Xeriscaping (from the Greek xeros, meaning dry) is an approach to gardening that specifically focuses on conserving water.
Xeriscaping is growing in popularity in the Southwest, where water is scarce and native plants have evolved to tolerate long dry periods. These drought-resistant species include cacti, as well as other plants with adaptations like waxy coatings on their leaves to reduce evaporation, spines to deter thirsty animals, and wide-reaching root systems that can absorb lots of water in a rare rainstorm.
Xeriscaping is about more than just choosing plants that need little water, though. It can also include arranging those plants in and around swales that funnel rainfall towards roots, making maximum use of the water that’s available. Water can also be channeled into rain barrels or cisterns – people in the driest regions of the country, receiving just 2 inches of rain per year, can store over 1,000 gallons of free water by collecting what falls on their roof.
While Wisconsin does have a native cactus, xeriscaping doesn’t necessarily mean limiting yourself to the plants with the lowest water requirements. Instead, it means planting species that can thrive with just the amount of water that comes to them naturally as rain – in other words, planting natives! We create the need for watering when we fill our yards with non-native species adapted to rainier regions.
As explained in the last post, an “average” plant needs an inch of water a week. But how should that be distributed across the seven days?
In general, plants prefer to receive water in big doses, rather than in little sprinkles. Don’t worry that the plant won’t be able to absorb and store a lot of water all at once – a mature tree can take up hundreds of gallons in a heavy rainstorm.
A good rule of thumb is to water the plant, wait a minute for the water to sink into the ground, then water the plant again. If the second dollop of water isn’t quite fully absorbed after another minute, then the soil is well-saturated, and the plant has plenty of water.
If a rainfall provides half an inch of water, there’s no need to rush out and provide the other half-inch right away. But it’s not necessary to water a little bit every day, either. Plants are more than capable of dealing with a somewhat irregular watering schedule.
Plants should be watered when they need it.
How do you know when a plant needs water? An “average” plant needs an inch of water a week. Of course, some plants can get by on much less, while others need to be constantly wet. Knowing the plants in your garden and the different site conditions they require will tell you how much water they need each week.
But that is not how much you should water them. If it has rained recently – or if it’s expected to rain soon – subtract the amount of rainfall from the amount of supplemental water you give your plants. Your local weather forecast may tell you how much rain your area has received lately. Or, you can set an empty tin can in the ground as a simple rain gauge. (You can also use the can to track how much supplemental water you’ve given nearby plants.)
If your plants are watered automatically by a timer system, be sure to turn the system off when the plants have already received enough water from rainfall! Too much water can harm a plant, just the same as too little.
The best time to water plants is in the morning or evening, rather than in the middle of the day. There are two reasons for this.
First, it is usually warmer in the middle of the day, leading to more evaporation. Watering in the cool morning or evening means that more of the water will stay on the soil, rather than moving into the air.
Second, as mentioned in the previous post, plants don’t like their leaves to be wet. In the morning and evening, plants are often wet anyway because of dew. Watering around noon leaves the plants soggy for more of the day, increasing the risk of disease.
One way to water on a schedule is to use a sprinkler system on a timer. The next post will cover a downside of that approach.
We often think of watering plants by pouring water over the top of them. Plants, in fact, don’t like this. They need water at their roots, and can be harmed by water on their leaves, since the dampness can invite mold and other diseases.
But wait. Aren’t plants watered in nature by rain falling on top of them? Yes! Plants have evolved to deal with this by developing various strategies for moving water off their leaves and down to their roots. These strategies also work pretty well when the water is coming from a hose, sprinkler, or watering can, rather than from rain.
But this is a case where we can do better than nature. We can water plants directly at their roots, keeping their leaves dry.
It might seem intuitive to do this by watering at the base of the plant’s stem, but that’s not quite what the plant wants. When plants water themselves by moving rain off their leaves and down to their roots, that water doesn’t end up next to the plant’s stem. It falls along a circle defined by the plant’s outermost leaves. That circle is called the drip line.
Pouring water on the ground in a circle that approximates a plant’s drip line is the most efficient way of putting the water where the plant can absorb it.