Papa Geno's Garden Blog

Hydrangea is a genus of about 70-75 species of flowering plants native to southern and eastern Asia  and North and South America. Most are shrubs 1-3 m tall, but some are small trees, and others lianas reaching up to 30 m by climbing up trees. They can be either deciduous or evergreen, though the widely cultivated temperate species are all deciduous.

                        
The flowers just above are "lacecap" hydrangeas - 'Nigra', 'Blue Lacecap' and 'Pink Lacecap'         

Hydrangea flowers are produced from early spring to late autumn; they grow in flower-heads at the ends of the stems. In many species, the flowerheads contain two types of flowers, small fertile flowers in the middle of the flowerhead, and large, sterile bract-like flowers in a ring around the edge of each flowerhead. Other species have all the flowers fertile and of the same size.

                         
The flowers just above are hydrangeas - 'Hobella', 'Homigo' and 'Nigra'        

In most species the flowers are white, but in some species (notably H. macrophylla), can be blue, red, pink, or purple. In these species the exact color often depends on the pH of the soil; acidic soils produce blue flowers, neutral soils produce very pale cream petals, and alkaline soils results in pink or purple. Hydrangeas are one of very few plants that accumulate aluminium. Aluminium is released from acidic soils, and in some species, forms complexes in the hydrangea flower giving them their blue colour.

                                     
The flowers just above are hydrangeas - 'Cardinal Red', 'Annabelle' and 'Nikko Blue'  

Hydrangeas are popular ornamental plants, grown for their large flowerheads, with Hydrangea macrophylla being by far the most widely grown with over 600 named cultivars, many selected to have only large sterile flowers in the flowerheads. Some are best pruned on an annual basis when the new leaf buds begin to appear. If not pruned regularly, the bush will become very 'leggy', growing upwards until the weight of the stems is greater than their strength, at which point the stems will sag down to the ground and possibly break. Other species only flower on 'old wood'. Thus new wood resulting from pruning will not produce flowers the following season.

For more botanical info, go to: http://en.wikipedia.org/wiki/Hydrangea

The  images  just above are of Tardiva tree hydrangeas - 3 years and 2 years old.

About flower color
The bloom color of the hydrangeas will vary considerably due to the type of soil they are growing in. The blues are best in acid soil. The amount of aluminum available in the soil and the ability of a particular variety to absorb it will control the degree of blueness. The reds, and pinks enjoy an alkaline or neutral soil. The whites will stay white but usually enjoy the same conditions as the reds or pinks.

You'll need to raise the acidity of the soil to encourage "blueing" of the flowers. This can be done by soaking the soil around the plant several times at weekly intervals in the spring and again in the fall with aluminum sulfate. The aluminum sulfate should be applied at the rate of 1/4 ounce per gallon of water. Powder form can be worked in the soil but concentrations vary depending on the brand. Read the instructions on the box carefully before application.

Apply lime to lower the acidity of high acid soil to encourage pink to red blooms. The lime should be applied at a rate of one pound to every ten square feet of surface area once or twice a year until the desired color is obtained.

Please note that color correction takes some weeks or even months to occur, so you'll want to be patient. Rain, irrigation, and soil composition also affect the acidity of your soil.

The best time to plant hydrangeas depends on your local climate, but as a general rule of thumb you can plant in the spring after the last chance of frost. Planting in the fall or summer is also an option if you live in a more mild climate.  Most hydrangeas will be happiest  in a location sheltered from wind and hot afternoon sun.

Papa Geno