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Now I know there is a bit of a fad about creating different ways of disclosing the sex of an expected baby but... this isn't about that... well not really, although it is important to most of us what colour our hydrangea flowers will turn out to be each season. An interesting quirk of beautiful hydrangea flowers, well the ones of the macrophylla kind at least, is their potentially to change colour. The colour has nothing to do with sex in this instance, it's all to do with the makeup of the soil; I believe aluminium ions are quite dominant in NZ soils, and it's not often that you will see pink flowering hydrangeas here in kiwi land, unless they are in pots.

Macrophylla hydrangeas are the classic MOPHEAD or LACECAPS – Mopheads have ball-shaped flowers whilst Lacecaps have a flatter pincushion like centre with an outer row of flowers.  

So we knowing that hydrangea flowers can change colour - from blue to pink, and vice versa – we need to know also that this is usually an indication that the soil the plant is in may have a pH level that is too high (alkaline) or to low (acidic).   So what soil type is best for growing these beauties - acidic, neutral or alkaline?   Well that depends on the flower colour.  

BLUE flowering Hydrangea require aluminium (Acid) – this is naturally occurring in NZ soils in small quantities but add more to ensure continuing intense blue blooms.  Aluminium is not a plant food and enters the plant via roots – aluminium is usually applied in liquid form (premixed blueing is available).  Coffee grounds (or even a rusty iron nail!) add extra acidity when added to the soil. 

PINKS flowering Hydrangea need an Alkaline soil, add LIME to raise the soil PH level, or add a fertiliser with a high PH level (ratio 25-10-10).  Lime can be sprinkled around the base of the plant, follow manufactures instructions if using a fertilizer or purchase a pinking solution.

WHITE flowering Hydrangea can show of either pink or tan their flowers, but you cannot change a White Hydrangea into a fully pink or blue flower.  

Most potting mixes do not include aluminium, therefore PINK and WHITE flowering Hydrangea are fine, BUT, a BLUE flowering hydrangea in a container will need added blueing / Aluminium regularly.