Extension Educator, Horticulture
People are 55-75% water. We would last just a few days without water. However on day two a person is alive, but I'll bet they don't feel so well. Plants need water too. For example watermelons and tomatoes are more than 90% water. So how long can our plants last before they literally "bite the dust" from lack of water? As one of my horticulture professors was fond of saying, "It all depends".
As a general rule garden plants need about an inch of water a week, but that depends on soil type, plant species, and if the plants are well established. Clay soils tend to stay wet longer, but are harder to rewet once they turn to pottery. Anything planted this year and any trees or shrubs planted over the last two years need extra water. New plantings and containers often need water daily. Even plants listed as drought tolerant will need extra water if newly planted. Vegetables and fruit plantings need water especially during fruiting.
Generally new trees purchased as balled and burlapped should be watered with one gallon of water per diameter inch of trunk every 5-7days if rain is not adequate. For example a 2-inch diameter tree should be given 2 gallons. Trees and shrubs purchased in containers will need to be watered more often, perhaps daily, depending on temperature and wind. Established trees (more than 3 years in present location) should be watered once a month during dry periods. Apply water at the dripline, not at trunk.
With lawns it depends on whether you want the lawn to stay green or just alive. Cool season grasses such as Kentucky bluegrass naturally go dormant when it gets hot and dry. Once they are dormant, it's best to leave them there during hot dry periods. Cycling between green-up and dormancy drains plant reserves. A dormant lawn may not look as nice, but is less prone to insect attacks. The lawn greens up once cooler, wetter weather returns.
The common question is how much water is enough to keep the lawn alive? Applying at least 1/3 inch of water every 3 weeks should be enough to maintain moisture in the crowns and roots for turf to survive. Use empty tuna fish cans in area covered by sprinklers to determine how long the sprinklers need to run. Remember to mow lawns higher in summer between 2.5 to 3.5 inches and avoid applying nitrogen fertilizer during hot, dry conditions. Limit traffic on a dormant lawn. Water in morning to reduce disease problems and lessen water loss due to evaporation.
Use soaker hoses to efficiently water landscape plantings. Check soil after half hour of soaking to determine proper watering period. An inch of water will wet an average of 6-15 inches of soil, depending on soil type.
Use 3-4 inches of wood chip mulch around trees and landscape plantings to conserve moisture and reduce soil temperatures. Consider plants such as many native prairie plants that once established will tolerate drought periods.
Grey water from showers, bathtubs, dishwashers, washing machines and sinks can be used to water plants. Check out our website for more information about using greywater. Or stop by our office for a brochure. Save water and shower with a friend or a friendly plant.
Searching for plastic barrels to make your own rain barrel? Rural King in Rantoul sells them.