The impulse to water plants multiple times a day during a heatwave is understandable, as high temperatures accelerate water loss through both soil evaporation and plant transpiration. However, the answer to whether you should water twice daily is generally no for most established garden plants. Effective heat management for plants relies not on simple frequency, but on a strategic approach that dictates how and when water is applied to the root zone.
Why Watering Twice Daily is Often Detrimental
Frequent, shallow watering is counterproductive to plant health. This practice only moistens the top layer of soil, encouraging the plant’s roots to remain near the surface where they are most exposed to the sun and heat. Shallow root systems are highly vulnerable to rapid drying and become significantly less resilient during periods of prolonged drought. A plant with surface roots will suffer stress and wilt much faster than one with roots that extend deep into the cooler, moister subsoil.
Maintaining constantly saturated soil creates an environment conducive to root suffocation and fungal diseases. When the soil remains waterlogged, oxygen levels drop, which can lead to root rot. Damp foliage, especially if it stays wet overnight, provides an ideal breeding ground for pathogens like powdery mildew and various leaf spots. Watering during the middle of the day, even if done a second time, results in significant water waste due to rapid evaporation before the moisture can penetrate the soil deeply.
Optimal Technique: Timing and Depth
The most beneficial watering strategy in hot weather is a deep, infrequent soak that saturates the entire root zone. This technique encourages the plant to grow deep, robust roots that can access lower soil reserves. For most in-ground plants, this means applying enough water to penetrate the soil to a depth of at least six inches.
The best time for this thorough watering is early in the morning, ideally between 5:00 a.m. and 9:00 a.m., before the sun’s intensity increases. Watering at this time minimizes water loss to evaporation because temperatures are lowest. It also allows any moisture on the plant foliage to dry quickly, which significantly reduces the risk of fungal disease development overnight. If morning watering is not feasible, the late afternoon or early evening is the next best choice, provided that you focus the water on the soil at the base of the plant to keep the leaves dry.
Site-Specific Adjustments for Hot Weather
While deep, infrequent watering is the general rule, the specific location of a plant dictates the necessary adjustments to frequency. Container plants are the primary exception to the “no twice-daily watering” rule because their limited soil volume heats up and dries out much faster than in-ground soil. During extreme heat, a sun-exposed container may need a deep soak in the morning and a second, equally deep watering in the late afternoon to prevent the root ball from completely drying out.
For plants growing directly in the ground, soil composition is the main factor determining frequency. Sandy soils, which drain very quickly, may need water two to three times per week, while heavy clay soils retain moisture longer and may only require a deep soak once a week. An actionable way to determine the need for water is the “finger test,” where you push a finger two inches into the soil; if it feels dry at that depth, the plant needs water. This simple check prevents both overwatering and underwatering.
Non-Watering Methods to Combat Heat Stress
Beyond efficient watering, several environmental modifications can reduce a plant’s water needs and heat stress. Applying a two to four-inch layer of organic mulch, such as wood chips or shredded leaves, around the plant base is effective. This layer insulates the soil, keeping the root zone cooler and reducing surface evaporation by up to 30 percent.
Providing temporary shade during the hottest part of the day can prevent leaf scorch and excessive transpiration. Simple shade cloth can be rigged over vulnerable plants to block the intense afternoon sun. For container gardens, grouping pots closely together creates a beneficial microclimate by shading the pot walls, which prevents the soil from overheating. Moving containers against a cool wall or under the canopy of a larger plant offers protection from direct, intense solar radiation.