James L. Gibson, Todd J.
Cavins, and Lane Greer
NCSU Floriculture Research
is late May, you have just sold the majority of your second turn, and
your third turn is in flower and ready for June sales. By now, like all
greenhouse growers, the muscles are a little sore and you are finding
it hard to get up in the morning. You feel good about spring sales and
are ready for a break. The third turn has been on display for about a
week and you begin to observe customers selecting only the finest material
from flats of bedding plants. You yourself are beginning to see why
they’re being so selective. The lower leaves are turning yellow, the plants
are slightly stretched, and the flowers are spent. What you are experiencing
is what many other growers encounter every year– improper management of
plant nutrition in the retail setting.
establish a fertility program in the garden center or retail location?
Plants continue to grow in retail
environments, thus demand nutrients. But, remember that managing nutrition
may include ceasing, reducing,
continuing, or increasing fertility. Monitoring your crops’ nutrition
is a crucial part of
managing it. Other reasons for establishing a fertility management program
- It maintains healthy crops
throughout the marketing period.
- Foliage color is retained
and more flowers are produced.
- Quality plants boost sales,
which means increased revenues.
- Knowing how to manage
fertilization increases your awareness of species’ requirements.
- It’s environmentally conscious.
you are recognized as being a reputable establishment, then you have created
a niche for yourself.
You are the retailer who has healthy material in the summertime, and not
just during the busy weekends of
Mother’s Day and Memorial Day! The ultimate advantage you have over large
garden centers or mass-market
chains is that you still have total control over the crop’s nutrient regime.
You know how the crop
was fertilized from potting to market date. This knowledge is beneficial
for maintaining healthy
plants that sell quickly.
is important to remember that fertilizers are not medicine. Overcoming
deficiencies, especially in the retail area, will take longer because
nutrient uptake is not rapid in the post-production stage. More importantly,
monitoring the crops’ pH and electrical conductivity (EC) so that deficiencies
never occur should be common practice.
By maintaining the proper pH and EC, many
nutritional problems can be avoided. The pH directly influences nutrient
availability. The general pH range for most floriculture crops is 5.4
to 6.8, but maintaining the pH between 5.6 and 6.2 is recommended.
Electrical conductivity measures soluble
salts, all of the dissolved salts in the substrate solution. Some salts
provide nutrients while others are not essential for plants and may interfere
with plant growth. Refer to Tables 1a,
b, and c
for pH and EC ranges for popular floriculture crops in the post-production
You may be concerned with fluctuations in
sales that may sometimes lead to cutting back plants or manipulating the
environment constantly. Both actions require a tremendous amount of labor.
Knowing the pH and EC values of a crop can help determine the amount of
fertilizer to apply while preventing damage to plants. Maintaining compact
growth while avoiding nutrient deficiencies should be relatively easy
by simply monitoring the substrate EC levels. In most cases, conducting
one analysis one to two weeks after displaying the crops will provide
pH and EC values to direct nutrient management decisions.
The most practical means of attaining
pH and EC values is by using the PourThru method, a substrate analysis
technique that retail growers can use to make on-site decisions about
the nutrient status of the crop. The technique involves pouring a known
volume of distilled water over a containerized substrate in order to attain
50 mL or about 1.5 ounces out of the mix for nutrient analysis. It is
a sound and credible technique that requires little economic input or
time. The steps to achieving a representative pH and EC value for a crop
in the post-production stage are as follows:
1. Because a once weekly fertilization is the recommended practice in
the retail sales area, sample 2 to 3 days after fertigation. If clear
water only is being applied to a crop on the sales bench, sample on the
day of irrigation.
2. Sample from at least 5 pots or bedding plant packs.
3. One hour after irrigation place saucers under the pots, or if bedding
plant flats are being tested, one cell pack is required from the flat.
4. Pour the published volume (Table
2) of water onto the surface of the pot to achieve uniform coverage.
5. Collect 1.5 ounces or 50 mL of leachate and sample with a pH and EC
6. Record and plot values for specific crops and make adjustments in the
fertilization program as needed. Refer to Tables 1a, b, and c for specific
PourThru pH and EC values for specific crops.
Table 1a. Post-production
fertilization strategies for moderate
to heavy feeding bedding and pot crops.
Table 1b. Post-production fertilization
strategies for medium feeding
bedding and pot crops.
Table 1c. Post-production fertilization
strategies for light feeding
bedding and pot crops.
detailed information about the PourThru method visit www.pourthruinfo.com.
Principles behind pH and EC and information about pH and EC meters can
also be found at this site. The PourThru manual, with detailed information
on procedures, pH, EC, and other nutrient parameters is available for
$15.00 from www.nccfga.org.
has been suggested that for most floricultural crops at visible flower
bud, fertilization be discontinued or reduced significantly because plants
require less nutrients. However, when the crop is marketed, nutrients
should still be applied at an appropriate level. Many growers apply liquid
fertilizer with a constant liquid feed program, and reduce the rate by
half when the plant begins to show flower buds. Another method is a once
weekly fertilizer application to continue a nutrient charge in the substrate.
