Many of you have come to me asking why many of our blue flowering Hydrangeas are not coming out as blue as in the past. This is a good observation and I would like to explain why this is happening. The blue color in the Hydrangea is because of the element Aluminum being available in the soil. The pH of the soil plays a vital role in whether or not the aluminum would be available to the Hydrangea. Aluminum becomes more available as the pH drops. At a pH of 5 it is nearly 100% available to the plants. As the pH goes up it becomes less and less available until it reaches 7 (neutral) which at that point the aluminum can be in the soil but the plants can’t take it up because of the high pH. This is why you don’t see blue Hydrangeas in the mid-west. The soil pH out there is very alkaline and even when the aluminum is in the soil the plant has no ability to take it up.
The pH in our container mix for Hydrangea is nice and low. (5 to 5.5) But in order to get blue flowers we have to apply aluminum to our soilless mixes. Timing is important. Normally we apply the aluminum to our Hydrangea in August when the plants are still growing actively and can absorb any element that is available to them. Last August we were in the throes of a severe drought. With our water supply dangerously low we were giving our plants just enough water to get through each day. Aluminum, like other elements we apply to the soil is a salt. In order to apply the Aluminum without hurting the root systems we have to apply enough water to move it through the soil. If we don’t the aluminum accumulates to dangerous levels which can severely hurt the plants root system. For this reason we made a conscious decision to wait until late September to apply our aluminum. Because the plants begin to shut down and flower bud development has already occurred at this time the aluminum was there a bit too late to really get it into the flower. We knew we were taking a chance but in hindsight it was the right thing to do considering our options.
Please pass this on to your customers. Their plants will definitely come out blue for them down the road. As far as our plants go we have every reason to believe that we will be back on schedule for next year. Thanks for your understanding.
Mike & Evan