More commonly referred to as flowering onions, these are the species whose underground organs are full of nutrients, which allows the plant to reform its aerial parts year after year.

From a botanical point of view

From a botanical point of view, the nature of the subterranean organs is very varied. It can be:

  • Bulbs (example: genus Tulipa, tulip);
  • Stumps formed from short roots, thick, fleshy and fasciculate, referred to as the claw (example: genus Ranunculus, ranunculus);
  • Tuberous strains, designated under the name of leg (example: genus Anemona, anemone);
  • Rhizomes (example: genus Iris);
  • Tubers (example: genus Dahlia)

The underground organs of bulbous plants last for several years.

In some cases, the duration of the underground organ is limited to a single year during which a new organ appears; harvested at the end of the vegetation, it makes it possible to once again ensure the reproduction. This is the case for the genus Gladiolus (gladiolus), for a hybrid of the genus Iris: the Dutch iris and for the genus Tulipa.
In other cases, the subterranean organ develops for several years, the plant attached to it then assimilates to a perennial. This is the case of the bulb of species of the genera Hippeastrum (amaryllis) and Lilium (lily) and of the tuberous strain of species of the genus Sinningia (gloxinia).

The annual vegetation cycle presents variable forms according to the species. Some of them present a continuous vegetation, which can be maintained artificially (genus Cyclamen), and require constant care throughout their existence.
In other species, on the contrary, a vegetative break improperly qualified as a period of rest is necessary each year. This occurs in winter (from November to March-April) for bulbous plants with summer or autumn flowering whose leafy vegetation does not resume until the following spring (eg gladiolus genus); on the contrary, it is located in summer (from June to September-October) for species flowering in spring (example: genus narcissus, Hyacinthus, hyacinth, and Tulipa).
During the vegetative break, the organs of bulbous plants must be stored in a dry place, in a room at constant temperature (cool in summer, without heating in winter).

Bulbous Plants Amaryllis
© istock

The two groups of bulbous plants

Bulbous plants are generally classified into two groups, depending on whether or not they can be grown outdoors and in temperate climates.

Hardy bulbous plants

They are divided into two series, depending on the flowering time:

Hardy bulbous plants with spring bloom ;

Hardy flowering bulbous plants summer or fall.
The hardy spring-flowering bulbous plants must be planted in the fall. They can, moreover, be the subject of a forced culture during the winter, which then replaces the autumn planting.
The hardy bulbous plants with summer or fall flowering should be planted in the spring and placed under shelter during frost, because few species can withstand the cold of winter without risk.

Bulbous, non-hardy plants

Most of these come from regions with a warm climate and therefore require shelter during the winter.
The rhythm of their vegetation in our regions is identified with that which they manifest in their country of origin: most of them claim a period of rest during the dry season in hot countries. Apart from some species of the genus Begonia, there are a very small number of non-hardy bulbous plants which can be grown on balconies or terraces.

Read also : When to plant tulip bulbs?

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