Keep in mind that root development may be
significant in the retail setting if pathogen infection and high EC levels
have not damaged the root system. Water demand will be great, especially
in late spring/early summer, and irrigation may be required daily in the
retail setting if temperatures and light intensity are high. Therefore,
multiple fertilizations each week may be required for crops, especially
vigorous growing plants like petunias and combination plantings of vegetative
Fertilization Research and References
plants with a boost of highly concentrated fertilizer before marketing
can severely affect quality. Applying too high of a rate can cause undesired
growth which will lead to leggy plants or cause too high of an EC level
which may damage plant roots. Although growth still occurs, nutrients
are required only in minimal amounts to keep plants healthy and toned.
A low phosphorus/ammoniacal-nitrogen fertilizer
should be used in the retail setting. High levels of phosphorus have been
shown to increase stem elongation, and ammoniacal-nitrogen causes lush
growth with less flowering. Use fertilizers like 13-2-13,
in the retail sales area weekly at concentrations of 50 to 100 ppm N.
Release Fertilizers-Best Management Practices
the cost of slow release fertilizers is too high to incorporate into bedding
plant substrates. Further, nutrients can be released quickly due to high
temperatures, which may introduce undesired levels of ammoniacal-nitrogen
in the substrate, a causal agent of lush and leggy growth. The lack of
ability to control the release rate is a deterrent to some growers.
A liquid fertilizer program is popular amongst
many retail growers due to cost and ability to control fertilization rates.
However, if you decide to use a slow release fertilizer, use a fertilizer
that contains both ammonium and nitrate, such as Osmocote
Also keep in mind the release period. Most plants only need a temporary
fertilizer boost before being transplanted into ground beds (usually just
a one or two week time period). With this in mind, an 8-9 month release
pattern is not very practical. Check with your fertilizer suppliers about
the release pattern. Several companies are beginning to offer "custom"
release patterns that may better suit your retail conditions.
the post-production stage there usually are 6 to 7 common nutrient disorders
that can occur when the pH or EC is too high or low. Refer to Table
4 for corrective procedures of pH, EC, and nutritional problems. (1)
Iron deficiency (interveinal chlorosis of the upper growth) can occur
when the pH rises above 6.6. (2) In contrast,
iron and manganese toxicity can occur when the pH is too low(<5.5).
Low salts can result from too many clear
water irrigations in the retail sales area. Deficiencies like (3)
nitrogen (lower leaf yellowing), (4) phosphorus
(lower leaf purpling), (5) potassium (lower
leaf marginal chlorosis), and (6) magnesium
(lower leaf interveinal chlorosis) deficiencies are common when PourThru
EC values are below 0.5 mS/cm.
calcium demand is less in the post-production stage when plants are at
their mature stage (less cell division and elongation), calcium in the
irrigation water should be adequate. However, the demand for calcium will
increase if plants are cut back because of stretchy growth in the retail
sales area and a new plant canopy is forming.
Micronutrients like boron, copper, manganese,
and zinc are generally provided by the breakdown of organic substrate
components or from the irrigation water. One application of a complete
fertilizer like 20-10-20 should provide sufficient micronutrients until
plants are planted in garden soils. However, deficiencies may occur if
the pH is > 6.5. Detailed information pertaining to nutrient disorders
is available on www.floricultureinfo.com. In addition, color photo cards
with pictures of and corrective procedures for nutrient disorders are
available at www.nccfga.org.
Factors Affect Plant Quality
nutrition plays a major role in how plants appear in the retail setting,
several other external
factors contribute to plant quality in the post-production stage. Because
this article mainly focuses
on nutrient effects on plant quality, these factors will not be discussed
extensively, but don’t
- Irrigation—Water should
be reduced at the visible bud stage, and the growing substrate should
be allowed to dry
- Light—Levels should be
reduced in the retail setting. Provide shade to plants when temperatures
are greater than or
equal to 68°F. Tiered shelving is highly recommended in the display
area as the bottom and top shelves will receive
similar light levels.
- Temperature—It has been
suggested to reduce temperatures by 5 to 8°F during the post-production
stage. Lowering temperatures
will also enhance flower color.
- Ventilation—Maintain airflow
in the retail setting to avoid disease and air pollutant accumulation.
- Substrate Selection and
Container Size—Select a mix that provides proper aeration and good water
Large containers (greater than packs) will help reduce the frequency
- Propagation and Potting
Times—Late season production should be kept to a minimum because it
may lead to discarding
final product due to slower sales, even if plants are looking their
best in the retail area.
Growth Retardants (PGRs) —PGRs will keep plants more compact in
the sales area. They also reduce
water demand, and may enhance foliage color.
- Employee Competence and
Education—Train employees to handle plants responsibly.
is just one component of plant production that affects flower and foliage
longevity. Cultural factors including production temperature, irrigation,
light, substrate, and container size affect post-production longevity.
If these factors are ideal for plant growth then fertilization is not
a large issue, but the reality is many retail environments are not perfect.
Maintaining proper pH and EC values for specific crops is one of the best
management tools you can use. Fertilizing at the appropriate growth stage,
along with applying the right rate and concentration of nutrients, prolongs
the visual quality of plants and will establish you as a producer of quality
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