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J. Raymond Kessler, Jr. and Gary
J. Keever
Coreopsis
verticillata ‘Moonbeam’
is a herbaceous perennial, which blooms in late spring to early
summer. It has no vernalization requirement, but an obligate
requirement for long photoperiods (>14 hours or night-break
lighting) to flower. Because vegetative growth and flowering
can be controlled using photoperiod, it may be possible to develop
the plant as a greenhouse pot crop. However, Coreopsis
may grow too tall in small containers under greenhouse conditions
for market acceptance, and therefore may benefit from plant growth
retardants. This study was conducted to determine the plant growth
retardant type, application method, and rate required to produce
a marketable greenhouse pot plant of Coreopsis verticillata
‘Moonbeam’ in 4-inch pots.
METHODS
Terminal cuttings ( 2.5
inches long) of Coreopsis verticillata ‘Moonbeam’
were removed from vegetative plants and stuck in 72-celled flats
containing Fafard Germinating Mix. Cuttings were rooted using
intermittent mist in a shaded glass greenhouse under natural
short photoperiods with 85oF bottom heat. Rooted cuttings
were removed from mist after 27 days and placed in an unshaded
glass greenhouse with a heat set point temperature of 65oF
and ventilation at 78oF. All cuttings received a soft
terminal pinch 2 days after removal from propagation. Cuttings
were transplanted to 4-inch square pots containing Sunshine Mix
1 19 days after pinching, and initially placed pot-to-pot on
a greenhouse bench. Fertilization throughout the experiment was
applied as a constant liquid feed consisting of 150 ppm nitrogen
using a 20-10-20 with one clear water application per week to
prevent soluble salts buildup. Plants were watered/fertilized
when the medium appeared dry, but before plants wilted. All cuttings
were sheared to 2.5 inches above the pot rim 13 days after transplanting.
Plant growth retardant treatments were applied 10 days after
shearing. Long photoperiods were started the same day by lighting
plants from 10:00 p.m. to 2:00 a.m. using a minimum of 10 foot-candles
from incandescent lamps (60 watt). Growth retardant treatments
consisted of A-Rest drench at 0, 0.125, 0.25, or 0.375 mg a.i./pot;
Bonzi drench at 0, 0.125, 0.25, or 0.375 mg a.i./pot; B-Nine
spray at 0, 2,550, 5,100, or 7,650 ppm; Bonzi spray at 0, 12,
24, 36, 48, or 60 ppm; Cutless spray at 0, 25, 50, 75, 100, 150,
or 200 ppm; or Royal Slo-Gro spray at 0, 360, 720, 1,080, 1,440,
or 1,800 ppm. Foliar spray solutions were applied at a rate of
0.5 gallon per 100 square feet using a pressurized CO2
sprayer calibrated at 20 psi. Soil drench solutions were applied
at 2 fluid ounces per pot. After treatment, plants were spaced
on 8-inch centers. Data recorded at the time of first open flower
was flower date, shoot height, growth index [(height + width1
+ width2)/3 where width1 is at the widest point, and width2 is
perpendicular to width1], market quality rating (1=very poor,
unsalable; 2=poor, unsalable; 3=average, salable; 4=good, salable;
5=excellent, salable), and length of the five longest lateral
shoots.
RESULTS
All growth retardants resulted in decreased shoot height, growth
index, and lateral shoot length with increasing concentration
except for Bonzi and Royal Slo-Gro sprays (see table). The highest
rate of A-Rest and Bonzi drench, B-Nine, and Cutless decreased
shoot height compared to untreated plants by 36%, 30%, 21%, and
36%, respectively. Bonzi spray did not affect shoot height, growth
index, or lateral shoot length while the highest rate of Royal
Slo-Gro increased shoot height by 30% and lateral shoot length
by 19% compared to untreated plants, but had no effect on growth
index. A market quality rating of 4.0 or higher (good, salable)
was given to plants treated with B-Nine at 5,100 or 7,650 ppm
or Cutless at 150 or 200 ppm. Plants given a Bonzi drench received
poor market quality ratings despite plant size reductions similar
to those treatments receiving average or good ratings because
of distorted lateral shoots with an unacceptable increase in
branch angle. The highest rate of B-Nine and Royal Slo-Gro delayed
flowering by an average of 5 and 16 days, respectively, compared
to untreated plants. The increase in shoot height and lateral
shoot length with increasing concentration of Royal Slo-Gro was
possibly due to delayed flowering resulting in more time for
vegetative growth.
