Althea, which goes by the scientific name «Althea syriacus,» is a large ornamental plant. It is undemanding and adapts to harsh climate conditions in temperate regions. Of the Malvaceae family, the Hibiscus genus contains over two hundred species. The Hibiscus syriacus (or Althea) is represented by two varieties, one of which is single-flowered and the other with double flowers. Their selections produce different cultivars. 

Able to reach a height of 6.5 to 10 feet, Althea makes do with well-drained soils and can even adapt to calcareous soils. The Hibiscus syriacus produces fast-growing lateral shoots and sheds its leaves every autumn. On the newly produced shoots, the flower buds bloom into a burst of colours throughout the summer until early fall. The Hibiscus syriacus is propagated by seeds, but can also be propagated from cuttings taken from the branches’ tips. Despite all its vigour, it must be protected against infestation by scale insects and against the aggression of black aphids during spring and summer. Also, to bring out its best floral potential, it must be grown in accordance with the technical standards of planting and seasonal maintenance to ensure its rapid growth and harmonious development.

Planting an Althea 

In addition to the seedlings or the germination of seeds fallen at the base of mature Althea plants, you can also grow plants from cuttings in spring. In that case, preserving the cuttings in a water container accelerates the release of the first roots. The plant must be exposed to the sun, or at least installed in semi-shade. Furthermore, it does not enjoy continuous exposure to cold winds. It can be planted in a large pot throughout the year. The planting of Hibiscus syriacus in the ground requires a 5-foot interval, in every direction, between seedlings. The plant is used to decorate a lawn, to form a flower bed or even a hedge. Grown in a mixed hedge, it can be planted with several species of flowering shrubs, such as Weigela or Elaeagnus. In any case, it needs soil that is thoroughly fertilized by a supply of spring compost or manure containing sufficient minerals.

Maintaining an Althea 

The Althea is mainly grown for its continuous and abundant production of flowers, all of which have specific colours depending on variety. Also, the various types of maintenance administered to Hibiscus syriacus aim at maximizing flower production during the warm season.

Depending on the species, the plant then generates a profusion of purple, blue, light blue, white, pink or dark red corollas. After planting and during the next two years, the plant is watered every two weeks. During a major heat wave, watering should be abundant and undertaken late in the day. In highland areas and in areas with harsh winters, it is necessary to mulch the foot of the plant. Every spring, the plant receives a supply of fertilizer to boost its growth. Indeed adult shrubs, under favourable conditions, can lengthen their shoots by about 12 to 16 inches. Among these maintenance procedures, pruning plays a major role and should not intervene too late in the season because it would compromise the bloom to come. Thus, young shrubs undergo shape pruning. For an older plant, each quinquennial bloom is followed by a shortening of the longest branches, lopping them if necessary to preserve the shape of the ribbing. To do this, the new twigs are lopped from the fourth inch of their length. This way, the plant cannot lignify excessively, which would potentially strip down the bottom of its main trunk. Grown in pots, Hibiscus should be subjected to rigorous pruning every year around February-March to preserve the compactness of its shape. It should be repotted in a larger container every two years.

A multitude of varieties 

Among simple inflorescence cultivars, we can cite varieties such as “Woodbridge,” “Blue Bird,” “Hamabo,” or “Red Heart.” Famous double-flowering cultivars include “Speciosus,” “Lady Stanley,” “Leopoldi,” and “Duc de Brabant.” Nevertheless, Hibiscus syriacus has nothing to do with the Hibiscus rosa-sinensis, or with the common hollyhock also known as Althaea rosea. These plants are all quite different.

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Published in Flowering shrubs by Alexander on 04 Jul 2011