Report from Spring Trials: Helichrysum and Vinca

August 9, 2002 - 09:33

Learn how to control these popular component plants, as well as which cultivars have the best landscape performance.

At the University of Florida trials, a section focuses on
some of the component plants often used in mixed containers. For 2002, we selected
Vinca major and Helichrysum. The idea was to come up with basic production
guidelines for these crops based on southern cultivation and also to evaluate
their field performance for landscape use. Both of these crops are vigorous in
production and often get too large before sale. We wanted to determine early
plant growth regulator treatments that would help keep them under control. We
also wanted to take a look at them under southern landscape conditions to see
what their true season was under the South’s high heat and humidity.

Helichrysum

Helichrysum comes from South Africa and is an old-fashioned
plant, recently overhauled and put into specialty annual production. There are
several forms on the market, but all have a felted leaf surface and usually a
rich gray color. The standard form, sold as Helichrysum petiolare, is the most
common, but there are variegated and lime green forms. A separate species with
smaller leaves and a more prostrate form is sold as mini or petite licorice.
All of these plants are great for combinations and work well with most mixed
basket recipes; however, in mixed containers, they may have a tendency to
outgrow other plants, so early PGR applications could be helpful.

Growers have several chemical options to control excessive
growth on Helichrysum. As an example from this year’s trials, we treated
Helichrysum with liner soaks and drenches to 4-inch material. We are learning
that if liners are treated before transplanting, growers save money on the
amount of chemical they use and gain control over early stretch. The liner
grows out of the liner root ball when transplanted, and the effects of the PGR
wear off. Liner soaks are a quick, easy and effective way to control growth.
The rates discussed in this article are for plants grown in Florida; other
growers should make adjustments according to their growing conditions.

Liner Soak.
Helichrysum White, Petite, Lemon and Splash liners (EuroAmerican Propagators)
were soaked in Bonzi dilution at 0, 2, 4, 8 and 16 ppm. Each root ball was
soaked for 30 seconds and planted into a 4-inch container on January 25. These
plants were fertilized every watering with 150 ppm of 20-10-20. Data and
pictures were taken at five weeks after planting.

The four Helichrysum varieties used in this trial responded
differently to the Bonzi liner soak. Helichrysum White responded well to the
2-ppm treatment and had reduced plant length of 42 percent, which produces a
salable, attractive plant. A higher rate of 8 ppm was effective control for
Helichrysum Petite and reduced plant length by 26 percent. Lemon and Splash are
much less vigorous; as a result, our lowest treatment of 2 ppm was still too
much chemical. The big message is know your cultivars — not all
Helichrysum need PGRs, and northern growers will use less chemical than
southern growers.

Bonzi Drench. We
evaluated Bonzi drench applied to 4-inch plants. Helichrysum
‘Licorice’ (Ball Floraplant) were planted on January 24 and
fertilized at every watering with 150 ppm of 20-10-20 fertilizer. The plants were
pinched one time at four weeks from planting and treated one week later on
March 1 with Bonzi drenches at 0, 1, 2, 4 and 8 ppm using two fluid ounces of
solution per pot. At time of treatment, plant size (average of width and
height) was measured at 3.5 inches. Final data was collected three weeks later.

Bonzi at 2 ppm gave the best results, and plant size was
held to 32 percent of untreated plants. After the 2-ppm drench, plants grew
four inches, showing that plant growth was slowed but did not stop. Higher
concentrations were too strong for quality production, and plants looked
stunted. A rate of 1 ppm might work well under cooler production situations.

Field trials. The
trial gardens are in full sun; soil was amended with mushroom compost and
mulched with cypress mulch. Plants were planted at one plant per one sq.
ft.  spacing and fertilized with
Osmocote 18-6-12 at six grams incorporated per plant.

‘White Licorice’ (EuroAmerican Propagators),
‘Licorice Vine’ (HMA) and Helichrysum Licorice (Ball Floraplant)
were trialed. All lines did equally and showed vigorous early season growth,
reaching 2 ft. high x 3  ft. wide.
For early season color, this form was excellent. However, as soon as summer
evening rains began in late June, all began to show signs of Botrytis and
insect damage.

