Grafting

Grafting is a method of asexual propagation used widely in horticulture. Unlike cuttings, the other method we will explore, grafting works by connecting two plants together.

This video explains a bit about why grafting is used, and shows some different grafting techniques. A list of questions from the video is below. These questions are in the "Grafting questions" test on Blackboard.

Watch the video about grafting linked here.

Complete the grafting quiz on Blackboard (LMS). The quiz is not timed & the questions are as follows.:

Questions for quiz (on video)

1. What layer of stem tissue allows the tissues to heal together? This is important, because we will need to align these layers when we make graphs.

2. Using the example of avocado, why might it be useful to attach the stem of one fruit tree to the roots of another?

3. Why might a grafted fruit tree be a good option for a home gardener lacking space for many trees?

4. Look ahead to the Coleus experiment - which type of graft are we performing?

Procedure

We will graft the top of one Coleus plant onto the rootstock of the other, creating a multi-colored Coleus. In a graft, the top part is called the scion and the bottom is the rootstock. Choose the Coleus with the wider stem for the rootstock and the one with the narrower stem for the scion. You will decapitate the plant being used for the rootstock. When you do so, remember that you will use the removed top part as your cutting in the cutting experiment. Have a cup of water ready so you can place the stem of the removed top part into water immediately after cutting it off. This should help to prevent the formation of air bubbles in the cut xylem and increase the chance that the cutting will survive.

1. On the plant that will be rootstock (the one with the wider stem), cut the main stem just below a node (in other words, just below a pair of leaves), leaving at least 2 - 3 inches of stem sticking up above the soil. You can leave even more stem than this if you want to, but remember that the thicker the stem, the easier it will be to graft. From top cutting- Pull off the bottom couple sets of leaves from this cut stem and put the stem in water - you will use this for your cutting experiment later.

2. Cut the stem from the second plant (which will give you the scion) at least 2 - 3 inches from the top of the plant. Cut just above a node, so the scion has a long section of internode at its base. Try to choose a place to cut where the stem is a similar width to the stem of your rootstock, so the stems can align well. Remember that you do not want the scion to be too tall because it can fall over, and because it will have trouble acquiring water until the cuts heal.

3. Remove most of the leaves from the scion. Leave the top couple of pairs of leaves - if you leave more than this, the scion will transpire too much and dry out.

4. Make a diagonal 1-inch cut on the base of scion stem, like this:

Diagram from: http://www.ableweb.org/volumes/vol-21/mini.8.readel.pdf

5. Make a second cut long the scion stem starting one-third of the way along the diagonal cut from the very point of the first cut. Don't get too close to the edge, or the stem can break. Make the cut about 1/2 inch long and parallel to the edge of the stem, as shown below:

Diagram from: http://www.ableweb.org/volumes/vol-21/mini.8.readel.pdf

6. Make the same two cuts on the top of the rootstock stem.

7. Fit the scion onto the rootstock. Make sure the scion and rootstock are lined up at least on one side of the stem. This is more important than centering the scion over the rootstock to ensure that the vascular tissue aligns. Lightly press the stems together to open up the wedges on the cut stems. Hopefully, the scion can stand in this position without you holding it in place. Photograph the stem before you tape it, make sure the cleft cut is visible (like in the photo below). You will further attach it with tape in the next step.

6. Make the same two cuts on the top of the rootstock stem.

7. Fit the scion onto the rootstock. Make sure the scion and rootstock are lined up at least on one side of the stem. This is more important than centering the scion over the rootstock to ensure that the vascular tissue aligns. Lightly press the stems together to open up the wedges on the cut stems. Hopefully, the scion can stand in this position without you holding it in place. Photograph the stem before you tape it, make sure the cleft cut is visible (like in the photo below). You will further attach it with tape in the next step.

Diagram from: http://www.ableweb.org/volumes/vol-21/mini.8.readel.pdf

8. One of your bags includes first-aid tape wrapped around a pencil. Use a couple of inches of that tape to seal the rootstock and scion together. Wrap around the stems, and completely cover the two cuts. Achieve a reasonably tight seal, as there needs to be a firm connection between the two plants for healing to occur.

9. Find in your supply box a ziploc bag with petroleum jelly. Use a toothpick or cotton swab to rub petroleum jelly over the places where the first-aid tape meets the stem. This will help to create a water-tight seal. Photograph the plant at this point.

10. Find a large ziploc-style bag (there should be one in your lab supplies). Cut small slits in its bottom corners. Invert the bag over the plant. This will create a humid environment, which will be important until the graft fully heals. Put the plant in a saucer. Photograph the plant at this point.

11. Put the plant under diffuse light (high light is okay but direct sunlight is too much until the graft heals). You can put the plant under a fluorescent or LED bulb instead (remember that incandescent bulbs are not good because they get quite hot). Bottom water the plant - this means you will put water into the saucer and it will get pulled up into the soil. This will let you water without needing to remove the bag as much. You should keep 1 - 2 cm of water in the pot for the next seferal weeks, until the graft heals. You will know when or if this occurs when you start to see the scion grow and make new leaves.

What to turn in:

• Answer questions on the "Grafting questions" quiz.

• Add to "Coleus cutting and graft" Padlet the photos of your graft in progress and once completed. These go below the photo of your coleus cutting on the Padlet. There should be 4 photos (1 of cutting, 3 of grafting).

Illustrations from and directions modified from: http://www.ableweb.org/volumes/vol-21/mini.8.readel.pdf