Gabriel Vicari: Water conservation in the garden

Water is a precious resource for both recreation and human health. Take, for example, the unique spring systems, multiple rivers and stoic lakes in Marion County. The consistent increase in Florida’s population also means increased water use. The health of our ground and surface water depends on the amount of water that enters and leaves these systems. If groundwater pumping exceeds what is needed for them to thrive, our water bodies can experience a decline in health. To protect our water resources today and in the future, we should pay careful attention to the quality and quantity of these exceptional water resources. Aside from conservation, water is becoming more expensive. Saving water in the garden also can mean protecting your wallet if you irrigate your garden with municipal water. Efficient garden watering and feeding can be accomplished using specialized irrigation equipment, fertilization technologies, a bit of plant research and some basic math.

The current industry standard for garden and farm irrigation is micro irrigation. This watering method uses tubing, drippers and emitters to distribute low amounts of water to the plant’s root zone. This method allows for the measured and controlled application of your water. Most often, a mainline of 1/2- or 3/4-inch tubing carries the water from the source to your garden. Then, depending on the needs of the plants, specific emitters are installed to deliver the water. Emitters are chosen by various factors like flow rate, irrigation footprint and design.

Micro irrigation provides some critical advantages compared to hand- or overhead watering. These advantages are ease of irrigation, decreased water use and increased efficiency. You also can use valves or timers to control irrigation of multiple zones and potentially the whole garden. Turning a valve or programming a timer saves you a lot of time compared to hand-watering each plant. It also provides consistent water to your plants, leading to increased yields. When you use micro irrigation instead of overhead sprinklers, most of the water is directed into the plant’s root zone and slowly discharged into the soil. This way, less water is lost to wind, evaporation or groundwater via quickly draining soil. Irrigating at the root zone also keeps excess water off the plant leaves and vegetable surfaces, decreasing the chances of molds, fungus or other diseases.

In a perfect world, efficient irrigation would mean that the plant consumes 100% of the water leaving the system. Unfortunately, this does not happen in practice, although properly utilized micro irrigation can get us close. Because micro irrigation delivers fixed volumes over more time, surface runoff, overspray and excess watering can be avoided.

Micro irrigation also has some disadvantages to note as well. There are costs associated with tubing, emitters, drippers and timers. Though not incredibly expensive, it certainly cannot beat the price of a hose and nozzle. Another consideration of micro irrigation is maintenance. Emitters and drippers can get plugged from debris, algae or hard water deposits. And, of course, a rogue shovel or weed eater can easily cut a line.

You do not need to be handy or hire professionals to install your micro irrigation system. They are meant to be DIY, and all of the components easily fit together. The only specialty tool you need is a hole punch, which comes with most kits. The hole punch is a standard-sized plastic spike that connects emitters and tubing to the main line that delivers water from your water source to your garden. Do not worry if you punch a hole in the wrong place; there are barbed plugs called “goof” plugs that you can use to mend the pipe.

You also can use your micro irrigation system to feed your plants. Fertigation is a method of fertilizing your plants through your irrigation system. This is an excellent option because of its advantages over granular fertilizer. Just as micro irrigation delivers water to the root zone, fertigation through this system does the same. Fertigation increases fertilizer use efficiency and allows for more frequent application in smaller amounts. Using this method to meter plant nutrients allows the plants to take in more and reduces the chances of excess fertilizer moving below the root zone and into our groundwater. Not only does this save on fertilizer costs, but it also protects the water quality of our local water bodies by protecting them from excess nutrient inputs.

Fertilizer injection into your irrigation system sounds challenging, but it easily integrates into your garden. One of the most inexpensive and easy-to-install fertigation devices is a venturi-style injector with garden hose threads on either side connected directly to the mainline into your garden. These injectors use a vacuum created from the movement of water through the device to draw liquid fertilizer into the system. The purchase price of these injectors can start at around $25. Other injectors and injection systems can cost much more, but it all depends on the size of the garden or small farm and the needs of the plants.

