Propagation by Leaf Cuttings

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This year I have attempted to maintain a very clean* "cuttings" operation for two reasons. First, one commercial grower speculated that the main reason for a low survival rate when taking cuttings was contamination. In the past, about 70 percent of my sprout cuttings and only 50 percent of my leaf cuttings survived. Recalling how I did the cuttings in the past, I was convinced that contamination had to be a major factor. Second, in order to learn what variables (growing mediums, temperature, humidity, etc.) are important to survival when taking cuttings, it would be necessary to control contamination.

Using the "leaf cutting" procedures described below, two experiments are underway. One experiment compares the leaf cutting survival rate of 96 split pair cuttings when grown in a commercial mix (Sunshine Basic Mix 2) on the one hand and when grown in "Oasis" cutting cubes on the other. A second experiment makes the same comparison with 32 split pairs between the commercial mix and an equal mix of playsand, vermiculite, and perlite. Taking advantage of the "split stem leaf cutting" procedure, one leaf, stem, and meristem from a node is placed in one medium and the other leaf, stem and meristem from the same node is placed in another medium.

Cuttings placed in "Oasis" resulted in a 97 percent success rate. Those placed in Sunshine Basic Mix 2 resulted in a 93 percent success rate. Those placed in "Oasis", however, did not do very well later when planted in pots and then in the outside beds. The final result in the beds was only 62 percent success. Additionally, when tubers were harvested, the "Oasis" was in the approximate location of the eyes. It was difficult to remove, and appeared to stop the development of the eyes.

In comparing the sunshine mix with the sand, perlite, and vermiculite mixture, the Sunshine Mix 2 did better than in the first comparison, resulting in 96 percent success. The sand, perlite and vermiculite mixture achieved 91 percent success.

*Clean--as in pasteurize, disinfect. This should kill most pathogens. However, it will not kill viruses.

After the potted tuber has produced a plant with 4 to 6 sets of leaves and the "meristems" [groups of cells that form the very tip of any growth shoot of a plant] are visible between the stem and the leaf stalk, the plant is ready for leaf cuttings to be taken. Preferably, the meristems will be at least 1/4" long before taking cuttings. While topping the plant will speed up the growth of the meristems, they may not grow at the same rate. Consequently, the 1/4" length is desired but frequently not always possible. The plant on the right has at least seven pairs of leaves and three sets of meristems visible in the picture. Some people refer to meristems as "axils". An axil is the angle between the stem and leaf stalk or the line of growth.

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The meristems referred to above are shown in the adjacent picture.

In the next few steps we are going to cut the stem in such a manner as to leave part of the stem attached to the petiole (leaf stalk). There are two methods of making these cuts--the "heel cutting" method and the "split stem" method. The former requires considerable skill and we will not illustrate it here.

When we have taken the cutting, we intend to plant it so that the meristem will grow into a regular dahlia plant.

If you start early enough, up to 30 leaf cuttings may be derived from one plant.

In most instances, no matter where you cut the plant off, another shoot will develop from the tuber or from a node on the stem so that the tuber will continue making a plant that can be transplanted into your dahlia garden.

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We cut the plant as shown in the adjacent picture. A pair of leaves remain and typically a pair of meristems will grow from the crotch (axil) made by the junction of the stem and the petiole or leaf stalk.

In some cases, taking cuttings from the top of the plant downward is advantageous. That produces just two cuttings at a time, giving ample time to trim the leaves if necessary, dip the cutting in the rooting hormone, and insert it in the growing medium minimizing the possibility of an embolism forming in the stem. Sometimes the meristems at the upper nodes of the plant will be ready for cutting but the meristems at the lower nodes will be just barely visible. Taking a few cuttings from the top of the plant will stimulate the growth of the meristems at the lower nodes. Thus after taking a few cuttings involving the two upper nodes, the plant can be set aside to continue growing. A few days to a week later the meristems at the lower nodes of the plant will have developed and be ready for taking more cuttings.

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We make the second cut as shown in the picture on the right.

In general, the stem below the node (to the left of the node which is to the left of the knife blade) should be as long as possible but not to extremes, say longer than one and one-half inches. As you can see, it is not always possible. Some cultivars leave 1/2" or less between nodes.

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