Watering vegetables properly is an important skill to learn

Here, I will look at four things:

1. When to water
2. How to water
3. How to make the most of the water you use
4. Watering pots

When to water

When the soil is full of water, it is said to be saturated. In this condition, plant roots suffer from lack of oxygen. The aim in watering vegetables is to help maintain the soil moisture at a level where there is sufficient amounts of both water and air for healthy plant growth.

In the sun, soil will dry out only to a depth of a few inches, only plants can remove moisture from greater depths. This means that watering vegetables whenever the soil surface looks dry will in fact be over-watering.

To know if the water is needed, we must know how moist the soil is within the root zone of our plants. Of all the high-tech gismos and widgets on the market today, there is really only one instrument that can properly tell if soil is moist or dry - The Human Finger!

Use a trowel to remove the top 3 or 4 inches of soil and stick your finger into the soil at the bottom of the hole. If it feels moist, then do not water yet. Its as simple as that.

Another trick, invented by French wine growers, uses a form of companion planting. Grape vines and roses originate from the same part of the World, but roses have a much shallower root system. This means that as the soil dries out, a rose will wilt before a grape vine will, so the best time to begin irrigating vines is when roses (planted nearby) begin to wilt.

Watering vegetables can use the same trick, by partnering deep rooted plants like sweet corn, with shallow rooted plants like beans, or herbs like Basil (which has both shallow roots and large, soft leaves). Of course, you would have to make sure the Sweet corn did not shade the other plant, or the trick may not work.

One group of vegetables that can fool you is the cucurbits (Pumpkin, squash, melons, etc.), which have very large leaves. On hot days, they simply cannot take up enough water to prevent wilting and so the leaves droop. This is only temporary wilting and the plants will recover when the sun goes down (as you can see in the pictures below). Use the finger test to check if you think the wilting is worse than it should be.

How to Water

Watering vegetables can damage the soil if it is not done properly. By far the best implement to use is a round rose, which is pointed upwards so that the water falls on the soil like a soft rain. It is also important not to water too quickly as surface run-off of water can quickly strip away soil and nutrients.

When watering vegetables with a hose or sprinkler, it is often best to protect the soil with a layer of mulch. Click here to read more about the use of organic mulching.

The aim of watering vegetables is not simply to wet the soil, but to apply sufficient water to fully wet the entire root zone of the plant. Using less than this will force you to water too often and more than this is simply wasted. Experience is your best guide. Watching plants with root systems of varying depths will help you get a feel for how deep your watering has gone and how long it lasts. Done properly, most soils (except very sandy soils) should be able to support plants for a week between waterings.

Another method of watering vegetables that is very water efficient is drip irrigation. This is based on research that showed a plant can survive and grow on only one quarter of its root system. So not only does this system deliver smaller amounts of water directly to the base of each plant, but it needs to only wet one quarter of the roots of each plant to be effective.

Even more efficient is the use of sub-surface trickle and 'leaky-pipe' watering systems. However, these may only be suitable for watering vegetables in areas of the garden devoted to perennials such as Asparagus - so they are not being continuously dug up or damaged by cultivation. Another possible application for these systems could be a no-dig garden, where they may be covered only by a layer of mulch.

How to make the most of your Water

Water is a precious commodity and we must continually strive to find ways to make more use out of every drop. As a general rule, every 10 square metres of vegetable garden will require about 6,000 litres of water per year. For those in non-metric countries, that is about 115 gallons per square yard.

On the bright side, however, this amount can be easily supplied from tank water collected off the roof of the house, or by a domestic grey-water system. Also, the requirement can also be substantially reduced by using the so-called 'Bio-intensive' method.

Of course, even simple techniques like using plenty of compost in the soil and applying organic mulches can substantially improve water efficiency. As can the use of raised garden beds - if they are properly constructed and managed.

Watering Pots

Plants in pots need to be carefully monitored - especially in warm weather. The same finger-tip method of checking moisture level applies to pots as well, but watch for signs of wilting as well - things tend to happen a lot more quickly in a pot.

Once you decide it is time to water, again be sure not to skimp. Water slowly to prevent overflows that can wash the potting mix away. Then continue until water begins to flow from the drainage holes. Its as simple as that.

For more on growing herbs and vegetables in containers click here.

Of course, with climate change, the whole subject of watering vegetables is becoming more important and more difficult, so we will need to be adding more information from time to time. To help keep up with the latest relevant information there are some useful links below, but you can also subscribe to our Free email newsletter - The Food Gardener.

Further reading and useful links

An important way to improve the efficiency of watering vegetables is actually improving soil balance.
There are 5 steps in using the Mikhail system to reliably improve the structure, friability and moisture retention of any soil.

Using a raised vegetable garden to increase the depth of soil available to plants.
The only way a raised garden can be truly effective for improving water retention is if the physical condition of the new soil on top is matched to that of the existing soil beneath.