Determining the water needs of a cucumber plant requires more than reading the seed packet. The quality of the soil, local climate and irrigation method used all affect the amount of water necessary to grow productive cucumbers. Irrigation needs change throughout the gardening season. You must remain attentive throughout the gardening season and determine the cucumber's water needs on a weekly basis.
Soil and Moisture
The type and quality of the soil in the garden influences the water needs of the cucumber plants. The optimum garden provides rich, well-drained soil, but cucumbers can grow successfully in less-optimum soils with proper irrigation. Sandy soils drain quickly so they dry out more often. Cucumbers grown in sandy soil usually require additional irrigation. Clay soil retains water and tends to compact, which inhibits water movement around the cucumber roots. Adding compost or peat moss to the bed before planting aids drainage in heavy soils.
Cucumbers typically need 1 to 2 inches of water each week. The plants may require no irrigation when rainfall supplies the required amount of moisture. Feeling the soil before irrigating is a more reliable method of supplying sufficient moisture than sticking to a rigid watering schedule. Cucumbers require watering when the top inch of soil is dry, but before the soil dries at a greater depth. Feel the soil two to three times a week when there is no rainfall and water when necessary. An inch of water thoroughly moistens the top 6 inches of the soil.
Mulch and Water Needs
Mulch affects the amount of watering necessary to maintain your cucumber plants. Plastic mulch applied over the bed before you plant retains the most moisture in the soil, so less watering is necessary. Plastic makes it more difficult to check the soil and deliver water. Installing drip irrigation under the mulch ensures the moisture reaches the soil beneath the mulch. An organic mulch, such as straw, also retains moisture so less watering is necessary. It's possible to water plants with a hose or watering can when organic mulch is applied, and you can still feel the soil beneath the mulch to determine the moisture level.
Watering the cucumbers in the morning ensures the moisture penetrates to the root zone of the plants before the water evaporates during the heat of the day. Plants watered in the morning may require less irrigation than those watered in the afternoon. Supply the water directly to the soil at the base of instead of from overhead. Overhead watering makes the foliage wet and more prone to fungal growth. More moisture is also lost to evaporation when you overhead water, necessitating more frequent irrigation.