The Centaurea genus, which also includes the cornflower, brings together about three hundred species of annual and perennial herbaceous plants originating in Europe, Asia and North America. These plants have alternate leaves, usually bright green, in some silver-gray species, sometimes covered by a fine whitish down.
The flowers bloom on long stems, usually gathered in bunches, with fertile internal flowers and sterile external ones. The colors can be various: the typical color of the cornflower is certainly the blue, but there are pink, violet, yellow and white species.
The Centaurea cyanus is an annual plant about 60 cm high, with blue, yellow, pink or white flowers; Centaurea moschata has fragrant flowers, is annual. Centaurea montana is perennial, with flowers of various colors. Centaurea babylonica is perennial with yellow flowers and gray leaves.
As for the correct display of Centaurea cyanus, it is good to know that these plants particularly like the positions in full sun; Perennial plants do not suffer from winter cold, except for some cases, so before placing them in the garden it is good to know precisely the species we are planting.
The cornflower is not particularly sensitive to the cold, but it particularly loves the sunny positions, where it can receive several hours of sun a day, but it suffers during the hottest days, if the sun is particularly strong. In temperate climates the Centaurea cyanus is cultivated as an annual, given that too low temperatures cause it to dry.
Cornflower plants need a good amount of water, supplied regularly, leaving the soil to dry between one watering and another to avoid the formation of dangerous stagnant water, which could cause problems and rot radicals. Supply fertilizer for flowering plants every 15-20 days mixed with the water used for watering.
The cornflower grows without problems in any garden soil, however preferring fertile and loose soils, rich in organic matter. It can also grow successfully in the common universal soil, as long as it has the correct drainage, to prevent excess water from causing problems for the plants. In temperate climates this plant also grows spontaneously, since it can easily adapt to different types of soil.
The multiplication of plants belonging to this variety usually occurs by seed; both annual and perennial plants can be sown without problems at the beginning of spring directly at home. To obtain a better flowering it is advisable to sow the cornflowers in late summer or in autumn, in the seedbed, which must be kept protected throughout the winter; the seedlings thus obtained must be planted in the spring, or in any case when the thermometer is unlikely to fall below zero.
Pests and diseases
These plants have a rather resistant character and are not easily attacked by pests or diseases. However, they may present problems and the onset of fungal diseases may occur if the soil does not present the correct drainage and water stagnation occurs. Therefore carefully check that the water is disposed of properly.
Choice of seeds
The annual species (like the Centaurea Cyanus) at home can be propagated only by sowing.
For this purpose it is advisable to buy selected seeds, preferring them to those taken in kind. It will be possible to choose from countless colors (blue, pink, white) and dimensions. The dwarf varieties, for example, are more suited to the first rows in the borders or to the cultivation in pots: they will give more abundant blooms and we will run less the risk to see the stems bend following a thunderstorm or simply for the wind.
Seeds harvested in the wild can work well to give life to a natural lawn, perhaps mixing them with poppy seeds or field daisy.
When to sow?
Sowing can be carried out both in autumn and in spring: but it is advisable, if possible, to proceed in autumn (September or October). The seedlings, in fact, exceed very well the cold months and almost always give better results.
Spring sowing is recommended only if we live in an area with particularly cold winters, long and wet.
Sow cornflower in the ground
We choose higher varieties if we want to use cornflower in the second row in the borders, otherwise we focus on dwarf varieties. We work in depth the area and add pebbles and siliceous sand to improve drainage, if the soil is too compact.
Spread the seeds around and cover them with sand or light soil. We irrigate abundantly and regularly, but gently. The plants should be grown in about 10 days. At that point we proceed with the thinning: the ideal distance between the rows and on the row, depending on the variety, ranges from 20 to 40 cm.
Sowing in pots
There are no substantial differences with the one in the open land. It is only advisable to choose a fairly deep vessel (at least 25 cm) and to particularly cure the water draining: ideal is a gravel bottom.
The ideal substrate is obtained by mixing 1/3 of calcareous soil, 1/3 of coarse river sand and 1/3 of soil for flowering plants.
Irrigation and topping of the cornflower
The cornflower is quite autonomous. Usually it does not require water interventions, except in the South, if the drought is very long-lasting. On the contrary, it may be useful, in the early stages of spring vegetation, to use the topping several times: we will obtain more compact, stable and floriferous plants.
The higher varieties will surely require support: we can use branches specially picked for the purpose (of hazel or white willow). Alternatively (especially if the plants grow in the front line in a border) we can prepare two or more tutors to which we will tie a horizontal thread: the plants will lean gently on them.
Annual cornflowers do not generally require fertilizing. Indeed, these can even be harmful. In fact, products too rich in nitrogen stimulate vegetative growth excessively. As a result we will have plants that are too tall, thin, with many leaves and few flowers.
If we want to stimulate the production of flower heads we can possibly administer, once or twice at the beginning of spring, a product for flowering plants. We carefully choose a formulation in which the nitrogen is almost absent and there is instead a good title in phosphorus and, above all, potassium.
Pests and diseases of cornflower
Cornflower is almost never attacked by insects. At the time of sowing, in autumn or spring, the seedlings can become the meal of snails or slugs. Move them away with special products or using beer-based traps.
A serious danger is instead represented by root rot and oidium. The first can be presented both in autumn and in spring. To prevent excessive humidity from causing the deterioration of the seedlings, first of all, care must be taken to cure the drainage and the quality of the soil. Moreover, if we live in very humid areas, we insert the cornflower only in full sun.
These same conditions, a poorly luminous exposure, environmental humidity and little air flow, are the cause of the most common fungal disease: oidium. If it were to occur we can act in two ways.
In less severe cases it is advisable to distribute wettable sulfur or powder (inserting it in a sock and shaking it on the leaves). If the condition is more extensive, it is better to visibly shorten the plants: they usually generously reject giving a second fairly abundant flowering.
Perennial species of cornflower
The most common cornflower is certainly the annual one. If we want a nice touch of blue without always having to sow we can go towards other species. For example, the Centaurea montana is very beautiful: it forms a beautiful enlarged bush, with flowers from bright blue to pink to white. In purple it is also very interesting the Centaurea dealbata and in pink the hypoleuca and the atropurpurea.
Cornflower is a herbaceous plant native to Europe, North America and Asia. Cyanus segetum and Centaurea cyan
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