Hydrangea

Plant Characteristics
Lifespan:	⌛	perennial
Origin:	✈	S&E Asia, N&S America
Poisonous:	☠	mildly toxic

Cultivation

Scientific Names
Hydrangeaceae >	Hydrangea >

Hydrangea is a genus of about 70-75 species of flowering plants. By far the greatest species diversity is in eastern Asia, notably China and Japan (See: Japanese Ajisai flower). 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.

Hydrangea flowers are produced from early spring to late autumn; they grow in flowerheads (corymbs or panicles) 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.

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 colour 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.

Hydrangeas are moderately toxic if eaten, with all parts of the plant containing cyanogenic glycosides. However, poisoning is rare, as the plant does not look like an enticing food source.

Species in the related genus Schizophragma, also in Hydrangeaceae, are also often known as hydrangeas. Schizophragma hydrangeoides and Hydrangea petiolaris are both commonly known as climbing hydrangeas.

Cultivation

Hydrangea calendar^?
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Notes:

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 until the following season.

Propagation

Pests and diseases

BACTERIAL DISEASES - Bacterial blight (Pseudomonas solanacearum), Bacterial leaf spot (Pseudomonas cichorii)
FUNGAL DISEASES - Bud and flower blight, (Botrytis cinerea), Interveinal chlorosisn (Lack of iron uptake due to alkaline soils), Fungal leaf spots (Cercospora hydrangeae), (Corynespora cassicola), (Phyllosticta hydrangeae), (Septoria hydrangeae), Powdery mildew (Erysiphe polygoni), Root rot (Pythium spp.), Rust (Pucciniastrum hydrangeae), Southern blight (Sclerotium rolfsii), (teleomorph: Athelia rolfsii (Curzi) Tu & Kimbrough)
VIRAL DISEASES - Phyllody (Hydrangea ringspot virus), Ringspots (Hydrangea ringspot virus), (Tobacco ringspot virus), (Tomato spotted wilt virus), (Tomato ringspot virus)