How To Water Wisely

While we all know what watering is, doing it well and at the correct intervals is a skill that takes good gardeners years to master. That's because there are so many variables, including the type and age of a plant, where it's growing, what time of year it is, what the weather's like and when the plant was last watered.

Don't let this make you anxious because you'll quickly develop a sixth sense that will help you identify when a plant needs refreshment.

Why water?

Plants need six things to survive: light, air, food, warmth, space, and... you've got it... water. If any of these are absent or restricted, then plants may not perform as well as they should. We water to support a plant's development and keep it healthy.

Plants only require watering when nature cannot provide what they need through natural rainfall or, occasionally, groundwater and watercourses. If humans did not grow plants outside their normal habitats, or have such a significant impact on the climate, then we'd hardly need to water at all. As it stands, we often grow plants in conditions that are far from what they've adapted to, and so we need to supplement one or more of the vital ingredients they need. A geographical map of the plants in your garden would likely show representation from all around the globe!

As we become more aware of our obligations to save water, we can devise ways to reduce the amount of watering we need to do. Here are a few suggestions:

1. If you have a lawn, resist the urge to water it during dry spells. The grass may turn brown, but it will soon green up again after the next significant rainfall. If brown lawns offend you, consider swapping them for gravel or close-knit planting, but not Astroturf, which is bad for the environment and gets incredibly hot.
2. Install one or more water butts and use rainwater before turning on the tap. All plants prefer rainwater over tap water. You can also save grey water from showers, baths and washing up, but avoid using this regularly if it contains soap or cleaning chemicals.
3. Add as much organic matter to your soil as you can. It's impossible to overdo it. Garden compost, mushroom compost, manure, seaweed and even shredded newspaper and cardboard will work. Organic matter absorbs water and holds onto it, meaning you can water less. It also helps to improve soil structure.
4. Water copiously at planting time and until a plant is fully established - in the case of trees, this can take up to 5 years. Watering generously to save water may sound counterintuitive. Still, a plant encouraged to develop a good, deep root system from the outset will require much less watering in its lifetime than one left to struggle.
5. Choose plants that come from similar climes to the UK or drier ones, such as the Mediterranean. Small, silver-grey and felty leaves are a sure sign that a plant has evolved to suit hotter, drier climates. Be aware that these may not thrive during cold, wet winters, so plant them where drainage is good year-round.
6. Restrict the number of plants you grow in pots as these are generally incapable of fending for themselves for any period of time.

When do I water?

We mostly need to water outdoor plants during the spring, summer and autumn at times when rainfall is low or absent. During the winter months, only potted plants will need frequent monitoring.

As far as time of day goes, you have three options, the most preferable being early in the morning and the least preferable being in the heat of the day:

• Early morning - when the sun comes up, plants begin to photosynthesise. Watering in the cool of the morning catches them just as they begin to draw up and lose water through the pores (stomata) in their leaves.
• End of the day - watering in the late afternoon and early evening is almost as good as in the morning. The only drawback is that wet surfaces and leaves may attract slugs and snails and encourage moulds and mildews. It's a little like leaving laundry in the washing machine overnight. Often needs must, and if a plant is wilting, it's better to give it a drink at the end of the day rather than wait until morning.
• During the day - the main drawback is that on warm, dry, sunny days, water will evaporate more quickly, so you may need to use more water than you would at either end of the day. There is no truth in the idea that water will cause leaves to scorch if splashed with water in bright sunlight. But if you live in a hard water area, you may leave visible white marks on foliage where chalky deposits are left behind.

Knowing when a plant needs watering is the 64 million dollar question, and there's no straightforward answer. Signs that a plant needs more water include:

1. Dull, limp leaves.
2. Wilting of the plant, starting from the top.
3. Slow or stunted growth.
4. Yellowing or browning of foliage.
5. Leaves, flowers and fruits dropping prematurely.
6. Pots feeling lighter than you might expect.

