Plant and Tree Watering Basics: Keeping Plants Healthy After Hotter Temperatures

Nan sterman headshotFinally it’s fall! Cool days and cool nights are a huge relief, for both people and plants. It also means it is time to change the way you are watering your garden.

In the hot, dry summer air, plants are under huge water stress. They lose water from their leaves faster than their roots can replace it with water from the soil. That’s why plant leaves can look droopy, especially towards the end of a hot afternoon.

Once the weather cools, and especially when the air is moist, plants don’t have nearly as much water stress. At the same time, the days are shorter and the sun sits lower in the sky. With the limited sunlight for photosynthesis, plant metabolism slows down. And with that, the plants’ water needs decrease.

If you water by hand, notice that it takes longer for soil to dry out now. There’s no reason to water wet soil, so wait longer between watering. I have a large collection of potted plants and in the summer, I water every plant twice a week and sometimes more often. In the winter, the potting soil stays damp longer, so I water just once a week.

If an old-fashioned manual irrigation clock controls your irrigation system it’s time to adjust your clock. Each zone should run less often, but for the same number of minutes as it ran during the summer. If your garden soil is clay, you might be able to water just once every few weeks through fall and not at all in winter, especially when (or if) it rains. If your garden soil is sand, sand drains very quickly so the irrigation needs to run more often, maybe once every week or two – unless it rains.

If your garden’s irrigation is managed by a “smart” controller, the controller is programmed to adjust the irrigation schedule seasonally, based on where your garden is located, the type of soil in your garden, types of plants, and a few other factors. Most systems have mini-weather stations that monitor heat, humidity, and rainfall to determine how often and how long to run each irrigation zone. Like with any other technology, you should check the controller’s log periodically to see how well it is doing its job. Now is a good time to do that check. Notice how often each zone runs and for how long. If the history doesn’t show your system running less often now, look for a button labeled “percent” or “%” and adjust the schedule there.

Wet plants

If it rains, smart controllers shut the system down until the soil dries out. Have you ever cleaned your smart controller’s rain sensor? Dead leaves, dirt and other debris can collect in the sensor and interfere with its operations. Look for your controller’s rain sensors as part of a self-contained unit typically mounted near the irrigation controller and on a high point, like your home’s eaves or roof.

If you are establishing new plants or a whole new garden, the newly installed plants need a little extra water this year, and maybe next year too. Establishing new plants in an existing garden can be a bit tricky since you want the new plants to get enough water, without overwatering everything else. I like to water each new plant with a small hose-end sprinkler set to make a fan only large enough to cover the soil beneath the plant’s canopy. I set the timer on my smartphone for 30 minutes or so.
Once the soil is saturated, I move the sprinkler on to the next new plant.

Establishing an entirely new garden is more straightforward, especially if you have an irrigation controller. Some smart controllers have a setting for establishing new gardens. If yours doesn’t, set the controller to run often enough to keep all the soil damp but not wet. Then, don’t just walk away. You’ll need to monitor the garden and make adjustments to the controller as needed.

And if we are very lucky this winter, Mother Nature will do all the watering for us.

Garden expert, designer, and author Nan Sterman specializes in low water, sustainable, and edible landscapes. Nan hosts A Growing Passion, a show about all the ways that San Diego and California grow. A Growing Passion airs on KPBS television Thursdays at 8:30 p.m. Episodes are also posted online at opens in a new Nan is also author of California Gardener’s Guide vII, Waterwise Plants for the Southwest and the upcoming Hot Colors, Dry Garden. More information is at opens in a new