Fertigation also carries some challenges. Water-soluble or liquid fertilizer needs to be used so that micro-irrigation emitters do not get clogged. In addition, injecting into improperly installed or maintained irrigation systems can result in uneven fertilizer distribution, which can starve some plants and over fertilize others.

A final note on fertigation is that backflow prevention is a crucial component of this system and is required by law. Backflow prevention can be accomplished by placing vacuum breakers or check valves between the spigot and your irrigation system to protect your water source from old hose water or fertilizer from getting sucked back into your well or municipal distribution system. These fittings are very inexpensive, simple to install, and most likely already installed on your spigots if you use municipal water.

Exploring the root architecture of your garden plant is essential to efficient irrigation. Does your plant species have a deep tap root? Maybe its roots are shallow but travel laterally through the soil. This knowledge can go a long way in your irrigation decisions. For example, suppose your plants have a tap root but little lateral branching. In that case, you could use a drip emitter with a longer irrigation time to allow for more vertical water penetration. Alternatively, it might be better to use a micro sprinkler with a larger wetting area and short but frequent irrigation events for a shallow but spreading root system.

With some basic math and a few general rules of thumb, root zone knowledge and the flow rate of your irrigation emitters, we can quickly determine a good starting point for irrigation volumes and times.

The first rule of thumb is that typical Florida sandy soils can hold around 1 inch of water per foot of soil. The second is that 1 inch of water in 1 square foot equals 0.62 gallons. Lastly, most vegetables need anywhere from a half inch to 2 inches of water per week. One quick note: If you have amended your soil with compost or other organic material, or brought in soil for raised beds, the water-holding capacity could be very different. For example, a 1% increase of organic material over an acre can increase water holding capacity by approximately 20,000 gallons.

Let us look at an example calculation for watermelon. Most of the roots of a watermelon plant are within the first 8 to 12 inches of soil. Suppose we assume 1 emitter per plant, with a 0.25 gallon per hour (gph) flow rate. In that case, we can use the following calculations to determine the irrigation time for 1 inch of water or 0.6 gallons of water:

(Flow Rate) x (Time) = (Irrigation Volume)

The calculation for one emitter with 0.25 gph output:

We want 0.6 gallons (1 inch of water) per week.

(0.25 gph) x (Hour) = 0.6 gallons Hour=0.60 gal/0.25 gph

2.4 hours or 144 mins per week.

Then divide the total number of minutes per week by seven if you wish to water every day.

144 minutes/7days = 20.5 minutes a day

The calculation above can be used as a baseline for your irrigation scheduling. Though this number is a great place to start, other contributing factors can impact your garden’s water needs. Weather patterns like rainfall and heat levels can either decrease the need for irrigation or increase soil evaporation before the plant can use it. Another element to consider is the life cycle of the plant. Tomato seedlings need a tiny fraction of the water that a fully grown fruiting plant requires. Efficient garden irrigation is a moving target. Be sure to revisit your irrigation scheduling several times a season and keep a close eye on your plants, especially during the hottest part of the day. Splitting irrigation into multiple events a day can decrease water loss to evaporation and help protect your plants from wilting in the heat.

Combining the techniques explained above with irrigation controllers allows for automated gardening. Irrigation controllers can range in style and price from a $15 rotary timer to a fully Wi-Fi compatible or Bluetooth-connected system. These can be linked to rain sensors, soil sensors, automatic valves, and even send notifications of upcoming rain events, allowing you to place a rain delay on an upcoming irrigation schedule. The technology for these systems has come a long way, and connection to our devices provides straightforward programming. All of these materials are relatively low-cost and will buy you extra time to spend outside of the garden while still providing your plants with the water and food they need to produce a bountiful harvest.

For more information, call 671-8400 or email gvicari@ufl.edu.

— Gabriel Vicari is the Water Resources Extension Agent 1 at the UF/IFAS Extension Marion County. For more information, contact the office at 671-8400. The Extension Service is located at 2232 NE Jacksonville Road, Ocala, FL 34470.

This article originally appeared on The Gainesville Sun: Gabriel Vicari: Water conservation in the garden