Ed Rosenthal on Fertigation

May 17, 2017   

Fertigation is the method of supplying dissolved nutrients through an irrigation system. Because they are already in solution, the nutrients are immediately available to the roots. This gives growers the opportunity to provide the exact nutrient formula required to promote high level plant performance. Compare this to an enriched planting mix or dry fertilizers — once they are added to the planting mix, whether enriching the soil or as a slow release, they remain in the container until they are used, even if the plant requires a different nutrient formula.

With some experience you know the formulas that usually create peak performance, and mixing the nutrients into the planting mix may seem like the most efficient method of delivery. This is much easier to predict in greenhouses where environmental conditions are tightly controlled.

In one instance, a mandarin orange grower grew acres of plants in 5 gallon containers with a low EC medium. Over a season he supplied a uniform formula, then tested the water draining from the containers each day. By comparing the nutrients remaining each day he determined that there were 14 different stages to the fruit’s growth. The following season he adjusted his fertilizer formulas accordingly, saving fertilizer by providing the plants exactly what they needed at any given time.

In tunnel greenhouses or structures where there is a bit of temperature variation. Fertigation provides growers with more control over plant growth by customizing dissolved nutrients to account for environmental conditions. For instance, when the greenhouse is running a bit cool with low light, a higher N formula helps to keep plants growing a bit faster. Conversely, with high light and warm temperatures, plants stretch if given high N formulas, especially since the plants use more water that may increase the total nutrient delivered.

No matter what delivery system you are using to irrigate the medium, it can be adapted to accommodate fertigation. Drip, capillary mats, ebb and flow systems, flood tables, and even the much over-looked wick system can all be easily adapted for nutrient delivery. Delivering nutrients through the irrigation system makes targeted fertilization a much easier task. Since the amount of fertilizer delivered to each plant is dependent on the total amount of water it receives uniformity of delivery is an important consideration. Although the drip system is frequently used, it is the one least likely to maintain uniformity of water delivery, and it requires slightly different equipment if using organic fertilizers.

With some flowering and fruiting plants, such as cannabis, as the life stage changes from growth to flowering or fruiting the nutrient requirements change dramatically. With time release fertilizers and organic additives, a flush will rinse out only dissolved salts, and residual non-solubilized nutrients remain and will continue to dissolve. This makes it difficult to meet nutrient ratio targets. Fertigation makes this change simple. Flush out the old nutrients. They drain easily, because they are already dissolved in water. Then add the new nutrient/water solution.

Fertigation is a lot like hydroponic systems, since both deliver the nutrients through the water. However, most hydro systems use media, such as rockwool, vermulite/perlite or other non-carbon based ingredients. These have no buffering ability. 

Fertigation systems use natural media, such as peat moss and coir, that contain high percentages of carbon compounds. These molecules buffer the ingredients in the water by loosely holding some and releasing them into solution as it becomes more dilute. This buffering makes it much easier to maintain optimum conditions, because it’s not quite as exacting as hydroponics since the water/nutrient solution binds loosely with the medium’s carbon compounds. This organic (carbon) matrix also supports a healthy rhizosphere community of synergistic micro-organisms, which interact directly with the roots, both supplying them with nutrients and protecting them from pathogens.

One way to encourage root growth and discourage root infections is to use a coarser, rather than finer, particle planting mix. The course particles drain easily leaving large air spaces that provide roots with needed oxygen and preventing anaerobic conditions.

Using coarser mixes increases the frequency of irrigation required, because the mix holds less water. Generally speaking the smaller the container the finer the particles to be used. Conversely, the larger and deeper the container, the coarser the particles.

When using drip systems, one important task that should never be skipped or taken lightly is clearing the system of nutrients, flushing, before the system shuts off. This prevents clogged lines, which can be a major catastrophe, especially when they go unnoticed. With big systems it takes a long time to clear the lines, so the plants irrigated first get a flush at the end that often causes significant nutrient loss. Instead, use shorter parallel irrigation lines that can be flushed using less water. Irrigation can take place block by block to keep water pressure consistent.

Other types of systems, which do not have small diameter tubing are not nearly as susceptible to clogging.

Almost all fertigation systems use mineral fertilizers rather than organics, although a few commercial gardeners do supply compost teas and some liquid organics through their systems. If you plan to use anything but commercial nutrients on a drip system you might consider using wider dimension lines and emitters.

Install a backflow prevention device on the main line before the injector to prevent source contamination. No matter what fertilizers you are using, make sure to place a filter on the mainline past the fertilizer injector in order to make sure no particles flow into the system. This is doubly important when using drippers.

Fertigation can help simplify your life through automation. It isn’t costly and frees up labor and scheduling time. Best of all, it’s easy to install using Growers Supply and GrowSpan equipment and kits.