All plants require four things. The first is sunlight, necessary for photosynthesis. Second, they need air, specifically carbon dioxide, which the plant converts into sugars, protein, and other building blocks through the energy derived from the sun. Third, plants need 13 essential minerals: nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, manganese, molybdenum, boron, iron, copper, zinc, and chlorine, all of which are absorbed from the soil. Lastly, plants need water for a variety of functions. Water absorbed by roots makes its way to the leaves where some of the water molecules are split during photosynthesis, releasing oxygen and energy. Water not used in photosynthesis cools leaves in a process known as transpiration. Drought stressed tomato plants will be smaller with fewer fruit and more likely to succumb to disease and insects. Gardeners know that blossom-end rot increases with dry soils. Since there is little you can do to increase sunlight or carbon dioxide in the garden, and nutrients are easily provided with applications of organic matter or commercial fertilizer, water may well be the key factor in producing a bumper crop.

When water is applied to the soil, there are a variety of things that can happen. If too much is applied, some may runoff and never soak into the ground. This results in erosion and is certainly something we need to avoid. Some evaporates off the surface of the soil (and the surface of the leaves). How much depends on the temperature, humidity, and air movement. A sunny, dry, day with a bit of wind will result in much more evaporation than a cloudy, cool day. We hope that most of the water gradually seeps into the ground. How fast this occurs depends on the type of soil you have. Water is quickly absorbed in sandy soils but only slowly seeps into heavier loams and clays. The soil type also determines the spread of the water flowing through the soil. If water is applied in a narrow band (through trickle irrigation) on sandy soils, the water will seep in quicker and deeper than on a heavier soil. On loams and clay, the water spreads out more and requires larger amounts to reach the same depth. This is an important consideration and one that is easy to overlook. Excess water on a sandy soil could leach below the area where most of the roots are found Leaching water is also likely to take some soil nutrients with it, especially nitrogen. This requires you to add more fertilizer than you may otherwise need.

When watering plants, you need to maximize the water that roots absorb and transpire through the leaves. Transpiration refers to the process that plants use to cool themselves. As water evaporates from specialized areas of the leaf called stomata, it cools the leaf, similar to the way perspiration cools humans. If plants did not have this ability the leaf temperature would soar on a sunny day, eventually shutting down its biochemical processes and leading to death. If water becomes limited due to dry soils, tomatoes, like most plants simply close the stomata and limit water loss. When plants do this they not only lessen transpiration but also prevent carbon dioxide from entering the leaf. With reduced water and carbon dioxide, growth slows and yields are reduced.

Most people water their gardens with sprinklers. Hopefully, none of you water tomatoes by standing in the garden holding a hose. Although it seems very satisfying, I guarantee that if you dig into the soil when finished, you will find that only the top inch is wet. Most of us do not have the patience to stand in the garden for the length of time needed to water properly. To illustrate this, try to guess how much water you would need to properly irrigate tomatoes planted in a bed 20 feet long and three feet wide. Tomatoes need a minimum of one inch of water per week, preferably 1.5 inches in the heat of the summer. The bed measures 60 square feet (3 feet x 20 feet). One inch of water on one square foot is about a half gallon of water. For 60 square feet, you would need at least 30 gallons (60 feet x 0.5 gallons). That's a minimum amount needed in one week and you could easily double this amount in the summer. So lets say you need to apply 50 gallons and your hose at full blast provides 2 gallons a minute. You would need to stand there for 25 minutes to provide enough water for the plants. Unfortunately, even if you have the patience to stand there that long, most of the water will probably runoff anyway. The result, uneven watering that barely gets into the soil. The lesson here is don't water by hand and at the very least, buy a sprinkler. Although sprinklers are superior to hand watering, there are still disadvantages.

Overhead watering results in wet leaves. Since plants pick up all the water they need through their roots, there is no need to wet the leaves. Water on foliage leads to a greater level of disease, both bacterial and fungal. When the foliage is wet, stay out of the tomatoes since that is a perfect time to spread disease. To minimize the length of time the leaves remain wet, we recommend that you water in the morning so that the leaves will dry out during the day. If your house is anything like mine, however, the last thing I can think about is setting up a sprinkler first thing in the morning. It is easier in the evening but then you are back to wet foliage all night - a definite problem. Another drawback with overhead watering is it creates mud which can make getting back into the garden a messy experience. Watering the entire garden also encourages weeds to germinate between the rows. Mulch could take care of the weeds between the rows but many gardeners use plastic much. With overhead irrigation on plastic mulch, little water gets into the bed but instead runs off between the rows, wasting water. There is a more efficient way to water and its one that many professional growers use, trickle irrigation.

Trickle or drip irrigation is an effective alternative for watering tomatoes and other vegetables. Water is slowly applied through a hose or tube which decreases the amount of water needed by 50% or more. Little water is lost to evaporation. It is uniformly applied right at the roots. Leaves remain dry, disease may be reduced, and you can water at any time, day or night, whatever fits your schedule. You can even water while working in the garden! Try that with a sprinkler! Trickle irrigation is more costly to set up and will take some additional time. But the cost and time is a small price to pay for a system so easy to operate that it requires no more than turning a faucet to water the entire garden. Many of the components can be used year after year so the cost beyond the first year is minimal. Fertilizer can even be added through the trickle irrigation system, spoon feeding your plants and preventing leaching and over application of nutrients. Finally, you don't need any plumbing skills. Anyone can set up one of these systems with just a little guidance.

