Hydrangea

(Family Hydrangcaceac; formerly Saxifragaceae)

The common hydrangea with its large mop head, so often seen growing in parks and gardens and offered by florists as a pot plant, is of hybrid origin, mainly derived from Hydrangea maerophylla, which is a species of Japanese origin. There are two types of hybrids in the group, namely lace caps and honensia hybrids.

The variety known as 'Blue Wave' is a good example of the Lace Caps, which have dense heads with only a few outer florets showing the petals. The hortensia types have large round heads of sterile flowers with large petals which are fully open over the whole flower head.

Nurserymen usually force hydrangeas into flower in the spring and this is the best time to buy plants, which are usually available with flowers in shades of pink, red, white and blue. The pink-flowered varieties range from light pink to deep rose; and these can be changed into blue flowers by treating the soil with a hydrangea 'blueing compound' or aluminium sulphate. The lighter shades of pinks convert to the most attractive shades of blue. Only pinks can be changed to blue, because reds turn a mauvy-purple. It is apparently the absorption of aluminium by the plant which changes the colour from pink to blue; and when the soil is neutral or has a good lime content this seems to prevent the assimilation of aluminium by the plant. Consequently, in order to keep pink shades pure in shade the compost should have a good chalk or lime content. White flowers are unaffected by the acidity or alkalinity of the soil.

CULTIVATION

When the hydrangea you have purchased in the spring has finished flowering it should, by that time,

Hydrangea maerophylla 'Honensia', grown in alkaline soil.

Hydrangea maerophylla 'Honensia', grown in alkaline soil.

Flowering Pot Plants Flowering Pot Plants For Spring

k have produced some basal growths. In this case, cut out the old flowering branches. If there are no basal shoots apparent, severely prune the flowering branches and wait for new shoots to appear. When pruning always cut the shoot just above a node.

Hydrangeas do not require much heat at any time and plants should be put outside in the full sun as soon as flowering is over and kept growing in the best possible conditions, because the next season's flowers depend on the development of the plant at this time. You may have noticed that after a good summer the hydrangeas in the garden are a mass of flowers the following year, whereas after a cold wet summer the next year the flowers are few and far between.

Hydrangeas are gross feeders and also require to be kept well-watered. Feed the plant every 14 days until the end of the summer and then reduce the watering. Ideally, plants should be exposed to cold conditions in autumn in order to chill the plants, which causes the leaves to drop. It is important, however, not to expose plants in pots to frost as damage could result. A temperature of 35-45°F (2- 7®C) for a night or two should cause the leaf fall.

HyJrjngta macrnphylla 'Hortensia' hybrid is .in attractive put plan! and tan he planted in the garden when it grows ion tnrge lor its pot This is ihc colour produced by acid soil

When the plants have shed all their leaves, watering for the dormant period should be kept to a minimum, just sufficient to prevent the compost from becoming dry.

In winter, depending how early you wish your plants to bloom, repot the plants in fresh compost using JI No. 3 after removing the old compost from the roots with as little damage to the roots as possible. This is best done while the compost in the pots is dry.

After repotting in the same size of pot, or a size larger if necessary, the plants should be watered and placed in a temperature averaging about 50°F(10°C), until they show some sign of growth, when the temperature should be increased to 15-60°F (I i - 15°C). Keep the plants well watered, and in the case of blue-flowered plants treat with 'blueing compound* as soon as flowering buds start to show. If no buds arc seen after four pairs of leaves, the shooi is not likely to develop a flower bud.

Propagation of hydrangeas is by ant ings, which are best taken in spring. Select a ¡lowerless shoot and cut below the third or fourth node from the tip. Ideally cuttings should be about 3 or 4 in (7,5 or 10 cm) long. Remove all the leaves except the top one or two pairs, and insert about 1 in (2.5 cm) deep in soilless cutting compost. A hormone rooting powder helps. The cuttings need to be kept in a moist atmosphere until some roots have formed, as the leaves soon flag, so the pots need to be enclosed in a polythene or plastic bag for some seven to ten days. Cuttings take from three to six weeks to root, depending on the growing conditions, after which they should be potted in 3'/j-in (9-cm) pots in JI No.3 and kept growing steadily through the summer.

New plants can be treated in two ways. The plant can be grown as a single shoot with the object of producing one large bloom the following year, or alternatively it can be made to bush by the process of stopping. If a bushy plant is required, stop the shoot above the second or third pair of leaves. When new shoots appear, four are sufficient, but if there are fewer a further stop will be necessary. All stopping must be completed in mid-summer or there is not time for the flower buds to form and ripen for the following season's flowers.

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