‘Licorice Splash’ (EuroAmerican Propagators) and
‘Variegated Licorice’ (HMA) were the variegated forms evaluated,
and ‘Lime Licorice’ (HMA) and ‘Lemon Licorice’
(EuroAmerican Propagators) were the green forms trialed. All of these cultivars
did poorly in full sun and never achieved a good look. Green forms scorched,
and variegated forms showed reduced vigor, scorching, stunted growth and a
reversion to solid leaves as the season progressed. These plants needed a
little protection and probably would have done best in partly shaded plantings.

Several Helichrysum microphylla cultivars were trialed:
‘Mini Licorice’ (HMA) and ‘Petite Licorice’
(EuroAmerican). Again, not much difference between the two cultivars. Great
early season performance and strong color in the landscape although not as
bright as the larger-leaved forms. Both cultivars began flowering in June, and
this really detracts from appearance. Foliage problems set in with warm nights
and rains.

Vinca major

Vinca major is a challenging crop for three reasons: It
grows quickly and becomes tangled with other plants; it requires several
shearings to keep it under control; and long branches that hang over the pot
make shipping difficult. By using PGRs, growers can reduce stem length, which
can make for a higher-quality product.

Liner Soak. In our
spring trials, four cultivars — Vinca major ‘Expoflora’,
‘Variegata’ and ‘Maculata’ and Vinca minor
‘Illumination’ — were treated with a Bonzi liner soak. On
January 25, entire root balls of plugs were submerged for 30 seconds in 0, 1,
2, 4 and 8 ppm
Bonzi dilution.
The plants were potted into 4-inch pots and fertilized every watering with 150
ppm of 20-10-20. Data was collected after five weeks.

Variegata and Maculata were the most vigorous. A liner soak
of 2 ppm Bonzi reduced the cascade length by 23 percent compared to untreated
plants. Maculata required only 1 ppm of Bonzi to reduce elongation by 21
percent. At higher rates, Maculata appeared over-regulated. Illumination and
Expoflora do not require any plant growth regulators. Bonzi did not have any
effect on Illumination; the plants grew as though untreated, while Expoflora
appeared to develop at a manageable rate without treatment.

Vinca has a running habit, and as with many plants of this
type, using PGRs cannot control growth once stems begin to hang over the edge
of the pot. With all the varieties we trialed, once the branches were pointing
down, all bets were off on control.

Field trials.
Variegata (HMA & EuroAmerican Propagators), ‘Wojo’s Jem’
(Wojo’s Greenhouse), Maculata (HMA) and Expoflora (HMA) were the Vinca
majors trialed. We really didn’t expect Vinca major to do well in full
sun, but these cultivars surprised us by growing luxuriantly and quickly
covering their plots. Maculata, both lines of Variegata and Expoflora all
showed similar vigor and growth habit. Wojo’s Jem took almost twice as
long to cover its plot but was beautiful when it got there. None of the
cultivars flowered throughout the summer, and all have rated consistently high
marks throughout the season and were still impressive in late July.

The only Vinca minor trialed was Illumination (EuroAmerican
Propagators). Without comparison varieties, it’s a bit difficult to give
summaries, but we were unable to keep lower leaves on this plant even in our
greenhouse studies. The plant has a striking yellow variegation and is
distinctively different from the other Vinca in the trial. However, under full
sun in the landscape, all variegated leaves scorched, and there was some
reversion to solid green. This cultivar definitely needs shade in production
and you should avoid over watering, as it is not a vigorous plant under Florida
conditions.

About The Author

Rick Schoellhorn is assistant professor of horituculture and Erica Berghauer is a graduate student in the Department of Environmental Horticulture at the University of Florida. They can be reached by phone at (352) 392-1831 x364 or by E-mail at rksch@ufl.edu.

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