Hydrangeas – colourful but difficult

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THREE questions from readers this week and all about the same plant – hydrangeas. These are valuable shrubs for late summer colour when others are scarce, however, in this area they are not widespread on accounts of their likes and dislikes.

For real success they require rich soil, plenty of moisture (so watering in dry spells is essential) and protection from our Scottish winter frosts. The first two ‘wants’ are easy to provide, the third is more difficult and depends on the severity of the winter.

They are best planted where some natural protection is at hand, such as against a house wall. In a pre-winter tidy-up, leave them unpruned, then in the spring cut back hard any shoot which had flowered the previous year (some remnants of the bloom will probably still be there) and also any die-back on the others caused by severe frost. Any tops of the latter should be cut back to just above a new emerging bud. In mild areas of the country, all shoots are often to be seen cut back quite severely but not to be recommended in our area.

The flower heads can be white, pink or blue. The last-named are only possible if the plant is in an acid soil; should the soil be alkaline then the only way to get the blue flowers is to add a blueing agent from when growth starts in the spring and all summer long. The blueing product can be bought at garden centres.

Hydrangeas come in various types and flower form. The most common is H. macrophylla and there are two variations: mophead and lacecap. The former is the one most often seen, the heads being large and round as their name implies. The lacecaps are slightly different with each head flat topped with a group of small flowers in the centre, surrounded by a ring of larger ones. The lacecap types seem to suffer more in winter than their ‘cousins’, resulting in poor flowering.

H. paniculata Grandiflora is completely different. The flowers are white, tinged pink as they age, cone-shaped and quite spectacular. Annual hard pruning is reqired.

Different even more so is H. petiolaris, the habit of this type being a self-clinging climber. Once established it is vigorous and a highly prized specimen shrub. The flower heads are white, large and similar in form to lacecaps.