Reduce shrink

Features - Production

Try these culture scenarios to minimize product loss


In today's challenging economy, there's little tolerance for crop shrink. Shrink – the product losses that occur between planting and end user sales – is costly to bedding and pot-plant growers. Whether it's poor germination, pest damage or unacceptable quality, shrink means lost profits and decreased ability to meet retail demand.

Growers must manage shrink to profitably succeed at every step along the supply chain, from young plants to transportation to the retail bench. Adopting key cultural techniques and assessing costs, however, are two key ways growers can limit shrink at the greenhouse/nursery level.

Using PGRs
Unsightly and leggy plants are often left unsold during the shipping season. Product shrink associated with excessive growth is especially true when the window of sales is closed and plants cannot be rejuvenated. Cutting plants back is a method to revitalize a crop, but there is a downside – open wounds that facilitate disease, labor costs associated with trimming and the potential safety hazards with sharp objects like shears, scissors and mowers. Instead, growers can utilize plant growth regulators. PGRs do not reduce plant growth; they control it and are a valuable tool to minimize shrink.

Treating bedding plants with PGRs during production can result in greener, more compact plants on the sales floor. Using these chemicals also reduces post-production water demand and creates a stronger plant that minimizes damage caused by careless employee or consumer handling. Bonzi drenches, for example, can hold bedding plants prior to shipping if weather or inventory challenges arise in the greenhouse.

The scenario in the table represents drenching Bonzi on a bedding plant crop (1,000 trays, liter pots, 12 per tray) at market or staging drenches during periods of cold and wet weather to prevent stretch versus cutting a crop back.

Media costs with 5 percent shrink
5% of 756 is 37.8 filled pots; 37.8 pots x $1.75 = $66.15 in lost sales


Treating young plants with PGRs will maintain compact growth in high density trays and limit the incidence of poor establishment in finished containers. PGRs can be used in propagation or during the hardening off stage to prevent undesirable stretch if used cautiously and selected carefully. Propagators having difficulty with vigorous bedding plant species can fine-tune their approach with drench applications to trays of rooted cuttings through sub-irrigation, also called a liner soak or dip.

Liner dips can also eliminate the PGR treatment in finished containers, thus reducing the amount of PGR coverage and labor to treat plants. For example, a University of Florida researcher conducted a liner dip treatment with paclobutrazol at 3 ppm to a 72-cell tray of Salvia gauranitica. The total cost of the dip solution was $0.38 ($0.005 per pot), while a comparable foliar spray concentration of daminozide at 5,000 ppm was applied to only 10 plants with a cost of $0.15 ($0.015 per pot). Not only was the liner dip treatment less expensive, but the grower could re-use the dip solution to treat four more trays at a total cost of $0.001 per pot.

Growing Media
The limestone addition rate in a growing medium can make all the difference in nutrient availability, plant performance and fertilizer selection. Limestone is used to adjust growing medium pH. A growing media pH value outside of the optimal range can cause nutrient deficiency or toxicity problems. The general pH range for greenhouse crops is 5.4 to 6.8, but maintaining the pH between 5.6 to 6.2 is recommended. Poor uptake of nutrients, particularly boron, copper, iron, manganese and zinc, can occur if the pH of a substrate is above 6.5.

Iron-inefficient plants like petunia and calibrachoa can develop interveinal chlorosis on the young foliage if the media pH is too high. Producing these crops in a growing medium that has a lower lime charge than the standard rate (typically five to seven pounds of limestone per cubic yard) can eliminate the need of excessive acidic fertilizers or acid injection.

In the example below, a grower can experience a cost savings of $0.27 with a limestone reduction from six to three pounds per cubic yard.

High pH-requiring (6.0 to 6.6) crops like marigolds and geraniums can develop micronutrient toxicity symptoms if the pH is driven too low. Growing these crops in a higher lime-containing soil can prevent the use of supplemental limestone treatments to minimize the incidence of magnesium deficiency and manganese/iron toxicity.

