The two most basic rules of watering are very simple: Never water ANYTHING in the evening or at the height of the day.
- Morning is ALWAYS Right. Plants are most receptive to water at this time of day, because their cells are ‘opening up’ to accept the morning dew through their leaves. (This is why foliar feeding, when you spray something like compost tea directly on plants to feed them, should only be done in the early morning). The plants’ roots are also most receptive to water in the morning, and will utilize any moisture you provide with the utmost efficiency.
Especially if you wet the leaves! Morning is the only time its relatively safe to wet the leaves of disease-prone plants like tomatoes, roses and lilacs, because the rising sun will quickly dry those leaves off before disease spores can use that moisture to breed. That said, I STRONGLY suggest you only wet those leaves for a good reason, like foliar feeding. It’s always better to water plants at the base; and with the disease-prone, it’s often the difference between life and late blight.
- Never Water While the Sun Shines! As the day progresses, plant cells begin to slowly close to retain their moisture. By high noon on a blazing hot summer day, they’re closed up tight. Watering then insures you’ll waste the most water—the plants’ roots are absorbing as little as possible, and you’re losing the maximum amount to evaporation.
- Evening is the WORST Time! Those cells do open up again when the sun goes down, but this is the worst time to water, especially disease-prone plants and lawns. Those poor plants will be damp for a good 12 or 14 hours before the sun re-appears. By then, disease will have had its way with them.
- An Inch a Week. Get a rain gauge and chart what Nature provides. An inch of rain a week is perfect for every plant in your landscape in most climates most times of the year. If you live in the deep South, have desperately sandy soil and/or are being hammered by a heat wave, you can move up to two inches.
- Apply water in big lumps, not short spurts. Frequent shallow sprinklings ensure puny root growth, which is bad for all plants. It’s also the second biggest cause of persistent weed problems in lawns (the first is scalping). Frequent watering also risks the plants’ roots staying wet, which can rot them right there in the ground. Plants need to dry out between waterings.
- Mulch, of course! Have an inch or two of compost, shredded leaves or other non-wood mulch around (but never actually touching) your plants to keep moisture in the soil.
The Ideal scenario: After a week without rain, set your sprinkler, soaker hoses or irrigation system to come on around midnight and end around 8am. Your rain gauge will tell you if you need to adjust the time to achieve an inch ending right as the sun comes up. (It takes a LONG time to put an inch of water down). It’s OK to wet leaves at night if you don’t stop at night; the moving water will protect the plants and then the rising sun will dry the leaves. (Although ground level watering is always better.)
The Exceptions: Big New Plants. When you put new trees and shrubs in the ground in early Spring or Fall (NEVER in the Summer, when the risk of death is VERY high), let a hose drip water at the base of each new planting for a full 24 hours, and repeat every few days for several weeks if rain is scarce. Back off if rain is plentiful, but be ready to supply a several hour long ‘drip drink’ a couple times a week for a full year. Lack of water early on is the biggest cause of death for newly planted trees.
And if it never stops raining? Remove the mulch and hide the hose.