Propagating Plants from Cuttings

Background

Two general approaches to propagating plants (creating new plants) are by using seeds or by vegetative propagation. Each technique has advantages and disadvantages. Seeds are products of sexual reproduction, which means that gametes (eggs and sperm) are produced, and they fuse together in fertilization. One consequence of this is that seeds are not genetically identical to their parent plants or to one another, though they may be quite similar genetically. Many plants make many seeds, which provide a cheap way to quickly establish many plants. This is important for crops where we require many individuals and the individuals live for a year or less. Indeed, nearly all grains and vegetables are propagated by seeds. Some examples include corn, wheat, tomatoes, peas, to name just a few.

For other plants, vegetative propagation is the favored technique, for a few different reasons. Vegetative propagation refers to establishing plants without seeds, which means that the plants are produced asexually (without sexual reproduction). Asexual reproduction does not involve meiosis, so there is no formation of gametes or fusing of gametes in fertilization. This means that the offspring are genetically identical to the parent plant. Having identical offspring can be advantageous if the parent plant has highly desirable traits.

Vegetative propagation can occur by several techniques. Some plants form offshoots, such as rhizomes, runners or bulbs; these can be separated from the parent plant and easily grow into new plants. Because these plant organs are large and have stored nutrients, it can be easier to get the plants established and to quickly grow them to a large size than if seeds were used instead. Onions and garlic are both typically started in this manner.

Plants can also be started by cuttings – this involves removing a portion of an adult plant and exposing it to conditions that allow adventitious roots to regenerate from stem or leaf tissue. Some plants, including Coleus, root from cuttings very easily, while other plants need exposure to hormones, especially auxin, to stimulate adventitious root production. Although propagating plants from cuttings requires more effort than using offshoots, the benefits are similar – the technique allows production of genetically identical plants and can be faster than starting plants from seeds. Cuttings are used for vegetative propagation of long-lived plants for which exact copies are desired when the plants do not form rhizomes, runners or bulbs.

Grafting is a similar technique to cuttings because both techniques are methods of asexual propagation. The differences is that in grafting, the plant being grafted is attached to already existing roots, while for cuttings, the plant grows its own roots. Cuttings are easier to make but grafting allows new stem root combinations that might be more favorable for the environment (for example grapes well suited for wine making are grafted onto root stocks of grape plants whose roots are resistant to pests but whose grapes are less suited for wine production).

Supplies Provided in kit:

Scalpel

Plastic cup

Coleus plant

Experiment

In this experiment, you will grow Coleus from a cutting to observe adventitious root formation. In the Coleus grafting study, you cut off segment of stem a few inches long, and you were instructed to store it with its base immersed in water – you should use that stem piece as the cutting.

1. Remove the stem segment from the water. Ideally, it should be at least 10 cm long. If it is not, determine whether the non-graft plant has enough stem remaining that you can remove another 10 cm segment. If so, then do so; if not, then use the already cut stem segment, however long it is.

2. Pull off the bottom leaves so that there is at least 3 cm of stem without leaves. This leafless section of stem should include at least one node (location where leaves had been attached before you removed them). Put the stem in a cup and fill with tap water to a depth that more than covers one or two pairs of nodes. Do not submerge leaves - lower the water level or remove the leaves to prevent this.

3. If there are large leaves or a lot of leaves on the stem, rip off the ends to reduce the amount of leaf material. The goal is to reduce transpiration until roots develop.

4. Place the cup in a location with bright light, but not in direct sunlight. Take a photo with ruler and your sticker.

We will monitor its formation of roots over the next few weeks.

What to turn in

Photograph the cutting immersed to an appropriate height in its cup. Submit the photograph on the Coleus-cuttings-and-graft Padlet page.

Note to instructors:

Students turn in photos of their grafts to Padlet. Each student has their own column on Padlet. This allows them to see each other's work and helps them to see the task is able to be accomplished.