The Best Time to Water Plants

Have you ever wondered when is the best time to water plants? If you ask around, chances are one of your organic gardening friends will tell you, “The best time to water plants is whenever they’re dry.”

There is some truth to this common knowledge (you should, of course, water your plants when they’re dry). But it’s not quite that simple.

Figure 1 - Photo credit: mrsdkrebs via Foter.com / CC BY

There is an ideal time to water plants, and there are two factors that show us why this time is the best. The answer can be found by reading about the scientific research that has been done… or simply by sticking your finger into the soil to observe what happens when you water your plants.

How Plants Change on a Daily Basis

Like most living things, plants have a circadian rhythm. This means that plant behavior is based in part on adhering to an internal clock of sorts. Plants know what time it is, and they adjust their biological behavior based on the time of day.

Through observing the molecular changes in plant tissues, researchers have found that many plants do “sleep” at night. They relax their cells and appear to weep, or lay down. You can easily observe this phenomenon right in your own yard by taking a picture of a plant at midday, and then taking a picture of the same plant from the same vantage point at night.

When dawn approaches, the plants become erect again. Their cells expand and become rigid in anticipation of the arrival of sunlight.

It is at this time, just before dawn, when plants will benefit the most from having a fresh dose of water applied to the soil in which they grow.

Figure 2 - Photo credit: timabbott via Foter.com / CC BY-NC-ND

Want to Learn More?

If you’re interested in a more in-depth explanation about the circadian rhythm of plants, including how the process effects the growth, signaling, and behavior of leaves and organs, you can find a great free resource at this link: JSTOR – The Physiology of Circadian Rhythms in Plants.

This study features research conducted at Cambridge University that was first published in 2003. The circadian rhythms of plants are covered in great detail, with an emphasis on how these rhythms effect plant growth and photosynthesis.

Why Evaporation Matters

The second factor that dictates the best time to water plants is evaporation.

You have probably noticed that when you apply water to soil, over time the soil becomes dry again. Some of the water you applied was absorbed by the roots of plants in the area – but most of that water probably evaporated into the atmosphere.

The biggest factors that increase evaporation are sunlight, ambient humidity, and wind conditions. While you can’t control wind conditions, you can take advantage of the early hours of the day when sunlight is the least intense and ambient humidity is highest.

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When you water early in the day, the water you apply will soak down deep into the soil, and it will remain there for a longer time. When the water remains in the soil longer, your plants have more opportunity to absorb that water into their cells.

Providing Moisture Throughout the Day

When you water very early in the day, your plants have access to water at the most important time, while their cells are expanding and getting ready for the day’s sunshine.

Watering early also means that your plants will have access to water throughout the day. If you moisten the soil early – plants will have moisture available all day long. If direct afternoon sunshine dries the plants out, they can absorb more water from the already wet soil. This way, your plants are less likely to experience stress and sickness as a result of intense sunshine.

If you wait to water in the afternoon, your plants may not have the required water to properly expand their cells in the morning, setting them up for a stressful day. When afternoon sunshine dries them out, they are already stressed by a lack of water. You might enjoy seeing your plants perk up with an afternoon watering – but unfortunately the damage has already been done.

The Myth of Water Droplets Scorching Plants

While many gardeners are aware that the early morning hours are the ideal time to water, some of them are doing it for all the wrong reasons.

There is an old and widely-spread myth that water droplets can intensify the rays of the sun and cause tiny burns that harm the plants’ leaves. If you’ve ever used a magnifying glass to focus sunlight and start a fire – then you’ll understand the basic idea.

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This myth persists in many gardening circles, despite the fact that is has been disproven by scientific study. A group of scientists from Hungary and Germany tested this myth. While they were able to burn plant leaves with tiny glass beads – they were not able to burn plant leaves with droplets of water.

Despite what your friends might have told you – you should not fear getting your plant leaves wet in the afternoon. It is better to water your plants early in the day. But on hot, dry, or windy afternoons your plants would probably appreciate a light top-watering to wet their leaves. And there is no need to fear the sun scorching their leaves.

Other Things to Consider When You Water

While the early morning is in fact the best time to water your plants, there may be some days when it would be wiser to wait.

First, consider the current moisture level of the soil. If your soil is already wet, you will be more likely to cause problems by applying more water. Very few plants can tolerate overly wet soil, and it is usually better to give the soil a chance to begin drying out before you add more water.

You should also keep an eye on the weather forecast so that you know what conditions are likely to occur on any given day. If rain is very likely, it would be better to conserve the water and allow nature to water your plants. I’m sure you’ve noticed that your plants absolutely love rainwater. If possible, hold off on watering until the rain comes – your plants will thank you for it.

Likewise, if the forecast calls for high winds, high temperatures, or low humidity – you can assume that your plants are going to have a tough day. When conditions are going to be stressful for your plants, help them out by applying an especially deep and thorough watering before the high winds and intense afternoon sun arrive.

Why You Shouldn’t Water at Night

Watering your plants at night – or very late in the day – can be problematic for several reasons.

The first and most obvious problem is fungus. When your leaves sit wet for several hours without sunlight to dry them off, these are optimal conditions for fungus to flourish. If you water at night you will likely start to see white powdery mildew, black and green mold, and dark splotches of systemic fungi like anthracnosis.

