Sunday, March 2, 2008

Greenhouse - Growth Regulators and Mixed Containers

Mixed containers are one of the most popular and profitable greenhouse items for growers. However, controlling growth so one plant type does not overwhelm another can be challenging. The following is an article on the subject from the New England Greenhouse Update site.

Another complicated situation in spring is how does one handle growth when different species are mixed in the same container. Again the grower faces two complicated situations (1) plants in the same container have widely different vigor and require different PGR control and (2) the growth regulation objectives vary for plants in the same container. . For example in the first case we may have a dwarf banana or naturally dwarf angelonia that requires no PGR control in the center of a container surrounded by an extremely vigorous petunia cultivar that requires aggressive PGR control. In the second case, we may want to increase branching on an ornamental millet plant in the center of the mixed container but also control vigor of sweet potato vines planted along the margins.

In both of these cases it is obvious that we can’t apply single PGR treatment to the mixed container and achieve the desired result. The solution requires that we treat individual plants in the mixed container without affecting the others in the same planting.

To control growth of the most vigorous varieties or species without affecting the less vigorous plants, the best option is to pre-treat the transplants as needed. A ‘plug dip’ is a useful technique for this purpose. Here the plug flat is set in a tray of PGR solution and the rooting medium of the plugs is allowed to soak up the growth regulator. Allow the plug flat to sit in the solution for at least 5 minutes, some growers will allow 30 minutes but the plug root volume should reach saturation before that much time. After soaking allow the plug sheet to sit on the bench overnight before transplanting into the final container. Only root-active PGRs such as A-Rest, Topflor, Bonzi and Sumagic (and their generic equivalents) can be used for this purpose. These chemicals can remain active in the root zone for months, and they tend not to migrate far from the treated soil. Therefore, control is conveyed to just the individually treated plugs and not the other plants in the mixed containers. For rates, use Bonzi at between 4-16 ppm, use Sumagic at 2-8 ppm, for Topflor use 3-12 ppm. If you have not tried this before, start with rates in the lower half of the recommended range.

With groups of plants that have different growth regulator requirements such as increased branching associated with Florel versus height control associated with growth retardants, the option again is to treat the plants separately. Here you can go two ways. Transplant the plants that require Florel into the final container & spray, and then fill in with plugs of the vigorous species that have already been treated with a root-active PGR as previously described. Alternatively, the container can be planted with the treated plugs, leaving a space for the Florel requiring plants. Grow the plants that require Florel in small containers (e.g. 4-6”pot) until the treatment schedule is complete and then drop them into the empty space. Growers will often plant an empty pot to facility the late transplant with minimal disruption to the other plants growing the mixed container.

Article by Rich McAvoy, University of Connecticut. For more information and the original article go to

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