Learning: Dahlia Cuttings
To take cuttings you start the tuber(s) in barely moist growing medium. I like Sunshine mix or 50:50 peat/vermiculite. Bottom warmth is required -say a light bulb under a box, or a heating cable. The tubers will start to sprout and from then on light is required. Don't go too heavy with water.
When the shoot has made two good pairs of leaves, cut it with a razor or sharp knife, just below the lower leaf pair node. More shoots will come from below that. Strip off the lower pair and treat with rooting hormone. I have used Lee Valley's gel type for several years and I like it a lot, but Dahlias root very easily so use any type. Insert into a small pot of the same sterile mix and cover with a plastic bag or other such tent. For a small scale, Dairy Queen sundae bottoms plus the tall top are ideal! Lots of light and some heat(not much is really required) and you will have roots in 10 days or less. Bright green tips on the central growth is the rooting sign. Repot into a 3" pot of good mix, but no fertilizer beyond a trace. I use 50% sterile mix and 50% screened last years compost. Now LOTS of light and very little heat. They grow fast so don't start too early. Mid March in my NW zone. Pot on as you please and move to a cold frame as soon as frost danger is past. When you finally plant out, strip off the lower pair of leaves and bury the plant up to those nodes. This will produce more tubers for you.
Plants from cuttings will often outgrow plants from tubers. The plants from cuttings are also much more predictable in their growth, and timing for shows can be a more planned process. However, the tuber mass is not composed of as many discrete, dividable tubers, and traditional growers are not pleased by the crop. Those who like to grow cuttings/plants will leave one or more plants in its pot - just a 4 incher - and plant that pot so that roots can escape into the soil. The tuber mass will fill that pot and is called a pot root. It is very compact - don't divide it! - and will throw MANY cuttings the next Spring. Field grown plants from cuttings produce a tuber clump midway in size between a pot root and a normal clump. So you see you have some experiments to do to see if you like easy tuber planting, or more complicated, but more controllable pot roots.
Just a few notes on my experiences with taking cuttings, I have a success rate of about 99%, I rarely lose a cutting, and I'm not particularly regimental about my procedures. After I take my cutting I place them in miniature Greenhouses (actually discarded baby incubators), they can be easily made out of a wooden frame and plastic stapled on them. The cuttings are misted daily (once or twice) under lights (turned off occasionally), temperature about 75 degrees.
I've never had a problems with my cuttings using a weak fertilizer solution !!?, but it is weak. I've tried different soil mixes for striking cuttings, (sand/vermiculite/fine peat in different ratios) and except for how often you have to water once they are established, I've not noticed any optimal mix. Also, I was wondering if anyone has experimented with different rooting hormones, I've tried several different kinds (including none), but see no differences!!
Last but not least, the one thing that I am most reluctant to change is that I water the cutting (for the 1st time only) with the fungicide Banrot. I don't know if it's necessary, but I rarely (if ever) lose a cutting to any form of rot.
-Bob Romano, Pittsburgh Dahlia Society
With a little time, effort and reserved space it is quite simple to propagate your own Dahlia plants indoors. Two years ago, with a very primitive setup, advice from my mentor Mike Pryor and a trip to Marge's greenhouse for a short demonstration.......off I went.......the result of which was close to 100 beautiful Dahlia plants for my garden and friends. I started taking cuttings March 22nd and finished at the end of May. The cuttings generally took 12-20 days to root, depending on the variety. Last year, with "fear of the unknown" spent the previous year, the results were the same with much less effort. In fact, the little "babies" seemed to thrive when I was away on vacation for a week!
The most time consuming aspect my first year was constructing the various wooden boxes for each phase of the propagation process. Boxes (18" x 24") for eyeing tubers and for growing containers were made from 1 x 8 pine, with the propagating box (18" x 24")......fit the box to your available space.....made from 1 x 4's. I used galvanized screws to hold the boxes together with corner brackets at the top and bottom for stability. All of the containers were coated with "Cuprinol No. 10 Green Preservative" and two coats of "Thompsons Water Seal"......this dries very slowly so plan ahead. Keep in mind that I wanted my boxes to last many years, so a little extra time was invested! Wooden wine boxes or small plastic containers could also be used. To my surprise, a handful of tubers grown in one small plastic dishpan ($1), produced more cuttings than the time consuming wooden boxes constructed the previous year.........don't be afraid to experiment!!!!
For eyeing the tubers, use a light general purpose growing medium......"Pro-Mix BX" or "Customblen" by Scotts. Among other components, they both contain a wetting agent which is a definite plus. A heavier mix is used for planting the tubers after the eyes have formed, which consists of one part Mike's Cornell mix (1/3 soil, 1/3 vermiculite and 1/3 Pro-mix) to 3 parts Pro-mix. Fill the containers level with the top to provide for maximum air flow. For potting the rooted cuttings, Mike's special Cornell mix of 1/3 soil, 1/3 vermiculite and 1/3 Pro-mix was used.
In the propagating box I used screened masonry sand (sterilized in a 10% bleach solution and rinsed several times), again filled level with the top to prevent damping off. I have heard that sterilized Caribbean beach sand (readily available) works just as well.
The furnace room (70-75°F) served as a great location for eyeing the tubers. Bury the tubers, including the crown, several inches down in the "eyeing" medium, keep the mixture moist but avoid over-watering. After the eyes have formed and started to grow, the tubers are planted 4" down in the growing boxes (crown slightly above the surface) under 4' fluorescent shop lights (12 hr. cycle)......set about 12" above the boxes in the heated family room (70-75°F). Keep the growing medium moist but again avoid heavy watering. When three sets of leaves have formed, cut slightly above the crown (1/16 to 1/8") using a single edge razor blade or exacto knife. Cut again at the first leaf node and place in the propagating box with identification labels at each cutting (Variety and Date). To avoid spreading virus, sterilize the cutting device between cuttings. The sand was lightly watered daily and the cuttings checked for roots after 10 days.
It was recommended not to use rooting hormone (produces fibrous root clumps and fewer tubers), however some growers do. Once the cuttings developed roots (some with only tiny spikes) they were potted in 3" pots and placed in the holding trays under the lights for about two weeks. At this point the plants had started to show new growth and were placed outside in the cold frame. By adding heating cables or bottom heat to the boxes, cooler areas of your home could be used for propagating. Remember, growing Dahlias is not an exact science, but more of a personal science........experimenting lends itself to a more enjoyable hobby.
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