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Iron in ericaceous compost.

young codgeryoung codger Posts: 507
What if people buy this brand for their hydrangeas, without realising it contains iron?

There was a lady online wondering why her white hydrangeas had turned blue. It could have simply been iron in the garden soil originally.

I understand ericaceous is lime-free. However, I was surprised to read on a bag that there was iron added to ericaceous compost. What do others think?

I am only asking the question out of curiosity,  and to learn from the more knowledgeable members on here. I can confirm that I use JI No3 from this brand and feel it is very good. Maybe other brands put iron in their ericaceous too?


  • ObelixxObelixx Vendée, Western FrancePosts: 28,576
    edited May 2021
    The thing about ericaceous plants is that they cannot take up iron and magnesium when there is chalk or lime present in the soil or water and they become anemic and/or chlorotic.   Adding iron to the compost is therefore logical.

    The stuff that turns hydrangeas blue is aluminium which is also locked up by alkalinity in the soil or water.  If you don't want blue hydrangeas, keep the soil alkaline.  Hydrangeas don't mind as long as they have adequate moisture but the mopheads and lace caps will change flower colour according to soil type.
    "We don't stop playing because we grow old; we grow old because we stop playing." - George Bernard Shaw
  • FairygirlFairygirl west central ScotlandPosts: 49,148
    White hydrangeas don't change colour, other than later in the season when they're starting to fade. They may have a blue or pink tinge and that will often just depend on the soil type. 
    It's a place where beautiful isn't enough of a word....

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