What are Blooming Bulbs, Corms and Tubers?
What are Blooming Bulbs, Corms and Tubers?
There is no other group of plants that can produce such a wealth of colour for so little money or effort as this group. This is particularly true of the spring-flowering bulbs such asand crocuses, many of which, once planted, can be forgotten, to surprise one with their colourfulness year after year.
Although a bulb is popularly supposed to be just a root, it is in fact a whole plant, complete in itself, but in embryo and in miniature. It is very like those paper plants that children used to be given at Christmas which are folded up in small shells and which, when dropped into a tumbler of water, miraculously unfurl themselves. An onion is a typical bulb, and if you cut an onion exactly in half you can see precisely how a bulb is constructed. In the middle there is a bud containing the flower and the leaves. This central bud is surrounded by layers of white fleshy scales that are, in fact, modified leaves. Both the scales and the central bud are attached to a hard lump at the bottom called the base plate. It is from this that both stem and roots spring once growth begins. The roots are deciduous – that is they die off at the end of each season’s growth though in a few cases they are perennial. Most bulbs renew themselves each year, the old scales giving their substance to the new scales.
Most bulbs are protected by a further layer of modified leaves known as the ‘tunic’. The tunic may be white, brown or black. Such blooming bulbs are called ‘tunicated’. A daffodil is a typical tunicated bulb. These bulbs normally reproduce themselves by producing a second, smaller reproductive bud off the base plate but within the protective layer of scales.
Blooming bulbs that are not protected by a tunic are known as ‘imbricated’.are typical imbricated bulbs. The scales are usually thick and fleshy. Most imbricated bulbs are increased in cultivation by removing the scales and inserting them in boxes or pans of sandy .
A corm is an altogether more solid structure. It consists almost entirely of the fleshy base of the previous year’s stem. As with a blooming bulb, there is a base plate from which the roots spring and a bud, but the bud is tiny compared with that of a bulb: it is usually formed beside the old stem. Whereas bulbs renew themselves annually, corms usually wither and die, giving their substance to the new season’s growth; as this growth dies an entirely new corm is formed, usually on top of the old corm: in a few cases (cyclamen,and for example) the corm does not die but just goes on and on increasing in size until it degenerates with age.
Tubers are something different again. They are swollen underground stems whose function it is to store up plant nutrients accumulated during one season’s growth to start the plant growing again the following season. Unlike bulbs and corms they have no base-plate and no tunic: most have a multitude of dormant growth buds.
Reference is sometimes made to tuberous-rooted plants, which are something different again. Here it is the roots, not the stem, that store up one season’s nutrients to begin next season’s growth. There are no buds on the tuberous roots themselves; the buds congregate round the base of the previous year’s stem, from there the roots spread out in star-fish fashion.
Rhizomes too, are sometimes included among bulbs and corms. They can vary greatly in appearance, but in general are treated like corms.
Ideal Soil Conditions for Planting Bulbs, Corms and Tubers
In spite of their differences bulbs, corms and tubers are all very easy to cultivate. There is only one basic rule that must always be observed: all need a well-drained soil. If they don’t have a well-drained soil they will simply rot.
The ideal soil is a light, sandy one. Such soils are naturally well-drained. On other soils the aim should be to make the bulb areas as light and sandy as possible. On heavy and moderately heavy soils this can be achieved by working in ‘quantities of leaf-mould, well-rotted stable manure or peat and sharp sand. On the very heaviest soils the only answer is to grow bulbous plants incontained within low walls of brick, stone, or fallen tree-branches. The bed should be filled with a mixture of equal parts of ordinary garden soil, sand and well-rotted stable manure or leaf-mould.
The main planting season for bulbs is the autumn. The earlier in the autumn they are planted the better, as this gives them time to stall making root growth before frosts make this impossible. Consequently early planting is invariably rewarded by a better show in the spring.
Planting bulbs is the easiest thing in the world. However, there are two important rules which must be followed. Bulbs should generally be planted at twice their own depth, and the base of the hole in which the bulb is planted must be flat: it is simply no good taking out a hole shaped like an inverted dunce’s cap: the bulb will settle halfway down, leaving its roots dangling in thin air. The base-plate must be in contact with the earth at the bottom of the hole.
With large bulbs which are more likely to rot owing to the greater depth at which they are planted, it is essential to place a handful of sharp sand or grit at the bottom of the hole and seat the bulb on that. With exceptionally large bulbs it is also worth encasing the whole bulb in sharp sand before refilling the hole with earth.