|
Response of Coreopsis verticillata ‘Moonbeam’
to Drench Application of A-Rest or Bonzi or Spray Application
of B-Nine, Bonzi, Cutless, or Royal Slo-Gro |
Growth
retardant |
Rate |
Shoot
height (cm)1 |
Growth index2 |
Lateral shoot length (cm)1 |
Quality rating3 |
Days to flower |
|
|
Drench (mg a.i. per pot) |
|
A-Rest |
0 |
35.1 |
43.7 |
34.3 |
2.0 |
33 |
|
|
0.125 |
27.8 |
71.6 |
27.9 |
2.0 |
33 |
|
|
0.250 |
26.1 |
37.1 |
23.5 |
2.6 |
32 |
|
|
0.375 |
22.4 |
31.0 |
19.7 |
3.1 |
33 |
|
Bonzi |
0 |
34.4 |
48.1 |
34.4 |
2.0 |
33 |
|
|
0.125 |
27.6 |
45.3 |
31.1 |
2.0 |
33 |
|
|
0.250 |
24.9 |
40.4 |
29.4 |
2.0 |
33 |
|
|
0.375 |
24.0 |
38.9 |
26.9 |
2.0 |
33 |
|
|
Spray (ppm) |
|
B-Nine |
0 |
32.7 |
43.7 |
30.5 |
2.0 |
34 |
|
|
2550 |
28.2 |
33.6 |
23.3 |
3.4 |
37 |
|
|
5100 |
25.9 |
29.4 |
20.6 |
4.1 |
37 |
|
|
7650 |
25.9 |
29.0 |
20.4 |
4.1 |
40 |
|
Bonzi |
0 |
33.0 |
46.1 |
33.1 |
2.0 |
33 |
|
|
12 |
33.9 |
45.0 |
30.6 |
2.0 |
31 |
|
|
24 |
33.6 |
45.7 |
30.3 |
2.0 |
32 |
|
|
36 |
33.8 |
47.0 |
32.3 |
1.9 |
32 |
|
|
48 |
30.7 |
45.7 |
32.3 |
2.0 |
33 |
|
|
60 |
30.4 |
43.7 |
31.1 |
2.0 |
32 |
|
Cutless |
0 |
33.9 |
48.0 |
33.4 |
2.0 |
33 |
|
|
25 |
30.7 |
41.5 |
30.0 |
2.1 |
33 |
|
|
50 |
27.9 |
38.1 |
24.1 |
2.3 |
32 |
|
|
75 |
25.9 |
32.1 |
20.8 |
3.0 |
32 |
|
|
100 |
23.8 |
31.5 |
20.6 |
3.4 |
32 |
|
|
150 |
23.3 |
31.7 |
20.5 |
4.0 |
32 |
|
|
200 |
21.7 |
29.7 |
16.8 |
4.1 |
32 |
|
Royal Slo-Gro |
0 |
33.7 |
46.8 |
34.0 |
2.0 |
32 |
|
|
360 |
39.2 |
44.0 |
34.3 |
2.0 |
42 |
|
|
720 |
40.1 |
43.7 |
37.1 |
2.0 |
45 |
|
|
1080 |
42.3 |
45.6 |
39.6 |
2.0 |
45 |
|
|
1440 |
42.2 |
44.2 |
39.2 |
2.0 |
47 |
|
|
1800 |
43.7 |
44.0 |
40.4 |
2.0 |
48 |
1 English conversion 2.54
cm = 1 inch.
2 Growth index = (height + width1 + width2)/3 in centimeters.
Width1 is at the widest point, and width2 is perpendicular to
width1.
3 Quality rating: 1=very poor, unsalable; 2=poor,
unsalable; 3=average, salable; 4=good, salable; 5=excellent,
salable. |
When applied as a foliar spray, both B-Nine
and Cutless resulted in acceptable market quality plants of Coreopsis
verticillata ‘Moonbeam’ when grown in 4-inch pots
in the greenhouse. However, Cutless is not currently labeled
for application to ornamentals. B-Nine was equally effective
when applied at 5,100 or 7,650 ppm. However, the former concentration
may be a better choice because it resulted in less flower delay
(3 days compared to 5 days).
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