Watering seems like one of those bonehead tasks that everyone should get right on their first try, right? I wish! The truth is, I see more gardens that are sick and unhealthy due to water stress than any other single issue. Luckily, watering properly isn’t complicated once you know a few simple things.
First, if you’re under the impression that your plants don’t need any summer water because plants in nature do fine without it, read this. Unless you are growing plants that have a specific desire for dryness in summer, like many California natives (Ceanothus, Fremontodendron, etc), and you’ve adjusted your expectations of your plants to allow them to do whatever they do in nature (many wild flowers go dormant in summer!), you probably need to water regularly once the rains have stopped.
The exception to this is if you have a very mature garden of woody plants like trees and shrubs, with no flowering perennials (the soft, fleshy green plants that flower for a long season), then you may not need to water much at all. As a rule of thumb, the more you ask of your plants, the more you need to give in return. If you want them to grow bigger, bloom well for you, or have exceptionally healthy foliage, then you will want to water regularly so they can be at their best.
Here’s what you need to know:
First, the goal is to water very deeply, so you need to water less often. That means you really want to soak your plants so their roots are encouraged to spread deeply into the soil to drink. Plants that just get a shallow sprinkle form root systems right near the surface of the soil, which makes them dependent on you to water them again very soon, since the soil surface dries out faster than deeper down.
Second, the goal is to water the “drip line” of the plant, not the trunk of the plant. If you imagine a shrub or tree getting rained on, the water usually falls to the outermost branches and leaf tips and drips downward from there. If you were to draw an invisible circle around the canopy of your tree or shrub, that area would be called the drip line, and you should focus most of your water in that zone, rather than watering right against the tree or shrub’s trunk.
Third, try not to spray the foliage of your plants if possible. It’s not the end of the world if you do, but try to focus on watering the soil around each plant, since water droplets on foliage can sometimes cause sunburn spots (where the water drop acts as a magnifying glass for the sun’s rays and sunburns the leaves), and moist foliage can contribute to fungus problems like black spot or mildew.
Lastly, the best time of day to water is in the morning before the dew dries. Plants take up most of their water while they’re actively photosynthesizing in the daytime, and while they will drink some at night, it’s a bit of a waste to water in the evening because plants are winding down and won’t get the most benefit from having ample water then. Also, if you sprinkle their foliage at this time of day, the water can dry up slowly as the day gets warmer, and the plant won’t stay wet overnight and invite fungus to proliferate.
How do I know if I’m watering deeply enough?
This is easy: water as usual (either by hand, using your drip irrigation system, or whatever you normally do).
Then, 6-10 hours after you water, check your soil. Is it cool and moist all the way around the plant, and under all the areas where your plants have foliage? Poke your fingers two inches down into the soil – it should be evenly moist two inches down. If not, water more deeply next time, amend your soil with compost to help hold moisture, or add a 3” layer of mulch to keep roots cool and moist.
How often should I water?
This is a tougher question because it varies depending on your soil, what plants you are growing, if you have mulch, and how hot and dry the weather’s been. I can tell you how to figure it out, though!
Begin checking your soil for moisture the day after you water. Poke your fingers two inches down into the soil and see if it’s moist. Do this every day until the soil’s in that sweet spot where it is dry, but still crumbly and cool – that’s when you water. If the top two inches of your soil is dusty or powdery, or your plants are wilting, you’ve gone too long.
If you do this test in each of the seasons, you’ll get a general idea for how often you need to water in different types of weather. In the middle of summer, you may need to water almost daily, especially with fast-growing vegetables or flowers. In winter, you may not water for months since plants are growing less and don’t use up the natural rainfall.
Pay attention too if you have different kinds of planting areas. Lawn, veggies, container plants, flowering annuals or perennials, and newly-planted plants will all need more regular watering than mature shrubs and trees or sturdier perennials. You may like to soak your veggies and lawn every other day, and do your mature plantings 1-2 times a week, for example.
The main idea here is to get acquainted with what your soil’s doing in different areas of your garden so you have an intuitive sense of when it’s time to water.
How do I water with an irrigation system? Are they a good idea?
Yes, drip irrigation systems are totally awesome. Drip systems conserve water and save you money, because they provide just the right amount of water to the plant, exactly where the plant is using it. By contrast, when you water by hand, you’re wetting leaves, the sidewalk, etc – it’s rather inefficient.
Another great thing about automatic drip systems is how reliable they are. I don’t know about you, but sometimes I am rushing to work in the morning and don’t water, or I forget, or I am tired and do a sloppy job. You don’t get any such excuses out of your drip system.
With a drip system using 1 gph (gallon per hour) emitters, watering a mixed garden of perennials and shrubs, I usually set it for 3-4 days per week during the growing season, for around 30 minutes each cycle. You’ll need to adjust for your own mix of plants and soil conditions.
If you have a garden with a lot of annual flowers or reseeding perennials, I often use drip irrigation sprayers – little sprayers which attach to your quarter-inch tubing and will water a larger area – that way you don’t have to set up individual drippers for plants that may not be there next season. They’re less efficient and less healthy for plants, but for gardens with lots of tiny plants they can be the best solution.
If you’re using drip irrigation sprayers, I usually run the system for only 10-20 minutes because the sprayers let loose a lot more water than do drippers.
Lawns, of course, will use larger sprinklers, not a drip system. I usually set an automatic lawn sprinkler system to run 4 days a week for 10 minutes per day, but again, that’s just a guideline and will vary depending on whether you have sandy soil which drains quickly or clay which sops up the water and holds on.
There are also wildly cool new irrigation timers that have weather sensors that adjust the water based on the outside environment, either using satellite data or weather sensors on the timer.
As for how to install an irrigation system, it’s best to have a landscape contractor do this, but it’s possible and not too hard to do it yourself if you’re willing to take the time to research and learn.
Are there any weird bits of info about watering that are important to know but that I’d never think to ask?
If you don’t have mulch, please be particularly careful with how you water by hand. Don’t direct a jet of water at the ground, since it can compact the soil and cause a crust to form. Instead, use a gentle showering head on your hose to allow water to fall lightly on the soil.
In winter, don’t forget to water plants that are under eaves or overhangs and won’t get any rainfall. I’ve seen plants that are halfway under an overhang, and in winter, the back half that was not getting any water died out, while the front half that was getting rained on thrived.
If you are planting a new garden with an overhang and installing a drip system, you might consider setting up a second drip line just to water under the overhang in winter. Then when the rains begin, you can turn off all the automatic drip lines except for the one under the eaves, and you’ll know your plants will stay happy and healthy all winter.
One last thing to consider with drip systems is that as the plants grow, you’ll want to move the drip emitters to water where plants’ roots are. Since most plants start in a container, you need to start with the emitter over the root ball, but as plants grow, they take up water further and further out from their main trunk or stems, at their drip line (see above).
So every two years or so, brush your mulch aside and move the emitters outwards away from the main stem and closer to the drip line, so that you’re watering your plants in the area of their roots where they can actually soak it in.
I hope that answers some of your basic questions about watering and gives you a good foundation of information to go from. Watering seems like such a simple task, and yet so many gardeners have avoidable pest problems because of watering issues – either pest problems due to plants being stressed from lack of water, or fungus from the wet atmosphere caused by deliberately watering plants’ foliage. I hope this watering tutorial helps your plants be healthy and happy!