Unfortunately, symptoms 1-5 can equally be signs of overwatering. Test the surrounding soil or compost by sticking a finger or trowel in as far as you can to confirm whether it's too little or too much water. Watering an already waterlogged plant could kill it, so proceed with caution!

How do I water?

Generally speaking, we have a choice of using a hose, watering can or an irrigation system. The choice will be dependent on your personal preference and how much time and energy you can devote to the job. I prefer using a watering can as I can take my time and control the amount and flow of water precisely. However, for large areas, that's not a practical option.

Here are my top tips for watering effectively:

1. Water thoroughly or not at all - the little and often approach does not work with watering - indeed it can do more harm than good. A light sprinkle that wets only the first few millimetres of soil will encourage plants to develop delicate, fibrous roots just beneath the surface. When the soil dries out again, these roots will dehydrate and die. By watering thoroughly, so that the soil is evenly moist to at least a spade's depth, plants will be encouraged to develop deep roots that are protected when the upper layers dry out.
2. Apply water directly to the base of the plant - although there may be some satisfaction in wielding a sprinkler, the most effective and least wasteful method of watering is to direct the stream of water to the exact spot where the plant meets the ground. Watering bare earth in between plants will only encourage weeds. Wantonly splashing foliage with water can spread diseases, in particular blight and powdery mildew. Drip irrigation and seeper hoses are extremely effective at delivering water efficiently and are generally excluded from hosepipe bans.
3. Create a shallow basin around larger shrubs and trees to contain water and prevent it from running away. Some gardeners also use pipes or upturned plastic bottles, part-buried in the ground, to channel water past the surface layer to reach a plant's roots.

What else should I know?

There are a few situations where plants might require considerably more water than you'd expect:

1.  Walls, fences and trees create rain shadows, meaning that plants beneath or next to them may not receive as much rain as the rest of the garden. The heat retained by a wall can also result in plants such as clematis getting hotter and drier than they would like.
2. Trees draw up vast quantities of water from the ground. Established specimens generally don't require watering, even during a drought, but newly planted trees are vulnerable. The Arboricultural Association recommends that newly planted trees are given 50 litres of water per week during the summer months (May-Sept) for the first three years after planting; that's regardless of whether it rains. If the tree has been planted with a watering pipe next to it, half the water should be poured into the pipe to reach the deeper roots and the other half directed to the base of the tree, on the surface. Increasingly, new trees in streets and other public places are planted with a special watering bag attached. Anyone can fill these to help the tree stay alive - many councils and environmental organisations encourage this. If you're planting under a tree, seek out varieties suitable for dry shade or stick with those that grow in spring but die down in summer.
3. Wind is a gardener's worst enemy - it's unpredictable, hard to control and destructive. Wind can have an extreme desiccating effect on plants, particularly if they are already on the dry side. In exposed areas, plant a thick hedge or windbreak of tough shrubs and trees before trying to grow soft, sappy plants like foxgloves, dahlias and delphiniums.
4. Plants growing in pots will dry out long before those planted in the ground. This is because they have no option to send roots out beyond the confines of the pot to find water. If a potted plant is constantly wilting, it could be because it's pot-bound (filled with roots). Moving it to a larger pot may help. When watering plants in pots, assume they'll need the equivalent of 10% of their volume in water to soak them through - so a 35 litre pot will need at least 3.5 litres of water. As a rule, if you leave 5cm between the rim of the pot and the surface of the compost and top that void up each time you water, that should be sufficient.

Finally, Acid-loving or 'ericaceous' plants such as camellias, azaleas, rhododendrons, blueberries and heathers dislike hard water because it contains calcium, otherwise known as lime. Calcium is an alkali and restricts the uptake of essential nutrients in acid-loving plants. The key symptom is yellowing leaves, known as lime-induced chlorosis. This weakens growth and can eventually kill a plant—only water acid-loving plants with rainwater, which is naturally slightly acidic.

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