOT the same thing, whoever is telling you that hasn't got a clue. They might both contain iron but they are very different chemical species.

Iron phosphate is mainly used as slug killer, not to turn leaves red.

Iron sulphate is mainly used as a moss killer and lawn fertiliser, its acidifying effect helps avoid leaf yellowing in acid loving species (rhodos, camellias etc.) grown in slightly alkaline soils.

Cottage Compost · December 2023

Hence the confusion, I'm guessing that the retailer doesn't care as long as they sell something.

For now given that my plan is to just treat one tree with Sulphate of iron in 2024 I'll buy a 1.5kg box from my local garden centre even though it's so expensive. See what happens next autumn.

Phosphate Of Iron - confusion

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