Growing media can be a large component of a grower's production costs. Poor-quality raw materials and improper on-site mixing procedures may result in decreased plant quality and, ultimately, an increase in shrink. The growing medium must be formulated with desirable physical and chemical properties and must be properly handled to avoid compaction. The information presented in the table is primarily directed toward growers who have their own mixing facilities and the potential costs of media-related problems.

Components of the media can cause crop shrink if the potting mix is improperly irrigated. Media containing rice hulls can present issues to growers using this blend for the first time. Rice hulls tend to migrate to the upper strata of the soil column and may appear as a mulch, thus drying out on the top surface while remaining moist 1 to 2 inches below the soil surface.

Hand irrigating rice hull-containing media with unnecessary applications of forced downward water pressure can cause bridging of the hulls and compaction resulting in a tighter mix. It may be best to train irrigators how to properly water rice hull-containing media with some perlite included in the formulation. Irrigation practices should improve as the grower becomes accustomed to the blend.

Media costs with 10 percent discount.
$0.18 discount per pot x 756 pots per cubic yard = $136.08 in sales lost to discounting

Media costs with additional production time. $0.20 x $0.45 sq ft = $0.09 per pot; $0.09 x 756 pots per cubic yard of soil = $68.04 extra bench time cost per cubic yard of soil.

High EC in the irrigation water (result of elevated levels of sodium, chloride and/or bicarbonates) can cause plants to turn chlorotic and lead to poor growth. High chlorides can increase the water EC to above 0.5 mS/cm and growers should reduce the fertility (nitrogen concentration) to keep the growing medium EC within an acceptable range. This approach also reduces the cost of fertilizer used.

Wetting agents and polymers incorporated into the growing media can reduce the incidence of production shrink and reduce the amount of labor cost dedicated to irrigation. Wetting agents can better distribute moisture in the container, thus creating uniform wetting of the mix for proper root health and nutrient uptake. They can also be applied before shipping to improve post-harvest soil water uniformity and minimize extreme wilting. Extreme wilting can lead to crop shrink, increased maintenance or longer crop time on the bench. See crop loss scenarios for impacts on cost of production.

Media costs with additional maintenance labor.
$9/hr = $0.15 per minute of labor per pot; $0.15 x 756 pots per cubic yard is = $113.40 extra labor cost per cubic yard of soil


Improper monitoring and management of media pH and EC can result in poor quality crops. It has been estimated that proper monitoring of pH and EC can eliminate 90 percent of the nutritional problems. A non-destructive, on-site technique to measure crop pH and EC is the PourThru method – displacement of the rhizosphere solution by applying a known volume of water to the top of the soil column. The resulting leachate is then collected from the bottom of the container and tested.

The PourThru program is designed for growers to monitor and manage crops. It involves three parts: a simple technique for measuring pH and electrical conductivity (EC), charts for recording pH and EC values, and recommended ranges and procedures for maintaining substrate pH and EC.

PourThru steps, water volumes to add, charts for recording pH and EC values, interpretation values, and corrective procedures are all listed at the Floriculture Information Center ( Click on the topic: PourThru.

Testing may show the need to change the fertility program in order to minimize shrink. Specialty fertilizers can be applied to correct deficiencies and help in pH management. It is important to treat the plants before problems occur because moderate to severe leaf damage cannot be reversed. Fertilizer tools such as epsom salts and chelated iron can be used to improve soil/tissue nutrient content.

With minimal input costs, growers can minimize production shrink practically and affordably. Having a PGR toolbox to manage growth, adjusting lime rate of the growing medium and applying supplemental fertilizers are just some of the crop shrink mitigation activities for the greenhouse environment.


Bob Steinkamp and Michael Tilley are technical services representatives, Jamie Gibson is director of research and development, and Hugh Poole is director of technical services at Fafard;