Can I Make A Blue Hydrangea From A Pink One?

Is there a natural way to make them blue hydrangeas instead of pink? Will white pine needles as mulch do it? If not a natural way is there a chemical I can use to get blue blooms?

I live in northwest Michigan in zone 4 or 5 depending on the map I use. The plant was new last year and bloomed pink. I wasn't sure about pruning the plant back last fall so left it about a foot tall. It doesn't look like it made through the winter but new growth is coming from the bottom. Does that make it a new plant again this year or is that typical for hydrangeas? Thanks for all of your work and good info.

Doug says:

Sure there is a way to make them bloom blue.

You get out your paint spray can and when the blossom opens right up, you wail away and turn 'er blue. ;-)

No? OK. Hydrangea turn blue when the soil is acidic. They produce pinkish flowers when the soil is alkaline to neutral.

Acidic Fertilizer

To turn blue hydrangea blue you can use an acidic fertilizer - a chemical containing aluminum sulphate is used in that mix.

Frankly, this isn't an organic approach and there is some research that shows aluminum is responsible for killing off root hairs on plants.

Organic Approach

An organic approach is to use sulphur and peat moss to make an acid soil bed and plant the hydrangea in that. Naturally, I'd suggest you have your soil tested and then add things but most gardeners rarely do- they just add the sulphur a little bit year by year until they get the blue color. ;-) Your call.

Pine needles as mulch will not turn the soil acidic, neither will they maintain an acidic soil level.

The deal is though that Hydrangea roots are going out from the plant a long way and that you have to turn the entire bed acidic to really keep those feeder roots doing their thing. It isn't a one time shot as the soil will turn itself back to the surrounding acid level over time.

These Hydrangea macrophylla blue varieties bloom on old wood. So if the buds are pruned off last year or they die due to cold, you won't have blooms. Many cold area gardeners can grow the shrub itself but the buds all die during the winter. If you have to prune, do so within six weeks of blooming. Your particular plant may be alive but it won't bloom blue if it died to the ground (heck, it won't bloom at all if it died to the ground)

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Other Hydrangeas Don't Turn Blue

Other Hydrangea such as Hydrangea arborescens with common varieties 'Annabelle' and 'Grandiflora' can be pruned with a lawnmower and will bloom every year. However! They do not bloom blue - but rather white (fading to pink)

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