Figure 5 - Photo credit: Scot Nelson via Foter.com / CC BY

There are fungicides available on the market to handle each of these problems. But the old adage you learned from your grandmother holds true here, “An ounce of prevention is worth a pound of cure.” Allow your soil to dry out overnight and you will see much less mildew, mold, and fungus in the garden.

Wet soil at night will also attract many garden pests like snails, slugs, and pill bugs. These creatures go out in search of moisture each night, and you shouldn’t be surprised to find an abundance of them if your garden is the only wet spot in the vicinity.

The Way You Water Matters

Even if you water every day in the very early hours before dawn, you are not guaranteed to have success. A lot of your results will be dependent on the method you use to water your plants.

The root systems of plants extend deep into the soil, and that is the location where they will benefit the most from having moisture available. Evaporation is also less of a concern in deep soil, where several inches of soil insulates against harsh winds and sunshine.

For these reasons, it is very important that you choose a watering method that allows water to seep deep into the soil, well below the first two or three inches. A slow, sustained watering is what you are looking for here – rather than a quick pass with a watering wand or sprinkler.

One slow, deep watering is more beneficial for your plants than several shallow, light applications. When your plants are well-established and thriving, you can taper your watering back to about 1 or 2 inches of water per week. This is especially true for shrubs and trees. Tender annuals and vegetables are needier and may need to be watered every other day, even after they are fully established.

Choosing the Best Tool for the Job

When you’re attempting to optimize your watering practices – the most important thing to consider is the tool you choose to use.

Some tools lend themselves to deep, thorough watering – while others are more effective for watering potted plants, annual flowers, vegetable gardens. Some tools are designed to water a very large area – while some are more appropriate for small spots.

Let’s take a look at several different methods and discuss the strengths and weaknesses of each.

Lawn Sprinklers

Lawns sprinklers are designed for watering large areas to a depth of only a few inches. This is an appropriate technique for lawns… but not much else.

Figure 6 - Photo credit: Delwin Steven Campbell via Foter.com / CC BY

Because they spray small droplets of water for long distances, lawn sprinklers are very prone to evaporation, and a significant amount of the water they spray can actually evaporate before it even hits the ground.

For watering any type of plant other than a lawn, there is a better tool that will do the job more efficiently.

Spot Sprinklers

Small spot sprinklers are designed to apply water to a small area. These are available in different shapes to water an area in a circle, square, or rectangle pattern. By choosing the design that fits your spot, you can ensure that very little water is wasted.

Spot sprinklers apply larger drops of water to a smaller area than lawn sprinklers, and so they can be very efficient for watering small areas – such as the ground around one small tree or a small perennial flower bed.

One great feature of spot sprinklers is that the size of the watering pattern can be controlled simply by turning the handle on your water spout. A half turn to the left might be a foot larger, and a half turn to the right might be a foot smaller. In this way you can fine tune the watering pattern to ensure that no water is wasted.

Generally speaking, spot sprinklers are most effective when the water is turned down low enough so that most of the water has time to soak into the ground and very little water runs off along the surface.

Watering Wands, Watering Cans, and Hand-Held Nozzles

Hand-held watering devices are very effective for watering pots and containers. For most other tasks, they are inefficient. These devices apply a large volume of water in a short amount of time – which is not effective for deep watering.

While you might feel that you have watered thoroughly with a wand or nozzle, it is likely that you have only wet the top inch or two of soil. The best way to know for sure is to check the soil. Stick your finger in the soil and see how far down the water has seeped. You will probably find that you get better results with a different tool.

Soaker Hoses

Soaker hoses are great tools that do a good job of applying water slowly and deeply. Because they are light and mobile, soaker hoses can easily be moved from one spot to another to achieve deep watering all around your yard and gardens.

The biggest drawback of soaker hoses is the length of time it takes to deeply water an area. You can get around this obstacle by setting up a watering schedule and watering different parts of your garden on different days of the week.

Drip Irrigation

Without a doubt, the best watering method for most applications is drip irrigation. While there is some investment required initially to set up the system, you will quickly make that money back through decreased water bills.

Drip irrigation is specifically designed to apply water slowly, allowing maximum in-soak and minimal evaporation.

Figure 7 - Photo credit: CIMMYT via Foter.com / CC BY-NC-SA

Pro Tip – Mulch for Garden Success

Watering early in the day will help you to control evaporation, but mulch is the secret that the most successful gardeners use to keep their soil moist in difficult conditions.

Many different materials are available that will make an excellent mulch. Choose according to your aesthetic preferences and the requirements of your garden. Pine straw, wood chips, newspaper, and cardboard are all effective tools to insulate your soil from the sun and wind.

Water Your Plants Slowly and Deeply, Very Early in the Morning

The best time to water your plants is early in the morning. This is the time when your plants most need the water – and it is also the time when the water will be most likely to soak deep into the soil.

Apply a deep watering, very slowly, and you will find that your plants will be happier and you will not need to water as frequently.

Do you know another tip about the best time to water plants? Use the comments section below to share it with our audience.

Thanks for reading, and good luck with your garden! I’ll see you out there bright and early for tomorrow’s early morning watering.
James G. Craig
 

James G. Craig is a gardening enthusiast who splits his spare time between growing vegetables, preening his flower gardens, and blogging about his experiences at the Gardener Corner.

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