Turning plumbago flowers a deeper blue

Does anyone know if Plumbago flowers can be made more blue by adding aluminum to the soil or potassium sulfate in the fertilizer as one would for hydrangeas? I recently planted two Cape Plumbago in containers and noticed that the flowers on one are much darker blue than the other. (I am a garden novice in zone 9 and Plumbago seems to thrive here). Any help with boosting the blue color would be appreciated.

Thanks you, Maxx

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1 Comment To "Turning plumbago flowers a deeper blue"

#1 Comment By Alisma On 09/18/2016 @ 4:43 pm

Plumbago is not known to change its color in response to pH or to aluminum availability. In fact, aluminum can be harmful to plants that are not adapted to high-aluminum soil.

The difference between the two plants you have may be based on small genetic differences, but environmental factors like too-bright sunlight on the pale flowers could also play a role. Making sure the plants are well nourished with compost or fertilizer and a source of micronutrients won’t hurt:

https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/rock-phosphate-fertilizer.htm ^[1]

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