Cutting success! How have your cuttings done?
I've had great success with cuttings this spring. Last year I tried some and had only about a 30-40% success rate. This year it's around 95% success! I've even been successful taking cuttings from newly aquired tubers, but it required a lot of courage. It will be great to have 2 or 3 plants of some newly purchased expensive varieties instead of just one specimen. I've got around 185 cuttings that I've potted along into potting soil and about another 100 still in rooting media. I've learned a lot this spring from reading articles online and from advice (Thanks Ted!) shared here on the GW Dahlia forum and this has led to a big improvement in my cutting technique. I struck many more cuttings than I actually need simply as a way to develop my skill set. (I may have a one day plant sale to get rid of the excess as I now have many clones of the same varieties.)
Here's the basic formula that worked well for me: well draining media (I've come to prefer 50/50 vermiculite and perlite), high humidity, moderate temps in the mid 70s, 14+ hours of light and Green Light Rooting hormone powder. I don't know that the hormone is necessary (Ted says no) but I had it on hand so I used it. Next year i think I'll skip the hormone and see if my success rate differs.
Cutting diameter seems to be very important. Too thin and they wilt and rot, too thick and they take forever to root. 3/8 inch seems just about right. I also found that too much leaf area is bad and is stressful on the cutting. It's difficult to explain what the right ratio is but it becomes apparent after you take the first 50 or so cuttings and see which ones look stressed. Most of the small percentage of cuttings that I lost were from attempting to use a sprout that was too thin. i also gave up on a couple of fat sprouts that refused to root after a month even though they had not rotted or wilted.
I used 3 inch square pots and sometimes stuck as many as 4 sprouts into one pot. I pulled the rooted sprouts at around 14-16 days on average so the roots usually weren't too tangled even with 4 in a pot. I shook off most of the rooting mix to reuse and then potted the cuttings along into 6 inch pots filled with good potting soil. (I made many of the pots by cutting gallon jugs in half.)
I used translucent Sterlite tubs to maintain humidity around my cuttings and sprayed them occasionally with a hand mister. The last batches are now on the north side of my house in the shade because the greenhouse gets too hot on sunny days.
This nice potted cutting (Boogie Nites) was in rooting media from 5/1-5/20 and then was potted up into a larger container filled with good quality potting soil. I'm amazed at how fast the cuttings grow given optimal conditions, that's a 6 inch pot!
My greenhouse has shifted from pots of early potted tubers to pots of rooted cuttings.
Thanks everyone for your helpful tips and advice! My cutting season is almost done. I still plan to attempt a few tip cuttings from one-of-a-kind varieties that I planted straight out in the garden.
- Steve G.