Summer Blues

June 25, 2010

There are too many pleasures that come with the warm months of summer to list them all but one of the best is  spending time outside.  We have a small sitting area in our garden and I can sit there for hours, marveled by the intense growth of the plantings from early spring to now.  Everything is blowing up but the hydrangea are especially insane this year.  literally 5 ft tall in some spots, it’s as if someone snuck in and fed them monster food (come to think of it… it was a good year for peonies too, but sadly their short time in the garden is over).  I have cut 3 arrangements for the house already and just look how many flowers I still have in the yard!

Hydrangea with bloom colors that range from pink through blue and purple usually belong to the hydrangea cultivars known as mopheads and lacecaps. These types of hydrangea have the interesting ability to change the color of their blooms based on the chemistry of the soil. When grown in alkaline soil, the bloom colors are pinker. When grown in acidic soil, the bloom colors are bluer.  Because it’s the soil chemistry that determines the bloom color, the variety names given to these types of hydrangea means very little when it comes to bloom color. For instance, Nikko Blue, Pretty in Pink, Forever Pink and Blue Deckle, all have an almost equal chance of blooming pink or blue, depending on the soil they are planted in.

So remember that even if you purchase a hydrangea in bloom, you cannot be sure the plant will produce the same color flowers once it’s growing in your garden.  To manipulate the color of a hydrangea’s blooms, you need to manipulate your soil’s pH level and mineral content. This is not something you do just once. In order to maintain growing conditions that result in a specific bloom color, you may need to apply special soil amendments several times during the growing season… Here is your lesson for the day:

To encourage blue hydrangea flowers, grow the plant in soil that has a pH of 5.2-5.5. If your soil is more alkaline, you can lower the pH by applying garden sulphur at the rate specified on the package. Soil pH can also be lowered (more gradually) by applying an acidic organic mulch, such as pine needles or pine bark.  If the pH of your soil is naturally quite high (alkaline) it will be very difficult to get blue flowers — even if there’s plenty of aluminum in the soil. Alkaline soil tends to “lock up” the aluminum, making it unavailable to the plant. (However, you can grow fabulous pink hydrangeas!)

If you prefer pink blooms, your hydrangea should be deprived of aluminum by growing it in an alkaline soil with a pH of 6.0-6.2. You can apply a high phosphorus fertilizer to further discourage the uptake of aluminum. To raise the pH of a naturally acidic soil, apply garden lime at the rate specified on the package.

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