Hello, seedsower. You can probably say that all H. Macrophyllas that bloom on 'new' wood were made specially for you and all people in Zones 4-5. After all, if the cold weather kills the buds created in the Fall, you can count on more buds in the Spring to take their place!!! Other hydrangeas that also bloom in 'new' wood are Penny Mac (Zone 5-9), David Ramsey (Zone 4-9), Decatur Blue (Zone 5-9) and Oak Hill (Zone 5-9). Other possibilities (though not Macrophyllas) are H. arborescens Annabelle (Zone 3a) and H. paniculatas (like PeeGee, Big Ben, Chantilly Lace, Little Lamb, Pink Diamond, Tardivia, Lime Light, Quickfire, The Swan) which bloom on new wood.
By the way, feel free to experiment changing the color of your Hydrangea Macrophyllas though. While it is true that attempting to change the color could kill the plant, they will tolerate quite a bit of errors. They will also give you signs when one is exceeding the plant's comfort zone.
The thing to remember when doing color changes is not to exceed the suggested amounts of lime or aluminum sulfate and to perform soil tests very frequently. Twice (early Spring and Fall) every year if you can or once a year minimum. And I am suggesting tests done by the Agricultural Extension Service or those done by local nurseries partnered with universities. The PH Meters sold at Home Depot/Lowe's are not accurate enough and provide limited data (an approximation of the soil PH Level and that is it). You have to monitor the levels of aluminum in order to know if you have enough aluminum and need to use sulphur instead. And it probably pays to keep an eye on other minerals, such as phosphorus and pottasium.
Blue flowers need a PH of 5.0 to 5.5 and pink flowers need from 6.0 and higher. If your Ph goes below 5 or above 8, I would stop adding chemicals and consider switching to another variety of Macrophylla if I do not like the color tones at that point. Always water the soil before applying these chemicals and choose plants that are around 2-3 years old or older; some hydrangeas will resist color change when they get old.
If you are trying to change flowers from blue to pink/red, add one cup of dolomitic lime per 10 square feet and water it into the soil. Or try one tablespoon of hydrated lime in a gallon of water but avoid splashing on leaves, bark, face or skin as it can burn. Also, switch to a fertilizer with high phosphorus content. This color change is more difficult than pink-to-blue and occurs more slowly.
If you are trying to change flowers from pink to blue, apply a solution of 1/2 oz (1 Tbsp) aluminum sulfate per gallon of water and use a fertilizer low in phosphorus and high in potassium.
Finally, some things that can undo all the hard work are: concrete from house foundations will leech lime and make the soil near the house alkaline; soil in an area where you have water dripping all the time will tend to become alkaline until the drip is corrected; water from some sources, like from rivers and underground sources in Texas, can also be very alkaline.
Good luck, Luis
