Spirea of Japan - Spiraea japonica

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Spirea

Japan spirea is a very interesting plant for gardening lovers.
It is in fact less demanding shrubs, easy to cultivate, with rapid growth and, at the same time, very floriferous. They produce beautiful umbels or corymbs in shades of white, pink and red. illuminating green spaces in spring or summer, depending on the variety.
Genus that includes some medium-sized shrubs, deciduous, originating from Asia and Europe; the species, and the numerous varieties that derive from it, are divided into two large groups: the white, fast-growing spiree, which can reach 2-3 meters in height, bloom in spring; the pink species, more compact and slower than the previous ones, produce deep pink flowers in summer and autumn. They are easy to grow shrubs, which are used both as single specimens and to form colored hedges. They lose their leaves in winter, and some have a lively autumn color. S. vanhouttei is an arched shrub, which produces inflorescences in the shape of a small umbrella, of a pure white color, in late spring; Spirea japonica has pink flowers, the growth is slow and the leaves become orange-colored in autumn, flowers in summer; S. cantoniensis has white flowers, double, bloom brought by short petioles, along the thin dark branches; S. thumbergii has white flowers.
The white flower spiree are pruned after flowering, slightly shortening the top and removing the weak or very old branches; the pink spiree are pruned at the beginning of winter or at the beginning of spring, the removal of withered flowers generally favors the production of a second flowering.

Classification and origins

The genus Spirea belongs to the Rosaceae family and includes, depending on the classifications, from 50 to 80 species of deciduous shrubs.
Almost all belong to the mountain flora of the northern hemisphere. They come from areas with a cool and temperate climate in Europe, Asia, northern Africa and North America, reaching as far as the heights of Mexico. They are very common in the woods, on the rocks or near streams.
Among these is the spiraea japonica is widely used in the gardens for its beauty and the production of ornamental flowers.

Land and exposure

The spirea plants of Japan love sunny positions, produce flowers in profusion even in semi-shaded places; generally they do not fear the cold and they can easily withstand the scorching heat of July and August.
Abundant blooms occur with sunny exposures or bright partial shade. Some cultivars (especially those with golden or reddish leaves) like a little more fresh and shade to keep these colors unaltered.
The plants of spiraea japonica are very tolerant plants in terms of soil and positioning. However, for the best results it is advisable to insert them where the soil is rich in organic substance and able to remain moderately moist for a long time.
These easy shrubs grow smoothly in any terrain; they prefer well-drained soils rich in organic matter. In summer it is good to mulch the soil at the base of the plants, in order to keep it fresh.

Characteristics of the spirea

A large number of different species belong to the genus Spirea, each with particular characteristics. It is therefore rather difficult to make a general description of it. We can say that they are almost all with a rather compact and rounded habit and that they can range from 40 up to 2.50 m in height. The leaves, deciduous, have a serrated margin, usually of medium green color, although there are cultivars with shades of yellow or reddish.
Flowering can occur in spring or late summer. In these periods there is the production of bunches or bunches of flowers in shades of white, pink or red, sometimes very fragrant.
Growth is, in optimal conditions, very fast and allows you to fill large spaces quickly (or the creation of beautiful hedges). They also adapt very well to different climatic and exposure conditions and have proved to be very resistant to the attack of cryptogams and pests.

Uses of the Spirea

Spiree, depending on their specific characteristics, can be used in different ways.
The large ones are excellent as isolated specimens or in combination with other shrubs. They are in addition to this excellent for creating free hedges, alone or with other essences (they are good companions for example of berberis with red leaf).
The cultivars belonging to the spirea japonica species, and therefore of smaller dimensions, can be inserted in flower beds, in borders or even in rocky gardens in the company of other shrubs or herbaceous plants.
Today, even smaller varieties are available (which barely reach 40 cm in height). They are very suitable as a ground cover, for creating siepine or even for growing in containers.
The spiree all have the virtue of attracting many insects, for example bees and butterflies. I am therefore a great essence for those who want to make their garden more alive. Inserting some plants near the vegetable garden can also help pollination and guarantee a more abundant harvest.

Planting

The best time to plant a spirea is undoubtedly the autumn: in fact, the root system will have plenty of time to develop and begin to explore the surrounding area before the warm weather arrives. We will have a good vegetative growth and a beautiful flowering from the first year.
However, it is also possible to proceed at the end of the cold season, especially if the subject is in a vase and care is taken not to break the earthen bread.
It is important, to stimulate growth, to place at the bottom of the hole a good quantity of mature flour manure (or some handful of roasted cornunghia).
In case we want to create a hedge let's remember that the ideal distance between two subjects, to obtain a fast development, is generally 60 cm. The egg-covering specimens, on the other hand, are spaced about 50 cm apart
If we want to grow a small specimen in a vase we will need a deep container at least 40 cm wide. The ideal substrate, in that case, is a mixture of garden soil, soil for flowering plants and mature manure.

Watering

The young plant water themselves abundantly after planting them; generally the spiree are satisfied with the rains, being able to withstand even long periods of drought, it is however advisable to water the plants sporadically during the hottest months of the year, especially the summer-flowering species.
The interventions are necessary only during the first year of the planting. Initially it will intervene profusely once a week, then every month. At the end of the season the plant should have completely franked and the following years should be autonomous.
However, let us monitor it carefully, especially if we live on the coasts or in the central-southern part of the peninsula (and in the case of long periods of drought).
In a container it is advisable to always keep the substratum slightly damp, but avoiding the use of saucers.

Multiplication

It occurs by seed or by cutting. Given the ease of taking root it is generally preferred to propagate the spiree by cuttings, taking them from the branches of the year, semi-woody, in summer.
The propagation is very simple for the species that produce suckers: we proceed with the division at the end of winter.
For other varieties you can instead proceed with the semi-woody cutting, around June or at the end of summer (depending on the flowering period).

Pests and diseases

They are not seriously affected by pests or diseases, sometimes aphids can ruin flowers.

Crop care

The withered flowers of Japan's spirea should be eliminated as soon as possible to stimulate regrowth from the plant (where, for many species, there will be flowering the following year).
When summer comes, especially if we live in the center-south, it can be useful to prepare a thick mulch with leaves, straw or cut grass. It will significantly slow the evaporation of water, keeping the soil moist longer.

Composting

To keep the soil vital, it is a good idea to distribute a good quantity of mature manure or pellets in the autumn. When spring comes, it is good practice to stimulate growth and flower production by spreading a few handfuls of synthetic fertilizer, preferring a product with good amounts of potassium and phosphorus.

Pruning

It is not always necessary. We can however intervene with containment cuts or to rejuvenate the subjects. The rules to follow, in general, are the following:
Spring flowering species: we intervene as soon as the corollas appear withered. It is cut in correspondence of a branching, possibly very low so that the plant is stimulated to produce new and more dense branches. Branches that have not brought flowers must be shortened by half.
We eliminate those that are dry or sick at the base. It is also important to free the center of the plant favoring the passage of air and light.
The adult plants must be carefully monitored by removing at least one quarter of the older branches at the base, so that new shoots are produced from the head.
If you want to completely renovate a specimen, you can intervene by cutting all the branches about 10 cm from the ground.
Species with summer-autumn flowering: we intervene in spring, leaving at most 3 buds from the base. We always eliminate the sick or too old branches.

Repotting

Repotting takes place at the beginning of spring. The bread is removed from the ground and the less vital or damaged portions of the root are eliminated. We can transfer the entire specimen to a larger container or proceed with the division if necessary.
We use a mixture of garden soil, manure and soil for flowering plants. On the bottom we always create a drainage layer of expanded clay or gravel.