Cut snapdragon (Antirrhinum
majus) production has been on the rise in the US. Growers are
finding that cut flowers can increase cash flow during periods of low
bedding/pot plant sales and in some cases, provide full-time work for
their employees. Many growers believe that the traditional, ground bed
method (Fig. 1) produce the highest quality
snaps. A few growers have grown snaps in raised benches (Fig. 2) . Growers are looking new ways to make
their growing facilities work harder in today's highly competitive
market. This study explored the potential for using the greenhouse
gravel or cement floor for different and more profitable crops.
Practicality and economical feasibility were important criteria in the
study which evaluated the quality of snapdragons grown in trays (Fig. 3) versus those grown in ground beds and
aimed at identifying any differences in quality due to tray size.
How we grew the plants
Five snapdragon crops were grown in a commercial glass covered
greenhouse located in Columbus, Ohio. Plants were grown in a single
ground bed. The experiment had five treatments. Treatment one
consisted of plants grown in small trays (16" x 12" x 3") on top of the
ground bed. Treatment two consisted of small trays that rested on top
of a turned-over tray. This upside-down tray served as a barrier to
the ground bed so that roots could not grow through the bottom of the
tray into the ground bed. Treatment three consisted of snapdragons
grown in larger trays (19.5" x 13.8" x 3.7") laid directly on top of the
ground bed. In treatment four, plants were grown in large trays
resting on top of a turned-over tray. Treatment five consisted of
snapdragons grown directly in the ground-bed and served as a control for
the experiment since this has traditionally been the most commonly used
method of production. Both small and large trays were used to observe
any differences among snapdragons due to increased medium volume and
depth. While the large trays were only 0.6" deeper, their volume was
approximately 60% larger than the small ones. The in-ground bed plots
were of equal size (area) as the small trays.
Five different plantings were conducted over 1.5 years, and three
snapdragon cultivars (Potomac Pink, Potomac Light Pink, and Winter
White) appropriate for the particular time of year when the plantings
took place were studied in the experiment. Common snapdragon cultural
practices were used.
Plugs were planted in trays using a soil-less medium (LC1; Sun Gro
Horticulture, Inc). The ground bed medium consisted of a combination of
soil, peat moss, bark, styrofoam, and haydite. This medium was
pasteurized by the commercial grower after two or three plantings,
depending on observed disease levels.
An irrigation system consisting of three separate watering lines (Fig. 4) was developed for this experiment to
satisfy the specific needs of treatments: one line was used to water
small trays, a second line watered the large trays, and a the third
watered the ground-bed-grown snapdragons and were adapted to meet the
watering needs of the individual trays.
Plants received a liquid fertilizer of 15-16-17 at a 250 ppm N
concentration as a starter fertilizer. The finishing fertilizer
contained 15-5-15 also at a concentration of 250 ppm N. Due to a more
frequent watering schedule during the summer months, fertilization was
usually applied every other watering. However, the longer intervals
between watering during the cooler months required fertilization each
time.
Plants were supported by three levels of wire mesh. Temperatures
throughout the experiment ranged from 50 degrees F nights to 64 degrees F days in the
winter months, to 70 degrees F nights to 100 degrees F days in the summer months.
Stem length, flower spike length, stem diameter at the top, middle,
and bottom of the stem, and dry weights of the spike, stem, and leaves
from sample plants were measured. Dry weights of the flower spike,
leaves, and stem were measured after these parts had dried for 72 h at
135 degrees F. The flowering shoots were graded according to standards used by
the commercial grower, which are a modified version of the Society of
American Florists' (SAF) standards.
What results did we get?
- We found that the quality of flowering shoots from snapdragon
plants grown in small or large trays was not significantly different
from plants grown in ground beds.
- For all but one planting, there were no significant differences
between the snapdragons grown in ground beds and those grown in trays on
the ground.
- Tray size did not have an effect on snapdragon quality in these
experiments.
- Very few roots were observed growing into the ground in the
on-ground treatments
- Flowering shoot stem diameter did not differ from the on-ground
tray plants. Flower spike length, and days from planting to harvest
were not affected by growing method.
As an example, we are showing in Fig. 5 and Fig. 6 results of shoot dry weight and shoot
length (two important characteristics of flower quality) for the
cultivar Potomac Pink.
What does it mean?
Although tray or container production has been used by some
snapdragon growers, this is to the best of our knowledge, the first
research report comparing container with ground bed production.
Snapdragon quality from plants grown in flats on the ground can be of
similar to those grown in ground-beds. Snapdragons raised in trays
(separated from the ground) also produced salable flowering shoots but
of lower quality than those from trays located on the ground. The
reason for the quality difference will need to be explored in future
work. We speculate that higher growing mix temperatures and faster
drying of the growing mix in raised containers may be the cause. It is
very important to minimize water stress when growing snaps in flats!
Growers may want to try this alternative method of snapdragon
production because a trays can be quickly removed from the greenhouse
floor after snap harvest and a new container crop (e.g., bedding plants)
can be promptly moved in. This gives growers more flexibility with their
annual crop schedule. You may ask: How about support for the flowering
stems? Yes, it is very important but our experience is that growers who
are using this method have very light support systems that can be
removed easily from the greenhouse before a new crop is moved
in.
