From The Old Farmer's Almanac.
When we talk about hydrangea flowers which part of these extraordinary blooms are we referring to? Do we mean the large ball shaped flower seemingly suspended about a salutary bunch of offset leaves? Or, are we suggesting the individual colourful bracts that make up the whole?
Actually, hydrangea flowers are neither the massive dome-shaped bloom or the bracts that make it up. No. hydrangea flowers are the minutiae encased within the tonal bracts. But let's not be semantical!
So for this post we're going to take the view that hydrangea flowers are the dome-shaped blooms that catch our eye the moment they unfurl. And for the most part we're going to be looking at why their colours differ so vastly even when they are grown on the same bush in the same location.
H.macrophylla is the most common of the hydrangeas - probably the one your grandmother grew in her garden. It's responsible for many cultivars and differ in flower colour from heavily pigmented blues to pinks and reds and every shade in between. The bushes, mostly grown as perennial shrubs, can also range in size from 1-3m in height and similar width dimensions.
What I like most about hydrangea flowers is their ability to change colour. While a chameleon will change colour to fit in to its current habitat, hydrangea blooms change colour because of their habitat - namely their soil pH.
We've all heard the legend that adding some rusty nails to the soil surrounding your hydrangea will turn the blooms blue. In effect, this is quite possible as the rusty metal will increase the soil's acidity and alter the hue of the blooms. However, I'm not sure that putting rusty nails into the garden is a positive enhancement. It's great if you know exactly where they're located and how many you emptied into your garden. It would be disastrous for your children to find them before you did - and they found them in the bottom of their little feet!
Rusty nails aside, there are ways to alter the colour of your hydrangeas and this is where they become the litmus paper for your garden. Ours, for example, is delightfully pink - the colour demonstrating an alkaline soil - and it makes sense because our rhododendron planted next to it is struggling (R.'s appreciate slightly acidic soils).
If you're blooms are mostly blue and you'd like a change then the goal is to alter the pH of your soil. Note: achieving this in containers is far simpler than trying to make this happen in your garden soil - but it's still very possible.
Raising the pH level means adding lime - dolomitic lime to be exact. A few handfuls over the soil surrounding your plant every 3-4 months should ensure that the pH balance raise beyond 6-6.5. If your soil is a clay-based loam you may find that every 6 months is more appropriate and for sandy soils possibly every 2-3 months.
Blue hydrangea flowers are the seemingly be-all-and-end-all of the bloom colours. Our desires far more favour trying to reach this colour than the pink. Fortunately it's just as easy to achieve, but again you'll have more success in a container than your own garden soil.
To increase the acidity of your soil in favour of blue flowers you will need to add some aluminium sulphate. It's not a hard trace element to get hold of and most nurseries would stock it. The application would be as per the producers directions but usually a teaspoon or two in a 9l watering can would suffice. This is then applied to the plant during its growing season.
If your soil is as alkaline as mine then you might want to consider beefing it up with some home-made compost well before the season starts. Even mulching your hydrangeas with lawn clippings would be a helpful practice.
If you're looking for more resources on hydrangeas and how to change their colour try this site.
Its nine o'clock on a Monday night. This is a Blue Tit from Saturday. It was so foggy and cold this morning. Only by lunchtime had the fog cleared for some winter sunshine.