Yellowing on Thryptomene saxicola

[proninyaroslav]

I keep getting yellowing on my Thryptomene. Treating the leaf with iron or repotting helps, but then chlorosis begins again. I grow in a well-draining substrate and fertilize 18-18-18 times a week. What am I doing wrong? Maybe too much phosphorus? But as far as I know, myrtaceae are not sensitive to phosphorus.

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[Sno]

Do you use a slow release fertiliser as well , or just a weekly feed ?

[shibui]

18.18.18 is a crazy ratio for fertiliser. That amount of P in a fertiliser is way out of whack and could possibly be the problem here. Plants just do not use nutrients in those ratios so much of it will be wasted or, more importantly, ends up in our waterways to cause pollution and blue green algae.

Do you have other plants in the same mix and with the same fertiliser/watering regimes? I guess nothing else is showing similar signs?

If iron helps reduce the issue I'm pretty confident you already have the cause. One of the problems associated with very open, inorganic potting mixes is there's almost no nutrient holding capacity and no reserves of micronutrients. Iron deficiency was a common problem when we moved tosoilless mixes many years ago so all commercially made potting mixes must have slow release iron included in the mix.
I would try some longer term iron products. I think EDTA iron is the product used in commercial mixes but not sure where you would get some.

Check if the fert you are using has trace elements. Find an alternative if it does not. (I'd find an alternative anyway) This plant obviously need more frequent additions of iron to do well.