Extension Educator, Horticulture
To be a good gardener you have to be a good waterer. The when and how of watering is as mysterious to novice gardeners as the attraction to reality TV is to me. The dynamics of good watering include an understanding of the interrelationships of weather, plants and soil; and of course the trial and terror of killing a few plants. 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. It takes about one half gallon of water per square foot to get an inch of water. Anything planted this year including plants listed as drought tolerant and any trees or shrubs planted over the last two years need extra water. New plantings and containers often need water daily.
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. Container plants are usually grown in soilless mixes which tend to dry very quickly even once planted. 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 www.extension.illinois.edu/cfiv 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.
Mark your calendars for area Garden Walks – UI Extension Master Gardeners Champaign County in Champaign/Urbana Saturday June 23, PH: 217.333.7672; UI Extension Master Gardeners Vermilion County in Danville Sunday June 24, PH: 217.442.8615; and Village Gardeners of St. Joseph Sunday July 8. Check out area garden centers for tickets.