The benefits of CRF in greenhouses

Greenhouse growers are working harder than ever to keep their businesses profitable. This ongoing quest has caused many growers to scrutinize their production systems, looking for ways to save money on materials and labor. Recent university and grower trials have shown that a change in fertilizer practices can give growers a chance to significantly cut costs, produce higher quality crops and be more environmentally friendly.

Adapting to greenhouse use

Applied at the beginning of a crop cycle, controlled release fertilizers (CRFs) are coated fertilizers that deliver nutrients to plants over a defined period. Generally, CRF nutrient release is driven by average soil temperature with higher soil temperatures causing a faster nutrient release. Greenhouse growers have greater control over the production environment compared to outside container nurseries, where CRF use is more prevalent.

While they’re not necessarily the norm, CRFs can fit into greenhouse production if growers avoid excessively low or high production temperatures. In this case, CRFs can deliver nutrients far more efficiently, better matching crop nutrient demand as compared to a nutrition program consisting of water-soluble fertilizers.

CRF advantages

Incorporating CRF into growing media, especially during soil mixing, requires no extra application labor. It is easy to vary the amount of CRF applied to crops with different feeding needs. Because CRFs deliver nutrients slowly and evenly in a manner that not tied to irrigation frequency, they provide more consistent nutrition which contributes to a higher quality product. Application of CRF on properly irrigated crops results in lower root zone pH than water-soluble fertilizers resulting in less stress.
Depending on rate and crop, CRFs may produce more compact plants that require less use of growth regulators. CRFs continue to feed plants under cool weather conditions. This is especially important during the busy shipping season. Depending on the rate and product, CRFs can continue to feed plants throughout the retail stage and beyond, resulting in more satisfied customers.

Choosing a CRF

Choosing the right CRF and rate is critical for success. Some greenhouse growers have seen poor results after selecting unsuitable CRFs and/or applying incorrect rates. It’s important to consult with other growers or product experts to find the right CRF for your specific needs. Generally, greenhouse CRF rates tend to be very low. Growers new to CRFs should start with a conservative rate of approximately 3-6 pounds per cubic yard.

Take precautions

Depending on product and rate, growing medium containing CRF should generally be used as soon as possible, typically within a month after incorporation to avoid soluble salt build-up. If greenhouse temperatures are excessively high, it’s important to increase irrigation frequency to cool plants and avoid excessive salt build-up.

Combination fertilizer programs

Research at Cornell and Ohio State have shown it’s possible to produce high quality greenhouse crops using CRFs only. But since this can be a major production change for growers accustomed to applying only water-soluble fertilizers, it’s sometimes best to start with a combination program. Water-soluble products and CRFs can work together to provide greater benefits than either can alone. This is especially true when growing a wide variety of crops. Water-soluble fertilizers can be used at one concentration for all, and the CRF rate can be increased as needed for heavy feeders or plants with special fertilizer needs. CRFs can provide plants with nutrients during cool weather, lower light conditions, and when irrigation isn’t possible. Clear-water leaches also work better if there is CRF in the growing medium providing nutrients during this time. This can lead to more uniform feeding throughout the crop production cycle and better leaf color. By selecting the correct CRF product, growers can provide sustained fertilization for retailers and consumers, providing a value-added component.

Environmental factors

Recent research conducted at Ohio State indicates that traditional, overhead hand-watering causes approximately 60 percent of the fertilizer to miss the container medium or to splash out and be wasted. This can lead to significant amounts of fertilizer entering the environment. Additionally, many of the nutrients in water-soluble fertilizers that reach the container often leach through drainage holes.

Application of CRFs can dramatically reduce harmful environmental impact as more of the fertilizer ends up in the growing medium to be taken up and used by the plants.

Do the math

CRF can be just as effective when applied in lower doses than water-soluble fertilizers. Studies have shown that although water-soluble fertilizers tend to cost less, they can be far less efficient over time. Applying more fertilizer over the entire production cycle makes the cost-in-use significantly higher, especially in long-term crops. Additionally, CRF requires less labor as there’s no need to mix stock solutions and monitor injector accuracy.