Bulbs, Corms, Tubers and Rhizomes - What Do You Do WithThem After Flowering?

After your bulbs, corms, tubers and rhizomes have finished flowering for the year, what do you do with them next?

Firstly what are bulbs, corms, tubers and rhizomes? While 'bulb' is a generic term for all four, there are differences between them.

Bulbs are short, modified underground stems which are usually surrounded by fleshy modified leaves. The leaves store food for the new shoot which is in the centre of the bulb. Onions and tulips are examples of plants which grow from bulbs.

Orchid Dahlia(53797)Credit: Wikimedia

Orchid dahlia - example of a root tuber (above)

Rhizomes are underground creeping stems which grow horizontally and send out roots and shoots from the nodes. The iris is an example of a plant which propagates from a rhizome

Tubers are fleshy, swollen, (usually) underground stems. Buds arise from the tubers and force their way to the surface. Tubers are known as stem or root tubers. Dahlias are root tubers, cyclamen and tuberous begonia stem tubers. Tubers should only be lifted when the plants have completely died down. The tubers can be placed in sawdust or vermiculite in a dry area, preferably at a temperature of about 40oF.

Corms are short, solid underground stems. They are thick and sometimes have papery scale leaves. The crocus and gladiolus are both plants which grow from corms.

The fleshy and/or swollen parts of bulbs, rhizomes, tubers and corms all store food for the new plant.

Pink TulipCredit: Wikimedia

Tulips - propagate from bulbs (above)

So, having got that sorted, should such plants be left alone, dug up and discarded, or dug up and moved elsewhere? Naturally, the same advice does not apply to all. Some need to be lifted each year; some can be left for three to five years, while others under certain conditions can be left alone almost indefinitely.

Overcrowding is the main reason for lifting bulbs. As they multiply and become crowded, they must be divided and the old ones discarded. The young ones should be grown on in new soil. In general, bulbs produce their best flowers in their first year. Each year after, the flowers become smaller and there is reduced vigour. With few exceptions, bulbs are best not kept longer than five years.

Any bulbed species that are susceptible to disease should also be lifted each year and put into fresh soil. The same applies if where is an outbreak of disease among normally hardy bulbs.

Some species which have been grown as rock plants may be left undisturbed from year to year. Tulips should be lifted however. Others grown in drifts under grass may also be left undisturbed but do not mow off the leaves until they have yellowed and died down.

Lift bulbs once the leaves have started to turn yellow but do not wait until they have completely lost their green tinge. The green leaves make food which is stored in the bulb. All the energy required for spring growth is stored at this time and the leaves and flower buds for the following season initiated. Anything that interferes with food production will have an adverse effect upon the bloom the following year.

Purple IrisCredit: Wikimedia

Iris - example of a rhizome (above)

Every effort should be made to keep the leaves alive as long as possible so that they can perform their vital function. When they're ready the leaves will turn yellow and they will be easy to remove at this point. Cutting off the green leaves or burying them under the soil will virtually guarantee a shortage of blooms the following year.

Although bulbs appear to produce all their leaves and flowers in a few short weeks of spring growth, they actually begin growth the year before. After spring flowering, all the energy of the bulb should go into producing a new flower for the following year. None should be diverted to seed pod formation. Snap off fading tulip flowers before the petals fall to prevent seed pod production and possible onset of disease from the fallen petals.

A bulb needs care and attention after flowering. Feed it with a good commercial fertiliser. Restrict watering as the leaves begin to dry up until no water is being given at all. Store and keep dry until the following autumn when growth can be initiated once more.

Pink gladiolusCredit: Wikimedia

The gladiolus grows from corms (above)

Sometimes, such as when moving house, bulbs may need to be dug before they are fully ripe but they may still develop a flower if handled properly. If you need to lift bulbs early, dig the plants retaining as many roots as possible and quickly replant them in rows where they are able to continue the ripening process. The leaves do not have to be erect. The plant may be tilted at an angle to conserve space. Keep them watered and cared for as with any newly transplanted plant. If there is no space available for planting, heel them in deep boxes of soil and allow to ripen in that way.

Obviously it is best to let the bulbs mature naturally. Every time it is disturbed the amount of food produced is lessened with subsequent detriment to the blooms of the next season.

After lifting, tie the bulbs in bunches and hang to dry in a dry airy place. Once dried, they can be stored in cartons, paper bags, old nylon stockings or baskets. Plastic bags are not suitable as they don't allow adequate ventilation.

Basal rot of bulbs is often caused through damp and badly ventilated storage. Affected bulbs should be destroyed.

The following bulbs are either very susceptible to disease or need a complete rest during their dormant season. They should be lifted and stored according to the follow notes.

  • Anemones – lift all but the dwarf alpine species.
  • Gladiolus- Remove flower spikes as soon as the flowers are finished. Leave the plants in the ground for 4 to 6 weeks to allow proper formation of the new corms. Once you have dug up the corms, cut off the stems close to the corms. Wash off surplus soil and spread the corms out to dry. After curing, remove the old corm and the roots. Dust with DDT powder and store. Leave the husks on till ready to plant out.
  • Hyacinths – Both English and Dutch hyacinths should be lifted.
  • Ranunculus – lift and store but only keep the best of the claws.
  • Tulips - lift and store. Keep the healthy bulbs and burn the rest.
  • Daffodils, jonquils and other narcissus should be divided occasionally, possibly every 3 to 5 years.
  • Dwarf bulbous species of iris, including I.reticulata, should be lifted. Some sources suggest lifting every second year. Store them in a cool, dry, well-aired place.

Other bulbs, rhizomes, tubers and corms such as abiana, camassia, chinodoxa, crosus, freesia, ixia, lachenalia, muscari, ornithogalum (sometimes called chincherinchee) scilla, snowdrop (galantus), snowflake (leucojum), sparaxis and watsonia can be left in the ground indefinitely.