Garden Column for the Salisbury Post

Darrell Blackwelder

May 12, 2005

     I get quite a few calls in early spring from homeowners that have problems with their hydrangeas. The hydrangeas that have the most problems are the typical old fashion macrophyllas which are blue or pink. The two major questions I receive are: My hydrangeas won’t bloom and how do I make my hydrangea turn pink?

     Basically there are three major reasons why hydrangeas fail to bloom. These are: late spring freeze, improper planting and improper pruning.

     A late spring freeze may be light and often go unnoticed. Most flower buds develop on the old stems. Once these stems are damaged in a late freeze, new flowers will not appear until the following year and only then if it is a milder spring. This is usually the rule for the vast majority of hydrangeas but there are hydrangea cultivars that will bloom despite this damage.

     Improper planting is another key problem. Many plant those that are not adapted to this area. Florist type plants often do poorly when planted outdoors. Deep shade also impedes bud formation. Hydrangeas, like crepe myrtles, do not usually need to be pruned to produce flowers. There are some exceptions to remove dead stems and blooms. But if your hydrangea is getting much too large you may need some judicious pruning. Prune hydrangeas only in the summer before August. Pruning into August is risky because they may already have set their bloom buds for the next year. If those stems are removed pruned in the fall, winter, or spring, the bloom buds will be removed, and there can be little or no bloom that year.

  Changing the color of hydrangeas may be a little tricky and may be impossible in some soils. Aluminum in the soil is what gives the plant its blue color. It is much easier to change a hydrangea from pink to blue than it is to change it from blue to pink. Changing a hydrangea from pink to blue involves adding aluminum to the soil; however, this isn’t a problem here because our soils are naturally high in aluminum. The majority of blooms you see in our area will be blue.                                                  To change a blue hydrangea to pink you must add dolomitic lime several times a year. This will help raise the pH of our naturally acidic soils and inhibits the availability of aluminum. The goal is to obtain a pH of about 6.0 to 6.2. If the pH goes above 6.4 hydrangeas will often turn yellow with iron deficiency. Also, fertilize hydrangeas with high levels of phosphorus to prevent aluminum from creeping into the system of the hydrangea.                                                In our area soils naturally produce blue hydrangeas so if pink hydrangeas is a must, try planting them in large pots with a soil-less mixture. These mixes don’t have high amounts of aluminum and it will be much easier to control the requirements for growing pink hydrangeas.

Darrell Blackwelder is an agricultural agent in charge of horticulture with the North Carolina Cooperative Extension Service in Rowan County. For archived garden columns or other information, visit the Rowan County Master Gardener web site at www.rowanmastergardener.com , e-mail Darrell_Blackwelder@ncsu.edu