# Paclobutrazole (Bonzi) PGR for shrubs



## Darrell (Mar 22, 2018)

I'm interested in using a PGR next year on my Indian Hawthorne, loropetalum, and roses. Paclobutrazole is intriguing because, from what I've read, it can regulate plant height, shorten internode distance, deepen the green color, increase blooms by diverting energy from linear growth to flower production, and it is an antifungal.

Has anyone here used it for shrubs and ornamentals? It's quite pricey, but all PGRs are; I don't know how the price compares with other anti-GA PGRs.


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## Ecks from Tex (Apr 26, 2018)

I wouldn't spend my money on paclobutrazole for woody ornamentals. Bonzi is actually intended to be a drench application for nursery plants, although it can be a spray (if sprayed, it must hit the stem).

I've seen you asking questions about shrub PGRs before, so my advice to you as a novice is that this is nothing like applying stuff to the lawn - it's an art and requires trial and error. Do not dive in; dip your toes and wade around for a minute first. Trust me. You won't kill anything, but you'll buy stuff you don't need. And it is crazy expensive for the homeowner.

I suggest you try flurprimidol in granular form - Cutless .33G. It's about $180 for a bag that will last you a long time. Flurprimidol is in a separate chemical class from paclo but it has similar chemical characteristics. It will do everything you are looking for and, if timed appropriately, will not screw up your flowering blooms in the slightest. In fact, it will keep azaleas (which bloom only 1 time per year in most species) from blooming at staggered intervals and force them to bloom uniformly.

I have sprayed Atrimmec to my indian hawthornes recently and they look fine, growth has regulated well and the foliage is dark green. But that was because I had run out of Cutless. Cutless would have done the same thing except better.

Cutless is much more user friendly and will not overcomplicate this process for you. Try it, and then if you want to start experimenting on your annual plants, come back and let's talk turkey.

If you're dead set on going all in, then you will probably have to tank mix to get optimal results. Those specialty nursery PGRs are not meant to do everything we as homeowners require. They are meant to regulate certain types of plants so that they can be sold to the consumer before bloom, etc. But if you tank mix piccolo + configure, you might be able to get what you wanted. That's about 3X the cost of Cutless, and application is complicated.


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## Darrell (Mar 22, 2018)

Thanks, Ecks.

I appreciate the advice. That's why I'm tossing around thoughts now, anticipating next spring.

There are many challenges. I don't want to waste a lot of money, and that would be easy to do given the price of these products. Another challenge is that I have plants I want to regulate immediately adjacent to those I don't. Ex., my Indian Hawthornes have annuals planted around them (violas fall to spring, impatiens spring through summer). My loropetalums are adjacent to a young oak leaf hydrangea and garden phlox.

In my mind it makes sense that a foliar app would allow a more focused applicatio than a granular. Neither do I mind using a "weaker" pgr requiring reapplication to a once-and-done product.

I much prefer science to art, but I do understand the trial and error involved here. Given the challenges above, how would you use Cutless in my landscape?

Side question, if you don't mind - do you and @Greendoc have science backgrounds? The generic names of these products seem to easily roll off your tongue/keyboard. I'm impressed!


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## Darrell (Mar 22, 2018)

@Ecks from Tex , I just found this re: Cutless for Indian Hawthorne and loropetalum.

http://www.lsuagcenter.com/portals/communications/publications/agmag/archive/2012/winter/usingplantgrowthregulators-inthelandscape

Thanks for prodding me in this direction.


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## Ecks from Tex (Apr 26, 2018)

I have zero science background I'm a paper pushing lawyer who has been learning and using plant growth regulators in the landscaping for awhile but is still learning more every day. Greendoc is a licensed applicator and I think has specific schooling/degree related to this field, he knows his shit.

One point - the most effective growth regulation is from the root system, not foliar. When you apply foilar, a GI inhibitor has to travel through the plant down into the root system to effectively regulate growth as intended. When you apply a chemical pincher through foliar, it stays in the leaf and "pinches" new growth. That's the only exception to the rule that root regulation is better. That is why Cutless is so effective, it goes on the ground and gets watered in.

Your comment about annuals nearby the indian hawthorwn is somewhat of a concern. I would be cautious there. But a foliar spray will just as easily get drift on the annuals as well, so you are going to have problems to contend with regardless.

If you could apply growth regulator early spring, and then plant annuals mid-spring, that might be a way to avoid problems. But Cutless is going to require more applications for some plants.


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## Darrell (Mar 22, 2018)

Ecks from Tex said:


> If you could apply growth regulator early spring, and then plant annuals mid-spring, that might be a way to avoid problems. But Cutless is going to require more applications for some plants.


This is a brilliant idea.


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