Furrow irrigation saturates the furrows between plants. Furrows are most useful when plants are in rows, as in vegetable gardens. Water is let into each furrow from one end, usually with a garden hose, until the entire furrow is filled and water soaks into the soil. Because the leaves don’t get wet, leaf diseases are avoided, which makes this an attractive method for plants that are particularly susceptible, such as squash or peas.
The pitch, or downhill slope, of furrows should be balanced with the rate at which the soil absorbs water so that all plants in each furrow receive the same amount of water. If the pitch is too steep, plants at the downhill end will be overwatered and those at the uphill end will be underwatered; if the pitch is too slight, water may never reach the plants at the downhill end.
If adjusting the pitch of furrows is impractical, break them into short segments: the shorter the furrow, the less difference the pitch makes (but the more often the gardener has to move the hose).
To plan a vegetable garden for furrow irrigation, lay the garden out parallel to the slope, so all the furrows are fairly level. If your garden is flat, you can lay out the furrows in any direction.
To make a dry place to walk while watering, lay out furrows on one side of each row and leave a dry walkway on the other side of the row. The plants will still get enough water.
Furrows are easiest to manage in soil with a slow infiltration rate. You can slow down the infiltration rate by running enough water in the furrows to get them wet all the way to the end, then watering another furrow while the first one drains. Come back later and fill the furrow for irrigation. When the soil in the furrow gets wet and then drains, the soil surface seals so later water soaks in more slowly, making it easier to get water to the end of the furrow and allowing it to soak in evenly all along its length.
Keep the water from the hose from eroding the furrow by using a water breaker, setting the hose end on a board, or by tying a nylon stocking or similar fabric sack to the end to slow the force of the water.