When to water
Water in the mornings, if you can, as this is when the sun comes up and plants will start to use water. The foliage and soil surface is also likely to stay drier for longer than evening watering, discouraging slugs, snails and mildew diseases. Plants start to transpire in sunlight, drawing water from the soil, through their roots, up their stems and out through tiny pores on their leaves called stomata. Evening watering is also fine, as the cooler conditions mean less water is lost to evaporation.
Watering in the heat of the day is not a good idea as much water is lost through evaporation from the surface of the soil and the plants will use water more efficiently if watered in the cooler parts of the day.
Watering frequency
We're frequently advised to 'keep plants well watered' but just how often should that be and how do we know if a plant is getting enough water?
There is no simple rule of thumb for watering as each plant has different needs - for example, a container plant in hot sunny weather may need watering daily, whereas a mature shrub might only need a drink in extreme drought. But below are some things to think about and look for to help you get it right for your plants. It's good to remember, plants will use more water if more water is made available to them, so you can allow them to dry out a little between watering and they don't need to be wet all the time.
Factors that affect how often you need to water:
- Size, species and stage of growth of the plant - the larger and more leaves a plant has, the more water it is likely to lose and the more nutrients are needed to grow flowers and fruit. These are mainly taken up through the roots, dissolved in water, so more water is generally needed to produce flowers and fruit.
- Texture, structure and compaction of the soil or growing media and its organic matter content. Plants cannot extract every drop of water from soil and some soils may still feel damp even though plants have started to wilt. This tends to happen in clay soil. A clay soil can hold more water than a sandy one but plants are able to extract more water from sand than clay. In contrast, sandy soil can feel dry even though there may be moisture still available to plant roots. Sandy soils tend to need smaller amounts of more frequent watering than clay. Caring for your soil by adding organic matter will improve its water holding capacity
- Whether the plant is growing in a border or container or with root restriction e.g. next to a wall. A large plant in a small pot will need more frequent watering than one planted in a border. In a border, the roots are free to grow wherever they are able to find water and hence draw moisture from a much larger volume of soil than if the roots are confined in a pot. Plants that are potbound (i.e. have more roots than compost in the pot) dry out particularly quickly
- Season and weather (e.g. rainfall, hours of sunshine, temperature, wind and humidity) will affect the rate of water use. Generally speaking, plants use more more water in the warmer summer months and less in the cooler winter months. They will also use more in hot, sunny and windy weather. And watering will need to be more frequent during prolonged dry spells with no decent rain (light showers are of little use to plants as the water simply evaporates or only wets the very surface of the soil where there are few roots)