Written by s • How to Water Your Plants – Part 1, Basic Principles and Watering Outdoors

Some of the most common gardening questions revolve around watering. We might think nothing could be easier that pouring some water on your plants, but it doesn’t work out that way. In the traditional Japanese system for training gardeners, apprentices had to work for 7 years before they were allowed to water a plant – that’s how important and complex those gardeners saw watering. Now I’m not saying you should wait and study for 7 years before watering your garden, but it will pay off if you take the time to understand the basics, and know how to do it properly. Let’s start be thinking about water, plants, and soil.

Plants Need Water

Well, yes, I guess we knew that already! Plants use water continuously, for three main purposes. First of all, water makes the leaves and young stems rigid, holding those leaves out in the sun for successful photosynthesis. We have all seen plants droop and wilt in hot, dry weather, and a wilted plant can’t grow.

The second purpose is to carry mineral nutrients up from the roots into the leaves and growing tips of the plant. A plant inside is many very thin tubes, with open tops (more on those openings in a minute). Water evaporates from the top, and because the tubes are thin, water is drawn up from lower down, inside the roots. Removing that water from the roots sucks more water, mixed with dissolved minerals, into the plant, keeping a continuous supply coming.

To keep that supply of watering minerals coming, the water must evaporate. It does this inside the leaf, escaping as vapor through spaces on the underside of the leaf called ‘stomata’. But it isn’t a one-way street. At the same time, carbon dioxide comes in through those spaces, and yes, you guessed it, is used for photosynthesis and growth. The oxygen that plants make from that process escapes through those same holes, into the atmosphere. That gas-exchange is the third vital purpose of water for plants.

Dryness upsets that process. When the water supply from the roots becomes reduced, those stomata close tight, conserving water and putting the plant into drought mode. Without the gas exchange, photosynthesis stops, and so does growth. So a plant in drought-resistant mode isn’t growing, just surviving. That’s why it is best to water even the toughest plants, especially when they are young, if you want them to grow.

Water in Soil

We have blogged about soil before, but for our purposes here, it’s important to realize that your garden soil has two parts – the solid bits and the spaces in between those particles. Both are essential. Water and air sit in those spaces, and for most plants that air is just as important as the water. That’s where the phrase ‘well-drained soil’ comes into it. If you aren’t sure what that means, check out an earlier blog in this vital subject. The deeper into the soil you go, the more water there should be in those spaces. This draws the roots of trees and plants downwards, and acts as a reserve when the top layers become dry. For good growth plants need the solid minerals parts of soil for nutrients, they need the water, and they need the air too, in those spaces. Roots need oxygen to survive, which is why wet soil can be so damaging to your plants. [I’m not getting into the role of organic matter here, but it too is essential for good soil – take a look at this blog].

Practical Watering Out in Your Garden

Now you know why water is important, so let’s talk about how to achieve that most efficiently, especially in this era of water shortage and ‘water-wise’ gardening. First, think about nature. Plants get water when it rains, and then the soil dries out until the next time. Watering should be the same. To me it sounds a bit like a Zen concept – “When watering, water. When not watering, don’t.”

In other words, the first thing you have to do is break that habit of giving your plants ‘a sprinkle’. Light watering is worse than no watering at all, since it only wets the top inch (check your soil if you don’t believe me) and draws the roots upwards, making your plants more vulnerable to dryness. As well, when you start their feeling righteous spraying water around, much of it is evaporating into the air before it even reaches the ground, so it’s more like ‘water-stupid’ than ‘water-wise’.

How to Water Your Garden – By Hand

If you have a smaller garden, watering by hand is practical, and a great way to be with your plants close-up, enjoying them, and noticing problems sooner. Trade in the spray nozzle for a rain-head that puts out a gentle spray like you get from a watering can. One attached to a long rigid handle makes reaching out into your beds easier. That fine spray might look pretty, but it doesn’t water efficiently. Forget about the foliage, instead water directly at the base of the plant, standing and letting the spray soak in for a while. With newly-planted material, make sure you soak right against the stems, where the roots are. With older plants water the whole area further out, covering an area beyond the spread of the foliage. Take your time, and soak everything thoroughly. A quick spray at the end to wash the foliage is fine, but it’s the roots that need water, not the leaves.

For trees and larger shrubs the best attachment is a small burlap bag, made of 2 or 3 layers of burlap. You can also find ‘bubbler’ ends, which spread out the water slowly, over a bigger area. Lay the hose near the base of the tree, and leave it running slowly for at least a ½ hour. Deep soaks like that will be good for at least a week, and often longer.

How to Water Your Garden – Fixed Watering Systems

Consider replacing your overhead sprinklers with soaker hoses running through your beds. This avoids evaporation, and the slower output means better penetration of the water. The only time trickle doesn’t work too well is if you have very sandy soil, since the outward spread of the water will be minimal, and won’t reach far. The more clay in your soil, the wider it will spread from the trickle hose, so the wider you can space them apart. The best soaker hoses to use are the ‘leaky pipe’ style, where the material of the hose itself is porous, letting water out all along its length, like the picture at the top.

Systems with spaced outlets are harder to set up, and the outlets easily block after a while, so it takes a lot of maintenance. Avoid the suggestion of burying that leaky pipe in the ground. It sounds like a good idea, but minerals clog it up quicker, shortening it’s effective life, and even worse, it seems to act as a magnet for spades, so you always end up accidentally cutting through it whenever you are out working in your beds! You can lay it partially beneath mulch, but leave a bit showing so you know where it is, to avoid damaging it.

Just like you did when watering by hand, leave your system running long-enough for the ground to soak thoroughly, and don’t water again until you see that the soil has become dry – drier for established plants, not so dry for new beds. Always let the top couple of inches dry out before watering again.