Watering Flowers: Cold Water or Room Temperature?

Should houseplants and garden flowers be watered with cold water straight from the tap, or should the water be left to warm up first? Gardening specialists quoted by the gardening website The Spruce say water temperature matters, but it is more important to give plants the right amount of moisture and to avoid extremes.

Why temperature matters

Water temperature affects the temperature of the soil and root zone, which in turn can influence plant growth. Very cold water can briefly chill the roots, slowing their activity and the plant's growth. Water that is too warm can overheat the roots and add stress, particularly for potted plants or in hot weather. For most plants, the safest option is moderate-temperature water. Houseplants often do fine with water that has stood in the room for a while and reached room temperature.

Which plants are more sensitive

Extra care is advised with newly transplanted plants, seedlings, warmth-loving vegetables, tropical houseplants and potted plants, since the small amount of soil in a pot changes temperature faster than a garden bed. That does not mean every such plant will suffer if watered with cooler water; the effect also depends on the species, soil and air temperature.

The risks of hot water

Water that is too hot can directly damage plant tissue and roots. In summer, water left in a garden hose lying in the sun can get very hot, so it is advisable to let it run for a minute or two before watering. Boiling or very hot water should never be used on plants, even if warmth seems likely to speed up growth.

Three rules for healthier flowers

• Check soil moisture instead of following a rigid schedule. If the soil is dry at a depth of about 5–7 centimetres, the plant may need water, though species requirements differ.
• Water the soil near the roots rather than the leaves, because constantly wet leaves can encourage disease in some plants.
• Water in the morning when possible, so leaves and topsoil have time to dry before night, which can reduce the risk of fungal diseases.

The main principle: water when the plant needs it, use moderate-temperature water and avoid overwatering.