The Bay Gardener’s Guide to the Water-Wise Garden
Design your vegetable garden for trickle irrigation
You can reduce the amount of water you use for your vegetable garden by 70 percent and count on a bountiful harvest. If you lay out your garden in rows, trickle irrigation can make a world of difference.
Its virtues are many. You irrigate only the rows you plant — not between the rows where the weeds grow. The trickle of water also carries water-soluble fertilizer to the roots of desirable plants; again, the weeds get none. Because water is applied slowly in drops directly on the soil, there is no water loss to the atmosphere by evaporation. Because the foliage of plants remains dry, there are fewer problems with disease. Weeds are less a problem when the soil between the rows remains dry.
Follow the rules and it will work for you.
You’ll need a real trickle hose. A soaker hose isn’t good enough. Water weeps out from around the entire surface of the hose, which is made of recycled ground rubber tires. The trickle hose has pinholes every six to 12 inches, and they are laid face down so the water goes directly into the ground and does not evaporate.
I recommend drip tape for your trickle hose. No working length can be longer than 300 feet. The rows in your garden need to be level or nearly level. Water must be clean and free of particles running at a minimum pressure of 10 PSI (pounds per square inch). Well water is safe to use, but surface water from ponds or streams must be filtered to remove solids.
Trickle irrigation supplies are not available from local suppliers, garden centers or farm supply dealers. I buy mine from Farm Tek. As drip tape is sold only in 1,000-foot spools, you might consider encouraging friends or neighbors to join you in ordering.
Streamline 636 drip tape (110742) is made of eight-millimeter black polyethylene with drip holes spaced 12 inches apart.
For each row, you will also need a twist lock that attaches the drip tape to the water supply. I use the 110736 twist lock. Consider the 110740 twist lock with a valve should you wish to shut off lines not in use.
To insert the twist lock into the water supply line, I recommend purchasing the 110746 8-mm punch. Purchase a small supply of 110738 twist lock couplings in case you damage a drip tape or wish to extend a line.
You’ll also need a garden hose, three-quarter-inch black plastic pipe and adapters, all available at your local hardware store. To determine the amount of black plastic pipe needed, measure the length of the garden hose that will be supplying water. You’ll also need a three-quarter-inch garden hose, an H-adapter for every supply line, as well as one three-quarter-inch end plug and clamp.
For uniform watering, lay your drip tape as level as you can in the rows soon after seeding or transplanting. I hand-water transplants first to firm the soil around the roots before installing the drip tape. The drip holes should be in contact with the soil.
Cut the drip tape two feet longer than the row, knot it at the farther end and bury that end to prevent wind movement. If the drip tape is being laid on a warm, sunny day, allow slack because it will contract as it cools.
The three-quarter-inch black pipe water supply line should first be laid in the sun to warm and make it straight since it comes in coils.
While the black polyethylene pipe is warm, use the 8-mm punch to make a hole in the pipe and insert the twist lock. Unscrew the open end of the twist lock and insert it into the end of the drip tape. Insert the end plug and attach with a clamp at one end of the water supply line and the female hose adapter and clamp at the opposite hose end.
To make a single drip tape line, you’ll need only one half-inch female hose adapter, which attaches to a length of drip tape with a pipe clamp. Additional rows and lines to irrigate them each need a twist lock. They should all be installed in a straight line on the water supply line.
You may also need more than one water supply line, depending on the scope of your garden.
I rotate crops every year, so I have three different water supply lines of different length. The water line that supplies water to my corn patch is designed with a row spacing of two and a half feet. For all other crops, I use three-foot row spacing.
With proper care, both drip tape and water supply lines can be used for many years. Use care with cultivating and hoeing so as not to cut the drip tape. (Damaged Drip Tape can be mended by using twist lock coupling 110738.) Store the lines in a shed or garage when not in use.
Using Your System
Water is applied in drops under the drip tape, but capillary action will eventually create a band of moist soil from 10 to 18 inches wide under the surface of the soil. Enough water must be applied to penetrate to a depth of six inches before the flow is turned off.
With this system, the irrigation needs of most vegetable gardens vary from once to twice weekly, depending on heat and wind. Turn on the water before plants wilt.
When starting to irrigate, turn water on at full capacity and operate the valve at full capacity until all of the drip tapes have been filled and are dripping water. Next, lower the volume of water until the drip tapes at the highest point on the water supply lines begin to have reduced pressure. At this point, if you gently press the drip tape near the water line, it will collapse. Wait a minute or so until all drip tapes appear to be less turgid before walking away.
Operate the system for at least four hours in sandy soils and six hours in heavy soils.
By lowering the volume of water entering the supply lines, you are essentially lowering the pressure. The pressure will vary if you are on well water, but the variation will not seriously affect the flow of water through the drip tape.
To maximize space and use of water, I sow parsnips, carrots, beets and lettuce in double rows 12 inches apart with the drip tape between the rows. I grow my sweet corn in blocks of five rows two and a half feet apart, sowing seeds six to eight inches apart in short rows 10 to 12 feet long. I fold the drip tape at the end of each row immediately after sowing so I am not wasting water by irrigating ground that I have not sown. I use the same method when sowing snap beans.
When lifting the Drip Tape after the crop has been harvested, try not to stretch it. For storage, I fold it like an accordion and tie with cotton string. When preparing to reuse the drip tape, remove an inch before attaching it to the water supply.