Here’s a general rule of thumb in the gardening world:
Most plants require about 1 inch of water per week.
Although it sounds simple enough, it’s hard to know what 1 inch of water looks like. And without a rain gauge, you really have no way of knowing.
A rain gauge allows you to keep track of rainfall and irrigation production so as not to overwater—which is not only wasteful, but can encourage disease and damage plants.
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There are some fancy models on the market, but for the home gardener, high-tech equipment isn’t really necessary.
In fact, you can even make your own if you want. Here is everything we will cover in this article:
With this basic tool, you’ll be able to take better care of your garden and spend less time watering unnecessarily.
What is rain gauge?
It is an instrument used to measure precipitation, often rain. There are many types, but as a gardener, you’ll only need standard gauge.
The basic model is a graduated cylinder that catches precipitation. It is marked with a measurement, usually inches in the US.
When the rain stops, you read the cylinder just like a measuring cup. it’s that easy.
Other models include tipping buckets, weighing gauges, and optical gauges. All of these can do more than the standard version, and are used to get more refined readings.
For example, a tipping bucket can measure the rate of precipitation.
The weighing gauge measures the rain mass by means of a sensor. Because it uses mass, it can also measure snow and hail.
And the optical gauge is crazy advanced and detects optical irregularities. I’ll be honest – this is way over my head and way more than what is needed for gardening purposes.
Let’s keep things simple!
How to Use It (and Where to Buy)
Rain gauges are great for not only measuring rainfall, but also measuring water put out by sprinkler systems.
Stratus Precision Rain Gauge via Amazon
There are many different versions of the standard model, from the more expensive ones geared toward professionals to the very basic that you just keep on the ground.
If you choose to stick one directly into the ground, be aware that you may get some splashback that can screw up the reading.
AcuRite Magnifying Acrylic Rain Gauge via Amazon
In addition, the leaves of any plants above can block rain from reaching the cylinder, or even cause moisture from their leaves to drip into the cylinder, causing your readings to be skewed.
Because of these factors, place the gauge slightly off the ground and in an open area to ensure the most accurate reading.
The model I have is mounted on my deck. It’s in a spot that’s easy to see right when I walk out my door, so I don’t have to go out of my way to check it.
Ornamental options are also available, like this decorative frog, available from Plow & Hearth, to add a touch of whimsy to the landscape.
Ornamental Frog, available from Plow & Hearth
Once the sky is clear, I examine it, make a mental note, and plant it. That’s it.
If it has a minimum of 1 inch of water, I don’t worry about my perennial plants that week. And honestly, I don’t worry about my perennials anyway unless it’s been dry for at least a couple of weeks, or I see signs of wilting.
Many perennials can handle a long dry period. But you need to know your plants. Hydrangeas and other heat-sensitive plants may need staking during a drought.
I myself prefer to stick with native perennial plants, which are more tolerant of drought and local soil conditions.
For annuals and edibles, you’ll want to be more diligent in checking your soil’s moisture levels.
measuring sprinkler output
If you want to measure sprinkler output, finding a good open spot for your gauge can be a bit tricky—unless you’re focused on your lawn.
In the garden, do your best to keep the gouge out from under the plants but still in the middle of the action.
If you use sprinklers regularly, it’s helpful to estimate how long it takes your system to produce one inch of water.
To do this, set your rain gauge on the lawn. Then start your sprinkler at the top so the gauge is within the path of the sprinkler.
After 15 minutes, check the amount collected. Pay attention, and then dump it.
Repeat this process two to three times and average the results. The last measurement gives you a general idea of how much water your sprinkler produces over a 15-minute period.
Use this measurement to figure out how long you’ll need to run your sprinkler to provide one inch of water to your garden or lawn.
Running out and checking all the time would be annoying, so having an idea of your sprinkler’s flow rate will allow you to set your system on a timer and forget about it.
Keep in mind that sprinklers cause more runoff and evaporation than other forms of irrigation, such as drip irrigation.
No matter what, I always test the soil, especially around my annuals and edibles.
The best way to get an idea of moisture needs is to test the soil. If the top 2 inches are dry, it’s time to hose down.
And while 1 inch of rain per week is sufficient in most cases, there are exceptions.
If it is a heavy, short rain and there is significant runoff, you may be surprised at how little infiltration occurs.
Also, if you have a raised bed, the soil will dry out quicker than in a garden planted at ground level. So plan for more frequent hand watering in raised beds than in ground level gardens in the absence of rain.
One inch of water should penetrate the soil to a depth of between 6 and 15 inches. But your soil type can affect this dramatically.
Clay soil, which is denser, will not penetrate as deeply as loam and sandy soils in the event of 1 inch of rain.
Also, if temperatures are consistently above 90°F, moisture needs may increase from 1 inch per week to 2 inches per week.
As a general practice, try to water in the morning before the heat starts. This will help reduce heat stress on your plants.
This will also give your plants time to dry completely during the day. Wet conditions in the cool of night make for a nice, comfortable environment for diseases to thrive – and we don’t want that!
Mulching your garden with wood chips, pine straw, or organic materials is also a great way to retain soil moisture and reduce the need for hand watering.
As basic and essential as water is to your garden, it’s not always easy to know when to supplement, or how much your garden needs.
And for some reason, it’s easy to think that your garden needs more water than it actually does.
Using a rain gauge is a great way to get some idea of this.
This simple tool gives you a general idea of how much water has hit the soil, which will limit how often you find yourself reaching for the hose.
And along with testing your soil before you water, it’ll give you a lot more confidence in tending your garden.
I don’t know about you, but I often have a hard time remembering what I did yesterday, let alone the last time I showered.
So having a rain gauge as a reference keeps me from drowning my garden and gives me more confidence in how often I choose to get the hose out.
Have you used a rain gauge? Do you find this helpful? Share your favorites (or DIY building tips) with us in the comments!
For more gardening basics, check out some of these guides:
© Ask the Experts, LLC. All rights reserved. See our TOS for more details. Originally published on May 24, 2018. Last updated on April 15, 2023. Product photos via AcuRite, American Science & Surplus, and Plow & Hearth. Uncredited photos: Shutterstock. With additional writing and editing by Allison Sidhu.