Above ground, plants usually grow within an upright habit or clump forming pattern. However, below ground, root structures vary immensely. Roots can be lateral or fiborous, but the organ that stores the goodness is intentionally underground as a safety measure from animals or environmental conditions.
Corms are usually smaller but similar to bulbs. Montbretia / crocosmia (or often associated with red ‘Lucifer’ montbretia and crocosmia orange flowers. This plant usually flowers summer to early autumn. It likes full sun, well drained soil and can cope with drought conditions. The benefits are delicate flowers and little maintenance – the corms multiply by themselves. The method to propagate is divide the cluster. This also helps with regeneration and performance. After flowering, just cut back spent growth and the plants will regenerate the following year. Corms include watsonia species, gladiolus and crocuses: all flowering in spring.
Bulbs can be differentiated by the scaly coating on corms. The organ corm tends to be smaller, in a cluster too. True bulbs include narcissus, agapanthus, tulips, snowdrops and alliums. After flowering, these plants need to be left for the nutrients to return to storage before cutting the spent growth back. An indication is when the debris flops and sags from the plant or several weeks after. It can be a pain if naturalised in a lawn but important to adhere to. If the growth is cut back prematurely it can impede the following years performance or the plant may come back blind (without flowers).
Rhizomes usually are close to the surface. The stems run horizontally sometimes just protruding on the soil surface. Bergenias (elephants ears) are a rhizome. The leaves when spent should be pulled of to prevent rotting on the surface. A low maintenance, drought tolerant perennial. Pink, spiky flowers will give you a show late winter to early spring. Its leaves, large and attractive with a purple-red tinge. Other rhizomes include irises and ginger, water lillies and bamboo.
Tubers are vessels formed from the parent plant itself. A swollen stolon will produce offshoots. These shoots will form the new growth from the original plant using its nutrients. The new growth then disperses for its season leaving the debris of the parent plant to decompose. These organs can be divided in late summer to early winter and is why you should really dig up your dahlias. For this reason, and the plant has a tendency to rot in wet soil. Cyclamens are tubers too as are potatoes which most would know.