# The rain gauge helps to water well

In my experience, gardeners often overestimate rainfall. A downpour may appear to have completely saturated the ground, but scratch an inch and you might find dry ground.

Because watering – neither too much nor too little – is one of the keys to a successful garden, it pays to be more analytical about that downpour.

The amount of rain that has fallen, the length of time to water your plants, or the amount of water the plants need are often expressed in inches. Typically, plants need about 1 inch of water per week to truly thrive. It’s easily measured with a rain gauge, which you can buy or make at home with nothing more than a coffee or other can, and a ruler.

Because I’m the one with the rain gauge, my neighbor usually calls from across the fence in the morning after a night shower: “How many inches have we had? “

A rain gauge can tell you how long you need to use your sprinkler to get that inch of water in the garden. Because the water distribution may not be uniform, place a few cans at random over the area to be watered. Then turn on the faucet and keep it on until the sprinklers have filled the water cans to 1 inch deep.

To cover an acre of water 1 inch deep, it takes about 27,000 gallons. On a 150 square foot garden, one inch of water equals 90 gallons.

If you are watering from a bucket or watering can, use the 1-inch measurement to determine the amount needed for an individual plant. (It is especially important that newly planted trees and shrubs are watered the first season.)

First, estimate the area – as the crow flies – over which the roots extend. Usually this is assumed to be the same as the horizontal spread of branches. The roots of a rose bush that I planted last spring, for example, are now probably extending over a few square feet. Two square feet, or 288 square inches, multiplied by 1 inch of depth is equivalent to 288 cubic inches, or about 5 gallons of water.

The rule could also be translated as follows: each week, apply 2 1/2 liters of water per square foot. With a watering can, it’s easy to see how much water you are using. If you are using a hose, calculate its flow rate over time, then calculate how long you need to stay there to get enough water for the area you are watering. It’s probably longer than expected.

This watering recommendation applies to soils that have not dried out too much. If the soil is dry because you haven’t watered or because it hasn’t rained for three weeks, you need to wet it completely first. Then in a week, give that inch, or 2 1/2 pints per square foot.

In addition, this “inch” rule applies to plants whose roots are found primarily in the upper foot of the soil, which includes most annual vegetable and floral plants. Plants that root deeper than a foot need more water; corn roots, for example, are 3 feet deep.

Every gardener should have a rain gauge. Mechanical or computerized gauges will tell you the amount of precipitation (depth, in inches) to the nearest hundredth of an inch. Even a straight-sided can of coffee is probably accurate to an eighth of an inch.

A rain gauge will tell you if a summer downpour dropped enough water that you could forget to water for a week, or if what you thought was pouring rain was just a small drop of water a quarter of an inch. If you only get a quarter of an inch of rain, the remaining three-quarters of an inch, or a few gallons of water per square foot, will need to come from your garden hose or watering can.