Originally printed in the Feb. 4, 2004 edition of the Illinois Valley News
January is not the normal time to work in the garden. Besides being wet and cold, most soil is very clumpy and difficult to work. However, this year there was a week or so of dry weather and it warmed up some in the afternoon, so I started on a task which had been put off for a number of years. We have an iris bed that has been largely ignored for many years, not even getting any watering. The underground portion had become so matted and tangled that it had pushed up a few inches above the soil level. I decided it needed to be thinned out.
Most people call the part of a plant above the ground the stem and leaves, and the part below the ground roots. However, biologists and some gardening experts like to make things more complicated. Some plants have underground stems and irises are an example. They are not considered true roots because of the arrangement of the xylem and phloem.
Xylem cells form tubes that transport water in the roots and stems and are located on the inside of a stem but on the outside layers of roots. Phloem cells also form tubes, but are microscopically different from xylem. Phloem transports sugar from the leaves where it is produced during photosynthesis, and carries this energy source to all other parts of the plant, including the roots. The phloem layers are located on the outer layers of a stem, but make up the inner portion of the root. Underground stems are very common among plants. An example would be grass plants and ivy which send out runners in order to spread to new areas. Strawberry plants also produce runners but these are mostly above the soil surface. Runners, called stolons by botanists, usually do not have a stored food supply and so are thin and fibrous.
Irises have thick, swollen underground stems which are called rhizomes. Rhizomes grow through the soil, sending up new growth tips into the air and new roots down into the soil. Over the years this combination of roots and rhizomes made the thick mat with the roots acting like ropes which bound it all together. It also prevented water from soaking in and slowed down all activities of the plants. It needed to be thinned.
Another type of underground stem is called a tuber. Potatoes are a good example, as well as begonias which grow from tubers. Unlike rhizomes, tubers grow out in all directions, rather than in a line, and they have numerous spots called eyes where a new shoot can form if they are left in the ground. Some plants, like dahlias and daylilies, produce tuberous roots. These are true roots but swell with stored food and also enable the plant to send out new growth shoots.
Two other forms of underground stems are bulbs and corms. They look very much alike with one growth area for a shoot and one region which will produce roots. Bulbs, such as onions, garlic, and daffodils have a papery skin and then many layers which make up the bulb. Corms, such as crocuses and gladiolas, are very similar to bulbs but have no layering inside the skin. Both corm and bulb plants will produce new corms and bulbs which is one way the plants are able to reproduce. These new growths can be dug up, separated, and replanted.
All of these thickened forms of underground stems enable the plants to reproduce and to survive dry periods of time in order to remain alive. My iris rhizomes are now being replanted in Medford, Rogue River and hopefully other places within the Illinois Valley. They are hardy and only need to be planted in good soil to produce many beautiful blossoms.