There are basically two types of trickle irrigation you can use. The easiest to use is the soaker hose. This is a rubber hose (manufactured from recycled tires) with tiny pores along its entire length. Water leaks out of the hose slowly and evenly (about 1/2 gallon of water per minute per 100 feet of hose). Depending on your soil type, the water will spread 2 to 3 feet across the top of the bed.

The second type of trickle irrigation is the kind that professional growers use. These are plastic tubes (trickle tapes) with holes spaced evenly along its length. The holes or emitters are spaced at either 8, 12, 18, or 24 inches. In general the 12 inch spacing would be recommended for sandy soils and the 18 inch spacing for loams and clay soils. Don't worry about the spacing of your tomatoes, the trickle tape, like the soaker hose, will provide a continuous zone of moisture. Which is best for you? Lets look at what each can do and you can decide yourself!

In general the trickle tape is more versatile than the soaker hose. Although both are effective in slowly providing water, soaker hoses are not very effective when stretched more than 200 feet for a single bed. Also, if the water you are using is very hard or your source of water is from a pond or rainwater, you will be better off with the trickle tape. Water containing impurities will more likely clog the soaker hose even after filtering. Now lets look at what you need to set up a system. The prices and equipment described below are from the Irrigation Sourcebook, put out by Gardener's Supply Company (128 Intervale Rd., Burlington, VT 05401; 800-234-6630). This is an excellent catalog with lots of diagrams and recommendations. You could also find irrigation kits at many garden centers and with a little more experience, you could probably get most of these items at a plumbing supply store.

Let's assume that you will be using water supplied through either a 1/2 or 5/8 inch hose. Both systems will need a pressure regulator. The typical pressure of water in most homes is probably around 80 pounds per square inch(PSI). Trickle irrigation operates on the principle of applying water using low pressure. The easiest way to lower the pressure is by putting a pressure regulator on the hose. Regulators are designed to keep the pressure constant at 30 PSI, ensuring uniform watering. To keep the system operating without a problem, it is a good idea to use a filter, even with tap water. If you are using pond water or "biologically active" water (collected rain water), you may need to get a better filter for a little more money. You can also buy some optional equipment for the faucet end such as a water timer to water each day for a certain amount of time. In addition, you can purchase a fertilizer injector that will automatically mix fertilizer with the irrigation water at the proper amounts. All of these parts can be hooked up right to the faucet. From there, connect a standard garden hose and bring that to the garden. You now have a hose that is sitting at the garden ready to be hooked up to the trickle system.

In the garden, lay one irrigation line (either trickle tape or soaker hose) for each row of tomatoes, a few inches to the side of the plant. The lines should run parallel to each other and all end at one side of the garden. The lines could be buried a couple of inches deep and covered with soil or put on the top of the bed and covered with plastic or organic (straw, grass clippings, paper, etc.) mulch. Put an end cap at one end of the trickle tape or soaker hose. On the other end, you need to connect the irrigation lines to plastic tubing (1/2" blank tubing). Do this using 1/2" T connectors. You will need one T for each irrigation line you placed in the garden. Connect the blank tubing to the garden hose using a hose connector. Once that connection is made, the system is ready to go.

The next question to ask yourself is how often should you run your irrigation system. The answer depends on a number of factors. Let's use an example to illustrate our point. Lets say you have planted 4 rows of tomatoes, each row is 25 feet long. That means that each row takes up 50 square feet (25 feet x 2 foot bed width). Notice it makes no difference if you have spaced your plants at 1 foot or 3 feet between plants - we only need to know how long the tomato row is. We know that one inch of water on one square foot is approximately 0.5 gallons. And we know that we want at least one inch of water on our tomatoes each week. So we need a minimum of 25 gallons per bed (one inch of water on 50 square feet equals 25 gallons). Now lets take all those numbers and figure out how long to run our system.

The soaker hose will deliver 30 gallons of water per hour per 100 feet of hose. That means on our 25 foot long tomato bed we will be applying 7.5 gallons of water per hour (30 gallons x 0.25). We will need to run the system for a little more than three hours each week to give us the minimal amount of water for our plants. For best results, I would water three times per week at two hours each time so the ground stays relatively moist. Of course if it rains, you can cut back on the watering.

If you are using trickle tape, you need to know the emitter spacing (spacing between holes in the tape) and how much water will come out of each hole over time. Let's say we purchase tape with emitters spaced every 18 inches and each emitter will have one gallon per hour seep out over one hour. For our example, each 25 foot row of tomatoes would have about 16 emitters (one every 1.5 feet). If each emitter puts out 1 gallon per hour, that means we would need to run the system about 90 minutes to supply the minimum amount of water. As before, I would recommend running the system about 1 hour every other day, assuming you have no rain.

I have noticed a big difference in my garden since I started using trickle irrigation. In 1995 when the Northeast was plagued by a terrible drought, my tomatoes grew just fine. The systems are really easy to install and simple kits can be bought in many garden centers. For even more options, contact the Gardeners Supply Company. You will be sure to find them very helpful. For large market gardeners or small growers, you may want to try Zimmerman Irrigation (R.D. #3, Mifflinburg, PA 17844; 717-966-9700). They offer supplies for larger growers and are extremely helpful. Although the initial cost will be higher for a trickle system, many of the components can be used year after year. And I guarantee that you will be very pleased with the results.

Dr. Steve Reiners, sr43@cornell.edu, Horticultural Science