Nuts & Bolts of Growing
By ANDREW RISTVEY
Regional Specialist
Commercial Horticulture
Wye Research and Education Center

Irrigation workshop
goes international

Rarely do we get an opportunity like this. In February, my colleagues Drs. John Lea-Cox and David Ross and I hosted a workshop at the University of Maryland Research Greenhouse, focusing on substrate and irrigation management. Like recent nutrient management programs offered in the past, this was very much hands-on, yet, what really separated this workshop from the rest were our guests. In the past several years we have been invited to Costa Rica for substrate and irrigation workshops. This time we wanted to return the favor and so we invited our counterparts from the University of Costa Rica (UCR) to participate in our program. They included Carlos Mendez, director of Horticultural Research at UCR, and Gustavo Quesada and Guillermo Chacón, both Extension agents. Our goal was to have lessons given in Spanish concurrently with the lessons in English. We felt as though there was a need to educate Latino and Latina nursery employees in their native language, so nothing would be lost in translation, even though most have done well learning and utilizing English.
The two-day workshop featured substrate management the first day. Participants were asked to bring substrates from their respective nurseries, and they learned how to perform tests that determine physical properties, including how much air and water the substrates will hold. This information is vital when it comes to making your own substrates from component materials. Each component like pine bark or peat moss has its own properties, and mixing them together creates infinite possibilities depending on the proportions you choose.
Some introductory lectures were followed by hands-on testing of substrate physical properties. We had the participants compare two measurement techniques. A field test which involves weighing a water-saturated container of substrate and then comparing that water-saturated weight with same substrate, drained. The other test is a version of a laboratory analysis using porometers, or devices that measure the pore space in a substrate in a similar way as the field test. Most of the participating nurseries make their own substrate mixes and evaluations such as these are important to assure the proper mix. Just like our program in Costa Rica, we wanted to be sure the participants understood how proportions of components could be manipulated to change the physical properties. There is no “magic bullet” proportion or mixture, but you must adjust your irrigation program based on how your substrate holds water and air.
Here in the United States, we have available many different substrate components, most of which have been thoroughly tested through time. However, in Costa Rica, components like pine bark and peat moss are too expensive to be utilized by smaller nursery operations. For our last program in Costa Rica this past August, we developed a four-day program to teach growers and substrate suppliers to test potting mixes from local materials that would retain essential physical characteristics to suit plant growth. These materials included rice hulls, palm leaf fibers, coir (coconut fiber and dust), milled trees, coffee waste compost, charcoal and other organic and soil based components. Most of the substrate components could be combined to form mixes with adequate air-filled porosity and water-holding capacity. It was a learning experience for my colleagues and me, as we learned about the resourcefulness of Costa Rican growers and substrate manufacturers. I should like to return soon to see how our lessons, developed from the combined knowledge of UMD and UCR researchers, influenced Costa Rican substrate development.
The second day of our program focused on irrigation management, and participants learned how to test an irrigation system for efficiency and to maintain a system at peak performance. Sounds interesting? Do you know how to efficiently irrigate plants arranged in square blocks using circular irrigation patterns from a spinner? You increase the coverage by using more spinners down the lateral. Several circular patterns overlapping each other will cover plants in the block more efficiently. Just make sure you have the pressure to operate them.
What about pressure? Do you check the pressure loss in your irrigation system using pressure gauges? Not only does each spinner reduce your pressure, but the inside of your PVC pipes resist water flow and create friction, further reducing the available pressure down the line. The efficiency of your irrigation spinners relies on a consistent operating pressure. A pressure variation of more than 20 percent down the irrigation line will create a very inefficient irrigation system, overwatering plants at the top of the block and under-irrigating plants at the end. There are ways to improve your irrigation efficiency and if you are upgrading soon, there is no time like the present.
What about your water quality? Have you had it tested recently? Do you know the alkalinity of your irrigation water? If you are making your own substrate, do you know how much lime to use? It is based on your water quality. The higher your water alkalinity, the less lime you need.
So after you make sure your substrates have the right properties, and your irrigation system is as efficient as possible, how well are your plants growing? Do you record growth or have any method for evaluating your plant quality? Our Costa Rican counterparts also brought some suggestions of different evaluation measurements for determining if the work you put into making your growing system more efficient paid off.
Interested? We hope to see you at our next program so you can learn all the secrets to grow better plants more efficiently.
For more information on upcoming programs such as this, call (410) 827-8056 Ext. 113.