The Function of Roots

Roots are usually the first part of the plant to emerge when a seed germinates. This tells us something about their importance in the life of a plant and the role they play. Roots have two main functions. First, they anchor the plant to the soil or compost in which the plant is growing.

Second, they take in water and minerals (sometimes referred to as salts) which are needed by all parts of the plants for growth. They also take in oxygen from the compost. Oxygen is as necessary to plants as it is to animals; like animals, plants breathe by taking in oxygen and giving off carbon dioxide.

Some roots have other important roles. One of these is to help in propagation; some plants can be increased from root cuttings, which are either placed on the surface of the compost and lightly covered, or inserted vertically into the compost.

In addition, roots are sometimes modified and adapted to fulfil very special function.

Root or stem?

Most roots grow below the surface of the compost, and grow downwards. Stems grow upwards and are supported mainly by the toughened cells close to their surface. Roots are supported mainly by the growing medium. In addition, roots do not bear leaves or buds, but have fine hairs which absorb water and minerals.

Root hairs

Minerals dissolved in water are absorbed by the tiny hair roots, and pass through into the vascular cylinder and up into the plant.

How roots absorb water

Small, hair-like structures which grow from the main roots absorb water, and minerals dissolved in water, from the compost. Weak solutions of water and minerals pass through the root membranes and into solutions already present in the roots, by a process known as osmosis.

Osmosis will only take place as long as the water inside the plant contains a higher concentration of minerals than the solution in the compost. If the compost contains too high a concentration, the process will be reversed and water will pass out of the roots into the compost.

Storage roots

Storage roots that swell to become food have many different shapes. Carrots, and horseradish produce long, cone shaped roots. Other plants produce spherical bulb-type roots, such as hyacinths and tulips. Other plants produce swollen storage roots in the form of tubers (dahlias) and rhizomes (bearded irises).

Checklist

• Don’t water plants with a high concentration of fertilizer, as it will damage the roots. Apply fertilizers only in the strength recommended by the manufacturer.
• Pot plants on into a larger pot as soon as the edges of the soil-ball are lightly covered with roots. Although some plants like being pot-bound, in most cases this can lead to root damage. Excess roots growing through drainage holes can be easily damaged when removing the soil-ball from the pot.
• Don’t repot a small plant into a very large pot. The plant will be unable to absorb the relatively large amount of water quickly. The result will be stagnant moisture that will keep the compost cold and encourage roots to decay.
• Make certain the compost does not become extremely dry. As the compost shrinks, the fine root hairs that absorb water will break.
• Don’t allow strong summer sun to overheat the compost, as this too can damage the roots. Packing moist peat around pots placed in shallow window-boxes will help to keep the compost and the roots cool. Double potting also helps to keep roots cool, as well as increasing the humidity around the plant.

Other types of roots

• Aerial roots grow from stems above the compost, and are able to take in moisture from the air. Stilt roots act as supports for plants. They grow downwards from the stem and into the soil or compost, enabling them to bear much of the weight of the plant.
• Climbing roots, which cling to vertical surfaces, help to support climbing plants.
• Storage roots act as food reservoirs. Bulbs, corms and tubers are two examples of modified roots that store food which the plant can draw on as necessary.

Root pests and diseases

The pests and diseases that attack roots are often difficult to detect. Root mealy bugs look like small white woodlice. They feed on the root and are usually found in clusters. An infected plant will wilt, seemingly for no apparent reason.

Treat by drenching the compost with a preparation containing malathion. To help the plant recover, place it in partial shade.

Root aphids sometimes feed on the roots of house plants. They can be eradicated by drenching the compost with malathion.

Vine weevil beetles chew the leaves of certain plants, but it is the larvae that chew the roots. These pests are about 25mm ( I in) in length, creamy-white with brown heads. House plants that are prone to attack include cyclamen, cinerarias, tuberous-rooted begonias, primulas, pelargoniums and ferns. Early symptoms are wilting, followed by collapse. As soon as adult beetles are seen on the leaves, drench the compost with an insecticide. In severe attacks, destroy the plant.

Fungus gnats are small black flies that often flitter around plants. They do little harm, but they sometimes lay eggs in the compost. The larvae feed on decayed vegetation in the compost, but may also chew the roots, causing wilt. Spray the compost with a malathion solution.

Root rot is a disease which can attack African Violets, begonias, palms, cacti and other succulents. They are encouraged by excessively wet compost. The plants first wilt, the leaves turn yellow, and finally the plants collapse. Root rot can be prevented by ensuring that the compost is not continually wet.