W hen you tell friends you grow plants for a living, how many times do you hear, “Oh, I just kill plants. I have a black thumb”? And how many times have you walked through a retail location selling (gulp) your plants, and they no longer look like the healthy, vigorous specimens you shipped a few weeks earlier? While some factors, such as light and water are no longer under your control, a recent study conducted at the University of Florida shows adding residual fertilizer can help improve shelf life and consumer success.
“We know many consumers are not going to fertilize the plants when they get them home,” says Dr. Paul Fisher, professor and Extension specialist at the University of Florida. “I feel like we have a responsibility as growers to make things as easy and successful as possible for the consumer.”
Spurred by several factors: comments by friends and coworkers about being disappointed with their efforts to grow plants, seeing plants decline at retail and learning about dual-coated controlled-release fertilizers, Fisher and his colleages, Suede de Oliveira and Dr. Simone da C. Mello, decided to see if adding residual fertilizer in a variety of forms would make a difference.
Four Different Strategies
Using Petunia ‘Supertunia Vista Bubblegum,’ the team grew the plants in two phases — a production phase and a consumer phase. Rooted cuttings were transplanted into trade 1-gallon containers filled with a 70% peat/30% perlite mix without a pre-plant nutrient charge.
During the six-week production phase, four different strategies of fertilization were implemented:
- Water-soluble fertilizer (WSF) at 200 ppm nitrogen (N) of 15-5-15 with each irrigation
- Controlled-release fertilizer (CRF) consisting of five- to six-month 18-6-12
- Combinations of a low rate of both WSF (100 ppm N) and incorporated CRF (4 lbs/cubic yard)
- WSF at 200 ppm N, with a delayed-release (double-coated) CRF incorporated before planting at 10 lbs/cubic yard.
During the consumer phase, plants were not fertilized at all and were simply irrigated with clear water. They either remained in the 1-gallon containers or were planted in the landscape in sandy soil.
When asked how his team determined which residual fertilizer strategies to evaluate, Fisher says they used strategies growers
“The treatments we had were almost a survey of what people can do with follow-up fertilizer,” he says. “We want to make the point that there are multiple ways to provide fertilizer for your customers. We chose treatments in consultation with growers and fertilizer companies, and we added the double-coated CRF product to see what it could do.”
Residual Fertilizer Works
All the strategies except the control (with no residual fertilizer) resulted in increased performance in leaf greenness and numbers of flowers in the consumer phase. Fisher said growers should choose the method that works with their growing system and is the most cost effective. He cited a scenario where a grower is already using CRF as the main fertilizer source. In that case it may be best to include some long-term fertilizer such as the double-coated CRF so there is some left over for the customer. Or if a grower is using water-soluble fertilizer he may want to top dress with CRF immediately before shipping or incorporate CRF at planting with a five- to six-month release period.
“There are certainly options that can be applied to any given situation,” Fisher says. “All the results were pretty similar. The bottom line is to provide some fertilizer for the customer.”
Is the Extra Input Cost Worth It?
Nursery and bedding plant growers who grow plants outdoors have been incorporating CRF for years already. But greenhouse growers often fertilize with WSF using fertilizer injectors and are not usually providing residual fertilizer to the customer. Of course, like all good things, adding residual fertilizer comes with a price.
“I think all growers would like to produce the best-quality product they can, but they have to be able to stay in business, as well,” Fisher says. “It’s a cost-benefit decision, and for those growers who are in an industry where every penny really counts, unfortunately it drives decisions sometimes that are going to work against consumers’ success. One aspect of that might be fertilizers, another one might be growing media, a smaller container size — it’s a whole range of choices growers need to make.”
When asked if he thought most growers would see the value of the additional input cost and add residual fertilizer to their growing programs, Fisher said he feels some will and some won’t, depending upon each operation’s business goals.
“I think all of the growers we talked with understand the importance of this; it’s just whether they can make it worthwhile monetarily,” Fisher says. “For example, if you’re trying to differentiate yourself in the marketplace by producing a really high-quality product for an independent garden center, it may pay off. Or if you are thinking long-term — you may be doing pay-by-scan, so the success of your customer and repeat sales the following year will really impact your own sales.”
Dual-Coat CRF Offers Promise
Fisher says he was especially pleased with the dual-coat CRF.
“It actually worked as advertised,” he says. “You see a lot of new technologies come along that simply don’t pan out. The only reason I ended up including it in the research was because I was visiting growers in New Zealand that knew about it, and it actually does have a place.”
Dual-coat CRF has been around for some time, but it’s new to the U.S. greenhouse industry, Fisher says. It’s not really being actively promoted, but it is available.
“One advantage is that you can grow the plant in the greenhouse the same way as you would even if it didn’t have the dual-coat CRF incorporated,” Fisher says. “You can still use water-soluble fertilizer, and dual-coat controlled-release fertilizer doesn’t release nutrients until later in the crop cycle when the consumer has the plant.”
Once the nutrients begin to be released, they will continue to sustain the plant for five to six months — slightly less in warmer temperatures.
More Options Are Being Explored
Fisher and his team are continuing their research by looking into additional strategies to add residual fertilizer. Among the methods being evaluated are the addition of a low-cost top-dress fertilizer at shipping time, organic fertilizers, and types of water-soluble fertilizers that are easy to apply just before shipping that would provide some residual nutrients. The goal is to continue to find cost-effective ways for growers to provide this additional benefit to consumers.
“I think it’s really important to be thinking about consumer quality,” Fisher says. “Researchers like me — and growers, too — we’re trained in production. We put all these resources into creating beautiful plants. But if you don’t look after them, it falls apart. We’re supposed to be bringing beauty and joy and then we get people saying, ‘Oh, I just kill plants,’ so we’re not doing something right.”