Using a Rooting Hormone?

Dr. P. Allen Hammer

One question I get asked often: Should I use a rooting hormone in propagation? I’ve answered that question several times during the last poinsettia propagation season. And although my answer is always firm—use a rooting hormone powder for poinsettia propagation—growers often argue with me and are always very quick to point out greenhouses that don’t use a rooting hormone. I’m always intrigued with the question and the argument concerning the use of a rooting hormone, which certainly provides a discussion much larger than the simple, “Should I use a rooting hormone?” question. So why do I always say use a rooting hormone powder for poinsettia propagation?

Every detailed scientific study I’ve done with poinsettia cuttings has shown a significant increase in root numbers and uniformity of roots when a rooting hormone powder is applied to the cuttings. The increase is not large, but it’s always significant. And I also understand the argument of experimental significance and economic significance. I’ve argued that myself many times in the past. And I completely understand when a grower argues about the economic significance of the better rooting when compared to the added cost of applying the rooting hormone to the cuttings. 

The economic significance of using a rooting hormone powder in poinsettia propagation is extremely difficult to measure because it’s so hard to “see” a significant improvement in liner quality. With such a tiny improvement in liner quality, it’s very easy to simply decide the extra step is not worth the bother. 

However, back to the science … a rooting hormone treatment always increases the number of roots and uniformity of rooting, so I argue over time, poinsettia liners will always be better when treated with a rooting hormone. It’s certainly true that a rooting hormone treatment will at the very least increase the uniformity of liners over the propagation season. The question growers must answer is this: Does liner uniformity have any economic value? I argue that a subtle improvement in liner quality does also lead to an economic improvement.

An important question overlying the whole discussion of using or not using a rooting hormone is related to my strong feelings that greenhouse crop production and quality is all about the details. It’s certainly not a disaster if growers don’t use a rooting hormone, just like a lot of other greenhouse production decisions. I am, however, more and more convinced production quality is definitely related to the smallest of details, even if the specific economic significance of the specific decision can’t be readily measured. 

Growers have to be extremely careful in cutting corners to save production steps and production costs. Most often I see many of those seemingly small cost-cutting measures do in fact reduce plant quality. Cheating a few degrees on temperature, avoiding that PGR application, spacing just a little tighter are but a few examples of those seemingly small savings that I’m sure reduce plant quality.

This is also similar to discussions I’ve had with students over the years. With a little work, most students can earn a C grade. It requires a little more work to earn a B, but the A grade requires a lot of extra work for most students. And the question is always raised: Is all the extra work worth the effort for an A? I think you can easily figure out my answer—anything less than the best simply isn’t good enough.

So the rooting hormone question translates into another question: Are you okay with a C-grade poinsettia crop or are you aiming for an A-grade poinsettia crop? I know some will quickly argue that greenhouses are not getting enough return to grow the grade A poinsettia, which sounds a lot like the argument I’ve often heard from students. However, greenhouses that aim for the grade A crop will, over time, see an economic return in increased sales and reduced shrink.

Greenhouse production is about all the details. Consumers’ purchase of our plants is all about what the product looks like on the retail shelf. Anything less than the best hurts us all. GT


Dr. P. Allen Hammer is a retired professor of floriculture at Purdue University, West Lafayette, Indiana, and is now in product development and support for Dümmen USA.