Magnesium Deficiency in Orchids

As the winter draws on, we are all wrapping up warm and looking after ourselves to prevent coughs and colds getting the better of us. I’ve been looking at my orchids lately, two in particular, and thinking “why don’t you look 100%?”

Google is quickly becoming my best friend.

Two of my orchids (my oldest Phal and my little Cattleya orchid) appear to be demonstrating a nutrient deficiency. Some of the older leaves look yellow in comparison to the new ones. This fits with a magnesium deficiency. Magnesium is a nutrient that your orchid is able to relocate around itself to help with various functions, mainly photosynthesis. The newest leaves always look much greener than the older leaves because the magnesium has been drawn from them into the new ones. It certainly accounts for why the oldest leaves on my oldest orchid look the way they do – I did originally think they were dying off, but after a year like this, I don’t think so any more.


So, what is a solution to this? There are a few fertiliser products on the market that do have magnesium as a main ‘ingredient’ – referred to as a macronutrient. The best way I can explain a macronutrient in the simplest terms is to relate it to human nutrition. Magnesium is very important to humans as well as plants as it is responsible for so many different things within our bodies – it is the same with orchids.

Unfortunately, the fertiliser I have recently purchased does not appear to have this nutrient as a key ingredient but there is a way around it. After a bit of research online, I found two solutions. The first is to find a source of magnesium that I can add to my watering regime – namely Epsom Salts. My plan is to add Epsom Salts to water every other week, to see if this makes a difference. The concentration I plan to use is a little lower than suggested by some sources, but I’d rather provide less than more of this solution at this stage. If in a few weeks, it does not appear to be having an adverse affect, then I will consider increasing the dosage slightly.

My second plan will be to purchase a fertiliser that contains Magnesium as a macronutrient. I have found a product on the market that I am considering but I would like to see how my orchids do with the Epsom Salts for the time being. When the fertiliser runs out, then I will consider purchasing a new type.

Another experiment now begins – the results will be posted in a few weeks.



4 thoughts on “Magnesium Deficiency in Orchids”

  1. Your bottom phal leaves are also wilty. I noticed that your roots are silver down to the bottom, which suggests you’re not watering often enough. You don’t need to let phals dry hard between waterings. When the bottom quarter is still green but the rest are dry, you can water again. Put the plant in a bowl of water, put the whole thing in a sealed plastic bag, and put it on a seedling heat mat overnight (top of the fridge works well too..anywhere with bottom heat). You can do this overnight or even longer. Sometimes the very bottom leaves are wilted too much and won’t improve dramatically, but I use this trick all the time when I forget to water a plant that is hiding or before and after a vacation. It sounds scary, but you won’t rot the plant unless it’s cold. You want to create a saturated, ‘steamy jungle’ environment for a day or two.


    1. This is such a strange orchid. I tend to water once a week (more often in the summer) and her roots were green a day or two before I took that photograph. But I take your point. I’ll try soaking her in water when she needs it rather than flushing her through to see if that makes a difference in the next few weeks – if not, I’ll try the method you suggested. Have you ever had problems with crown or stem rot with this treatment?


  2. Oh yeah, I forgot to tell you that the formula Michigan state university came up with is a compel ste fertilkzer for orchids. Lots of different companies make it..try to find one that is homogenized like miracle grow. Lots just throw the different ingredients in, so you have particles of one nutrient that are a different size and shape from the others and if you’re mixing up small batches (like using a 1/4tsp), you can get an uneven application of nutrients because some nutes fall to the bottom. I haven’t yet found an msu fertilizer made like miracle grow, but I think maybe Greencare has a homogenous version. Also, you need to know what you’re water is like so you can choose the correct formula, (either RO or hard water). There’s an article, ‘a new fertilizer without high phosphorous proves itself with orchids). K lite is another good one for orchids..I decided to try it two weeks ago and I think I’m seeing improvements in some things but I also am convinced that I have a phosphorous deficiency from sodium in my RO water.


    1. I have been experimenting with orchid feed for the last few years but I’m now trying a different feed recommended by other orchid growers I have spoken to. I have to say, I’ve only been using it a few weeks, but it seems to be working really well. It’s not MSU but it has the granular look and I have to keep it airtight.
      Our water is quite hard here (compared to where we lived previously) but I haven’t seen any build up of salts or anything on the media. I did check that I could use the newest fertiliser with my tap water and all seems ok. Will keep an eye on that though.
      I’ll look at the article and do a bit more reading – thank you for your suggestions 🙂 they’re really helpful!


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