By Ted & Margaret Kennedy (teddahlia) on January 13, 2016
Making leaf cuttings is an advanced subject and if you have not done traditional cuttings from tubers successfully, I would not recommend trying to do leaf cuttings. Please start at 'The Beginnerâ€™s Guide to Dahlia Cuttings' in the Article Section for a step-by-step tutorial on tuber cuttings.
It is a common practice to root dahlia cuttings taken from sprouting tubers. These cuttings root easily and are very easy to do. Dahlia cuttings can be taken in another method that I call leaf cuttings. Tuber cuttings are taken when the sprout is about two inches tall and removed from the tuber by slicing it off the tuber just above where it emerges from the tuber. The cutting, when taken in this manner, has primordial tissue near where it attached to the tuber that has the ability form roots very easily. Leaf cuttings are taken from a dahlia plant that has been allowed to grow to a height of 12 to 18 inches or so and involves the removal of the leaf nodes along with some leaf material to provide material for rooting.
Leaf cuttings are rooted in much the same way that tuber cuttings are rooted. Both are rooted in some sort of damp medium such as sterile potting soil, mineral wool, Oasis cubes, sterile sand and others. I use sterile potting mix called germination mix. It is a peat moss based product that has some vermiculite or perlite, a bit of lime to raise the pH, and a surfactant to allow the mix to absorb water quickly. Note that it has no fertilizer in it and fertilizer is not recommended for use in rooting dahlias.
Leaf cuttings take much more time to root than tuber cuttings. They also require that you have a dahlia plant that is 12 to 18 inches tall and that means that the cutting material must be started several weeks before one would start tubers for tuber cuttings. The added time to obtain cutting material and for the cuttings to mature into a plant large enough to be placed into the garden is a negative factor for many people. However, the advantage of leaf cuttings over tuber cuttings is that you can harvest many more cuttings from the green plant, perhaps as many as 12 to 15 in some cases. The plant may be vigorous enough to be grown on for another round of 5 to 10 cuttings and in total from one plant it is easily possible to get 20 or more rooted cuttings.
So to summarize: Tuber cuttings are much easier to do as compared to leaf cuttings. Tuber cuttings root much faster than leaf cuttings and tuber cuttings reach planting size much quicker than leaf cuttings. Leaf cuttings have the potential to give you many more plants than tuber cuttings. In the garden there is little difference between plants grown from tubers, tuber cuttings or leaf cuttings. They will all grow tall and healthy and produce wonderful flowers. However, the plants grown from tuber cuttings will have smaller more compact tuber clumps than those grown from tubers. The tuber harvest yield will be about 50% less from tuber cutting plants. Leaf cutting plants will have even smaller tuber clumps but will still yield useable tubers. The exact yield of useable tubers from leaf cutting plants is very dependent on the tuber making capabilities of the dahlia variety. Those varieties that make very small or very few tubers may have no useable tubers when grown from a leaf cutting. One excellent use for plants grown from leaf cuttings is the production of pot tubers. Leaf cuttings produce enough tuber material for a nice pot tuber. So leaf cuttings are an excellent way to increase stock especially if you want plants for excellent flowers or you need cuttings to make pot tubers.
Leaf cutting instructions: Before I outline the leaf cutting process, I need to emphasize the need for sterile materials. The rooting mix must be sterile and although the germination mix I use is not technically sterile, it works very well. The pots and flats that you use must be sterilized and I have found that soaking pots and flats in a laundry bleach solution of about one cup per 30 gallons overnight works well. Another issue is that the plants you use for the leaf node cuttings must be free from fungus disease. In my indoor propagation area, fungus disease is not a problem.
And finally let's discuss the actual process of taking the cuttings. As explained above, you need a dahlia plant that has been grown to 12 - 18 inches tall. That plant can either be a tuber that was allowed to grow tall or a rooted tuber cutting that has been grown to that height. I use tuber cuttings to produce my plants.
I cut off the plant about 1/2 inch above the first nodes. I leave this pair of nodes because it is possible to grow the plant on for more cuttings and it will send up shoots from these nodes. If you cut it off below the nodes, the plant will probably die. You now have plant material for the cuttings. The plant you have grown will have 4 to 6 pairs of leaves emanating from the stem. Now cut them off about 1/2 inch above and below the inter node. You will then have a piece of stalk with two leaves coming out of it. Using a scalpel or razor blade, carefully cut down the middle of the stem and you will have two cuttings to root.
Since the cutting will take so long to root, it is advisable to remove ½ of the leaf to reduce surface area. You will notice at the junction between the leaf and the stalk that here is a miniature sprout(called an axillary bud). It is this tiny sprout that will form roots. Unlike tuber cuttings this tiny sprout not only produces roots, but it also produces leaves. The tiny axillary bud needs to be placed under the rooting medium so that it is just barely under the soil. Firm the soil around the cutting to ensure that it is solidly in place. The cutting is now placed under lights just as tuber cuttings are placed under lights. Note that I do not use any rooting hormone or other chemicals.
The leaf cutting will root in about 3 weeks. The process is that a tiny plant will emerge from the axillary bud. The original leaf above the axillary bud will die. Because the plant is so small, you must keep it under the lights for some additional time for it to grow. At three weeks a very weak liquid fertilizer can be given to encourage growth.
During the time that the leaf cutting is rooting, the plants must be kept moist. For 20 years or so now, we have been placing our cuttings into a sealed plastic bag to conserve moisture. We use white 13 gallon kitchen bags that holds a flat of 36 pots(10 x 20 flat, 2.5 inch pots). The flats are placed under florescent lights(2 to 6 inches above the flat). The ideal temperature is 70 degrees. Colder or warmer is much less effective.
Leaf cuttings can help you propagate large numbers of plants but as you can see the process is more complicated than taking tuber cuttings. Success rates for rooting leaf cuttings can be very high, easily over 90%. That is very comparable to tuber cuttings. It is the extra growing time that the plants need to mature that is the biggest negative in the process.
We have been growing dahlias since 1988 and began breeding new ones in 1995. We call our small nursery in Oregon City, Oregon, Hollyhill Dahlias. We grow about 3500 dahlia plants each year and about 1500 of those are grown from rooted cuttings. We enjoy entering dahlia shows and attend about six of them each year. Margaret specializes in showing flower arrangements and baskets and bouquets. I am a Senior dahlia judge and Margaret is now an Honorary Senior judge.